WO2017030166A1 - ランガテイト系単結晶の製造方法及びランガテイト系単結晶 - Google Patents
ランガテイト系単結晶の製造方法及びランガテイト系単結晶 Download PDFInfo
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- 239000013078 crystal Substances 0.000 title claims abstract description 145
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 28
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 44
- 239000007789 gas Substances 0.000 claims abstract description 35
- 238000009413 insulation Methods 0.000 claims abstract description 33
- 230000001590 oxidative effect Effects 0.000 claims abstract description 23
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 13
- 239000011261 inert gas Substances 0.000 claims abstract description 10
- 239000002994 raw material Substances 0.000 claims abstract description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 35
- 239000001301 oxygen Substances 0.000 description 35
- 229910052760 oxygen Inorganic materials 0.000 description 35
- 238000002485 combustion reaction Methods 0.000 description 30
- 230000007547 defect Effects 0.000 description 20
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 18
- 229910052733 gallium Inorganic materials 0.000 description 18
- 239000000463 material Substances 0.000 description 14
- 239000000155 melt Substances 0.000 description 14
- 208000010392 Bone Fractures Diseases 0.000 description 12
- 206010017076 Fracture Diseases 0.000 description 12
- 239000007858 starting material Substances 0.000 description 12
- 238000001704 evaporation Methods 0.000 description 10
- 239000000203 mixture Substances 0.000 description 10
- 230000008020 evaporation Effects 0.000 description 9
- 238000001816 cooling Methods 0.000 description 7
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 6
- 229910005191 Ga 2 O 3 Inorganic materials 0.000 description 6
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 229910052741 iridium Inorganic materials 0.000 description 4
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 4
- -1 Ta 2 O 5 Inorganic materials 0.000 description 3
- 206010010214 Compression fracture Diseases 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 229910044991 metal oxide Inorganic materials 0.000 description 2
- 150000004706 metal oxides Chemical class 0.000 description 2
- 239000010453 quartz Substances 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000003746 solid phase reaction Methods 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- 229910001260 Pt alloy Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- AJNVQOSZGJRYEI-UHFFFAOYSA-N digallium;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Ga+3].[Ga+3] AJNVQOSZGJRYEI-UHFFFAOYSA-N 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 229910001195 gallium oxide Inorganic materials 0.000 description 1
- 230000002706 hydrostatic effect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910001936 tantalum oxide Inorganic materials 0.000 description 1
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Classifications
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/02—Single-crystal growth by pulling from a melt, e.g. Czochralski method adding crystallising materials or reactants forming it in situ to the melt
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/10—Crucibles or containers for supporting the melt
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/16—Oxides
- C30B29/22—Complex oxides
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/16—Oxides
- C30B29/22—Complex oxides
- C30B29/30—Niobates; Vanadates; Tantalates
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D35/00—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for
- F02D35/02—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions
- F02D35/023—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions by determining the cylinder pressure
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L23/00—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid
- G01L23/08—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid operated electrically
- G01L23/10—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid operated electrically by pressure-sensitive members of the piezoelectric type
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/08—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of piezoelectric devices, i.e. electric circuits therefor
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/09—Forming piezoelectric or electrostrictive materials
- H10N30/093—Forming inorganic materials
- H10N30/095—Forming inorganic materials by melting
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/30—Piezoelectric or electrostrictive devices with mechanical input and electrical output, e.g. functioning as generators or sensors
- H10N30/302—Sensors
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/853—Ceramic compositions
Definitions
- the present invention relates to a method for producing a highly insulating and highly stable piezoelectric oxide crystal. More specifically, the present invention relates to a method for producing a langate single crystal which is a piezoelectric oxide suitable for use in a piezoelectric element such as a combustion pressure sensor for measuring a combustion pressure in a combustion chamber of an internal combustion engine. The present invention also relates to a langate single crystal obtained by the production method.
- a combustion pressure sensor using an element of an oxide piezoelectric material exhibiting a piezoelectric effect (a charge is generated as a result of polarization generated in response to an applied force (pressure)) is used to detect the combustion pressure in the combustion chamber. It is used.
- the LTGA single crystal is produced by calcining a mixture of starting materials La 2 O 3 , Ta 2 O 5 , Ga 2 O 3 , and Al 2 O 3 that are weighed to give the target stoichiometric single crystal composition. It is carried out by a method (Czochralski method (CZ method)) or the like in which the produced LTGA sintered body (polycrystalline material) is melted, a seed crystal is immersed in the melt and gradually pulled up. .
- CZ method CZ method
- Patent Document 1 as a method for producing a langate single crystal by the Czochralski method, growth is performed in a gas growth atmosphere in which oxygen is mixed with an inert gas at a maximum of 2%, and the oxygen concentration is lowered from the growth atmosphere.
- a gas growth atmosphere in which oxygen is mixed with an inert gas at a maximum of 2%, and the oxygen concentration is lowered from the growth atmosphere.
- heat treatment in an inert gas atmosphere not containing an oxidizing gas reduces the coloration due to defects. It is described that the temperature dependency of resistivity is reduced, and a piezoelectric sensor (combustion pressure sensor) for high temperatures of 100 to 600 ° C. using a piezoelectric element made of a single crystal subjected to such heat treatment is described. ing.
- the stoichiometric ratio of the starting materials of lanthanum oxide, tantalum oxide, and gallium oxide is used when manufacturing a single crystal of an oxide piezoelectric material from a melt. It is also known to grow a single crystal in a mixed gas growing atmosphere in which the oxygen concentration in the inert gas is 0.2 to 5% by changing from the theoretical composition (see, for example, Patent Document 2).
- the piezoelectric material used in the piezoelectric element of the combustion pressure sensor is required to have high insulation (high resistivity of the piezoelectric material) and a certain level of strength that does not cause breakage such as cracking with respect to the pressure acting on the piezoelectric element. .
- an insulation resistivity of 3 ⁇ 10 8 ⁇ ⁇ cm or more is required at 500 ° C. due to the necessity of high-temperature operation in the internal combustion engine, and a pressure of 30 MPa or more is necessary due to the necessity of being used in an internal combustion engine of an automobile. On the other hand, it is required not to destroy.
- the present invention solves this difficulty and can be used for a piezoelectric element of a highly reliable combustion pressure sensor useful for measuring a combustion pressure in an internal combustion engine combustion chamber.
- the object is to provide a method which allows the production of crystals. It is also an object of the present invention to provide a rangate single crystal obtained by this production method.
- the method for producing a langate single crystal according to the present invention is a method for producing a rangate single crystal for growing a langate single crystal by the Czochralski method of pulling up a crystal from a raw material solution, and an atmosphere gas for growing the langate single crystal Is a mixed gas containing an oxidizing gas in an amount of more than 5% by volume in an inert gas.
- the raw material solution is preferably accommodated in a platinum crucible to grow a langate single crystal.
- the single crystal growth axis is preferably the Z axis, and the oxidizing gas is preferably O 2 .
- the Langatate single crystal of the present invention is characterized in that the compressive fracture strength in the X-axis direction at 200 ° C. is 1500 MPa or more.
- the langate single crystal of the present invention is also characterized by having an insulation resistance of 3.0 ⁇ 10 9 ⁇ ⁇ cm or more at 500 ° C.
- the langate single crystal of the present invention may be La 3 Ta 0.5 Ga 5.5-x Al x O 14 (0 ⁇ x ⁇ 5.5).
- the present invention it is possible to realize a langate single crystal having high insulation resistivity and high strength after growth.
- a piezoelectric element produced from the langate single crystal of the present invention it can be used for applications such as a combustion pressure sensor for measuring the combustion pressure of an internal combustion engine that requires high pressure measurement.
- the present invention relates to a langate single crystal and a method for producing the same.
- “Langate single crystal” is generally a single crystal of a compound represented by the formula La 3 Ta 0.5 Ga 5.5 O 14 (sometimes abbreviated as “LTG” here).
- the “Langatate single crystal” includes LTGA (La 3 Ta 0.5 Ga 5.5-x Al x O 14 (0 ⁇ x ⁇ 5.5)) in which a part of Ga is substituted with Al (here Is also abbreviated as “LTGA”).
- an LTGA single crystal As a starting material for the production of an LTGA single crystal, the following formula, y (La 2 O 3 ) + (1-xyz) (Ta 2 O 5 ) + z (Ga 2 O 3 ) + x (Al 2 O 3) ) (In this formula, 0 ⁇ x ⁇ 0.40 / 9, 3.00 / 9 ⁇ y ⁇ 3.23 / 9, 5.00 / 9 ⁇ z ⁇ 5. 50/9, more preferably 0.17 / 9 ⁇ x ⁇ 0.26 / 9, 3.06 / 9 ⁇ y ⁇ 3.15 / 9, 5.14 / 9 ⁇ z ⁇ 5.32 / 9
- An LTGA single crystal may be produced from a starting material having a composition represented by (A).
- Each of the starting materials La 2 O 3 , Ta 2 O 5 , Ga 2 O 3 , and Al 2 O 3 can be weighed to have a desired composition and mixed with a ball mill or the like to prepare a starting material mixture.
- the prepared starting material mixture is pressurized and calcined, and a sintered body having a target crystal structure can be produced by a solid phase reaction.
- the sintered body thus produced generally contains many polycrystals.
- a method for producing a langate single crystal is generally a method in which a single crystal is grown from a molten starting material.
- a single crystal is immersed in a melt of a polycrystalline material in a crucible and gradually pulled up.
- Examples include the Czochralski method (CZ method) for obtaining crystals. More specifically, the crucible is filled into the crucible, the crucible is heated to melt the sintered body in the crucible, and the seed crystal with crystal orientation is rotated on the melt surface. Then, after bringing the seed crystal into contact with the melt, the seed crystal is pulled out of the melt and the single crystal is grown in the Z-axis direction to grow an LTGA single crystal.
- CZ method Czochralski method
- the Z-axis direction in the Z-axis growth refers to the main axis (c-axis) direction of the seed crystal and is also referred to as a single crystal growth axis.
- the a-axis direction perpendicular to the Z-axis is the X-axis.
- the LTGA single crystal can be completed by separating the grown LTGA single crystal from the melt and cooling it to room temperature.
- FIG. 1 is a graph showing the relationship between the oxygen concentration in the growth atmosphere and the amount of gallium evaporated.
- the evaporation rate of gallium is a relative value where the evaporation rate is 1 when the oxygen concentration in the atmosphere is 0% by volume. As the oxygen concentration in the growth atmosphere increases, the amount of gallium in the raw material melt decreases.
- Evaporation of gallium in the raw material melt causes generation of gallium defects in which a part of gallium does not exist inside the single crystal to be grown.
- By growing in an atmosphere containing an oxidizing gas It is possible to reduce the amount of gallium evaporated and reduce gallium defects contained in the grown single crystal.
- the inventor of the present invention has a higher insulation resistivity, by making the oxidizing gas concentration in the inert gas in the growth atmosphere higher than that of the conventional method, specifically by making the oxidizing gas concentration such as oxygen higher than 5% by volume.
- the oxidizing gas concentration such as oxygen higher than 5% by volume.
- the lower limit of the oxygen concentration may be 6% by volume, and more preferably 10% by volume.
- the insulation resistivity measured at 500 ° C.
- the insulation resistivity required as a combustion pressure sensor is 3.0 ⁇ 10 8 ⁇ ⁇ cm or more at 500 ° C., preferably 3.0 ⁇ 10 9 ⁇ ⁇ cm or more, more preferably 3.4 ⁇ 10 9. It is ⁇ ⁇ cm or more, more preferably 6.3 ⁇ 10 9 ⁇ ⁇ cm or more.
- the piezoelectric material used in the piezoelectric element of the combustion pressure sensor requires an insulation resistivity of 3 ⁇ 10 8 ⁇ ⁇ cm or more at 500 ° C. because it needs to operate at a high temperature in an internal combustion engine.
- the langate single crystal can satisfy this requirement by making the oxidizing gas concentration of the above higher than 5% by volume. It has also been confirmed that the langate single crystal according to the present invention has an insulation resistivity of 6.5 ⁇ 10 9 ⁇ ⁇ cm, and this may be the upper limit of the insulation resistivity according to the present invention. The insulation resistivity will be described later with reference to FIG. Moreover, the compressive fracture strength in the X-axis direction at 200 ° C. of the langate single crystal obtained by the present invention is 1500 MPa or more, preferably 1700 MPa or more, more preferably 1750 MPa or more.
- the piezoelectric material used in the piezoelectric element of the combustion pressure sensor is required not to break down to a pressure of 30 MPa or more because it is required to be used in an internal combustion engine of an automobile. Can do.
- the Langate single crystal according to the present invention has also been confirmed to have a compressive fracture strength of 1875 MPa, and this may be the upper limit of the compressive fracture strength according to the present invention.
- the compression fracture strength will be described later with reference to FIG.
- oxygen defects increase in a high-concentration oxidizing gas atmosphere, and it is feared that the increase in oxygen defects reduces the insulation resistivity and strength.
- gallium defects caused by gallium evaporating from the molten liquid surface are generated throughout the entire single crystal, molecules leak out to the outside due to the partial pressure of oxygen in the growth atmosphere, which is the external environment for crystal growth. Since the oxygen defects generated are mainly defects on the surface layer of the single crystal, the presence of gallium defects has a greater effect on the properties of the single crystal, such as insulation resistivity and strength, than the oxygen defects.
- the ionic radius and the atomic radius of gallium are larger than that of oxygen. This is considered to be one of the reasons that the presence of gallium defects has a greater influence on the properties of single crystals than oxygen defects.
- the upper limit of the oxygen concentration is not particularly limited. However, when the oxygen concentration is increased to a certain level or more, characteristics such as insulation resistivity and strength tend to be saturated and the service life of the crucible is shortened. It may be 10% by volume.
- iridium, platinum, platinum alloy, or reinforced platinum in which a metal oxide is dispersed in platinum can be used as a crucible for storing a melt of a polycrystalline material. It is desirable to use a so-called platinum crucible mainly composed of platinum, such as reinforced platinum.
- the platinum crucible may have a platinum purity of 85% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 100%. Platinum has a lower evaporation rate than iridium. If the evaporation rate of iridium is 100, platinum is about 8.
- the crucible evaporation rate in the production of a single crystal is one of the important factors for obtaining a single crystal with good characteristics.
- the langate single crystal according to the present invention may be substantially free of iridium or the like. Substantially free refers to inevitable impurity levels, which may be less than 10 15 atoms / cm 3 , preferably less than 10 13 atoms / cm 3 , more preferably less than 10 11 atoms / cm 3. .
- the langate single crystal according to the present invention may slightly contain platinum derived from a platinum crucible, and its concentration is about 10 11 atoms / cm 3 or more to about 10 15 atoms / cm 3. There is no impact on
- the single crystal growth axis is preferably the Z axis.
- a single crystal is obtained by immersing a seed crystal in a melt and gradually pulling it up. For this reason, the pulling speed of the single crystal is a factor, and the interatomic distance of the single crystal in the pulling axis direction may deviate from the ideal and cause distortion in the single crystal.
- Piezoelectric materials exhibit a piezoelectric effect depending on the crystal axis direction, but if the crystal axis that generates electric charges is distorted, the piezoelectric characteristics are affected. Therefore, in the present invention, a single crystal manufacturing method that suppresses generation of strain during growth can be realized by raising and growing in the Z-axis direction in which no charge is generated even when a load is applied.
- Example 1 Hereinafter, the Langate single crystal of the present invention and the method for producing the same will be described by taking the LTGA of the Langate single crystal as an example.
- the starting raw material mixture is pressurized under a 1 ton hydrostatic pressure press and then calcined to produce a sintered body having a target crystal structure by a solid phase reaction.
- the temperature raising conditions at this time were a temperature rising rate of 180 ° C./h, a holding at 500 ° C. for 2 hours, a holding at 900 ° C. for 2 hours, and a holding at 1350 ° C. for 5 hours.
- the sintered body is filled in a reinforced platinum crucible in which metal oxide is dispersed in platinum.
- Melts (melt surface temperature 1500 ° C.).
- the seed crystal with crystal orientation is brought into contact with the melt surface while rotating at 10 rpm, and the shoulder is formed by pulling the seed crystal out of the melt by automatic control using a computer.
- the Z-axis growth of the single crystal is performed by the automatic control, and an LTGA single crystal having a diameter of 50 mm and a straight body length of 70 mm is manufactured.
- the single crystal is raised and separated from the melt, cooled to room temperature by automatic control using a computer, and then taken out of the chamber to complete the LTGA single crystal.
- the growth atmosphere of the LTGA single crystal is a mixed gas atmosphere containing an oxidizing gas such as oxygen of 6 to 15% by volume in a nitrogen gas atmosphere, and the LTGA single crystal is also cooled in the same atmosphere.
- the insulation resistivity measured at 500 ° C. of the completed single crystal was in the range of 3.4 ⁇ 10 9 to 6.5 ⁇ 10 9 ⁇ ⁇ cm.
- the insulation resistivity is determined by cutting a grown single crystal block into a resistivity measurement wafer, placing a measurement sample in which an electrode is formed so as not to short-circuit between bulks to be measured, in an experimental tubular furnace, was measured after the temperature of the sample wafer reached 500 ° C.
- the compressive fracture load in the X-axis direction of the single crystal was 6800-7500N.
- the compressive fracture load is 0.5 mm / mm in the X-axis direction of the single crystal in an environment of 200 ° C.
- the oxygen concentration (oxidizing gas concentration) in the growth atmosphere of the LTGA single crystal described in Example 1 is set to 0.3 to 2% by volume, and the oxygen concentration is gradually lowered from the growth atmosphere in the cooling atmosphere, so that the inert gas atmosphere
- the LTGA single crystal was manufactured under the conditions for cooling.
- the reason why the oxygen concentration is lowered from the growth atmosphere at the time of cooling is to reduce the temperature dependency of the high insulation resistivity and the insulation resistivity by suppressing the generation of oxygen defects, and was measured at 500 ° C. of the completed single crystal.
- the insulation resistivity was 5.3 ⁇ 10 8 to 1.37 ⁇ 10 9 ⁇ ⁇ cm.
- the compressive fracture load in the X-axis direction of the single crystal was 4700 to 5500 N (1175 MPa to 1375 MPa in terms of compressive fracture strength).
- Example 1 The insulation resistivity of Example 1 was higher than that of the comparative example.
- the single crystal was manufactured under the condition that the generation of oxygen defects was suppressed by reducing the oxygen concentration during cooling, whereas Example 1 was manufactured under conditions where oxygen defects were easily generated during cooling. Nevertheless, high insulation resistivity can be obtained.
- the compressive fracture strength of Example 1 was higher than that of the comparative example.
- FIG. 2 is a diagram showing the relationship between the oxygen concentration during growth and the insulation resistivity of LTGA
- FIG. 3 is a diagram showing the relationship between the oxygen concentration during growth and the compressive fracture strength of LTGA. The higher the oxygen concentration in the single crystal growth atmosphere, the higher the insulation resistivity and compressive fracture strength.
- the insulation resistivity is higher than that of a conventional single crystal grown in a growth atmosphere containing an oxidizing gas such as oxygen of 5% by volume or lower. It can be seen that a high-strength single crystal can be obtained as the absolute value increases. Furthermore, since there are few gallium defects in a single crystal, it can be expected that a single crystal having a small change in insulation resistivity with respect to a temperature change can be obtained. Moreover, it turns out that the single crystal obtained by the manufacturing method of the present invention has high insulation resistivity and high strength.
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Abstract
Description
出発原料La2O3、Ta2O5、Ga2O3、Al2O3のそれぞれを所望の組成となるように秤量し、ボールミル等で混合して出発原料混合物を調製することができる。次に、調製された出発原料混合物を加圧した後に仮焼し、固相反応により目的とする結晶の構造の焼結体を作製することができる。このようにして作製された焼結体は概して多くの多結晶を含む。
本発明により得られるランガテイト系単結晶の500℃で測定した絶縁抵抗率は、3.4×109~6.5×109Ω・cmの範囲であった。燃焼圧センサとして求められる絶縁抵抗率は500℃で3.0×108Ω・cm以上であり、好ましくは3.0×109Ω・cm以上であり、より好ましくは3.4×109Ω・cm以上であり、さらに好ましくは6.3×109Ω・cm以上である。燃焼圧センサの圧電素子で用いる圧電材料には、内燃機関における高温で動作する必要から、500℃で3×108Ω・cm以上の絶縁抵抗率が求められるが、本発明のように酸素等の酸化性ガス濃度を5体積%より高くすることでランガテイト系単結晶はこの要求を満たすことができる。本発明によるランガテイト系単結晶は、6.5×109Ω・cmである絶縁抵抗率を有することも確認されており、これを本発明による絶縁抵抗率の上限としてもよい。絶縁抵抗率については、図2を用いて後述する。
また、本発明により得られるランガテイト系単結晶の200℃におけるX軸方向の圧縮破壊強度が1500MPa以上であり、好ましくは1700MPa以上であり、より好ましくは1750MPa以上である。燃焼圧センサの圧電素子で用いる圧電材料には、自動車の内燃機関に利用される必要から30MPa以上の圧力に対し破壊しないことが求められるが、本発明によるランガテイト系単結晶はこの要求を満たすことができる。本発明によるランガテイト系単結晶は、1875MPaである圧縮破壊強度を有することも確認されており、これを本発明による圧縮破壊強度の上限としてもよい。圧縮破壊強度に関しては、図3を用いて後述する。
以下、本発明のランガテイト系単結晶及びその製造方法について、ランガテイト系単結晶のLTGAを例にとり説明する。
実施例1で説明したLTGA単結晶の育成雰囲気の酸素濃度(酸化性ガス濃度)を0.3~2体積%とし、冷却雰囲気を育成雰囲気より酸素濃度を徐々に低下させ不活性ガス雰囲気での冷却となる条件により、LTGA単結晶の製造を行った。冷却時に酸素濃度を育成雰囲気より低下させるのは、酸素欠陥の生成を抑えることで高い絶縁抵抗率と絶縁抵抗率の温度依存性を小さくするためであり、完成した単結晶の500℃で測定した絶縁抵抗率は、5.3×108~1.37×109Ω・cmであった。単結晶のX軸方向の圧縮破壊荷重は4700~5500N(圧縮破壊強度に換算すると1175MPa~1375MPa)であった。
Claims (7)
- 原料溶液から結晶を引き上げるチョクラルスキー法によってランガテイト系単結晶を育成するランガテイト系単結晶の製造方法であって、
前記ランガテイト系単結晶を育成する雰囲気ガスが、不活性ガス中に酸化性ガスを5体積%より多く含む混合ガスであることを特徴とするランガテイト系単結晶の製造方法。 - 前記原料溶液を白金坩堝に収容しランガテイト系単結晶を育成することを特徴とする請求項1に記載のランガテイト系単結晶の製造方法。
- 前記酸化性ガスはO2であることを特徴とする請求項1または2に記載のランガテイト系単結晶の製造方法。
- 単結晶育成軸がZ軸であることを特徴とする請求項1~3のいずれか一項に記載のランガテイト系単結晶の製造方法。
- ランガテイト系単結晶の200℃におけるX軸方向の圧縮破壊強度が1500MPa以上であることを特徴とするランガテイト系単結晶。
- 500℃で3.0×109Ω・cm以上の絶縁抵抗を有することを特徴とする請求項5に記載のランガテイト系単結晶。
- 前記ランガテイト系単結晶は、La3Ta0.5Ga5.5-xAlxO14(0<x<5.5)であることを特徴とする請求項5または6に記載のランガテイト系単結晶。
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