JP4938340B2 - Piezoelectric ceramics obtained by sintering nano-sized barium titanate powder having dielectric and piezoelectric properties, and method for producing the same - Google Patents
Piezoelectric ceramics obtained by sintering nano-sized barium titanate powder having dielectric and piezoelectric properties, and method for producing the same Download PDFInfo
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- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 title claims description 51
- 229910002113 barium titanate Inorganic materials 0.000 title claims description 51
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- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- 239000004372 Polyvinyl alcohol Substances 0.000 description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 2
- 150000004703 alkoxides Chemical class 0.000 description 2
- AYJRCSIUFZENHW-UHFFFAOYSA-L barium carbonate Chemical compound [Ba+2].[O-]C([O-])=O AYJRCSIUFZENHW-UHFFFAOYSA-L 0.000 description 2
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 2
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
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- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- Compositions Of Oxide Ceramics (AREA)
Description
本発明はセラミックス粉末からなる非鉛系セラミックス、特に、誘電、圧電体特性の優れたナノサイズのチタン酸バリウム粉末を焼結した圧電セラミックス及びその製造方法に関する。より具体的には、非鉛系であるナノサイズのチタン酸バリウム粉末の新規焼結条件により製造された圧電セラミックス及びその製造方法として提供するものである。得られた圧電セラミックスは各種圧電振動子、超音波探傷用等の素子、アクチュエータ、多くのセンサ類に好適な素材提供に関する。 The present invention relates to lead-free ceramics made of ceramic powder, and more particularly to piezoelectric ceramics obtained by sintering nano-sized barium titanate powder having excellent dielectric and piezoelectric properties and a method for producing the same. More specifically, the present invention provides piezoelectric ceramics manufactured under new sintering conditions of nano-sized barium titanate powder that is non-lead and a manufacturing method thereof. The obtained piezoelectric ceramics relates to provision of materials suitable for various piezoelectric vibrators, elements for ultrasonic flaw detection, actuators, and many sensors.
従来、誘電、圧電セラミックスとしては鉛成分を含むＰＺＴが用いられてきた。このため有害な鉛を全く含まないもしくはほとんど含まない圧電セラミックスの開発が環境問題として望まれている。例えば、層状ぺロブスカイト構造材料にぺロブスカイト構造の原料を混合した低鉛あるいは非鉛であって広がり方向モード及び横モードの圧電特性に優れたもの（特許文献１）、マイクロ波加熱とホットプレス加圧を利用した単結晶とセラミックス粉末からなる高ｄ３３値を有するコンポジットセラミックス（特許文献２）等がある。 Conventionally, PZT containing a lead component has been used as dielectric and piezoelectric ceramics. For this reason, development of piezoelectric ceramics containing no or little harmful lead is desired as an environmental problem. For example, a layered perovskite structure material mixed with a perovskite structure raw material that is low-lead or non-lead and has excellent piezoelectric characteristics in the spreading direction mode and transverse mode (Patent Document 1), microwave heating and hot pressing there is a composite ceramic (Patent Document 2) or the like having a high d 33 value of single crystal and ceramic powder using pressure.
しかしながら、これらの圧電セラミックスは複合材料からなる圧電セラミックスでは一般にｄ３３値が低いといった欠点があった。他の素材としてはｄ３３値は高く取れるが単結晶を用いる必要があるといった欠点があった。現在までにいくつかの成果が発表されているが、非鉛系材料の組成開発に関する報告で単独のナノサイズのチタン酸バリウムを使用したものでｄ３３値はせいぜい２００ｐＣ／Ｎ以下程度であった。この程度では、実用レベルの特性とは到底言えない。なお、ｄ３３値の測定は電界歪み曲線で行い、最大電界１０ｋＶ／ｃｍ，周波数２．５Ｈｚの傾斜より求めた値と定義する。実施例ではｄ３３メータにより、測定条件として加振させた値を採用した。 However, these piezoelectric ceramics have the drawback that the d 33 value is generally low in piezoelectric ceramics made of composite materials. Other materials had drawbacks such but take higher d 33 values it is necessary to use a single crystal. Although some results have been announced so far, a report on composition development of lead-free materials using a single nano-sized barium titanate, and the d 33 value was at most about 200 pC / N or less. . At this level, it cannot be said that the characteristics are at a practical level. The d 33 value is measured by an electric field distortion curve, and is defined as a value obtained from a gradient with a maximum electric field of 10 kV / cm and a frequency of 2.5 Hz. In the example, a value excited by a d 33 meter was used as a measurement condition.
また、「ドメイン制御による非鉛系圧電体結晶の性能向上」と題する微構造制御としてのドメイン制御技術についての報告がなされている。（非特許文献１）。これによれば、非鉛系材料としてチタン酸バリウムからなる圧電単結晶の改良にドメイン制御理論を導入したものであるが、これは圧電特性の改良の方向付けといえよう。
他方、トヨタ中央研究所、デンソーグループによる開発報告がなされている。（非特許文献２）。これによれば、非鉛系材料を使用したもので、高いｄ３３特性を得るためにはカリウム、ナトリウム、ニオブ系酸化物からなるセラミックスを用いるとの報告で単独のナノサイズのチタン酸バリウムを使用したものではなく、特定の材料と特殊な製造方法が必要と報告されている。（ｄ３３値が４１６ｐＣ／Ｎ）。
In addition, there has been a report on domain control technology as microstructure control entitled “Improvement of performance of lead-free piezoelectric crystals by domain control”. (Non-Patent Document 1). According to this, the domain control theory is introduced to the improvement of the piezoelectric single crystal made of barium titanate as a lead-free material, but this can be said to be the direction of improvement of the piezoelectric characteristics.
On the other hand, development reports have been made by Toyota Central Research Laboratory and Denso Group. (Non-patent document 2). According to this report, a non-lead-based material was used, and in order to obtain high d 33 characteristics, ceramics composed of potassium, sodium, and niobium-based oxides were reported. It is reported that specific materials and special manufacturing methods are required, not used. (D 33 value is 416 pC / N).
ペロブスカイト化合物のなかで非鉛系組成に代表されるチタン酸バリウム分野での開発の試みも見られている。一般に、チタン酸バリウム粉末は炭酸バリウムと酸化チタンを高温の電気炉中で焼成する固相法で合成するが水熱合成法等でも可能である。
このようなセラミックス粉末に分散剤を使用して微粉砕させ、固相法で作製する方法にあっては、従来焼結方法である抵抗加熱で焼成温度を上昇させると異常に粒成長し、密度の低下を引き起こす欠点が認められた。これを防ぐ目的で変性組成の実施、添加剤等を加えた改善策も試みられているが、ｄ３３値はせいぜい１００〜２００ｐＣ／Ｎ程度であり、実用レベルに達していない。
Among the perovskite compounds, attempts have been made to develop them in the barium titanate field represented by the lead-free composition. In general, barium titanate powder is synthesized by a solid phase method in which barium carbonate and titanium oxide are baked in a high-temperature electric furnace, but it can also be produced by a hydrothermal synthesis method or the like.
In such a method of using a solid phase method to pulverize the ceramic powder using a dispersant and to increase the firing temperature by resistance heating, which is a conventional sintering method, abnormal grain growth and density Disadvantages that caused a decrease in Exemplary purposes denaturing composition to prevent this, it has been attempted by adding an additive such improvements, d 33 value is at most about 100~200pC / N, it does not reach the practical level.
本発明にあっては、粒径、粒成長の語を用いたが、粒径の定義は焼結前の粉体の粒子径、焼結後の焼結体粒径の意味として用いられ、粒成長とは焼結粒径が焼結前の粒子径に比較し拡大することをいう。なお、圧電セラミックスの表面をエッチング法を用いて処理後、後述するＳＥＭによる観察で粒成長の有無を判定した。 In the present invention, the terms particle size and grain growth are used, but the definition of particle size is used to mean the particle size of the powder before sintering and the sintered product particle size after sintering. Growth means that the sintered particle size expands compared to the particle size before sintering. In addition, after processing the surface of piezoelectric ceramics using the etching method, the presence or absence of grain growth was determined by observation with an SEM described later.
また、セラミックス粉末、例えば、ナノサイズ原料のチタン酸バリウム（BaTiO3）粉末を固相法で作製した場合にはサイズの大きなセラミックス粉末の場合と異なる挙動を示すことがわかった。結果として前記固相法のセラミックス粉末より高い特性を得ることができるが（１５０〜２２０ｐＣ／Ｎ）、充分実用レベルの製品には達していない。 Further, it was found that when ceramic powder, for example, barium titanate (BaTiO3) powder, which is a nano-sized raw material, was produced by a solid phase method, the behavior was different from that of a ceramic powder having a large size. As a result, it is possible to obtain characteristics higher than that of the ceramic powder of the solid phase method (150 to 220 pC / N), but the product has not reached a sufficiently practical level.
本発明は、前記従来技術における課題として、ナノサイズ原料のセラミックス粉末からなる非鉛系セラミックス、特に、焼結条件に着目し、それにより製造された圧電セラミックス誘電、圧電体特性の優れたナノサイズのチタン酸バリウム粉末焼結の圧電セラミックス、その製造方法に関する。本発明のナノサイズのチタン酸バリウム粉末からなる新規焼結条件により製造された圧電セラミックスは、各種圧電振動子、超音波探傷用等の素子、アクチュエータ、多くのセンサ類に好適なものである。より高いｄ３３値を有する点で、従来欠点を改良した、実用性の高い、新規焼結条件によるチタン酸バリウム圧電セラミックス及びその製造方法を提供することにある。 The present invention, as a problem in the prior art, lead-free ceramics composed of ceramic powder of nano-sized raw material, especially the piezoelectric ceramic dielectric produced by this, the nano-size excellent in piezoelectric properties The present invention relates to a barium titanate powder sintered piezoelectric ceramic and a method for manufacturing the same. Piezoelectric ceramics manufactured by the novel sintering conditions comprising the nano-sized barium titanate powder of the present invention are suitable for various piezoelectric vibrators, elements for ultrasonic flaw detection, actuators, and many sensors. In that it has a higher d 33 values, conventional disadvantages and improving, highly practical, it is to provide a barium titanate piezoelectric ceramic and manufacturing method thereof according to a new sintering conditions.
本発明は、水熱合成法で作製し、誘電、圧電の性質を持つ平均粒径が０．０５から０．２μｍの非鉛チタン酸バリウム粉末を成型し、これを、少なくとも焼結過程で前記粉末を焼結させるため、焼結時の最高温度を１０５０から１２００℃の範囲まで室温度からおよそ１２時間で昇温、かつ、その温度で保持し、その後室温まで降下させることで焼結させることにより、粒径サイズ（ＧＳ）が０．５から２μｍの範囲内、圧電セラミックスの圧電定数ｄ３３値が２５０から５００ｐＣ／Ｎ及びアルキメデス法により算出される比重Ｘと見掛け密度Ｙとの比Ｐ値が１．３から１．６の範囲である誘電、圧電セラミックスにより提供される。 The present invention is produced by hydrothermal synthesis method, molding a lead-free barium titanate powder having an average particle size of 0.05 to 0.2 μm having dielectric and piezoelectric properties, and at least in the sintering process, In order to sinter the powder, the maximum temperature during sintering is raised from the room temperature to the range of 1050 to 1200 ° C. in about 12 hours, held at that temperature, and then lowered to room temperature for sintering. Thus, the particle size (GS) is in the range of 0.5 to 2 μm, the piezoelectric constant d 33 of the piezoelectric ceramic is 250 to 500 pC / N, and the ratio P between the specific gravity X and the apparent density Y calculated by the Archimedes method Is provided by dielectric, piezoelectric ceramics in the range of 1.3 to 1.6.
また、前記誘電、圧電セラミックスの結晶化度が１．９９から２．１８の範囲である請求項１記載の誘電、圧電セラミックスにより提供される。 The dielectric and piezoelectric ceramics according to claim 1, wherein the crystallinity of the dielectric and piezoelectric ceramics is in the range of 1.99 to 2.18.
さらに、前記粒径サイズ（ＧＳ）が０．６２から１．６４μｍの範囲である請求項１又は２記載の誘電、圧電セラミックスにより提供される。 Furthermore, it is provided by the dielectric and piezoelectric ceramics according to claim 1 or 2, wherein the particle size (GS) is in the range of 0.62 to 1.64 μm.
さらにまた、前記Ｐ値が１．４から１．６の範囲である誘電、圧電セラミックスの結晶化度が１．９９から２．１８の範囲である請求項２又は３記載の誘電、圧電セラミックスにより提供される。 Furthermore, the dielectricity and piezoelectric ceramics according to claim 2 or 3, wherein the P value is in the range of 1.4 to 1.6, and the crystallinity of the piezoelectric ceramics is in the range of 1.99 to 2.18. Provided.
また、ＳＥＭ写真で観察される微細構造における空孔が０．５から１μｍの範囲である請求項３又は４記載の誘電、圧電セラミックスにより効果的に提供される。 Further, the dielectric and piezoelectric ceramics according to claim 3 or 4 are effectively provided with pores in the microstructure observed in the SEM photograph in the range of 0.5 to 1 μm.
本発明の製造方法として、水熱合成法で作製し、誘電、圧電の性質を持つ平均粒径が０．０５から０．２μｍの非鉛チタン酸バリウム粉末を成型し、これを、少なくとも焼結過程で前記粉末を焼結させるため、焼結時の最高温度を１０５０から１２００℃の範囲まで室温度からおよそ１２時間で昇温させ、かつ、その温度で保持し、その後室温まで降下させ焼結させることにより、粒径サイズ（ＧＳ）が０．５から２μｍの範囲内、圧電セラミックスの圧電定数ｄ３３値が２５０から５００ｐＣ／Ｎ及びアルキメデス法により算出される比重Ｘと見掛け密度Ｙとの比Ｐ値が１．３から１．６の範囲である誘電、圧電セラミックスの製造方法により提供される。 As a production method of the present invention, a lead-free barium titanate powder having a dielectric and piezoelectric property and having an average particle size of 0.05 to 0.2 μm is molded, and this is sintered at least. In order to sinter the powder in the process, the maximum temperature during sintering is raised from the room temperature to the range of 1050 to 1200 ° C. in about 12 hours, held at that temperature, and then lowered to room temperature and sintered. The ratio of the specific gravity X and the apparent density Y calculated by the Archimedes method with the particle size (GS) in the range of 0.5 to 2 μm, the piezoelectric constant d 33 value of the piezoelectric ceramics of 250 to 500 pC / N, and the Archimedes method. It is provided by a method for producing dielectric and piezoelectric ceramics having a P value in the range of 1.3 to 1.6.
また、前記焼結時条件として酸素雰囲気中で酸素焼成される請求項６記載の誘電、圧電セラミックスの製造方法により提供され、さらには、前記酸素焼成として酸素流量が０．５リットル／分から５リットル／分を炉内に導入して焼結させる請求項６又請求項７記載の誘電、圧電セラミックスの製造方法により提供される。 The dielectric and piezoelectric ceramic manufacturing method according to claim 6, wherein oxygen firing is performed in an oxygen atmosphere as the sintering condition. Further, as the oxygen firing, an oxygen flow rate of 0.5 liter / minute to 5 liter is provided. The dielectric / piezoelectric ceramic manufacturing method according to claim 6 or 7, wherein / min is introduced into a furnace and sintered.
さらにまた、前記チタン酸バリウム粉末を室温度からおよそ１００℃／時間で前記最高温度に加熱させ焼結される請求項７又は８記載の誘電、圧電セラミックスの製造方法により効果的に提供され、また、前記誘電、圧電セラミックスの結晶化度が１．９９から２．１８の範囲、かつ、前記粒径サイズ（ＧＳ）が０．６２から１．６４μｍの範囲である請求項８又は９記載の誘電、圧電セラミックスの製造方法により効果的に提供される。 Furthermore, the barium titanate powder is effectively provided by the dielectric and piezoelectric ceramic manufacturing method according to claim 7 or 8, wherein the barium titanate powder is heated and sintered at a maximum temperature of about 100 ° C / hour from a room temperature. 10. The dielectric according to claim 8, wherein the crystallinity of the dielectric or piezoelectric ceramic is in the range of 1.99 to 2.18, and the particle size (GS) is in the range of 0.62 to 1.64 μm. It is effectively provided by the manufacturing method of piezoelectric ceramics.
本発明によれば、ナノサイズのチタン酸バリウム粉末を利用した圧電、誘電セラミックス、その製造方法及びそれを用いた圧電振動子を提供するものであり、焼結方法として、従来の固相法ではｄ３３値を高く取れないが、これに対して新規焼結方法では、従来の固相法より高いｄ３３値を達成できる。また、焼結温度の依存性もあり、適当な温度範囲を選択することでより効果的に、又、ナノサイズのチタン酸バリウム粉末を使用した圧電セラミックスにおける焼結後の顕微鏡観察による粒径分布（最大値）を小さくすることで高密度の圧電セラミックス及びその製造方法を提供できる。 According to the present invention, there are provided piezoelectric, dielectric ceramics using a nano-sized barium titanate powder, a method for producing the same, and a piezoelectric vibrator using the same. Although not higher take the d 33 value, new sintering method contrary, a higher d 33 values than conventional solid phase method can be achieved. In addition, there is also a dependency on the sintering temperature, so it is more effective by selecting an appropriate temperature range, and the particle size distribution by microscopic observation after sintering in piezoelectric ceramics using nano-sized barium titanate powder By reducing (maximum value), it is possible to provide a high-density piezoelectric ceramic and a manufacturing method thereof.
新規焼結を利用した焼結で焼結密度も理論密度（チタン酸バリウム６．０１２ｇ／ｃｍ3）の９８％以上に達し、圧電定数ｄ３３も非常に大きな値を示した。得られた圧電セラミックスは高ｄ３３特性を求められる各種の圧電振動子として好適である。 In the sintering using the new sintering, the sintering density reached 98% or more of the theoretical density (barium titanate 6.012 g / cm 3), and the piezoelectric constant d 33 also showed a very large value. Obtained piezoelectric ceramic is suitable as various piezoelectric vibrator sought high d 33 properties.
以下、本発明を具体的に説明する。
ナノサイズのセラミックス粉末として、チタン酸バリウムを用いた。かかる粉末の焼結方法として種々の焼結条件により焼結できる。これには圧電、誘電体の性質を持つ素材類としてナノサイズのセラミックス粉末が必須である。ナノサイズのチタン酸バリウム粉末からなるナノ構造セラミックス粉末は粒径効果に起因して、これを焼結して圧電セラミックスとすると圧電定数ｄ３３が極めて大きく従来にない用途開発が期待できる。
Hereinafter, the present invention will be specifically described.
Barium titanate was used as the nano-sized ceramic powder. Such a powder can be sintered under various sintering conditions. For this purpose, nano-sized ceramic powder is indispensable as a material having piezoelectric and dielectric properties. Nanostructured ceramic powder consisting of barium titanate powder of nano-sized due to the particle size effect, which piezoelectric constant d 33 when the piezoelectric ceramic by sintering can be expected very large not develop applications in the prior art.
このナノサイズのチタン酸バリウム粉末の作製法としては各種の合成によって得られる。特に、粉末の特性としては粒径のコントロールが容易なこと、ナノサイズの粒径分布のシャープさがポイントとなる。ナノサイズのチタン酸バリウム粉末の作製法には公知の水熱合成法、部分共沈法、アルコキシド法、蓚酸塩法、クエン酸塩法、ゾル・ゲル法及び固相反応法等によって得られる。それぞれ一長一短がある。 The nano-sized barium titanate powder can be produced by various synthesis methods. In particular, the characteristics of the powder are easy control of the particle size and sharpness of the nano-size particle size distribution. The nano-sized barium titanate powder can be prepared by a known hydrothermal synthesis method, partial coprecipitation method, alkoxide method, oxalate method, citrate method, sol-gel method, solid phase reaction method, or the like. Each has advantages and disadvantages.
ナノサイズのチタン酸バリウム粉末を作製する要点は粉末の粒度分布の正規分布的なバラツキが無いこと、成型性が良好なことが望ましい。例えば、水熱合成法では、高温高圧の水溶液を利用して無機化合物または有機化合物を合成する方法を基本としたものである。このなかでより好ましい作製法は水熱合成法が良好であった。得られた、ナノサイズのチタン酸バリウム粉末の粒径は０．０５から０．２μｍの範囲の粉末を使用すべきである。本発明では、かかる粉末原料の選択とともに所定の焼成時の最高温度をポイントとした焼結が必要である。 The essential points for producing nano-sized barium titanate powder are that the particle size distribution of the powder is not normally distributed and that the moldability is good. For example, the hydrothermal synthesis method is based on a method of synthesizing an inorganic compound or an organic compound using a high-temperature and high-pressure aqueous solution. Among these, a more preferable production method was a hydrothermal synthesis method. The resulting nanosized barium titanate powder should have a particle size in the range of 0.05 to 0.2 μm. In the present invention, it is necessary to select the powder raw material and perform sintering with the maximum temperature at a predetermined firing as a point.
また、蓚酸塩前駆体法（略称：蓚酸塩法）では，湿式合成された蓚酸塩前駆体を熱処理し，脱蓚酸することでナノサイズのチタン酸バリウム粉末を作製する。このほか、部分共沈法、アルコキシド法、クエン酸塩法、ゾル・ゲル法及び固相反応法等によってナノサイズのチタン酸バリウム粉末を作製することができる。これらによって得られたナノサイズのチタン酸バリウム粉末は特性のほか、作製法により焼結後の性状等が異なる。 In addition, in the oxalate precursor method (abbreviation: oxalate method), a nano-sized barium titanate powder is produced by heat-treating and de-acidifying a wet-synthesized oxalate precursor. In addition, nano-sized barium titanate powder can be prepared by a partial coprecipitation method, an alkoxide method, a citrate method, a sol-gel method, a solid phase reaction method, and the like. The nano-sized barium titanate powders obtained by these differ in properties and properties after sintering depending on the production method.
本発明の圧電セラミックスの製造方法について述べる。
ナノサイズのチタン酸バリウム粉末の選定並びに焼結条件の設定がポイントとなる。チタン酸バリウム粉末は焼成に先立ち、目的とする用途、形状等で決定された成型体を作製する。成型体は金型成型、押出し成型、ドクターブレード成型などで成形でき成型手法は限定されない。
A method for producing the piezoelectric ceramic of the present invention will be described.
The key points are the selection of nano-sized barium titanate powder and the setting of sintering conditions. Prior to firing, the barium titanate powder produces a molded body determined by the intended use, shape, and the like. The molded body can be molded by mold molding, extrusion molding, doctor blade molding, etc., and the molding technique is not limited.
図１は、チタン酸バリウム粉末を焼結し圧電セラミックスの製造を行う際の焼結スケジュールの様子を示したものである。図は縦軸が焼結温度及び酸素量、横軸が焼結時間である。 FIG. 1 shows a state of a sintering schedule when barium titanate powder is sintered to produce piezoelectric ceramics. In the figure, the vertical axis represents sintering temperature and oxygen content, and the horizontal axis represents sintering time.
１．チタン酸バリウム粉末の成型体作成 水熱合成で作製された、粒径０．１μｍのチタン酸バリウム粉末を使用し、焼結温度を図示しない何点かについて変化させ特性上良好な条件を検討した。ナノサイズの原料は成型時に凝集し易いので、５％のポリビニールアルコール（ＰＶＡ）に対してエタノールを１０ｗｔ％加えたものをバインダーとしてチタン酸バリウム粉末比で１ｗｔ％加えて成型体とした。成型圧力は２００ＭＰａで行った。 1. Preparation of molded body of barium titanate powder Using hydrothermal synthesis barium titanate powder with a particle size of 0.1μm, the sintering temperature was changed at several points not shown in the figure, and favorable conditions in terms of characteristics were examined. . Since nano-sized raw materials easily aggregate at the time of molding, 1 wt% of barium titanate powder was added to a molded article by adding 10 wt% of ethanol to 5% polyvinyl alcohol (PVA) as a binder. The molding pressure was 200 MPa.
２．焼結条件
室温から昇温速度１００℃／時で最高温度まで上昇させ最高温度で２時間保持する。焼結時の最高温度値は後述する表１に示す１０５０から１２９０℃の範囲について比較検討した。冷却は昇温速度と同じ割合で冷却させ室温度で取り出す。酸素焼成を行う場合は、酸素流量は０．５リットル／分から５リットル／分を炉内に導入し焼成する。また、酸素中で実施したが大気中での焼結を否定するものではない。図１に示すように酸素は室温度時から炉内に導入し、焼成終了まで継続する。なお、焼結手段としては、炭化珪素（ＳｉＯ）を発熱体に利用した抵抗加熱炉によった。
2. Sintering conditions The temperature is increased from room temperature to the maximum temperature at a heating rate of 100 ° C./hour and held at the maximum temperature for 2 hours. The maximum temperature value during sintering was compared in the range of 1050 to 1290 ° C. shown in Table 1 described later. Cooling is performed at the same rate as the rate of temperature rise and is taken out at the room temperature. In the case of performing oxygen firing, the oxygen flow rate is 0.5 liter / minute to 5 liter / minute introduced into the furnace for firing. Moreover, although it implemented in oxygen, sintering in air | atmosphere is not denied. As shown in FIG. 1, oxygen is introduced into the furnace from the room temperature and continues until the end of firing. The sintering means was a resistance heating furnace using silicon carbide (SiO) as a heating element.
実施例では、圧電セラミックスの製造を行う際の焼結スケジュールは図１として示したものである。チタン酸バリウム粉末を室温度からおよそ１２時間で最高温度に、すなわち昇温速度１００℃／時間にし、最高温度で２時間保持する。その後４００℃までおよそ１０時間で直線的に降下させ、さらに、室温度までおよそ１２時間で冷却させるプロセスで焼結させ圧電セラミックスを得た。更に酸素を導入して焼結する場合は室温度時に０．５リットル／分から５リットル／分を炉内に導入し、焼結終了まで継続して導入する。
焼結時の最高温度は１０５０℃から１１５０℃の範囲で変化させ焼結した圧電セラミックスについての圧電特性が良好な結果が得られた。１２００℃を超える場合には後述するような良好な結果が得られなかった。
In the embodiment, the sintering schedule when the piezoelectric ceramic is manufactured is shown in FIG. The barium titanate powder is brought to the maximum temperature in about 12 hours from the room temperature, that is, the heating rate is 100 ° C./hour, and is maintained at the maximum temperature for 2 hours. Thereafter, it was lowered linearly to 400 ° C. in about 10 hours, and further sintered to a room temperature in about 12 hours to obtain a piezoelectric ceramic. Furthermore, when sintering by introducing oxygen, 0.5 liter / minute to 5 liter / minute is introduced into the furnace at the room temperature and continuously introduced until the end of sintering.
The result was that the piezoelectric characteristics of the sintered piezoelectric ceramics were varied by changing the maximum temperature during sintering in the range of 1050 ° C. to 1150 ° C. When the temperature exceeded 1200 ° C., good results as described later were not obtained.
３．分極
分極は室温下シリコンオイル中にて１．０ｋＶ／ｍｍのＤＣ電界を３０分印加して行った。
４．使用したナノサイズのチタン酸バリウム粉末粒径の検討
表１、表３は粒径の違いにより結果が異なることを示したものである。表３は最高温度を表１の一部温度範囲で同一として対比することで、ナノサイズ原料の使用が望ましいとの結果が得られた。
3. Polarization Polarization was performed by applying a DC electric field of 1.0 kV / mm for 30 minutes in silicon oil at room temperature.
4). Examination of particle size of nano-sized barium titanate powder used Tables 1 and 3 show that the results differ depending on the particle size. Table 3 shows that it is desirable to use a nano-size raw material by comparing the maximum temperature as the same in the partial temperature range of Table 1.
５．最高温度とナノサイズ原料の組み合わせ
前記焼結時の最高温度範囲、その保持時間並びにナノサイズ原料の組み合わせが本発明で目的とする、諸特性の充足条件であることが確認された。特に、焼結初期段階で焼結を終了させ、それぞれの粒子がネッキングされた状態で大きさの等しい空孔を内包させる構造が高性能化の要因と考えられる。後述する図１２のＳＥＭ写真のような圧電体セラミックスとすることことが望ましい。
5. Combination of maximum temperature and nano-size raw material It was confirmed that the maximum temperature range during sintering, the holding time thereof, and the combination of nano-size raw materials are the satisfactory conditions for various properties aimed at by the present invention. In particular, a structure in which sintering is terminated at the initial stage of sintering, and pores of the same size are included in a state where each particle is necked, is considered to be a factor in improving performance. It is desirable to use a piezoelectric ceramic as shown in the SEM photograph of FIG.
６．結果 表１から表３、図２から図１３に示した。以下、それらを順次説明することで前記ナノサイズ原料の使用効果、焼結時の最高温度範囲の決定、それらの選定により得られた諸特性を明らかにする。
表１は「焼結温度」の欄に最高温度を示し、表の横にそれぞれ、密度、粒径（ＧＳは後述する）、比誘電率、径方向振動の電気機械結合係数ｋｐ、円板素子の厚みたて振動の電気機械結合係数ｋｔ、圧電定数ｄ３３を焼結温度ごとに示した。電気機械結合係数はインピーダンスアナライザー装置を利用して共振***振法で計測した円板素子の径方向振動の電気機械結合係数ｋｐ、円板素子の厚みたて振動の電気機械結合係数ｋｔを測定、誘電率（比誘電率）はＬＣＲメーター、圧電定数ｄ３３はｄ３３メーターでそれぞれ測定した。
6). Results Tables 1 to 3 and FIGS. 2 to 13 show the results. In the following, the effects obtained by using the nano-sized raw material, the determination of the maximum temperature range during sintering, and the various characteristics obtained by selecting them will be clarified by sequentially explaining them.
Table 1 shows the maximum temperature in the column of “sintering temperature”, and density, particle size (GS will be described later), relative permittivity, electromechanical coupling coefficient kp of radial vibration, disc element, respectively, next to the table electromechanical coupling factor kt in thickness freshly vibration of exhibited piezoelectric constants d 33 for each sintering temperature. The electromechanical coupling coefficient is measured by measuring the electromechanical coupling coefficient kp of the radial vibration of the disk element and the electromechanical coupling coefficient kt of the vertical vibration of the disk element measured by the resonance anti-resonance method using an impedance analyzer device. dielectric constant (relative permittivity) of LCR meter, piezoelectric constant d 33 was measured respectively at d 33 meter.
なお、粒径（ＧＳ）とは焼結後の粒径サイズとして定義した。
The particle size (GS) was defined as the particle size after sintering.
つぎに、表２は同様に「焼結温度」の欄に最高温度を示し、後述する方法で求められる結晶化度を示す。 Next, Table 2 similarly shows the maximum temperature in the column of “sintering temperature” and shows the crystallinity obtained by the method described later.
焼結の最高温度範囲の決定を目的として表１から図２以下を作成した。
図２は焼結温度に対するアルキメデス法で算出した密度（比重）と見掛け密度の変化図である。焼成後の圧電セラミックスについて焼結の最高温度を横軸に比重の変化と見掛けの密度を縦軸に表したものである。密度はアルキメデス法での測定値で比重として定義した。形状寸法を算出して求めた体積と重さから求めた密度を嵩密度として定義した。
図３は比重／見掛密度の変化図である。焼結の最高温度を横軸に比重／見掛密度の変化を縦軸に表したものである。ここで、Ｐは、Ｐ＝比重／見掛け密度から求められ焼結温度依存性として定義した。
For the purpose of determining the maximum temperature range of sintering, FIG.
FIG. 2 is a graph showing changes in density (specific gravity) and apparent density calculated by the Archimedes method with respect to the sintering temperature. With regard to the sintered piezoelectric ceramic, the horizontal axis represents the maximum sintering temperature and the vertical axis represents the change in specific gravity and the apparent density. Density was defined as specific gravity as measured by Archimedes method. The density obtained from the volume and weight obtained by calculating the shape dimension was defined as the bulk density.
FIG. 3 is a change diagram of specific gravity / apparent density. The maximum temperature of sintering is shown on the horizontal axis, and the change in specific gravity / apparent density is shown on the vertical axis. Here, P was obtained from P = specific gravity / apparent density and defined as the sintering temperature dependency.
図４はＰ値に対する圧電定数ｄ３３値の変化図である。比重／見掛け密度（Ｐ）を横軸に圧電定数ｄ３３の変化を縦軸に表したものである。
図５は比重に対する圧電定数ｄ３３値の変化図である。比重を横軸、圧電定数の変化を縦軸に表したものである。
FIG. 4 is a change diagram of the piezoelectric constant d 33 value with respect to the P value. Density / apparent density (P) on the horizontal axis illustrates a change in piezoelectric constant d 33 in the longitudinal axis.
FIG. 5 is a change diagram of the piezoelectric constant d 33 value with respect to the specific gravity. The specific gravity is represented on the horizontal axis, and the change in piezoelectric constant is represented on the vertical axis.
図６は焼結温度に対する粒径（ＧＳ）の変化図である。焼結の最高温度を横軸に粒径（ＧＳ）を縦軸に表したもので粒径の焼結温度依存性の様子を示したものである。図７は焼結温度に対する電気機械結合係数の変化図である。焼結の最高温度を横軸に電気機械結合係数を縦軸に表したものである。径方向振動の電気機械結合係数ｋｐで、円板素子の厚みたて振動の電気機械結合係数ｋｔである。図８は焼結温度に対する比誘電率の変化図である。焼結の最高温度を横軸に比誘電率を縦軸に表したもので比誘電率の焼結温度依存性の様子を示したものである。 FIG. 6 is a change diagram of the particle size (GS) with respect to the sintering temperature. The maximum temperature of sintering is expressed on the horizontal axis and the particle size (GS) is expressed on the vertical axis, and the state of the particle size depending on the sintering temperature is shown. FIG. 7 is a variation diagram of the electromechanical coupling coefficient with respect to the sintering temperature. The maximum temperature of sintering is shown on the horizontal axis and the electromechanical coupling coefficient is shown on the vertical axis. The electromechanical coupling coefficient kp for the radial vibration is the electromechanical coupling coefficient kt for the vertical vibration of the disk element. FIG. 8 is a graph showing the change in relative dielectric constant with respect to the sintering temperature. The maximum temperature of sintering is shown on the horizontal axis and the relative dielectric constant is shown on the vertical axis, showing the dependence of the relative dielectric constant on the sintering temperature.
図９から図１１はＸ線回折法（ＸＲＤ）による回折強度の変化図である。回折線の角度（２θ／ｄｅｇ）を横軸に回折強度（ＣＰＳ）を縦軸に表したものである。図９は焼結温度が１０５０−１１４０℃で処理した高性能な圧電体セラミックス、図１０は焼結温度が１２００−１２９０度で処理した低性能な圧電体セラミックスのＸ線回折法（ＸＲＤ）による回折強度の変化図を示したものである。図１１は焼結強度が１１７０度で処理した圧電体セラミックスのＸ線回折法（ＸＲＤ）による回折強度の変化図を示したものである。 9 to 11 are diagrams showing changes in diffraction intensity by the X-ray diffraction method (XRD). The angle of diffraction lines (2θ / deg) is represented on the horizontal axis and the diffraction intensity (CPS) is represented on the vertical axis. FIG. 9 shows a high-performance piezoelectric ceramic processed at a sintering temperature of 1050 to 1140 ° C., and FIG. 10 shows an X-ray diffraction method (XRD) of a low-performance piezoelectric ceramic processed at a sintering temperature of 1200 to 1290 degrees. The change figure of diffraction intensity is shown. FIG. 11 shows a change diagram of diffraction intensity by X-ray diffraction (XRD) of a piezoelectric ceramic processed at a sintering strength of 1170 degrees.
図１２及び図１３は圧電セラミックス表面性状のＳＥＭ（走査電子顕微鏡）写真である。図１２は焼結温度が１０５０−１１４０℃で処理した高性能な圧電体セラミックスのＳＥＭ写真、図１３は焼結温度が１２００−１２９０℃で処理した低性能な性能なＳＥＭ写真（写真は１２９０℃のもの）である。特に、図１３は抵抗加熱法でナノサイズのチタン酸バリウム粉末を焼結した場合発生した異常粒成長した状態のＳＥＭ写真である。試料は焼結した圧電セラミックスの上下面を研磨して厚さ０．８ｍｍにしてＳＥＭを利用して微細構造の確認、Ｘ線回折を利用して結晶構造の影響について評価した。研磨加工した厚さ０．８ｍｍの試料は上下面に電極を塗布した。また、電極はスパッタ装置で金を電極厚み３５００Å（オングストローム）で両面に塗布した。 12 and 13 are SEM (scanning electron microscope) photographs of piezoelectric ceramic surface properties. FIG. 12 is a SEM photograph of a high-performance piezoelectric ceramic processed at a sintering temperature of 1050 to 1140 ° C., and FIG. 13 is a low-performance SEM photograph processed at a sintering temperature of 1200 to 1290 ° C. belongs to. In particular, FIG. 13 is an SEM photograph of abnormal grain growth that occurred when nano-sized barium titanate powder was sintered by resistance heating. The samples were polished on the upper and lower surfaces of the sintered piezoelectric ceramic to a thickness of 0.8 mm, the microstructure was confirmed using SEM, and the influence of the crystal structure was evaluated using X-ray diffraction. An electrode was applied to the upper and lower surfaces of the polished 0.8 mm thick sample. Further, gold was applied to both sides of the electrode with a sputtering apparatus with an electrode thickness of 3500 mm (angstrom).
具体的装置は、図示しない抵抗加熱炉により焼結した。試料サンプルを加熱炉に入れ図１による酸素ガス雰囲気供給手段からガスを供給し焼結した。 A specific apparatus was sintered by a resistance heating furnace (not shown). The sample sample was placed in a heating furnace and gas was supplied from the oxygen gas atmosphere supply means shown in FIG.
表１は本発明の実施例を焼結温度の最高温度をパラメータとして示したものである。焼結時の最高温度を１０５０から１２９０℃の範囲で、図１に従い温度制御のもとに焼結させた。得られた圧電セラミックスの諸特性は前記図２から図１３として具体的に示した。 チタン酸バリウムの粉末種を用いた焼成プロセスで、焼結時の最高温度を１０５０から１１５０℃の温度範囲で好結果が確認された。ナノサイズのチタン酸バリウム粉末は、主として粒径が０．０５から０．２μｍの範囲である、いわゆるナノサイズ原料を用いた。後述する表３と表１を対比すると、ナノサイズのチタン酸バリウム粉末を使用しない場合に比較し本発明は焼結時の最高温度の依存性に注意すべきである。ナノサイズのチタン酸バリウム粉末を使用しただけでは、製造条件次第であり、ある特定の温度範囲内での焼結がポイントとなることである。粒径のみではないということに本発明は着目した点を強調しておく。 Table 1 shows an example of the present invention with the maximum sintering temperature as a parameter. The maximum temperature during sintering was in the range of 1050 to 1290 ° C., and sintering was performed under temperature control according to FIG. Various characteristics of the obtained piezoelectric ceramic are specifically shown in FIGS. In a firing process using a powdered seed of barium titanate, good results were confirmed at a maximum temperature during sintering in a temperature range of 1050 to 1150 ° C. As the nano-sized barium titanate powder, a so-called nano-size raw material having a particle size mainly in the range of 0.05 to 0.2 μm was used. When Table 3 and Table 1 described below are compared, it should be noted that the present invention is dependent on the maximum temperature during sintering as compared with the case where nano-sized barium titanate powder is not used. If only nano-sized barium titanate powder is used, depending on the manufacturing conditions, sintering within a specific temperature range is a point. It should be emphasized that the present invention focuses not only on the particle size.
表２は結晶化度について焼成温度１１１０、１１７０、１２９０℃の３点で測定した。測定結果は、１１１０℃で結晶化度２．１８と極めて良好な値が得られ、１１７０℃で１．９９でまずまず、１２９０℃で１．５６と低数値であった。これらの確認からより好ましい焼成温度範囲は１０５０から１１５０℃と確認された。 In Table 2, the crystallinity was measured at three points of firing temperatures of 1110, 1170, and 1290 ° C. As a result of the measurement, a very good value of crystallinity of 2.18 was obtained at 1110 ° C., and it was 1.99 ° C. at 1170 ° C. and 1.56 at 1290 ° C., which was a low value. From these confirmations, a more preferable firing temperature range was confirmed to be 1050 to 1150 ° C.
本発明ではナノサイズのチタン酸バリウム粉末を用いたが、比較例として従来法である固相法により合成されたチタン酸バリウム粉末で、特に平均粒径が０．５から１μｍ程度のものを使用して１２４０から１３６０℃の温度範囲でそれぞれ実施した。結果を表３に示す。得られた圧電セラミックスについてＳＥＭによる確認の結果（図示しない）は、見掛け上の粒径としては１００μｍ程度の異常粒成長が見られる。このような状態では圧電セラミックスとしての充分な機能を発揮できない。 In the present invention, nano-sized barium titanate powder was used. As a comparative example, barium titanate powder synthesized by a solid phase method, which is a conventional method, with an average particle diameter of about 0.5 to 1 μm was used. In the temperature range from 1240 to 1360 ° C., respectively. The results are shown in Table 3. As a result of confirmation by SEM (not shown) of the obtained piezoelectric ceramic, an abnormal grain growth of about 100 μm is seen as an apparent grain size. In such a state, a sufficient function as a piezoelectric ceramic cannot be exhibited.
本発明でナノサイズのチタン酸バリウム粉末を用い、かつ、所定の焼結条件で得られたた圧電体セラミックスは、図２ないし図１３を参照し、以下の点が見いだされた。
（１）アルキメデス法で測定した試料の密度（比重）が理論密度の９８％以上。ただし、本件のチタン酸バリウム構造は微小な空孔を含むため測定時に水が浸透し、結果として得た値は比重と考えるべきであろう。したがって、本発明では、アルキメデス法で測定した密度を比重と定義する。（図２参照）
（２）アルキメデス法で算出した密度（比重）Ｘと見掛けの密度Ｙ（比重／見掛密度）の焼成温度依存性を図３に示す。焼結時の最高温度をパラメーターとすると、１０５０℃で約１．６、温度上昇に伴い下降し１１５０℃で約１．４、１２５０℃を超えると１．０以下となる。
Piezoelectric ceramics obtained using nano-sized barium titanate powder in the present invention and obtained under predetermined sintering conditions have found the following points with reference to FIGS.
(1) The density (specific gravity) of the sample measured by Archimedes method is 98% or more of the theoretical density. However, since the barium titanate structure in this case contains minute pores, water penetrates during measurement, and the resulting value should be considered as specific gravity. Therefore, in the present invention, the density measured by the Archimedes method is defined as specific gravity. (See Figure 2)
(2) FIG. 3 shows the firing temperature dependence of density (specific gravity) X and apparent density Y (specific gravity / apparent density) calculated by the Archimedes method. If the maximum temperature at the time of sintering is used as a parameter, it is about 1.6 at 1050 ° C., decreases with increasing temperature, about 1.4 at 1150 ° C., and becomes 1.0 or less when it exceeds 1250 ° C.
（３）比重Ｘ及び見掛密度Ｙの関係Ｐを算出する。算出式を（ａ）に示す。更に算出したＰ値と圧電定数ｄ３３値の関係を図４に示した。
Ｐ＝Ｘ／Ｙ （ａ）
この図４から、Ｐ＝１．３〜１．６の範囲で高い圧電定数ｄ３３を示すことがわかる。
(3) The relationship P between the specific gravity X and the apparent density Y is calculated. The calculation formula is shown in (a). Further, the relationship between the calculated P value and the piezoelectric constant d 33 value is shown in FIG.
P = X / Y (a)
From FIG. 4, it can be seen that a high piezoelectric constant d 33 is exhibited in the range of P = 1.3 to 1.6.
（４）前記（２）、（３）から圧電定数ｄ３３値はアルキメデスで算出した密度（比重）に依存することから、これと対応する焼成時の最高温度１０５０ないし１１５０℃で極めて高い圧電定数ｄ３３を示すことが認められた。（図５参照） (4) Since the piezoelectric constant d 33 value from (2) and (3) depends on the density (specific gravity) calculated by Archimedes, the piezoelectric constant is extremely high at the maximum temperature of 1050 to 1150 ° C. corresponding to this. d 33 was observed. (See Figure 5)
（５）図６は焼成温度と粒径（ＧＳ）の関係を示したものである。これによれば、粒径（ＧＳ）が０．５μｍから２μｍ程度の粒径から形成される。粒径（ＧＳ）は電子走査型顕微鏡（ＳＥＭ）で観察しインターセプト法で算出した。粒径観察におけるインターセプト法としてはｄｇ＝１．５Ｌｎ／Ｎ （Ｌｎは測定長さ、Ｎは粒径の数）で定義した。 (5) FIG. 6 shows the relationship between the firing temperature and the particle size (GS). According to this, the particle size (GS) is formed from a particle size of about 0.5 μm to 2 μm. The particle size (GS) was observed with an electron scanning microscope (SEM) and calculated by the intercept method. The intercept method in the particle size observation was defined by dg = 1.5 Ln / N (Ln is the measurement length, and N is the number of particle sizes).
（６）圧電定数ｄ３３特性が高い試料と低い試料の微細構造の様子は図１２及び図１３に示した。圧電定数ｄ３３特性が高い試料の粒径は前記したように０．５ないし２μｍ程度の粒径から形成される。またそれぞれの粒子は焼成初期段階に見られるネックで形成されている。全体的には０．５から１μｍの空孔を含んだ構造になっている。（図１２参照）得られた圧電セラミックスは圧電定数ｄ３３が得られ高い性能が確認された。 (6) Piezoelectric constant d 33 The states of the microstructures of the samples with high and low characteristics are shown in FIGS. As described above, the particle diameter of the sample having a high piezoelectric constant d 33 characteristic is formed with a particle diameter of about 0.5 to 2 μm. Each particle is formed with a neck seen in the initial stage of firing. The overall structure includes pores of 0.5 to 1 μm. (See FIG. 12) obtained piezoelectric ceramic piezoelectric constant d 33 is obtained a high performance was confirmed.
一方、圧電定数ｄ３３特性が低い試料の粒径は１２５０℃以上で急激に粒成長して１００μｍ以上に達する。また１μｍ以下の空孔は観察できない。それぞれの粒子はネックでつながった様子は見られない。（図１３参照） On the other hand, the particle diameter of the sample having a low piezoelectric constant d 33 characteristic grows rapidly at 1250 ° C. or more and reaches 100 μm or more. Also, pores of 1 μm or less cannot be observed. Each particle is not connected by a neck. (See Figure 13)
圧電セラミックスの表面の性状の観察はＳＥＭで微細結晶構造が異常粒成長したかは、粒径が１００μｍをパラメータとして確認した。ナノ材料の固体表面の観察にはいわゆるスペクトロスコピーと称される固体表面の性状観察が望ましいからである。加速電圧は３０ｋＶ、試料は上下面を研磨し、厚さ０．５ｍｍにし、観察はＳＥＭ/ＥＤＸ(日本電子光学社製：ＪＳＭ−５６００)で行った。倍率は１００倍で図１３ではスケール幅１００μｍから算出した粒径は１００μｍ以上の粒成長が見られる。したがって、見掛け上の粒径としては１００μｍ程度の異常粒成長が見られる。このような状態では圧電セラミックスとしての充分な機能を発揮できない。 The observation of the surface properties of the piezoelectric ceramic was confirmed by SEM using a 100 μm particle size as a parameter to determine whether or not the fine crystal structure had grown abnormally. This is because, for observation of the solid surface of the nanomaterial, it is desirable to observe the property of the solid surface called so-called spectroscopy. The acceleration voltage was 30 kV, the upper and lower surfaces of the sample were polished to a thickness of 0.5 mm, and observation was performed with SEM / EDX (manufactured by JEOL Ltd .: JSM-5600). The magnification is 100, and in FIG. 13, grain growth with a grain size calculated from a scale width of 100 μm is 100 μm or more. Therefore, abnormal grain growth of about 100 μm is observed as an apparent grain size. In such a state, a sufficient function as a piezoelectric ceramic cannot be exhibited.
（７）電気機械結合係数Ｋｐ、Ｋｔの焼成温度依存性から焼成温度におけるＫｐ値とＫｔ値の平均値Ｍを算出式（ｂ）で求めた。（図７参照）
Ｍ＝（Ｋｐ値＋Ｋｔ値）／２ （ｂ） （各焼成温度において）
焼結時の最高温度をパラメーターとすると、１０５０℃でＭ＝約３１、１１５０℃でＭ＝約３２、１２００℃を超えるとＭ＝約２２以下となる。１０５０から１１５０℃の範囲で３０％以上の高い特性が得られた。
(7) The average value M of the Kp value and the Kt value at the firing temperature was determined by the calculation formula (b) based on the firing temperature dependence of the electromechanical coupling coefficients Kp and Kt. (See Figure 7)
M = (Kp value + Kt value) / 2 (b) (at each firing temperature)
If the maximum temperature during sintering is used as a parameter, M = about 31 at 1050 ° C., M = about 32 at 1150 ° C., and M = about 22 or less when it exceeds 1200 ° C. High characteristics of 30% or more were obtained in the range of 1050 to 1150 ° C.
（８）焼成時の最高温度をパラメーターとし、分極前後の比誘電率の変化を図８に示す。図から１０５０から１１７０℃の範囲で焼成した試料の比誘電率は、分極前後で変化し、分極後低下した。他方１１７０から１２８０℃の範囲で焼成した場合は分極後増加した。言い換えれば分極すると誘電率が低下する範囲では高い圧電定数ｄ３３値を示すことが見いだされた。
（９）高い圧電定数ｄ３３値の結晶化度は高く、圧電定数ｄ３３が低い場合の結晶化度は低いことが見いだされた（表２参照）。結晶化度は特開２００４−１２３４３１を参照して求めた。
(8) Using the maximum temperature during firing as a parameter, the change in relative permittivity before and after polarization is shown in FIG. From the figure, the relative dielectric constant of the sample fired in the range of 1050 to 1170 ° C. changed before and after the polarization and decreased after the polarization. On the other hand, it increased after polarization when fired in the range of 1170 to 1280 ° C. When the polarization in other words the dielectric constant was found to exhibit a high piezoelectric constant d 33 value in the range to be reduced.
(9) high crystallinity of the piezoelectric constant d 33 value is high, the crystallinity when the piezoelectric constant d 33 is low it was found low (see Table 2). The degree of crystallinity was determined with reference to JP-A No. 2004-123431.
（１０）Ｘ線回折法（ＸＲＤ）による回折強度の変化図（図９から図１１）は、回折角度（２θ／ｄｅｇ）を横軸に回折線の強度（ＣＰＳ）を縦軸に表したものである。測定はＸ線回折装置（リガク製ＲＩＮＴ２０００／ＰＣシリーズ）を用いた。結晶化度は特開２００４−１２３４３１号、段落００５７ないし００５８記載の方法により求めた。それによれば、高い圧電定数ｄ３３値が高い場合、結晶化度は高くなり、圧電定数ｄ３３が低い場合、結晶化度は低いとされている。 (10) Changes in diffraction intensity by X-ray diffractometry (XRD) (FIGS. 9 to 11) are shown with the diffraction angle (2θ / deg) on the horizontal axis and the diffraction line intensity (CPS) on the vertical axis. It is. An X-ray diffractometer (Rigaku RINT2000 / PC series) was used for the measurement. The degree of crystallinity was determined by the method described in JP-A No. 2004-123431, paragraphs 0057 to 0058. According to this, when the high piezoelectric constant d 33 value is high, the crystallinity is high, and when the piezoelectric constant d 33 is low, the crystallinity is low.
具体的には２θ＝４４．８０°付近の格子面（００２）面の回折ピークの強度、２θ＝４４．３０°付近の格子面（００２）面の回折ピークと上記格子面（２００）面の回折ピークとの間の谷部の強度を読み取った。回折ピーク及び谷部はＸ線回折装置の機械的換算手段により求めた。 Specifically, the intensity of the diffraction peak of the lattice plane (002) near 2θ = 44.80 ° and the diffraction peak of the lattice plane (002) near 2θ = 44.30 ° and the above-mentioned lattice plane (200) The intensity of the valley between the diffraction peaks was read. The diffraction peak and valley were determined by mechanical conversion means of an X-ray diffractometer.
高い圧電定数ｄ３３値のＸ線回折は図９のように４４°付近の格子面（００２）より格子面（２００）の方がピークは高く、結晶化度も高いことが認められる。他方、図１０は、ｄ３３値の低い範囲のＸ線回折ピークは格子面（００２）の方が（２００）より高く結晶化度が低いことが認められる。またその中間の１１７０°で焼結した試料は図１１のようにＸ線回折ピークは格子面（００２）（２００）のそれぞれのピークは同じ高さであることが認められる。圧電定数ｄ３３値の高い範囲は上記で述べるように結晶化度が高い領域となる。
これらの結果から、本発明について焼結時の最高温度、素材としてナノサイズのチタン酸バリウム粉末を用いることが望ましいが、さらに、最高温度の範囲も重要な要素であることが理解されよう。高い圧電定数を必要とする用途には、１０５０から１１５０℃の範囲が望ましいことが理解されよう。
It can be seen that the X-ray diffraction with a high piezoelectric constant d 33 value has a higher peak and higher crystallinity in the lattice plane (200) than in the lattice plane (002) near 44 ° as shown in FIG. On the other hand, FIG. 10 shows that the X-ray diffraction peak in the low d 33 value range is higher in the lattice plane (002) than in (200) and lower in crystallinity. Further, in the sample sintered at 1170 ° in the middle, as shown in FIG. 11, the X-ray diffraction peaks are recognized to have the same height on the lattice planes (002) and (200). The range where the piezoelectric constant d 33 is high is a region where the crystallinity is high as described above.
From these results, it is desirable to use a nano-sized barium titanate powder as a raw material for the present invention, and it is understood that the range of the maximum temperature is also an important factor. It will be appreciated that a range of 1050 to 1150 ° C. is desirable for applications that require high piezoelectric constants.
例えば、圧電定数ｄ３３値はこの試作では最大値４３０ｐＣ／Ｎの値が得られた。（図４）。従来技術では、せいぜい２３０ｐＣ／Ｎの値に留まっており、約８０％強の改善が認められた。しかも、ナノサイズのチタン酸バリウム粉末は共通で、焼結法の違いである。したがって、従来からの固相法により合成されたセラミックス粉末に比べ、さらに、大きな改善が図られていることが理解されよう。 For example, the maximum value of the piezoelectric constant d 33 was 430 pC / N in this prototype. (FIG. 4). In the prior art, the value is at most 230 pC / N, and an improvement of about 80% is recognized. Moreover, the nano-sized barium titanate powder is common and is a difference in the sintering method. Therefore, it will be understood that a great improvement has been achieved compared to the ceramic powder synthesized by the conventional solid phase method.
本発明の高ｄ３３、高密度の優れた圧電セラミックスを用いた圧電振動子としては、例えば、高感度振動子ピックアップ、ノッキングセンサーに最適である。より好ましくは、さらにバイモルフアクチュエータ等としての極めて高性能な振動子として期待される。これらの振動子の製造は公知のそれぞれの手段によって得られる。 The piezoelectric vibrator using the high d 33 , high density excellent piezoelectric ceramic of the present invention is suitable for, for example, a high sensitivity vibrator pickup and a knocking sensor. More preferably, it is expected as a very high performance vibrator as a bimorph actuator or the like. Manufacture of these vibrators is obtained by each known means.
本発明はナノサイズのセラミックス粉末、とりわけ、チタン酸バリウムに着目したが他のナノサイズ素材との複合材に対する産業上の利用可能性は否定するものではない。 Although the present invention focuses on nano-sized ceramic powders, particularly barium titanate, the industrial applicability to composite materials with other nano-sized materials is not denied.
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