JP2007261847A - Method for producing bismuth niobate-based fine particles - Google Patents
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本発明は、ニオブ酸ビスマス系微粒子の製造方法に関し、製造が容易で組成及び粒子径の均一性に優れ、特に好ましくは高い結晶性を有するニオブ酸ビスマス系微粒子の製造方法に関する。 The present invention relates to a method for producing bismuth niobate fine particles, and more particularly to a method for producing bismuth niobate fine particles that are easy to produce, excellent in composition and particle size uniformity, and particularly preferably have high crystallinity.
強誘電体材料は、絶縁性、強誘電性、圧電性、焦電性、電子光学効果等の優れた特性を多岐にわたり有することから、コンデンサー、強誘電体メモリー、フィルター、振動子等の電子部品の構成材料として広く利用されている。 Ferroelectric materials have a variety of excellent properties such as insulation, ferroelectricity, piezoelectricity, pyroelectricity, and electro-optic effect, so electronic parts such as capacitors, ferroelectric memories, filters, and vibrators It is widely used as a constituent material.
強誘電体材料としては、これまでにチタン酸ジルコン酸鉛系強誘電体(PZT、PZTN)などのペロブスカイト型化合物が知られている。なかでもPZTは、大きな自発分極値を有することから不揮発性強誘電体メモリーの構成材料として広く用いられている。しかし、PZTは分極反転(電圧印加)サイクルにともなう自発分極特性の劣化に対する耐性、いわゆる疲労耐性が低いという問題があった。 As ferroelectric materials, perovskite type compounds such as lead zirconate titanate ferroelectrics (PZT, PZTN) have been known so far. Among these, PZT is widely used as a constituent material of a nonvolatile ferroelectric memory because it has a large spontaneous polarization value. However, PZT has a problem of low resistance to spontaneous polarization characteristics due to polarization reversal (voltage application) cycle, so-called fatigue resistance.
この疲労耐性が優れた強誘電体材料として、Bi4Ti3O12、(LaxBi1−x)4Ti3O12[0≦x≦0.5]、SrBi2Ta2O9等に代表されるビスマス系層状ペロブスカイト型強誘電体(BLSF)が知られている。このBLSFは層状ペロブスカイト型構造を有し、擬ペロブスカイト構造の層(An−1BnO3.5n−0.5)と他の結晶構造の挿入層(Bi2O2)とが、一方向に一定周期で交互に積層した結晶構造を有するため、疲労耐性に非常に優れるという利点がある。 Examples of ferroelectric materials having excellent fatigue resistance include Bi 4 Ti 3 O 12 , (La x Bi 1-x ) 4 Ti 3 O 12 [0 ≦ x ≦ 0.5], and SrBi 2 Ta 2 O 9 . A representative bismuth-based layered perovskite ferroelectric (BLSF) is known. This BLSF has a layered perovskite structure, and a pseudo perovskite structure layer (A n-1 B n O 3.5n-0.5 ) and another crystal structure insertion layer (Bi 2 O 2 ) Since it has a crystal structure in which the layers are alternately laminated at a constant period, there is an advantage that it is very excellent in fatigue resistance.
強誘電性酸化物の1つであるニオブ酸ビスマス系強誘電体は、鉛を含まず環境に優しい物質であり、高い残留分極を示す等の優れた特性を有するほか、上記のBLSFと同様に層状ペロブスカイト型構造を取りうることから、疲労耐性に優れ、薄膜化しても劣化しにくく、共振周波数の温度変化(周波数温度変化)が小さい次世代の強誘電体メモリー用材料及び発振子用材料として期待されている(非特許文献1)。 Bismuth niobate-based ferroelectric, which is one of the ferroelectric oxides, is an environmentally friendly substance that does not contain lead, and has excellent properties such as high remanent polarization, as well as the above BLSF. As a layered perovskite-type structure, it is excellent in fatigue resistance, is not easily deteriorated even when thinned, and is a next-generation ferroelectric memory material and oscillator material that has a small temperature change (frequency temperature change) of the resonance frequency. It is expected (Non-Patent Document 1).
近年では特に、化学的溶液成膜法(溶液法)により安価かつ簡便に強誘電体薄膜を得る試みが多くなされており(特許文献1〜3参照)、そのため結晶性が高く、小粒子径でかつ粒子径の均一性に優れた、溶液法への適用に適したニオブ酸ビスマス系微粒子の製造方法を提供することが求められている。 In recent years, many attempts have been made to obtain a ferroelectric thin film cheaply and easily by a chemical solution film-forming method (solution method) (see Patent Documents 1 to 3). Therefore, the crystallinity is high and the particle size is small. There is also a need to provide a method for producing bismuth niobate fine particles that are excellent in particle size uniformity and suitable for application to a solution method.
本発明は、ニオブ酸ビスマス系微粒子の製造方法に関し、製造が容易で組成及び粒子径の均一性に優れ、特に好ましくは高い結晶性を有するニオブ酸ビスマス系微粒子を製造する方法を提供することを目的とする。 The present invention relates to a method for producing bismuth niobate fine particles, and provides a method for producing bismuth niobate fine particles that are easy to produce, excellent in composition and particle size uniformity, and particularly preferably have high crystallinity. Objective.
本発明は、酸化物基準のモル%表示で、MO(M=Mg、Ca、Sr及びBaからなる群より選ばれる1種以上)を25〜60%、Bi2O3を3〜25%、Nb2O5を2〜25%及びB2O3を15〜60%含む溶融物を得る工程と、前記溶融物を急速冷却して非晶質物質とする工程と、前記非晶質物質からニオブ酸ビスマス系結晶を析出させる工程と、得られた析出物から前記ニオブ酸ビスマス系結晶を分離する工程と、をこの順に含むことを特徴とするニオブ酸ビスマス系微粒子の製造方法を提供する。 The present invention is expressed in mol% on the basis of oxide, and MO (M = Mg, Ca, Sr and Ba selected from the group consisting of 25 to 60%), Bi 2 O 3 is 3 to 25%, A step of obtaining a melt containing 2 to 25% of Nb 2 O 5 and 15 to 60% of B 2 O 3 , a step of rapidly cooling the melt to an amorphous material, Provided is a method for producing bismuth niobate fine particles, comprising a step of precipitating a bismuth niobate crystal and a step of separating the bismuth niobate crystal from the obtained precipitate in this order.
本発明によれば、結晶子径が小さく、結晶性が高く、組成及び粒子径の均一性に優れたニオブ酸ビスマス系微粒子を製造できる。当該微粒子は、強誘電性、圧電性、焦電性、電子光学効果等に優れた微粒子であるため、誘電体素子及び圧電素子用の強誘電体薄膜を溶液法により得る際の構成材料として有用である。 According to the present invention, bismuth niobate-based fine particles having a small crystallite size, high crystallinity, and excellent uniformity in composition and particle size can be produced. Since the fine particles are fine particles with excellent ferroelectricity, piezoelectricity, pyroelectricity, electro-optic effect, etc., they are useful as a constituent material for obtaining dielectric elements and ferroelectric thin films for piezoelectric elements by the solution method. It is.
本発明のニオブ酸ビスマス系微粒子の製造方法において、溶融物は、M(M=Mg、Ca、Sr及びBaからなる群より選ばれる1種以上)源、Bi源、Nb源及びB源を含む混合物を溶融して得ることが好ましい。 In the method for producing bismuth niobate-based fine particles of the present invention, the melt contains an M (M = one or more selected from the group consisting of Mg, Ca, Sr, and Ba) source, Bi source, Nb source, and B source. It is preferable to obtain the mixture by melting.
まず、M源としては、Mの酸化物(MO)及び炭酸塩(MCO3)からなる群より選ばれる1種以上を用いることが好ましい。さらに、Mの硝酸塩(M(NO3)2)、塩化物(MCl2・mH2O)、硫酸塩(MSO4・mH2O)及び各フッ化物(MF2)からなる群より選ばれる1種以上を用いてもよい。さらに、溶融温度を低下させたり、後述する急速冷却によるガラス化を容易にする目的から、MOの一部をZnOで置換してもよい。なかでも、M=Srとすると、周波数温度特性に優れたニオブ酸ビスマス系微粒子が得られるため好ましい。 First, as the M source, it is preferable to use one or more selected from the group consisting of M oxide (MO) and carbonate (MCO 3 ). Further, 1 selected from the group consisting of M nitrate (M (NO 3 ) 2 ), chloride (MCl 2 · mH 2 O), sulfate (MSO 4 · mH 2 O) and each fluoride (MF 2 ). More than one species may be used. Furthermore, for the purpose of lowering the melting temperature or facilitating vitrification by rapid cooling described later, a part of MO may be substituted with ZnO. Among these, when M = Sr, bismuth niobate fine particles having excellent frequency temperature characteristics can be obtained, which is preferable.
次に、Bi源としては、酸化ビスマス(Bi2O3)、炭酸ビスマス(Bi2CO3)3)及び水酸化ビスマス(Bi(OH)3)からなる群より選ばれる1種以上を用いることが好ましい。また、硝酸ビスマス(Bi(NO3)3・mH2O)、塩化ビスマス(BiCl3)、硫酸ビスマス(Bi2(SO4)3)及びフッ化ビスマス(BiF3)からなる群より選ばれる1種以上を用いてもよい(以上のビスマス化合物は、それぞれのオキシ塩、例えば(BiO)2CO3をも含む。また、上記式において、mは水和数を示し、m=0の無水物の場合も含む)。 Next, as the Bi source, one or more selected from the group consisting of bismuth oxide (Bi 2 O 3 ), bismuth carbonate (Bi 2 CO 3 ) 3 ) and bismuth hydroxide (Bi (OH) 3 ) should be used. Is preferred. 1 selected from the group consisting of bismuth nitrate (Bi (NO 3 ) 3 .mH 2 O), bismuth chloride (BiCl 3 ), bismuth sulfate (Bi 2 (SO 4 ) 3 ) and bismuth fluoride (BiF 3 ). More than one species may be used (the above bismuth compounds also include their respective oxy salts, such as (BiO) 2 CO 3 , where m is the hydration number and m = 0 anhydride Also included).
また、Nb源としては、酸化ニオブ(Nb2O5又はNb2O3)を用いることが好ましい。また、塩化ニオブ(NbCl5)又はフッ化ニオブ(NbF5)を用いてもよい。 In addition, niobium oxide (Nb 2 O 5 or Nb 2 O 3 ) is preferably used as the Nb source. Alternatively, niobium chloride (NbCl 5 ) or niobium fluoride (NbF 5 ) may be used.
さらに、B源としては酸化ホウ素(B2O3)又はホウ酸(H3BO3)を用いることが好ましいが、Mのホウ酸塩、ホウ酸ビスマス、ホウ酸ニオブを用いてもよい。 Furthermore, boron oxide (B 2 O 3 ) or boric acid (H 3 BO 3 ) is preferably used as the B source, but M borate, bismuth borate, or niobium borate may be used.
所望の特性を低下させない範囲であれば、混合物中の構成材料の純度は特に限定されないが、水和水を除いた純度が99%以上であると好ましく、より好ましくは純度99.9%以上のものを用いるとよい。また、溶融して均一な溶融物が得られる範囲であれば、上記構成材料の粒度も特に限定されない。また、上記構成材料は、ボールミル、遊星ミル等の混合・粉砕手段を用いて、乾式又は湿式で混合してから溶融すると好ましい。 The purity of the constituent materials in the mixture is not particularly limited as long as the desired properties are not deteriorated, but the purity excluding hydration water is preferably 99% or more, and more preferably the purity is 99.9% or more. Use a good one. Further, the particle size of the constituent material is not particularly limited as long as it is within a range in which a uniform melt can be obtained by melting. The constituent materials are preferably melted after being mixed dry or wet using a mixing / pulverizing means such as a ball mill or a planetary mill.
溶融は、大気雰囲気で行ってもよいが、酸素分圧や酸素流量を制御しながら行うことが好ましい。また、溶融に用いるるつぼはアルミナ製、白金製、又はロジウムを含む白金製であると好ましいが、耐火物を用いることもできる。さらに、蓋付のるつぼを用いてもよい。また、溶融を抵抗加熱炉、高周波誘導炉又はプラズマアーク炉を用いて行うと好ましい。抵抗加熱炉は、ニクロム合金等の金属製、炭化ケイ素質又はケイ化モリブデン製等の発熱体を備えた電気炉であると好ましい。高周波誘導炉は、誘導コイルを備えており、出力を制御できるものであればよく、また、プラズマアーク炉は、カーボン等を電極とし、これによって発生するプラズマアークを利用できるものであればよい。さらに、赤外線又はレーザー直接加熱によって溶融してもよい。 Melting may be performed in an air atmosphere, but is preferably performed while controlling the oxygen partial pressure and the oxygen flow rate. The crucible used for melting is preferably made of alumina, platinum, or platinum containing rhodium, but a refractory can also be used. Further, a crucible with a lid may be used. Further, it is preferable to perform melting using a resistance heating furnace, a high frequency induction furnace or a plasma arc furnace. The resistance heating furnace is preferably an electric furnace including a heating element made of a metal such as a nichrome alloy, silicon carbide, or molybdenum silicide. The high frequency induction furnace may be provided with an induction coil and can control the output, and the plasma arc furnace may be any one that uses carbon or the like as an electrode and can use a plasma arc generated thereby. Further, it may be melted by infrared or laser direct heating.
なお、構成材料を混合した混合物は粉体状態で溶融してもよいし、あらかじめ成型した混合物を溶融してもよい。プラズマアーク炉を利用する場合には、あらかじめ成型した混合物をそのまま溶融し、さらに急速冷却することもできる。 In addition, the mixture in which the constituent materials are mixed may be melted in a powder state, or a previously molded mixture may be melted. In the case of using a plasma arc furnace, a previously molded mixture can be melted as it is and further rapidly cooled.
前記溶融物を得る工程を900℃〜1500℃で行うことが好ましい。900℃未満では、均一な溶融物を得難く、一方1500℃を超えると、原料の蒸発が激しくなり好ましくない。なかでも、1100℃〜1400℃で溶融を行うことが好ましい。また、得られた溶融物は、均一性を高めるために撹拌してもよい。 The step of obtaining the melt is preferably performed at 900 ° C to 1500 ° C. When the temperature is lower than 900 ° C., it is difficult to obtain a uniform melt. On the other hand, when the temperature exceeds 1500 ° C., the evaporation of the raw material becomes severe, which is not preferable. Especially, it is preferable to perform melting at 1100 ° C. to 1400 ° C. Moreover, you may stir in order to improve the uniformity of the obtained melt.
溶融物の組成は、酸化物基準のモル%表示で、MOを25〜60%、Bi2O3を3〜25%、Nb2O5を2〜25%、B2O3を15〜60%含むものとする。本発明者らが鋭意検討を重ねた結果、溶融物の化学組成を上記の範囲とし、前記溶融物を急速冷却して非晶質物質を形成し、さらに結晶化工程を行うことで、溶融前の構成成分中のBi源及びNb源のほぼ全部がニオブ酸ビスマス系結晶(以下、目的結晶成分ともいう。)中に取り込まれ、B源のほぼ全部が目的結晶成分以外の成分(以下、マトリックス成分ともいう。)となり、M源は目的結晶成分にもマトリックス成分にもなりうることが判明した。上記の組成域の溶融物は適度な粘性を有するうえ、続く急速冷却操作により溶融物が結晶化することなくガラス化して非晶質物質を得ることができるため好ましい。なお、この組成は溶融前の構成材料の化学組成(酸化物換算)とも対応している。溶融操作中に構成材料、特にBi及び/又はBの揮発等が生じて、所望の組成の溶融物が得られない場合には、原料となる構成材料の添加割合を調整すればよい。 The composition of the melt is expressed in mol% on the basis of oxide, MO is 25 to 60%, Bi 2 O 3 is 3 to 25%, Nb 2 O 5 is 2 to 25%, B 2 O 3 is 15 to 60%. % Included. As a result of repeated studies by the present inventors, the chemical composition of the melt is in the above range, the melt is rapidly cooled to form an amorphous substance, and further a crystallization step is performed. Almost all of the Bi source and Nb source in the constituents of bismuth are taken into the bismuth niobate crystal (hereinafter also referred to as target crystal component), and almost all of the B source is a component other than the target crystal component (hereinafter referred to as matrix). It was also found that the M source can be a target crystal component or a matrix component. The melt having the above composition range is preferable because it has an appropriate viscosity and can be vitrified without crystallization by the subsequent rapid cooling operation to obtain an amorphous substance. This composition also corresponds to the chemical composition (as oxide) of the constituent material before melting. When volatilization of the constituent materials, particularly Bi and / or B, occurs during the melting operation, and a melt having a desired composition cannot be obtained, the addition ratio of the constituent materials as raw materials may be adjusted.
溶融物中のNb2O5の含有割合が25%を超える場合や、MOの含有割合が25%未満又はB2O3の含有割合が15%未満の場合には、溶融物は急速冷却により結晶化しやすく、ガラス化して非晶質物質とすることが困難になるため、目的の組成を有するニオブ酸ビスマス系微粒子を得がたくなり好ましくない。一方、Nb2O5の含有割合が2%未満又はBi2O3が3%未満の場合や、MO又はB2O3の含有割合が60%を超える場合には、後に続く結晶化工程において、目的結晶成分が充分に析出しないおそれがあるため好ましくない。 When the Nb 2 O 5 content in the melt exceeds 25%, or the MO content is less than 25% or the B 2 O 3 content is less than 15%, the melt is cooled by rapid cooling. Since it is easy to crystallize and it is difficult to vitrify to an amorphous substance, it is not preferable because it is difficult to obtain bismuth niobate-based fine particles having a target composition. On the other hand, when the content ratio of Nb 2 O 5 is less than 2% or Bi 2 O 3 is less than 3%, or the content ratio of MO or B 2 O 3 exceeds 60%, in the subsequent crystallization step , Because the target crystal component may not be sufficiently precipitated.
なかでも、MOを30〜50%、Bi2O3を5〜15%、Nb2O5を5〜15%、B2O3を35〜50%含む場合、所望の組成を有するニオブ酸ビスマス系微粒子が得られやすくなり、かつ、その収率を高くできるため好ましい。 In particular, when MO is 30 to 50%, Bi 2 O 3 is 5 to 15%, Nb 2 O 5 is 5 to 15%, and B 2 O 3 is 35 to 50%, bismuth niobate having a desired composition is included. It is preferable because system-based fine particles can be easily obtained and the yield can be increased.
また、前記溶融物の化学組成が、酸化物基準のモル%表示で、酸化物基準のモル%表示で、MOを25〜60%、Bi2O3を3〜25%、Nb2O5を3〜25%、B2O3を15〜60%であると、Mを含む所望の組成の、層状ペロブスカイト型の結晶構造を有するニオブ酸ビスマス系結晶の微粒子が得られやすくなるため好ましい。ここで、特に、(Bi2O3+Nb2O5)を7〜35%、(MO+B2O3)を65〜93%含む場合、溶融物のガラス化が容易となり、目的結晶成分の析出量が向上する結果、ニオブ酸ビスマス系微粒子の収率を高められるため好ましい。 Further, the chemical composition of the melt is expressed in mol% based on oxide, expressed in mol% based on oxide, MO is 25 to 60%, Bi 2 O 3 is 3 to 25%, and Nb 2 O 5 is It is preferable that 3 to 25% and B 2 O 3 to be 15 to 60% because fine particles of a bismuth niobate crystal having a layered perovskite crystal structure having a desired composition including M can be easily obtained. Here, particularly when (Bi 2 O 3 + Nb 2 O 5 ) is contained in an amount of 7 to 35% and (MO + B 2 O 3 ) is contained in an amount of 65 to 93%, vitrification of the melt is facilitated, and the amount of precipitation of the target crystal component As a result, the yield of bismuth niobate fine particles can be increased, which is preferable.
さらに、前記溶融物の化学組成が、酸化物基準のモル%表示で、SrOを25〜60%、Bi2O3を3〜25%、Nb2O5を3〜25%、B2O3を15〜60%であると目的とする組成のニオブ酸ビスマスストロンチウム結晶の微粒子を収率よく得やすくなるため好ましい。 Furthermore, the chemical composition of the melt is expressed in mol% based on oxide, SrO is 25 to 60%, Bi 2 O 3 is 3 to 25%, Nb 2 O 5 is 3 to 25%, B 2 O 3 15 to 60% is preferable because fine particles of bismuth strontium niobate crystals having a target composition can be easily obtained in a high yield.
加えて、前記溶融物の化学組成が、酸化物基準のモル%表示で、Bi2O3/Nb2O5=40/60〜60/40であると、目的の組成を有するニオブ酸ビスマス系結晶の微粒子が得られやすくなるため好ましい。特に好ましくは、前記溶融物の化学組成をBi2O3/Nb2O5=50/50〜60/40とする。 In addition, the chemical composition of the melt is Bi 2 O 3 / Nb 2 O 5 = 40/60 to 60/40 in terms of mol% on the basis of oxide, and the bismuth niobate system having the desired composition It is preferable because fine particles of crystals are easily obtained. Particularly preferably, the chemical composition of the melt is Bi 2 O 3 / Nb 2 O 5 = 50/50 to 60/40.
上記のようにして得られた溶融物を急速冷却して非晶質物質とする工程には、高速で回転する双ローラーの間に溶融物を滴下してフレーク状の非晶質物質を得る方法や、高速で回転するドラムにより、溶融物から連続的にファイバー状の非晶質物質(長繊維)を巻き取る方法が好適に用いられる。急速冷却する際の温度は例えば100℃/秒以上、好ましくは1×104℃/秒以上であると好ましい。ここで、双ローラー及びドラムとしては金属製又はセラミックス製のものを用いる。また、高速で回転し、側壁に細孔を設けたスピナーを用いてファイバー状の非晶質物質(短繊維)を得てもよい。これらの装置を用いれば、溶融物を効果的に急速冷却して高純度の非晶質物質にできる。 In the process of rapidly cooling the melt obtained as described above to an amorphous substance, a method of obtaining a flake-like amorphous substance by dropping the melt between twin rollers rotating at high speed Alternatively, a method of continuously winding a fiber-like amorphous substance (long fiber) from the melt with a drum rotating at high speed is preferably used. The temperature at the time of rapid cooling is, for example, 100 ° C./second or more, preferably 1 × 10 4 ° C./second or more. Here, as the double roller and the drum, those made of metal or ceramics are used. Moreover, you may obtain a fiber-like amorphous substance (short fiber) using the spinner which rotated at high speed and provided the pore on the side wall. By using these apparatuses, the melt can be effectively rapidly cooled to a high purity amorphous material.
非晶質物質がフレーク状の場合には、その厚さが200μm以下、より好ましくは100μm以下となるように、また、繊維状の場合には、その直径が50μm以下、より好ましくは30μm以下となるように急速冷却することが好ましい。これ以上の厚さ又は直径の非晶質物質が形成するように急速冷却すると、続く結晶化工程における結晶化効率を高くできるため好ましく、上記以上の厚さ又は直径を有する非晶質物質が得られた場合には、粉砕を行ったうえで、続く結晶化工程に供することが好ましい。 When the amorphous substance is flaky, its thickness is 200 μm or less, more preferably 100 μm or less. When it is fibrous, its diameter is 50 μm or less, more preferably 30 μm or less. It is preferable to cool rapidly so that. Rapid cooling so as to form an amorphous material having a thickness or diameter larger than this is preferable because the crystallization efficiency in the subsequent crystallization process can be increased, and an amorphous material having a thickness or diameter larger than the above is obtained. In such a case, it is preferable to use the crystallization process after pulverization.
次に、非晶質物質からニオブ酸ビスマス系結晶を析出させる。非晶質物質からニオブ酸ビスマス系結晶を析出させる工程は大気中、600〜900℃で行うことが好ましい。加熱温度が600℃未満で24時間程度、連続して加熱を行っても結晶が析出しにくく、また、900℃を超えると、非晶質物質を含む結晶化物が融解するおそれがあるためいずれも好ましくない。さらに好ましくは、650〜800℃で行う。この結晶析出工程は、微視的には核生成、それに続く結晶成長の2段階からなるため、この2段階をそれぞれ異なる温度で行ってもよい。なお、加熱を高温で行うほど、析出する結晶の生成量及び析出する結晶の粒子径が大きくなる傾向があるので、所望の粒子径に応じて結晶化温度を設定すればよい。 Next, bismuth niobate crystals are precipitated from the amorphous material. The step of depositing the bismuth niobate crystal from the amorphous substance is preferably performed at 600 to 900 ° C. in the atmosphere. Even if the heating temperature is less than 600 ° C. for about 24 hours, it is difficult for crystals to precipitate, and if it exceeds 900 ° C., there is a possibility that a crystallized material containing an amorphous substance may melt. It is not preferable. More preferably, it is performed at 650 to 800 ° C. Since this crystal precipitation step is microscopically composed of two stages of nucleation and subsequent crystal growth, these two stages may be performed at different temperatures. Note that as the heating is performed at a higher temperature, the amount of crystals to be precipitated and the particle diameter of the precipitated crystals tend to increase. Therefore, the crystallization temperature may be set according to the desired particle diameter.
本発明においては、非晶質物質の結晶化工程により、結晶として主にニオブ酸ビスマス系物質及びMのホウ酸塩が析出する。Mのホウ酸塩及び溶融物の組成により生成する可能性のある微量のBiのホウ酸塩、Nbのホウ酸塩は続く溶脱処理によって同時に除去できる。 In the present invention, bismuth niobate and M borate are mainly precipitated as crystals by the crystallization process of the amorphous material. The trace amounts of Bi borate and Nb borate that may be formed by the composition of the M borate and the melt can be removed simultaneously by the subsequent leaching process.
また、結晶化にあたっては、上記の温度範囲に4時間〜96時間保つと、ニオブ酸ビスマス系物質を充分に結晶化できるため好ましい。その際、保持時間が長くなるほど、析出する結晶の生成量が多くなり、また析出する結晶の粒子径が大きくなる傾向があるので、所望の結晶析出量及び粒子径に応じて保持時間を設定すればよい。 In crystallization, it is preferable to keep the above temperature range for 4 hours to 96 hours because the bismuth niobate-based substance can be sufficiently crystallized. At that time, the longer the holding time, the larger the amount of crystals to be precipitated, and the larger the particle size of the precipitated crystals, so the holding time should be set according to the desired crystal precipitation amount and particle size. That's fine.
次に、上記によって得られたニオブ酸ビスマス系結晶を含む結晶化物から、ニオブ酸ビスマス系結晶を分離する。酸を用いれば、結晶化物からニオブ酸ビスマス系結晶以外の物質を容易に溶脱除去できる。酸としては、酢酸、塩酸、硝酸等の無機酸や、シュウ酸、クエン酸等の有機酸を用いることができる。特に3mol/L以上の酢酸水溶液であると、溶脱処理にともなう化学反応により水酸化ビスマス塩やオキシ水酸化ビスマス塩が生成した場合であっても、これらを再溶解して同時に除去できるため好ましい。また、溶脱処理を促進し、目的結晶成分の粒径を所望の範囲に調整するために、溶脱処理前に、ニオブ酸ビスマス系結晶を含む結晶化物を乾式又は湿式にて粉砕してもよい。粉砕を行う場合、ボールミル等の媒体を用いることが好ましい。また、溶脱反応を促進するために、酸を温めて用いてもよく、また、超音波照射を併用してもよい。この溶脱処理により、ニオブ酸ビスマス系結晶の一部が溶解する場合もあるが、粒子径を均一化できる点ではむしろ好ましい。さらに、この溶脱処理を数回、繰り返して行ってもよい。 Next, the bismuth niobate crystal is separated from the crystallization product containing the bismuth niobate crystal obtained as described above. If an acid is used, substances other than the bismuth niobate crystal can be easily leached and removed from the crystallized product. As the acid, inorganic acids such as acetic acid, hydrochloric acid and nitric acid, and organic acids such as oxalic acid and citric acid can be used. In particular, an acetic acid aqueous solution of 3 mol / L or more is preferable because even when a bismuth hydroxide salt or a bismuth oxyhydroxide salt is generated by a chemical reaction accompanying the leaching treatment, these can be redissolved and simultaneously removed. In order to accelerate the leaching treatment and adjust the particle size of the target crystal component to a desired range, the crystallization product containing the bismuth niobate crystal may be pulverized dry or wet before the leaching treatment. When pulverizing, it is preferable to use a medium such as a ball mill. Further, in order to promote the leaching reaction, the acid may be warmed and used, or ultrasonic irradiation may be used in combination. Although this leaching treatment may partially dissolve some of the bismuth niobate crystals, it is preferable in that the particle diameter can be made uniform. Furthermore, this leaching process may be repeated several times.
溶脱処理後、必要に応じて純水による洗浄を行い、ニオブ酸ビスマス系微粒子を得る。得られる微粒子の平均一次粒子径(異方性粒子の場合には長径を指すものとする。)は5〜200nmであると好ましい。得られる微粒子の平均一次粒子径が小さいほど、より液状媒体への分散性がよくなる傾向があり、その結果、溶液法により形成する強誘電体薄膜の均一性及び平坦性を向上できるため好ましい。 After the leaching treatment, washing with pure water is performed as necessary to obtain bismuth niobate fine particles. The average primary particle diameter of the fine particles obtained (in the case of anisotropic particles, the long diameter is indicated) is preferably 5 to 200 nm. The smaller the average primary particle size of the resulting fine particles, the better the dispersibility in the liquid medium, and as a result, the uniformity and flatness of the ferroelectric thin film formed by the solution method can be improved.
得られるニオブ酸ビスマス系微粒子が層状ペロブスカイト型の結晶構造であると、蛍石型構造のニオブ酸ビスマス系微粒子と比較して比誘電率に優れ、優れた誘電特性や圧電特性等を発現しやすくなり好ましい。 If the resulting bismuth niobate fine particles have a layered perovskite crystal structure, they are superior in relative dielectric constant compared to fluorite-type bismuth niobate fine particles, and easily exhibit excellent dielectric properties and piezoelectric properties. It is preferable.
また、前記ニオブ酸ビスマス系微粒子の化学組成がMBi2Nb2O9であると、優れた誘電特性や圧電特性等を発現しやすいため好ましく、特にSrBi2Nb2O9であると、周波数温度特性に優れたニオブ酸ビスマス系微粒子にできるため好ましい。 The chemical composition of the bismuth niobate fine particles is preferably MBi 2 Nb 2 O 9 because it easily exhibits excellent dielectric properties, piezoelectric properties, and the like. In particular, the frequency temperature is preferably SrBi 2 Nb 2 O 9. This is preferable because bismuth niobate fine particles having excellent characteristics can be obtained.
以下、本発明を実施例によって説明するが、本発明はこれらにより限定されるものではない。 EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited by these.
[例1〜9]
溶融物の組成がMO、Bi2O3、Nb2O5及びB2O3基準のモル%表示で表1に示す割合となるように、Mの炭酸塩(MCO3)、酸化ビスマス(Bi2O3)、酸化ニオブ(Nb2O5)及び酸化ホウ素(B2O3)をそれぞれ秤量し、乾式で混合・粉砕して原料混合物を得た。
[Examples 1 to 9]
M carbonate (MCO 3 ), bismuth oxide (Bi) so that the composition of the melt has the ratio shown in Table 1 in terms of mol% based on MO, Bi 2 O 3 , Nb 2 O 5 and B 2 O 3. 2 O 3 ), niobium oxide (Nb 2 O 5 ), and boron oxide (B 2 O 3 ) were weighed, mixed and pulverized in a dry process to obtain a raw material mixture.
得られた原料混合物を、ロジウムを20質量%含む白金製の、ノズル付きのるつぼに充填し、ケイ化モリブデンを発熱体とした電気炉で、表1に示す温度で1時間加熱して完全溶融させた。 The obtained raw material mixture was filled in a platinum crucible containing 20% by mass of rhodium with a nozzle and heated in the electric furnace using molybdenum silicide as a heating element at the temperature shown in Table 1 for 1 hour to complete melting. I let you.
次に、ノズルの下端部を電気炉で加熱しながらガラス溶融物を滴下させ、300rpmで回転する直径約15cmの双ローラーを通すことにより液滴を1×105℃/秒程度で急速冷却し、フレーク状の固形物を得た。得られたフレークは茶褐色を呈し、透明な非晶質物質であった。マイクロメーターでフレークの厚さを測定したところ、30〜50μmであった。 Next, the glass melt is dropped while the lower end of the nozzle is heated in an electric furnace, and the droplet is rapidly cooled at about 1 × 10 5 ° C / second by passing through a twin roller having a diameter of about 15 cm rotating at 300 rpm. A flaky solid was obtained. The obtained flakes were dark brown and were transparent amorphous substances. When the thickness of the flakes was measured with a micrometer, it was 30 to 50 μm.
得られたフレークの一部を用い、あらかじめ示差走査熱量測定(DSC)にて結晶化温度を求めておき、この結晶化開始温度より高い、750℃でフレークを8時間加熱してニオブ酸ビスマス系結晶を析出させた。 A part of the obtained flakes was used to obtain a crystallization temperature in advance by differential scanning calorimetry (DSC), and the flakes were heated for 8 hours at 750 ° C., which is higher than the crystallization start temperature. Crystals were precipitated.
次に、結晶化処理後のフレークを70℃の8.5mol/L酢酸溶液中に8時間以上放置して可溶性物質を溶脱した。溶脱した液を遠心分離し、上澄みを捨てた。この操作を5回行った後、水洗を5回行い、乾燥を経て、粒子径5〜100nmの微粒子を得た。 Next, the flakes after the crystallization treatment were allowed to stand in an 8.5 mol / L acetic acid solution at 70 ° C. for 8 hours or more to leach soluble substances. The leached solution was centrifuged and the supernatant was discarded. After performing this operation 5 times, washing with water was performed 5 times and dried to obtain fine particles having a particle diameter of 5 to 100 nm.
得られたニオブ酸ビスマス系微粒子の鉱物相を、X線回折装置を用いて同定した。その結果、例1〜9のいずれにおいても斜方晶であり、例1〜6については層状ペロブスカイト構造をなす既存のSrBi2Nb2O9(JCPDSカード番号:86−1190)の回折ピークと一致し、SrBi2Nb2O9単相からなる結晶性の高い粒子であることが判明した。また、例7〜9においても既存のSrBi2Nb2O9の回折ピークと類似する結果が得られた。例2で得られた微粒子のX線回折パターンを図1に示す。 The mineral phase of the obtained bismuth niobate fine particles was identified using an X-ray diffractometer. As a result, all of Examples 1 to 9 are orthorhombic, and Examples 1 to 6 are identical with the diffraction peak of the existing SrBi 2 Nb 2 O 9 (JCPDS card number: 86-1190) having a layered perovskite structure. As a result, it was found to be a highly crystalline particle comprising a single phase of SrBi 2 Nb 2 O 9 . Also, similar results to the diffraction peaks existing SrBi 2 Nb 2 O 9 in the example 7-9 was obtained. The X-ray diffraction pattern of the fine particles obtained in Example 2 is shown in FIG.
次に、平均一次粒子径を求めた。ここで、平均一次粒子径は結晶子径とし、X線回折線の広がりからScherrerの式に基づき算出した粒子径とする。その結果を溶融物の化学組成[mol%]及び溶融温度[℃]とともに表1に示す。表1より、得られた微粒子がいずれも非常に細かい粒子径を有していることがわかる。 Next, the average primary particle size was determined. Here, the average primary particle diameter is a crystallite diameter, and is a particle diameter calculated based on Scherrer's equation from the spread of X-ray diffraction lines. The results are shown in Table 1 together with the chemical composition [mol%] and the melting temperature [° C.] of the melt. From Table 1, it can be seen that all of the obtained fine particles have a very fine particle size.
[例10(比較例)]
溶融物の組成がSrO、Bi2O3、Nb2O5及びB2O3基準のモル%表示で表2に示す割合となるように、炭酸ストロンチウム(SrCO3)、酸化ビスマス(Bi2O3)、酸化ニオブ(Nb2O5)及び酸化ホウ素(B2O3)をそれぞれ秤量し、乾式で混合・粉砕して原料混合物を得た。得られた原料混合物を表2に示す温度で1時間加熱して完全溶融させた後、電気炉内で約300℃/時の速度で室温まで冷却したところ、不透明な固形物が生成し、非晶質物質は得られなかった。
[Example 10 (comparative example)]
Strontium carbonate (SrCO 3 ), bismuth oxide (Bi 2 O) so that the composition of the melt has the ratio shown in Table 2 in terms of mol% based on SrO, Bi 2 O 3 , Nb 2 O 5 and B 2 O 3. 3 ), niobium oxide (Nb 2 O 5 ) and boron oxide (B 2 O 3 ) were weighed, mixed and pulverized in a dry manner to obtain a raw material mixture. The obtained raw material mixture was heated at the temperature shown in Table 2 for 1 hour to be completely melted, and then cooled to room temperature at a rate of about 300 ° C./hour in an electric furnace. No crystalline material was obtained.
[例11、12(比較例)]
溶融物の組成がSrO、Bi2O3、Nb2O5及びB2O3基準のモル%表示で表2に示す割合となるように、炭酸ストロンチウム(SrCO3)、酸化ビスマス(Bi2O3)、酸化ニオブ(Nb2O5)及び酸化ホウ素(B2O3)をそれぞれ秤量し、乾式で混合・粉砕して原料混合物を得た。得られた原料混合物を表2に示す温度で1時間加熱して完全溶融させた後、例1〜9と同様にして急速冷却操作を行ったところ、透明なフレークが得られた。得られたフレークを例1〜9と同様にして結晶化し、溶脱、洗浄操作を行った結果、結晶性の微粒子はほとんど得られなかった。
[Examples 11 and 12 (comparative examples)]
Strontium carbonate (SrCO 3 ), bismuth oxide (Bi 2 O) so that the composition of the melt has the ratio shown in Table 2 in terms of mol% based on SrO, Bi 2 O 3 , Nb 2 O 5 and B 2 O 3. 3 ), niobium oxide (Nb 2 O 5 ) and boron oxide (B 2 O 3 ) were weighed, mixed and pulverized in a dry manner to obtain a raw material mixture. The obtained raw material mixture was heated at the temperature shown in Table 2 for 1 hour to be completely melted, and then subjected to a rapid cooling operation in the same manner as in Examples 1 to 9, whereby transparent flakes were obtained. The obtained flakes were crystallized in the same manner as in Examples 1 to 9, and leaching and washing were performed. As a result, almost no crystalline fine particles were obtained.
本発明により得られるニオブ酸ビスマス系微粒子は、結晶子径が小さく、結晶性が高くかつ組成及び粒子径の均一性に優れているので、当該微粒子は、強誘電性、圧電性、焦電性、電子光学効果等に優れたセンサー、超音波モーター、アクチュエーター、コンデンサー、強誘電体メモリー、フィルター、振動子等の電子部品の構成材料として好適である。
また、該微粒子は可視光応答性光触媒材料としての適用も可能と考えられる。
Since the bismuth niobate fine particles obtained by the present invention have a small crystallite size, high crystallinity, and excellent uniformity in composition and particle size, the fine particles are ferroelectric, piezoelectric, pyroelectric. It is suitable as a constituent material for electronic parts such as sensors, ultrasonic motors, actuators, capacitors, ferroelectric memories, filters, vibrators, etc., which have excellent electro-optical effects.
The fine particles can also be applied as a visible light responsive photocatalytic material.
Claims (9)
Method for producing a niobium bismuth-based particles according to any one of claims 1 to 8 chemical composition of the niobium-bismuth-based fine particles are MBi 2 Nb 2 O 9.
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