CN104109785A - Mg-Si-Sn-based nano-composite thermoelectric material and preparation method thereof - Google Patents
Mg-Si-Sn-based nano-composite thermoelectric material and preparation method thereof Download PDFInfo
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Abstract
The invention provides a Mg-Si-Sn-based nano-composite thermoelectric material and a preparation method thereof. The Mg-Si-Sn-based nano-composite thermoelectric material has a layered structure, and the chemical general formula of the Mg-Si-Sn-based nano-composite thermoelectric material is Mg2SixSn1-xMy, wherein M is a doping element and is one selected from Sb, Bi, Ga, Ag, Cu and Al, x is not less than 0.3 and not more than 0.9, and y is not less than 0.005 and not more than 0.15; the structures of all layers have different Mg:Si:Sn atom mole content ratios and different M doping concentrations; and the structure of each of all the layers comprises a Mg-Si-Sn matrix and a Mg-Si-Sn nanometer grain second phase dispersed in the matrix to form a coherent interface or a semi-coherent interface. The Mg-Si-Sn-based nanocomposite thermoelectric material has a coherent interface and a modulation-doped structure, so the Mg-Si-Sn-based nanocomposite thermoelectric material has the advantages of low thermal conductivity of lattices, and good thermoelectricity performance, and can be widely used in the fields of spaceflight, national defense, automotives and the like.
Description
Technical field
The invention belongs to semi-conductor thermoelectric material field, relate to a kind of Mg-Si-Sn base nano composite thermoelectric materials and preparation method thereof, particularly relate to a kind of Mg-Si-Sn base nano composite thermoelectric materials with coherent interface and modulation-doped structure and preparation method thereof.
Background technology
Energy scarcity and environmental pollution have become global Tough questions, and in energy use procedure, have 2/3rds energy to scatter and disappear with used heat form.Thermoelectric material is a kind of discarded energy generating such as residual heat of tail gas of automobile, industrial waste heat, hot spring that both can utilize, and can replace the new function material that freonll-11 becomes environment friendly and clean type refrigeration agent again.Due to the direct conversion that thermoelectric material utilizes electronics in solid material and hole carrier to carry out heat energy and electric energy, therefore have without moving-member, noiselessness, the advantage such as convenient, flexible, in fields such as space flight, national defence, automobiles, there is utmost point application prospect widely.The U.S., Japan and other countries are applied to thermoelectric material generating power by waste heat of tail gas of automobile, hot spring generating, the generating of waste incineration heat in succession.Thermoelectric material also can change electric energy into the temperature difference, and the semiconductor water dispenser based on thermo-electric conversion, semi-conductor wine cabinet, automobile thermoelectricity seat are used widely.The performance of thermo-electric device depends on zero dimension " figure of merit " ZT of material, and when material two ends temperature is respectively 630 ℃, 30 ℃, average ZT reaches 1.5, and theoretical generating efficiency can reach 20%.The ZT of material depends on three parameters that are mutually related: Seebeck coefficient S, conductivityσ, thermal conductivity κ, i.e. ZT=(S
2σ/κ) T.The thermal conductivity κ of material is by lattice thermal conductivity κ
phwith current carrier thermal conductivity κ
cform, i.e. κ=κ
ph+ κ
c.Good thermoelectric material should have high power factor S
2σ and low lattice thermal conductivity κ
ph.
The thermoelectric material at present with higher ZT comprises Bi
2te
3base alloy, PbTe alloy, CoSb
3, AgPbTe-GeTe based multicomponent alloy, but these materials are many by poisonous or expensive elementary composition, its large-scale application will be brought disadvantageous effect to environment.Mg-Si-Sn radical sosoloid alloy is a kind of middle warm area (200-600 ℃) thermoelectric material of better performances, has the advantages such as light weight, nontoxic, abundant raw materials, once obtain performance, breaks through, warm area PbTe, CoSb in being expected to substitute
3material is also played a great role at energy field.
Mg-Si-Sn base thermoelectricity material research up to now mostly relies on its special energy band structure and improves power factor, or reduces thermal conductivity by nanometer means.If will further significantly improve ZT, must break the interrelated of α in solid material, σ, κ, realize the independent regulation and control to electronics, phonon.Coherence nanostructure (being the second-phase nanostructure that crystal lattice orientation is consistent with matrix, have coherent interface) is to improve the effective way of ZT, and this is accomplished in some thermoelectric material system.For example, the coherence such as PbTe-SrTe, PbTe-PbS nanostructure is successively brought up to ZT by the performance of PbTe base thermoelectricity material
max=1.7 (Nat.Chem.3, p.160,2011), ZT
max=1.8(Nature489, p.418,2012).But up to now, also there is no document and patent report to cross to have the Mg-Si-Sn base thermoelectricity material of coherence/half coherence nanostructure.
On the other hand, modulation doping (modulation-doping) is also to improve thermoelectric material power exponentα
2the effective ways of σ.Modulation doping in semiconducter device refer to undope in narrow energy gap semi-conductor on one side (being proper semiconductor), and mix alms giver in wide different energy gap semi-conductor on one side, thereby near one side of proper semiconductor heterojunction boundary forms electronics potential well, and forms electronic barrier in doped semiconductor one side.The two-dimensional electron gas being provided by doped semiconductor is provided in proper semiconductor one side accumulation, but does not have the scattering process at ionized impurity center, so two-dimensional electron gas has high mobility and specific conductivity at in-plane.Bibliographical information ball milling-mixing hot-press method prepare by undoped SixGe1
-x and containing the nanometer second-phase Si of doped element
yge
1-y(x>y) the SiGe base alloy with modulation-doped structure forming, can obtain high carrier mobility and power factor (α
2σ), ZT value also so significantly improves.
Synthetic and the preparation of material be unable to do without phasor.Mg
2si-Mg
2in Sn pseudo binary system, have a region that cannot form single phase solid solution, i.e. miscibility gap (miscibility gap), is the structure regulating of this system condition of providing convenience.Yet in different phasors in early days, (Mg
2si)
n(Mg
2sn)
1-nthe border composition of miscibility gap is inconsistent, for example Russian scholar thinks that this miscibility gap region is 0.4<n<0.6 (Neorgan.Mater.4, p.1656,1968), and the Study of Phase Diagram result of Japanese scholars shows that the border composition of miscibility gap changes with temperature, at near room temperature, be 0.35<n<0.92 (Zh.Neorgan.Materialy2, p.870,1966).In recent years; scholars calculate by more accurate laboratory facilities binding isotherm; think that the bounds of miscibility gap becomes large with the reduction of temperature; near room temperature miscibility gap is about 0.28<x<0.91 (Proc.15th Int.Conf.on Thermoelectrics; Pasadena; USA1996, pp.133-136; J.Alloy.Compd.31, p.192,2007), even may extend to 0<x<1(J.Alloy.Compd.509, p.3326,2011).
Summary of the invention
The shortcoming of prior art, the object of the present invention is to provide a kind of Mg-Si-Sn base nano composite thermoelectric materials and preparation method thereof in view of the above, when reducing lattice thermal conductivity, improves power factor, realizes the significantly raising of conducting material thermoelectricity performance.
For achieving the above object and other relevant objects, the invention provides a kind of Mg-Si-Sn base nano composite thermoelectric materials, described Mg-Si-Sn base nano composite thermoelectric materials has laminate structure, and its chemical general formula is Mg
2si
xsn
1-xm
y, wherein, M is expressed as doped element, is selected from a kind of in Sb, Bi, Ga, Ag, Cu or Al, 0.3≤x≤0.9,0.005≤y≤0.15.
Preferably, every one deck structure has different Mg:Si:Sn atomic molar content ratios and different M doping contents.
Preferably, every one deck structure is comprised of Mg-Si-Sn matrix nanocrystal second-phase that distribute and phase interface and described matrix coherence or half coherence with disperse.
Preferably, the size range of described nanocrystal second-phase is 5～200nm.
Preferably, the span of x is 0.3≤x≤0.7.
Preferably, the span of y is 0.03≤y≤0.15.
Preferably, described Mg-Si-Sn base nano composite thermoelectric materials adopts rf induction furnace middling speed falling temperature method and heat treating method to make.
The present invention also provides a kind of preparation method of Mg-Si-Sn base nano composite thermoelectric materials, and described preparation method at least comprises the following steps:
1) according to chemical general formula Mg
2si
xsn
1-xm
ythe stoichiometric ratio of middle element takes raw material simple substance Mg, Si, Sn and M, and it is excessive 3%～10% that wherein Mg presses atomic percent, to compensate the vaporization losses of Mg in follow-up pyroprocess; Wherein, M is expressed as a kind of in Sb, Bi, Ga, Ag, Cu or Al, 0.3≤x≤0.9,0.005≤y≤0.15;
2) raw material taking is sealed in the double container being formed by inactive ceramic/conduction inductor block, afterwards this container is placed in and in rf induction furnace, is heated to the first temperature, at the first temperature, be incubated t1 and after the time, be cooled to the second temperature, at the second temperature, be incubated t2 and be quickly cooled to room temperature after the time;
3) described container is transferred in the process furnace of uniformity of temperature profile, at the 3rd temperature, anneals the t3 time, cooling after, obtain the thermoelectric material of laminate structure.
Preferably, described step 2) in, in rf induction furnace, pass into rare gas element, the supply frequency of rf induction furnace is greater than 100kHz.
Preferably, described rare gas element is high pure nitrogen or argon gas, and stove internal gas pressure is 0.05～6 normal atmosphere.
Preferably, described step 2) the first temperature in is 900～1100 ℃, and soaking time t1 is 30～120 minutes.
Preferably, described step 2) the second temperature in is 500～700 ℃, and soaking time t2 is 10～60 minutes, and wherein, the speed of being down to the second temperature from the first temperature is 10～100 ℃/min.
Preferably, in described step 3), under the protection of rare gas element, anneal, annealing temperature is 550～750 ℃, and annealing time t3 is 10～200 hours, and the rate of cooling after annealing is 1～10K/min.
Preferably, described rare gas element is high pure nitrogen or argon gas.
As mentioned above, Mg-Si-Sn base nano composite thermoelectric materials of the present invention and preparation method thereof, there is following beneficial effect: by rational experiment flow and experiment parameter, design, obtain having the Mg-Si-Sn based composites of stratiform modulation-doped structure and coherent interface nanostructure, doped element has different distributed densities between different layers, current carrier enters from the higher layer transition of doping content the layer that doping content is lower, effectively reduced the ionization scattering center in material, make material in the situation that overall doping content is constant, realize the raising of specific conductivity and power factor, and in follow-up heat treatment process, layer structure material original position diffusion-precipitation coherence nanocrystal second-phase that distribute, identical with matrix cystal direction does not affect electric property when effectively reducing lattice thermal conductivity.The growth in situ method that the present invention uses can reduce interface pollution, and preparation is simple and have good controllability simultaneously.
Accompanying drawing explanation
Fig. 1 is preparation method's schema of Mg-Si-Sn base nano composite thermoelectric materials of the present invention.
Fig. 2 is the XRD figure spectrum of the thermoelectric material of the embodiment of the present invention one preparation.
Fig. 3 a is the low range SEM figure of the thermoelectric material of the embodiment of the present invention one preparation.
Fig. 3 b is that the EDS in S1, S3 in Fig. 3 a, S5 region can spectrogram.
Fig. 4 a is the high magnification FESEM figure of the thermoelectric material of embodiment mono-preparation.
Fig. 4 b is the TEM figure of the thermoelectric material of embodiment mono-preparation.
Fig. 4 c is that details is amplified in the part of Fig. 4 b.
Fig. 5 a is that embodiment mono-prepares the Seebeck coefficients comparison curve in the thermoelectricity capability of material and prior art with Sb doped with Mg-Si-Sn thermoelectric material of identical component.
Fig. 5 b is that embodiment mono-prepares the power factor comparison curves in the thermoelectricity capability of material and prior art with Sb doped with Mg-Si-Sn thermoelectric material of identical component.
Fig. 5 c is that embodiment mono-prepares thermal conductivity κ and the lattice thermal conductivity κ in the thermoelectricity capability of material and prior art with Sb doped with Mg-Si-Sn thermoelectric material of identical component
phcomparison curves.
Fig. 5 d is that embodiment mono-prepares the ZT comparison curves in the thermoelectricity capability of material and prior art with Sb doped with Mg-Si-Sn thermoelectric material of identical component.
Fig. 6 a is the low range SEM figure of the thermoelectric material of embodiment bis-preparations.
Fig. 6 b is that the EDS in S1, S2 in Fig. 6 a, S3 region can spectrogram.
Fig. 7 a is the high magnification FESEM figure of the thermoelectric material of embodiment bis-preparations.
Fig. 7 b is the TEM figure of the thermoelectric material of embodiment bis-preparations;
Fig. 8 a is that embodiment mono-prepares the Seebeck coefficients comparison curve in the thermoelectricity capability of material and prior art with Bi doped with Mg-Si-Sn thermoelectric material of identical component.
Fig. 8 b is that embodiment mono-prepares the power factor comparison curves in the thermoelectricity capability of material and prior art with Bi doped with Mg-Si-Sn thermoelectric material of identical component.
Fig. 8 c is that embodiment mono-prepares thermal conductivity κ and the lattice thermal conductivity κ in the thermoelectricity capability of material and prior art with Bi doped with Mg-Si-Sn thermoelectric material of identical component
phcomparison curves.
Fig. 8 d is that embodiment mono-prepares the ZT comparison curves in the thermoelectricity capability of material and prior art with Bi doped with Mg-Si-Sn thermoelectric material of identical component.
Fig. 9 is Mg
2si
xsn
1-xcounterfeit binary phase diagram and composition are that the mixture of x solidifies the formation schematic diagram of temperature-fall period laminate tissue moderate speed.
Embodiment
Below, by specific specific examples explanation embodiments of the present invention, those skilled in the art can understand other advantages of the present invention and effect easily by the disclosed content of this specification sheets.The present invention can also be implemented or be applied by other different embodiment, and the every details in this specification sheets also can be based on different viewpoints and application, carries out various modifications or change not deviating under spirit of the present invention.
The present invention adopts rf induction furnace middling speed falling temperature method and heat treating method to prepare the technical process of Mg-Si-Sn base nano composite thermoelectric materials, and as shown in Figure 1, described preparation method at least comprises the following steps:
Step S1, according to chemical general formula Mg
2si
xsn
1-xm
ythe stoichiometric ratio of middle element takes simple substance raw material Mg, Si, Sn and M, and it is excessive 3%～10% that wherein Mg presses atomic percent, to compensate the vaporization losses of Mg in follow-up pyroprocess; Wherein, M is expressed as a kind of in Sb, Bi, Ga, Ag, Cu or Al, 0.3≤x≤0.9,0.005≤y≤0.15;
Step S2, the raw material taking is sealed in the double container being formed by inactive ceramic/conduction inductor block, afterwards this container is placed in and in rf induction furnace, is heated to the first temperature, at the first temperature, be incubated t1 and after the time, be cooled to the second temperature, at the second temperature, be incubated t2 and be quickly cooled to room temperature after the time;
Step S3, is transferred to described container in the process furnace of uniformity of temperature profile, at the 3rd temperature, anneals the t3 time, cooling after, obtain the thermoelectric material of laminate structure.
This preparation method is simple and controllability is better, is easy to produce in enormous quantities.
Say and be noted that, in radio-frequency induction sintering process, frequency is greater than the high-frequency current of 100kHz at the inner alternating magnetic field that produces of ruhmkorff coil, conduction inductor block surface in alternating magnetic field forms high-density eddy current, utilize eddy current and magnetic hysteresis loss to produce heat effect, inductor block rises to 900～1100 ℃ from room temperature within a short period of time.Sample in inactive ceramic crucible also heats up very soon under conduction of heat, and the thick inductor block of 10～30mm plays shielding effect to alternating magnetic field simultaneously, so in crucible, the metallic element such as Mg, Sn is affected by induction stirring hardly.
In addition, this rf induction furnace passes into rare gas element in sintering process stove, and the leak rate of body of heater is lower than 2Pa/ hour.Preferably, described rare gas element is high pure nitrogen or argon gas, and stove internal gas pressure is 0.05～6 normal atmosphere.
Below in conjunction with accompanying drawing, Mg-Si-Sn base nano composite thermoelectric materials of the present invention and preparation method thereof is described in detail.
Embodiment mono-
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.10si
0.3sn
0.7sb
0.03take simple substance raw material Mg, Si, Sn, Sb, these raw materials are sealed in the double container being formed by inactive ceramic/conduction inductor block, be placed in afterwards in rf induction furnace, under high pure nitrogen protection, be heated to 1000 ℃, being incubated fully melts it in 30 minutes, then the speed with 20 ℃/min is cooled to 600 ℃, be incubated and be quickly cooled to room temperature after 30 minutes, and then be transferred in the process furnace of uniformity of temperature profile under high pure nitrogen protection 600 ℃ of annealing 20 hours, after cooling with the speed of 5K/min, obtain having the Mg-Si-Sn base thermoelectricity material of stratiform modulation-doped structure and coherence nanostructure.
After obtaining required thermoelectric material, this material is carried out to morphology analysis and performance test.
The sample that adopts Bruker AXS D8ADVANCE type X ray polycrystalline diffractometer (XRD) to prepare the present embodiment carries out material phase analysis.XRD figure spectrum refers to accompanying drawing 2, can find out, sample is between Mg
2si and Mg
2between Sn diffraction peak, there are a plurality of diffraction peaks, prove the matrix material that sample is comprised of a plurality of Mg-Si-Sn solid solution phases with different Si:Sn ratios.
Adopt JEOL JSM-5400 scanning electronic microscope (SEM) to observe the microtexture of the present embodiment sample, as shown in Figure 3 a, can see, sample is comprised of the laminate structure with different contrasts.With with the supporting energy dispersion X ray spectrum instrument (EDS) of microscope, each layer being carried out to composition analysis, representative structure results as shown in Figure 3 b, S1 layer to the atomic molar content ratio of the Mg:Si:Sn:Sb of S5 layer is respectively 2.08:0.90:0.10:0.01,2.05:0.74:0.26:0.03,2.03:0.67:0.33:0.04,1.98:0.54:0.46:0.05,1.93:0.27:0.73:0.07, proof sample has stratiform modulation-doped structure, and every layer has different Mg:Si:Sn ratio and doping content.
Employing has the JEOL JSM-6700F field emission scanning electron microscope (FESEM) of high-resolution and grain-size and the interfacial state that Philips CM200FEG transmission electron microscope (TEM) is observed respectively the present embodiment material.The FESEM figure of Fig. 4 a is that details is amplified in the part in S5 region shown in Fig. 3 a, shows that second-phase (doping phase) nanocrystal that this layer material is of a size of 5～100nm by matrix and a large amount of disperse distribution forms.In the TEM of Fig. 4 b figure, A, B, C, D represent respectively to have identical face-centered cubic (FCC) structure and the slightly discrepant nanocrystal of spacing.Fig. 4 c is that details is amplified in the part of Fig. 4 b, therefrom can find out between crystal grain A-C and there is semicoherent interface, and interface between A-B, B-C coherence completely almost.
The carrier concentration and the mobility that adopt Quantum Design physical property measurement system (PPMS) measure sample, obtain in the present embodiment, and the carrier concentration of sample when 300K is 1.5 * 10
20cm
-3, carrier mobility is 136cm
2/ Vs, be about Sb doped with Mg-Si-Sn system of current bibliographical information maximum carrier mobility (Zaitsev, et al., Phys.Rev.B74,2006, p.045207; W.Liu, et al., Phys.Rev.Lett.108,2012, twice p.166601), confirms that modulation-doped structure can effectively improve the carrier mobility of material.
Adopt respectively thermal conductivity κ and electric property S, the σ of LFA1000 laser conductometer, LSR-3 thermoelectric measurement systematic survey sample.By Wiedemann-Franz formula κ
c=L σ T calculates the current carrier thermal conductivity κ of sample
c, wherein L is Lorentz constant (the L ≈ 2.45 * 10 of heavy doping degeneracy semiconductor
-8v
2k
-2), then by κ=κ
ph+ κ
cdraw lattice thermal conductivity κ
ph, then according to ZT=(S
2σ/κ) T calculates the ZT value of sample.Fig. 5 a-5d is respectively Seebeck coefficient S, the power factor S of the present embodiment sample
2σ, thermal conductivity κ and lattice thermal conductivity κ
ph, zero dimension figure of merit ZT variation with temperature curve and with reference 1(W.Liu, et al., Phys.Rev.Lett.108,2012, p.166601) in the contrast of sample.The sample of reference 1 is in current bibliographical information, to have Sb doped with Mg-Si-Sn thermoelectric material of the highest ZT, and composition is Mg
2.15si
0.28sn
0.71sb
0.006, and the sample of the present embodiment is very approaching.Reference 1 adopts long solid reaction process and the preparation of discharge plasma sintering method, and composition profiles is more even.By Fig. 5 a and 5b, can be found out, the Seebeck coefficient absolute value of the present embodiment sample is lower than the Seebeck coefficient absolute value of reference 1 sample, but power factor and specific conductivity, far above the latter, confirm that modulation-doped structure can effectively improve the power factor of material thus.By Fig. 5 c, can be found out, the overall thermal conductivity κ of the present embodiment sample is higher than reference 1 sample, but lattice thermal conductivity κ
phlower than the latter, the coherence nanostructure of proved embodiment can significantly reduce lattice thermal conductivity.From Fig. 5 d, can find out, the ZT of the present embodiment sample up to 1.50, surpasses the maximum of such material of international report at present in the time of 505 ℃, confirms that modulation-doped structure and coherence nanostructure can effectively improve the overall performance of material.
Embodiment bis-
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.10si
0.3sn
0.7bi
0.015take simple substance Mg, Si, Sn, Bi raw material, these raw materials are sealed in to the double container being formed by inactive ceramic/conduction inductor block, be placed in afterwards in rf induction furnace, under high-purity argon gas protection, be heated to 1000 ℃, being incubated fully melts it in 35 minutes, then the speed with 20 ℃/min is cooled to 600 ℃, be incubated and be quickly cooled to room temperature after 30 minutes, and then be transferred in the process furnace of uniformity of temperature profile under high-purity argon gas protection 600 ℃ of annealing 40 hours, after cooling with the speed of 5K/min, obtain having the Mg-Si-Sn base thermoelectricity material of stratiform modulation-doped structure and coherence nanostructure.
After obtaining required thermoelectric material, this material is carried out to morphology analysis and performance test.
The sample that XRD analysis obtains above-mentioned preparation is heterogeneous composite material, a plurality of Mg-Si-Sn solid solution phases with different Si:Sn ratios, consists of.
Fig. 6 a is the low range SEM picture of the present embodiment sample, and show sample is comprised of the laminate structure with different contrasts.Representative EDS composition analysis result as shown in Figure 6 b.The atomic molar content ratio of layer S1, the S2 indicating in Fig. 6 a, the Mg:Si:Sn:Bi of S3 is respectively 1.93:0.83:0.17:0.009,1.94:0.64:0.36:0.027,1.90:0.22:0.78:0.046, proof sample has stratiform modulation-doped structure, and every layer has different Mg:Si:Sn ratio and doping content.
The FESEM figure of Fig. 7 a is that details is amplified in the part of S3 layer shown in Fig. 6 a, shows that the second-phase nanocrystal that this layer material is of a size of 5-200nm by matrix and a large amount of disperse distribution forms.The TEM figure of Fig. 7 b further confirms, crystal boundary and the complete coherence of matrix of the second-phase nanocrystal that disperse distributes.
It is 3.62 * 10 that Hall test obtains the carrier concentration of this routine sample when 300K
19cm
-3, carrier mobility is 479cm
2/ Vs is almost maximum carrier mobility (Liu, the et al. of Bi doped with Mg-Si-Sn system of current bibliographical information, J.Solid State Chem.203,2013, p.333) 8 times, confirm that modulation-doped structure can effectively improve the carrier mobility of material.
The performance test results as shown in Figure 8.Fig. 8 a～Fig. 8 d is respectively Seebeck coefficient S, the power factor S of the present embodiment sample
2σ, thermal conductivity κ and lattice thermal conductivity κ
ph, zero dimension figure of merit ZT variation with temperature curve and with reference 2(Khan, et al., Scripta Mater.69,2013, p.606) sample, reference 3(Liu, et al., J.Solid State Chem.203,2013, the p.333) contrast of sample.Reference 2, reference 3 samples are the Bi doped with Mg-Si-Sn thermoelectric materials of the highest ZT that have of current bibliographical information.Reference 2 sample constituents are Mg
2si
0.6sn
0.55ge
0.05bi
0.03, adopt long-time ball milling and hot-press method preparation.Actual measurement composition with reference to 3 samples is Mg
2.12si
0.37sn
0.60bi
0.025, and this routine sample is very approaching, adopts long solid reaction process and the preparation of discharge plasma sintering method.By Fig. 8 a and 8b, can be found out, the Seebeck coefficient of the Seebeck coefficient of the present embodiment sample and reference 2, reference 3 is very approaching, but power factor higher than rear both, confirm that modulation-doped structure can effectively improve specific conductivity and the power factor of material.By Fig. 8 c, can be found out, the overall thermal conductivity κ of 500 ℃ of following the present embodiment samples is higher than the thermal conductivity of reference 2, reference 3 samples, but lattice thermal conductivity κ
phfar below rear both, confirm that coherence nanostructure can significantly reduce lattice thermal conductivity.From Fig. 8 d, can find out, the ZT of the present embodiment sample reaches 1.45 in the time of 509 ℃, surpasses the maximum of such material of international report at present, confirms that modulation-doped structure and coherence nanostructure can effectively improve the overall performance of material.
Embodiment tri-
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.10si
0.4sn
0.6bi
0.03take simple substance Mg, Si, Sn, Bi raw material; these raw materials are sealed in the double container being formed by inactive ceramic/conduction inductor block; be placed in afterwards in rf induction furnace and under high pure nitrogen protection and be heated to 1000 ℃; being incubated fully melts it in 40 minutes; then the speed with 20 ℃/min is cooled to 600 ℃; be incubated and be quickly cooled to room temperature after 30 minutes; and then be transferred in the process furnace of uniformity of temperature profile under high pure nitrogen protection 650 ℃ of annealing 40 hours; after cooling with the speed of 5K/min, obtain required Mg-Si-Sn base thermoelectricity material.
It is the stratified composite with modulation-doped structure and coherence nanostructure that microtexture and composition analysis obtain the present embodiment sample.The ZT value that performance test obtains this nano composite thermoelectric materials is 1.47 in the time of 514 ℃.
Embodiment tetra-
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.10si
0.45sn
0.55sb
0.03take simple substance Mg, Si, Sn, Sb raw material; these raw materials are sealed in the double container being formed by inactive ceramic/conduction inductor block; be placed in afterwards in rf induction furnace and under high pure nitrogen protection and be heated to 1000 ℃; being incubated fully melts it in 30 minutes; then the speed with 20 ℃/min is cooled to 700 ℃; be incubated and be quickly cooled to room temperature after 30 minutes; and then be transferred in the process furnace of uniformity of temperature profile under high pure nitrogen protection 650 ℃ of annealing 30 hours; after cooling with the speed of 5K/min, obtain required Mg-Si-Sn base thermoelectricity material.
It is the stratified composite with modulation-doped structure and coherence nanostructure that microtexture and composition analysis obtain the present embodiment sample.The ZT value that performance test obtains this nano composite thermoelectric materials is 1.45 in the time of 606 ℃.
Embodiment five
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.10si
0.7sn
0.3sb
0.03take simple substance Mg, Si, Sn, Sb raw material; these raw materials are sealed in the double container being formed by inactive ceramic/conduction inductor block; be placed in afterwards in rf induction furnace and under high pure nitrogen protection and be heated to 1000 ℃; being incubated fully melts it in 30 minutes; then the speed with 25 ℃/min is cooled to 600 ℃; be incubated and be quickly cooled to room temperature after 30 minutes; and then be transferred in the process furnace of uniformity of temperature profile under high pure nitrogen protection 750 ℃ of annealing 40 hours; after cooling with the speed of 5K/min, obtain required Mg-Si-Sn base thermoelectricity material.
It is the stratified composite with modulation-doped structure and coherence nanostructure that microtexture and composition analysis obtain the present embodiment sample.The ZT value that performance test obtains this nano composite thermoelectric materials is 1.36 in the time of 606 ℃.
Embodiment six
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.15si
0.7sn
0.3sb
0.045take the simple substance raw materials such as Mg, Si, Sn, Bi; these raw materials are sealed in the double container being formed by inactive ceramic/conduction inductor block; be placed in afterwards rf induction furnace and be heated to 1100 ℃ under high-purity argon gas protection; being incubated fully melts it in 60 minutes; then the speed with 25 ℃/min is cooled to 600 ℃; be incubated and be quickly cooled to room temperature after 30 minutes; and then be transferred in the process furnace of uniformity of temperature profile under protection of inert gas 700 ℃ of annealing 40 hours; after cooling with the speed of 5K/min, obtain required Mg-Si-Sn base thermoelectricity material.
It is the stratified composite with modulation-doped structure and coherence nanostructure that microtexture and composition analysis obtain this routine sample.The ZT value that performance test obtains this nano composite thermoelectric materials is 1.10 in the time of 607 ℃.
Embodiment seven
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.06si
0.4sn
0.6ga
0.015take the simple substance raw materials such as Mg, Si, Sn, Ga; these raw materials are sealed in the double container being formed by inactive ceramic/conduction inductor block; be placed in afterwards rf induction furnace and be heated to 1000 ℃ under high-purity argon gas protection; being incubated fully melts it in 30 minutes; then the speed with 20 ℃/min is cooled to 600 ℃; be incubated and be quickly cooled to room temperature after 30 minutes; and then be transferred in the process furnace of uniformity of temperature profile under protection of inert gas 600 ℃ of annealing 40 hours; after cooling with the speed of 5K/min, obtain required Mg-Si-Sn base thermoelectricity material.
It is the stratified composite with modulation-doped structure and coherence nanostructure that microtexture and composition analysis obtain this routine sample.The ZT value that performance test obtains this nano composite thermoelectric materials is 0.46 in the time of 315 ℃, surpasses the maximum of the Ga doping P type Mg-Si-Sn base thermoelectricity material of international report at present.
Embodiment eight
In being filled with the glove box of nitrogen, by stoichiometric ratio Mg
2.04si
0.3sn
0.7ag
0.03take the simple substance raw materials such as Mg, Si, Sn, Ga; these raw materials are sealed in the double container being formed by inactive ceramic/conduction inductor block; be placed in afterwards rf induction furnace and be heated to 1000 ℃ under high-purity argon gas protection; being incubated fully melts it in 30 minutes; then the speed with 20 ℃/min is cooled to 600 ℃; be incubated and be quickly cooled to room temperature after 30 minutes; and then be transferred in the process furnace of uniformity of temperature profile under protection of inert gas 600 ℃ of annealing 40 hours; after cooling with the speed of 5K/min, obtain required Mg-Si-Sn base thermoelectricity material.
It is the stratified composite with modulation-doped structure and coherence nanostructure that microtexture and composition analysis obtain this routine sample.The ZT value that performance test obtains this nano composite thermoelectric materials is 0.51 in the time of 300 ℃, surpasses the maximum of the Ag doping P type Mg-Si-Sn base thermoelectricity material of international report at present.
Embodiment nine
Adopt employing rf induction furnace middling speed falling temperature method and the heat treating method of embodiment six to prepare respectively nano composite thermoelectric materials Mg
2.10si
0.7sn
0.3cu
0.045, Mg
2.10si
0.7sn
0.3al
0.045, Mg
2.10si
0.6sn
0.4al
0.055, Mg
2.10si
0.4sn
0.6al
0.065, Mg
2.10si
0.5sn
0.5al
0.10, the thermoelectric material of gained is known after testing all has following structure properties and a thermoelectricity capability: in the XRD figure spectrum of sample, thing phase show sample is the stratified composite with modulation-doped structure and coherence nanostructure; The thermoelectricity capability of sample is improved on the whole.
If Fig. 9 is Mg
2si-Mg
2the counterfeit binary phase diagram of Sn, the cardinal principle of the Mg-Si-Sn base composite thermoelectric material with modulation-doped structure and coherence nanostructure forming is described in embodiment mono-to embodiment seven in conjunction with this figure: suppose that component of mixture is x, high temperature melting and be incubated for some time after with the speed of 20-100 ℃/min, lower the temperature.When melt cooling is to T
1temperature, forms the rich Si sosoloid S that minute quantity composition is b in the liquid phase that composition is a=x
b, continuing to reduce temperature, liquid composition changes along aA line, and solid phase composition changes along bC line.Because the cooling rate that hastens is very fast, diffusion has little time fully to carry out, therefore the rich Si sosoloid surface of formerly crystallization constantly nucleating growth go out sosoloid that Si content reduces gradually (for example, in temperature T
2time form sosoloid S
d), form the lamellar structure with gradient composition.The thickness of lamellar structure can be controlled by changing cooling rate.When temperature is down to peritectic line (ABC line), because cooling rate is very fast, Peritectic Reaction (L
a+ S
c→ S
b) have little time fully to carry out solid solution phase S
bthe sosoloid S that the layer component that surface coverage is very thin is A
a.Continuation is lowered the temperature, and residual solution phase composite changes along Ae line, and the solid phase composition of new nucleation changes along Bf line, the sosoloid stratiform structure adding gradually at the sosoloid stratiform tissue surface continuation formation Sn of rich Si content.
Because the segregation coefficients of doped element in Si such as Sb, Bi, Ga, Ag, Cu, Al are much smaller than 1 (J.Mater.Sci.17, p.3077,1982), corresponding, the segregation coefficient of these elements in the Mg-Si-Sn of rich Si based solid solution is also lower than 1.Therefore in above-mentioned process of setting, the concentration of these doped elements in the sosoloid of rich Si is far below the concentration in liquid phase.And be enriched in gradually in the rich Sn sosoloid of after coagulation, the concentration that forms thus doped element is along with Si content reduces and the stratiform modulation-doped structure that increases gradually gradually.
When temperature is down to T
3time, residue liquid phase starts crystallization and generates sosoloid S
x.When temperature is down to T
4time and miscibility gap left margin BD intersect, the layed solid-solution that component is x produces original position and is separated under thermodynamics drives, this chromatography goes out the cenotype S that component is h
h.Due to S
hwith S
xcompare and there is very large composition fluctuation, S
hto separate out with the mode original position of forming core growth, and form the nano particle that disperse distributes.When the crystal formation of two thing phases is identical, orientation is consistent, and lattice mismatch is while being less than 5%, both can form coherent interface (Pan Jinsheng etc., Fundamentals of Material Science, press of Tsing-Hua University, 2004, p.415).S
h, S
xcomponent respectively with Mg
2si
0.
4sn
0.
6, Mg
2si
0.
8sn
0.
2close, both lattice parameters are respectively afterwards
(R.B.Song, et al., Mater.Sci.Eng.B136,2007, p.111).So S
h, S
xlattice parameter difference be no more than 3%, between two-phase, can form coherent interface.The two-phase interface with coherent interface can be lower, in kinetics, is therefore also more stable.Because solid-state phase changes speed is slower, at above-mentioned temperature-fall period situ, be separated also not obvious.
In annealing process in follow-up uniformity of temperature profile process furnace, all will there is original position and be separated in each layer tissue satisfying condition under thermodynamics drives.As long as annealing temperature for example, lower than the crossing temperature of component lines x and miscibility gap border, temperature T
5, there is solid-state being separated in the lamellar structure of all the components between i-j, reaches final equilibrium composition, i.e. Si+S after the sufficiently long annealing time of experience
jtwo-phase structure.In like manner, suppose that annealing temperature is T
6, there is solid-state being separated in the lamellar structure of all the components between k-l, after the sufficiently long annealing time of experience, reaches equilibrium composition S
k+ S
ltwo-phase structure.Annealing temperature is lower, and two phase compositions that obtain differ larger, more easily obtains having the disperse distribution second-phase crystal grain of nanostructure, more easily can form coherent interface, but it is longer to reach thermodynamic(al)equilibrium required time when two-phase lattice parameter difference is no more than 5%.Meanwhile, along with the growth of annealing time, doped element diffuses into rich Si layer by rich Sn layer, and doped element trends towards being uniformly distributed in whole sample interior, and modulation-doped structure fades away.Therefore, suitable annealing temperature and annealing time are most important to the overall thermal electrical property of material.
In sum, the invention provides a kind of Mg-Si-Sn base nano composite thermoelectric materials and preparation method thereof, utilize up-to-date Mg
2si-Mg
2the feature of the counterfeit binary phase diagram of Sn, by rational experiment flow and experiment parameter, design, preparation has the Mg-Si-Sn based composites of stratiform modulation-doped structure, doped element has different distributed densities between different layers, in the situation that keeping doping content constant (Seebeck coefficient is constant) by realizing the raising of specific conductivity and power factor.And in follow-up heat treatment process, layer structure material original position diffusion-precipitation coherence nanocrystal second-phase that distribute, identical with matrix cystal direction does not affect electric property when effectively reducing lattice thermal conductivity.Simple, economy, effective means for the present invention, by Mg
2si-Mg
2the performance of Sn base thermoelectricity material is increased to ZT=1.5.
So the present invention has effectively overcome various shortcoming of the prior art and tool high industrial utilization.
Above-described embodiment is illustrative principle of the present invention and effect thereof only, but not for limiting the present invention.Any person skilled in the art scholar all can, under spirit of the present invention and category, modify or change above-described embodiment.Therefore, such as in affiliated technical field, have and conventionally know that the knowledgeable, not departing from all equivalence modifications that complete under disclosed spirit and technological thought or changing, must be contained by claim of the present invention.
Claims (14)
1. a Mg-Si-Sn base nano composite thermoelectric materials, is characterized in that, described Mg-Si-Sn base nano composite thermoelectric materials has laminate structure, and its chemical general formula is Mg
2si
xsn
1-xm
y, wherein, M is expressed as doped element, is selected from a kind of in Sb, Bi, Ga, Ag, Cu or Al, 0.3≤x≤0.9,0.005≤y≤0.15.
2. Mg-Si-Sn base nano composite thermoelectric materials according to claim 1, is characterized in that: every one deck structure has different Mg:Si:Sn atomic molar content ratios and different M doping contents.
3. Mg-Si-Sn base nano composite thermoelectric materials according to claim 1, is characterized in that: that every one deck structure is distributed by Mg-Si-Sn matrix and disperse and form with the nanocrystal second-phase of described matrix phase interface coherence or half coherence.
4. Mg-Si-Sn base nano composite thermoelectric materials according to claim 3, is characterized in that: the size range of described nanocrystal second-phase is 5～200nm.
5. Mg-Si-Sn base nano composite thermoelectric materials according to claim 1, is characterized in that: the span of x is 0.3≤x≤0.7.
6. Mg-Si-Sn base nano composite thermoelectric materials according to claim 1, is characterized in that: the span of y is 0.03≤y≤0.15.
7. according to the Mg-Si-Sn base nano composite thermoelectric materials described in claim 1～6 any one, it is characterized in that: described Mg-Si-Sn base nano composite thermoelectric materials adopts rf induction furnace middling speed falling temperature method and heat treating method to make.
8. a preparation method for the Mg-Si-Sn base nano composite thermoelectric materials as described in claim 1～7 any one, is characterized in that, described preparation method at least comprises the following steps:
1) according to chemical general formula Mg
2si
xsn
1-xm
ythe stoichiometric ratio of middle element takes simple substance raw material Mg, Si, Sn and M, and it is excessive 3%～10% that wherein Mg presses atomic percent, to compensate the vaporization losses of Mg in follow-up pyroprocess; Wherein, M is expressed as a kind of in Sb, Bi, Ga, Ag, Cu or Al, 0.3≤x≤0.9,0.005≤y≤0.15;
2) raw material taking is sealed in the double container being formed by inactive ceramic/conduction inductor block, afterwards this container is placed in and in rf induction furnace, is heated to the first temperature, at the first temperature, be incubated t1 and after the time, be cooled to the second temperature, at the second temperature, be incubated t2 and be quickly cooled to room temperature after the time;
3) described container is transferred in the process furnace of uniformity of temperature profile, at the 3rd temperature, anneals the t3 time, cooling after, obtain the thermoelectric material of laminate structure.
9. the preparation method of Mg-Si-Sn base nano composite thermoelectric materials according to claim 8, is characterized in that: described step
Rapid 2) in, in rf induction furnace, pass into rare gas element, the supply frequency of rf induction furnace is greater than 100kHz.
10. the preparation method of Mg-Si-Sn base nano composite thermoelectric materials according to claim 9, is characterized in that: described rare gas element is high pure nitrogen or argon gas, and stove internal gas pressure is 0.05～6 normal atmosphere.
The preparation method of 11. Mg-Si-Sn base nano composite thermoelectric materials according to claim 8, is characterized in that: the first temperature described step 2) is 900～1100 ℃, and soaking time t1 is 30～120 minutes.
The preparation method of 12. Mg-Si-Sn base nano composite thermoelectric materials according to claim 8, it is characterized in that: the second temperature described step 2) is 500～700 ℃, soaking time t2 is 10～60 minutes, the speed of wherein, being down to the second temperature from the first temperature is 10～100 ℃/min.
The preparation method of 13. Mg-Si-Sn base nano composite thermoelectric materials according to claim 8; it is characterized in that: in described step 3), under the protection of rare gas element, anneal; annealing temperature is 550～750 ℃; annealing time t3 is 10～200 hours, and the rate of cooling after annealing is 1～10K/min.
The preparation method of 14. Mg-Si-Sn base nano composite thermoelectric materials according to claim 13, is characterized in that: described rare gas element is high pure nitrogen or argon gas.
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| CN115915896A (en) * | 2023-01-16 | 2023-04-04 | 哈尔滨工业大学 | Preparation method of high-thermal-stability low-contact-resistance barrier layer based on MgAgSb-based thermoelectric material |
| CN115915896B (en) * | 2023-01-16 | 2023-06-02 | 哈尔滨工业大学 | Preparation method of MgAgSb-based thermoelectric material-based high-thermal-stability low-contact-resistance barrier layer |
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