JP3562947B2 - Piezoelectric material - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、共振器やフィルタなどの構成要素として用いられる新規な圧電体材料に関するものである。
【０００２】
【従来の技術】
これまで、光学物性又は電気物性を利用したバルク単結晶材料としては、水晶やアルミナとともに不定比による固溶体領域をもった複合化合物、例えば希土類ガーネット、ニオブ酸リチウム、タンタル酸リチウム、ゲルマン酸ビスマス、ケイ酸ビスマスなどが知られている。
他方、最近Ｃａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造をもつ圧電体材料が水晶と比較して大きな圧電特性を持ち、かつ水晶に近い圧電特性の温度安定性を有する材料として脚光を浴びている。
【０００３】
これらの材料は、配位数８の原子のサイト、配位数６の原子のサイト及び２種類の配位数４の原子のサイトから構成されている。そして、本発明においては、配位数８の原子のサイトをＡ−サイト、配位数６の原子のサイトをＢ−サイト、配位数４の２種類の原子のサイトをそれぞれＣ−サイト及びＤ−サイトと称する。場合によっては、これらの各サイト間での陽イオンの置換も行われたものもあるし、また各サイトに空孔を有するものもある。
【０００４】
ところで、このＣａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造を有する材料の中でＬａ３Ｇａ５ＳｉＯ１４、Ｃａ３Ｇａ２Ｇｅ４Ｏ１４及びＳｒ３Ｇａ２Ｇｅ４Ｏ１４は、電気機械結合係数ｋ１２がそれぞれ０．１６、０．１４５及び０．２６６であり、水晶の０．１０よりも大きく上回ることが知られているし［１９９３年ＩＥＥＥ「インターナショナル・フリクエンシー・コントロール・シンポジウム（Ｉｎｔｅｒｎａｔｉｏｎａｌ Ｆｒｅｑｕｅｎｃｙ Ｃｏｎｔｒｏｌ Ｓｙｍｐｏｓｉｕｍ）」，第３５１〜３５２ページ］、またＢａ３Ｇａ２Ｇｅ４Ｏ１４の圧電係数及び電気機械結合係数はＳｒ３Ｇａ２Ｇｅ４Ｏ１４のそれらよりも大きいことが知られているので（同誌，第３３９〜３４７ページ）、好適な圧電体材料である。
【０００５】
しかしながら、Ｓｒ３Ｇａ２Ｇｅ４Ｏ１４やＢａ３Ｇａ２Ｇｅ４Ｏ１４は、原料としてＧａ２Ｏ３やＳｉＯ２に比べ著しく高価なＧｅＯ２を用いなければならないため、コスト高になるのを免れないし、またそれらの融点付近すなわち１０００℃以上の温度域でＧｅＯ２は高い蒸気圧を有するため、結晶成長時にＧｅＯ２が蒸散し、高品質の単結晶の成長がむずかしいという欠点を有しており、これが実用化を妨げている。
【０００６】
【発明が解決しようとする課題】
本発明は、従来のＣａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造を有する圧電体材料のもつ欠点を克服し、結晶成長が容易で、低コストの、しかも優れた圧電特性を有する新らしいＣａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造の圧電体材料を提供しようとするものである。
【０００７】
【課題を解決するための手段】
本発明者らは、Ｃａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造をもつ圧電体材料について鋭意研究を重ねた結果、Ｃａ、Ｂａ、Ｓｒ及びＰｂの中から選ばれた少なくとも１種の元素、特にＳｒとＢａの少なくとも一方を導入し、ＮｂとＴａとＳｂの中から選ばれた少なくとも１種の元素、かつＧａとＡｌとＦｅの中から選ばれた少なくとも１種の元素及びそれ以外の元素からなる４種類以上の異なる陽イオンを組み合わせることにより、高価なＧｅＯ２の使用量を少なくして結晶成長時のＧｅＯ２の蒸散を減少させ、優れた圧電特性をもった単結晶が得られることを見い出し、この知見に基づいて本発明をなすに至った。
【０００８】
すなわち、本発明は、価数２＋で安定に存在し、配位数８をとることができ、この状態でのイオン半径が約１．１〜１．４Åの範囲にあるＣａ、Ｂａ、Ｓｒ及びＰｂの中から選ばれた少なくとも１種の元素と、価数５＋で安定に存在し、配位数６をとることができ、この状態でのイオン半径が約０．６〜０．７Åの範囲にあるＮｂ、Ｔａ及びＳｂの中から選ばれた少なくとも１種の元素と、価数３＋で安定に存在し、配位数４をとることができ、この状態でのイオン半径が約０．３〜０．６Åの範囲にあるＧａ、Ａｌ及びＦｅの中から選ばれた少なくとも１種の元素と、それ以外の元素からなる４種類以上の異なる陽イオンと酸素イオンで構成されたＣａ3Ｇａ2Ｇｅ4Ｏ14型結晶構造の化合物において、Ｇｅ含有率が０又は８．７０ａｔｍ％以下、ＣａとＢａとＳｒとＰｂの中から選ばれた少なくとも１種の元素の含有率が４．３５〜１３．０４ａｔｍ％の範囲にあることを特徴とするものからなる圧電体材料を提供するものである。
【０００９】
このＣａ3Ｇａ2Ｇｅ4Ｏ14型結晶構造をもつ化合物は、少なくとも４種類の異なる陽イオンとなっている原子と陰イオンとなっている酸素原子の２３個の原子から構成されているが、その中の２個以下すなわち８．７０ａｔｍ％以下がＧｅであり、ＣａとＢａとＳｒとＰｂの中から選ばれた少なくとも１種が１個以上すなわち４．３５ａｔｍ％以上、好ましくは２個以上すなわち８．７０ａｔｍ％以上である。そして、これが３個の場合は１３．０４ａｔｍ％になる。
【００１０】
上記のＧｅ、Ｃａ、Ｂａ、Ｓｒ及びＰｂ以外の陽イオンとなっている原子については、Ｃａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造中に置換可能なものであればよく特に制限はない。したがって、本発明の圧電体材料として用いうるものとしては、例えば一般式
Ｍ１ ｘＭ２ ３−ｘＭ３Ｍ４ ３＋ｘＭ５ ２−ｘＯ１４ （Ｉ）
（式中のＭ１はＬａ、Ｐｒ、Ｎｄ及びＢｉの中から選ばれた少なくとも１種の原子、Ｍ２はＣａ、Ｓｒ、Ｂａ及びＰｂの中から選ばれた少なくとも１種の原子、Ｍ３はＮｂ、Ｔａ及びＳｂの中から選ばれた少なくとも１種の原子、Ｍ４はＧａ、Ａｌ及びＦｅの中から選ばれた少なくとも１種の原子、Ｍ５はＳｉ、Ｇｅ、Ｔｉ、Ｓｎ、Ｚｒ及びＨｆの中から選ばれた少なくとも１種の原子であり、ｘは０≦ｘ≦２の数である）
で表わされる組成をもつＣａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造の化合物を挙げることができる。この一般式中のｘは、０から１までの数が好ましく、最も好ましいのは０である。
【００１１】
この一般式（Ｉ）において、Ｍ１及びＭ２で示される原子は、いずれも価数３＋及び２＋で安定に存在し、配位数８をとることができ、この状態でのイオン半径が約１．１〜１．４Åの範囲にあるものである。また、Ｍ３で示される原子は、いずれも価数５＋で安定に存在し、配位数６をとることができ、この状態でのイオン半径が約０．６〜０．７Åの範囲にあるものである。次にＭ４及びＭ５で示される原子は、価数３＋及び４＋で安定に存在し、配位数４をとることができ、この状態でのイオン半径が約０．３〜０．６Åの範囲にあるものである。
【００１２】
なお、ここにいうイオン半径とは、「アクタ・クリスタログラフィカ（Ａｃｔａ Ｃｒｙｓｔａｌｌｏｇｒａｐｈｉｃａ）」，１９７６年，第Ａ３２巻，第７５１〜７６７ページに記載されている有効イオン半径（ＩＲ ｅｆｆｅｃｔｉｖｅ ｉｏｎｉｃ ｒａｄｉｕｓ）を意味する。
Ｓｒ３Ｇａ２Ｇｅ４Ｏ１４やＢａ３Ｇａ２Ｇｅ４Ｏ１４の実用化を妨げる原因となっている原子のＧｅは、価数４＋で安定であり、配位数４をとることからＭ５に属するが、このＧｅはＭ４やＭ５の中のＧｅ以外の原子で置換することができるので、積極的にそれを行えば、コストを下げることができ、かつ結晶成長を容易に行いうるので、実用化が可能になる。
【００１３】
本発明の圧電体材料は、安定なＣａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造を形成しているが、このＣａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造はＡＳＴＭ（ＪＣＰＤＳ）カード３６−００９８に記載されている公知の結晶構造で、図１はこれをモデル的に表わした平面図である。なお、図中の（ａ）はＢ−サイト，（ｄ）はＣ−サイト，（ｅ）はＡ−サイト（ｆ）はＤ−サイトの陽イオンとなっている原子の位置を示す。
【００１４】
【発明の実施の形態】
本発明の圧電体材料を構成する化合物は、例えば前記一般式（Ｉ）を構成する元素の酸化物又は炭酸塩を、粉末状で所定の原子比になるように混合し、円柱状に圧縮成形したのち、大気中、１０００〜１５００℃で焼結し、気密性の保たれた結晶引き上げ装置内で、少量の酸素を含む窒素雰囲気下に融解し、常法、例えばチョクラルスキー（Ｃｚｏｃｈｒａｌｓｋｉ）法により、結晶成長させることによって製造することができる。この際の成長条件としては、通常結晶回転数１〜１００ｒｐｍ、好ましくは５〜５０ｒｐｍ、種結晶引き上げ速度０．１〜１０ｍｍ／ｈｒ、好ましくは０．５〜５ｍｍ／ｈｒである。このようにして直径約２５ｍｍ、長さ約７０ｍｍまでの無色透明な単結晶を得ることができる。この結晶の同定は、その一部を粉砕し、粉末Ｘ線回折し、その回折ピークを対比することによって行うことができる。
このようにして得られる単結晶は、重量変化率（ΔＷ／Ｗ１）が０．４％以下と小さく、電気機械結合係数（ｋ１２）が０．１７以上と大きかった。
【００１５】
【実施例】
次に、実施例によって本発明をさらに詳細に説明する。なお、各例中の重量変化率及び電気機械結合係数は、以下の方法により求めた。
【００１６】
（１）重量変化率
結晶成長開始直前の原料が充填された状態でるつぼ重量を秤量し、これをＷ１とする。次に結晶成長終了直後の、原料が残存した状態でのるつぼ重量を秤量し、これをＷ２とする。結晶成長により得た結晶の重量をＷ３とすると、結晶成長中に蒸散した原料の量ΔＷは以下のとおりになる。
ΔＷ＝Ｗ１−（Ｗ２＋Ｗ３）
したがって、重量変化率Ｗ（％）は、
Ｗ（％）＝ΔＷ／Ｗ１×１００
として求められる。
【００１７】
（２）電気機械結合係数
単結晶から１５×２．５×０．５ｍｍの板状体を作成し、１５×２．５ｍｍの面にアルミニウムを蒸着して電極面とした。この電極面は結晶方位のｘ面に対し平行であり、板状体長手方向が結晶方位ｙ軸に対し、平行となるように切り出した。次いで、この試料電極面に交流電界を印加し、ＩＲＥの標準回路の方法に従い共振周波数（ωＲ）と反共振周波数（ωＡ）とを測定し、次式から電気機械結合係数ｋ１２を求めた。
【００１８】
【数１】
実施例１
純度９９％以上のＳｒＣＯ３とＴａ２Ｏ５とＧａ２Ｏ３とＳｉＯ２とを原子比でＳｒ：Ｔａ：Ｇａ：Ｓｉが３：１：３：２になるように混合し、これを円柱状に圧縮して約１４５０℃において大気雰囲気で焼結させた。この焼結体を、直径５０ｍｍ、高さ５０ｍｍ及び厚さ１．５ｍｍのイリジウムるつぼに入れ、気密性の保たれた結晶引き上げ装置内で、２ｖｏｌ％の酸素を含む窒素雰囲気下で、誘導加熱して融解した。結晶の成長行程は、チョクラルスキー法による既知の方法で行い、結晶回転数５ｒｐｍ、種結晶引き上げ速度を１．５ｍｍ／ｈｒの条件で、長さ６８ｍｍ、直径２４ｍｍの無色透明な単結晶を得た。
結晶の一部を粉砕して粉末Ｘ線回折による相同定を行った結果、回折ピークは全てＣａ３Ｇａ２Ｇｅ４Ｏ１４構造を有する相として指数付けでき、その他の異相ピークは全く認められず単一相であることが確認できた。
結晶の表面状態は、荒れ、異物質の付着等は認められず、滑らかで光沢が認められる。結晶内に、気泡、割れ及びインクルージョンなどの巨視的な欠陥は認められず、偏光顕微鏡によるオルソスコープ像から均一な単結晶になっていることが分った。この単結晶は、水晶とほぼ同程度の硬度であり、室温付近で化学的、物理的に安定である。また、水晶等で用いられる通常の加工条件で、クラック発生等の問題もなく、結晶切断及び研磨ができ、結晶の取り扱いが容易であることが分った。このものの結晶成長前後での重量変化率ΔＷ／Ｗ１は、０．１％、電気機械結合係数ｋ１２は０．２５であった。
【００２０】
実施例２
純度９９％以上のＢａＣＯ３とＴａ２Ｏ５とＧａ２Ｏ３とＳｉＯ２とを原子比でＢａ：Ｔａ：Ｇａ：Ｓｉが３：１：３：２になるように混合し、これを円柱状に圧縮して大気雰囲気中で約１３００℃において焼結した。実施例１と同じ条件で、結晶成長を行い、長さ３３ｍｍ、直径２５ｍｍの無色透明な単結晶を得た。
この結晶は、Ｃａ３Ｇａ２Ｇｅ４Ｏ１４構造の単一相であり、表面に荒れ、異物質の付着等はなく、滑らかで光沢が認められる。結晶内に、気泡、割れ及びインクルージョンなどの巨視的な欠陥は認められず、均一な単結晶であることを確認した。また、結晶成長前後での重量変化率ΔＷ／Ｗ１は０．４％であり、成長中の蒸散はほとんどなかった。また、この材料の電気機械結合係数ｋ１２は０．２９と大きな値を示した。
【００２１】
実施例３
純度９９％以上のＬａ２Ｏ３とＳｒＣＯ３とＴａ２Ｏ５とＧａ２Ｏ３とＳｉＯ２とを原子比でＬａ：Ｓｒ：Ｔａ：Ｇａ：Ｓｉが１：２：１：４：１になるように混合し、これを円柱状に圧縮して約１３００℃において大気雰囲気で焼結した。実施例１と同じ条件で、結晶成長を行い、長さ３９ｍｍ、直径２２ｍｍのわずかに黄色を呈した透明な単結晶を得た。
この結晶は、Ｃａ３Ｇａ２Ｇｅ４Ｏ１４構造の単一相であり、表面に荒れ、異物質の付着等はなく、滑らかで光沢が認められる。結晶内に、気泡、割れ及びインクルージョンなどの巨視的な欠陥は認められず、均一な単結晶であることを確認した。また、結晶成長前後での重量変化率ΔＷ／Ｗ１は０．２％であった。また、この材料の電気機械結合係数ｋ１２は０．２０であった。
【００２２】
実施例４
純度９９％以上のＬａ２Ｏ３とＳｒＣＯ３とＴａ２Ｏ５とＧａ２Ｏ３とを原子比でＬａ：Ｓｒ：Ｔａ：Ｇａが２：１：１：５になるように混合し、これを円柱状に圧縮して約１３００℃において大気雰囲気で焼結した。実施例１と同じ条件で、結晶成長を行い、長さ３４ｍｍ、直径２３ｍｍの無色透明な単結晶を得た。
この結晶は、Ｃａ３Ｇａ２Ｇｅ４Ｏ１４構造の単一相であり、表面に荒れ、異物質の付着等はなく、滑らかで光沢が認められる。結晶内に、気泡、割れ及びインクルージョンなどの巨視的な欠陥は認められず、均一な単結晶であることを確認した。また、結晶成長前後での重量変化率ΔＷ／Ｗ１は０．３％であった。また、この材料の電気機械結合係数ｋ１２は０．１７であった。
【００２３】
比較例
純度４ＮのＳｒＣＯ３とＧａ２Ｏ３とＧｅＯ２とを原子比でＳｒ：Ｇａ：Ｇｅが３：２：４になるように混合し、これを約１３００℃において酸素雰囲気で焼結した。この焼結体を、直径５０ｍｍ、高さ５０ｍｍ及び厚さ１．５ｍｍの白金るつぼに入れ、結晶引き上げ装置内で、誘導加熱して融解した。結晶の成長行程は、チョクラルスキー法による既知の方法で行い、ＧｅＯ２の蒸散を抑制する目的で、酸素雰囲気を選択した。結晶回転数１０ｒｐｍ、種結晶引き上げ速度を１ｍｍ／ｈｒの条件で、長さ３２ｍｍ、直径１８ｍｍのわずかに黄色味を帯びた結晶を得た。
結晶の表面状態は、全体的にしわ状に荒れ、黒い粒状の白金と思われる付着物が認められた。特に、結晶後半部に割れ及びインクルージョンなどの巨視的な欠陥が多く存在している。この結晶からは、実施例１に示す大きさの圧電特性測定用の試料を作成することができなかった。
結晶成長前後での重量変化率ΔＷ／Ｗ１は２．６％で、成長中の原料蒸散量が非常に多かった。
【００２４】
【発明の効果】
本発明によれば、高価なＧｅの使用量が少なく、しかも結晶成長を容易に行うことができ、優れた圧電特性を有する実用化可能な圧電体材料が提供される。
【図面の簡単な説明】
【図１】Ｃａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造のモデルの平面図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel piezoelectric material used as a component such as a resonator or a filter.
[0002]
[Prior art]
Heretofore, as bulk single crystal materials utilizing optical or electrical properties, complex compounds having a non-stoichiometric solid solution region together with quartz or alumina, such as rare earth garnet, lithium niobate, lithium tantalate, bismuth germanate, silica Bismuth acid and the like are known.
On the other hand, recently, a piezoelectric material having a Ca 3 Ga 2 Ge 4 O 14 type crystal structure has attracted attention as a material having large piezoelectric characteristics as compared with quartz and having temperature stability of piezoelectric characteristics close to quartz. .
[0003]
These materials are composed of eight coordination atoms, two coordination atoms, and two coordination four atoms. In the present invention, a site of an atom having a coordination number of 8 is an A-site, a site of an atom having a coordination number of 6 is a B-site, and a site of two kinds of atoms having a coordination number of 4 is a C-site and Called D-site. In some cases, cations are substituted between these sites, and some have vacancies at each site.
[0004]
Incidentally, among the materials having the Ca 3 Ga 2 Ge 4 O 14 type crystal structure, La 3 Ga 5 SiO 14 , Ca 3 Ga 2 Ge 4 O 14 and Sr 3 Ga 2 Ge 4 O 14 have electromechanical coupling coefficients. k 12 are each 0.16,0.145 and 0.266, to have been known to exceed greater than 0.10 of the crystal [1993 IEEE "International FrequenSea control Symposium (International Frequency control Symposium) ", the 351-352 pages, and since the piezoelectric coefficients and electromechanical coupling coefficient of Ba 3 Ga 2 Ge 4 O 14 it is known is larger than those of Sr 3 Ga 2 Ge 4 O 14 ( The same magazine, pp. 339-347), suitable piezoelectric It is a material.
[0005]
However, Sr 3 Ga 2 Ge 4 O 14 or Ba 3 Ga 2 Ge 4 O 14 requires GeO 2, which is significantly more expensive than Ga 2 O 3 or SiO 2 , as a raw material. GeO 2 has a high vapor pressure near its melting point, that is, at a temperature range of 1000 ° C. or higher, and GeO 2 evaporates during crystal growth, which makes it difficult to grow a high-quality single crystal. This hinders practical application.
[0006]
[Problems to be solved by the invention]
The present invention overcomes the drawbacks of the conventional piezoelectric material having a Ca 3 Ga 2 Ge 4 O 14 type crystal structure, and facilitates crystal growth, is low cost, and has a new Ca 3 having excellent piezoelectric characteristics. An object of the present invention is to provide a piezoelectric material having a Ga 2 Ge 4 O 14 type crystal structure.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on a piezoelectric material having a Ca 3 Ga 2 Ge 4 O 14 type crystal structure, and as a result, at least one element selected from Ca, Ba, Sr and Pb, in particular, At least one of Sr and Ba is introduced, and at least one element selected from Nb, Ta, and Sb, and at least one element selected from Ga, Al, and Fe and other elements are used. By combining four or more different cations, the amount of expensive GeO 2 used is reduced, the evaporation of GeO 2 during crystal growth is reduced, and a single crystal having excellent piezoelectric properties can be obtained. The present inventors have found out the present invention based on this finding.
[0008]
That is, in the present invention, Ca , Ba , Sr, and cations having a valence of 2+ and having a coordination number of 8 and having an ionic radius in the range of about 1.1 to 1.4 ° can be obtained. and at least one element selected from among pb, stably exist in a valence 5+ may take a coordination number of 6, the range ionic radius at this state is about 0.6~0.7Å and at least one element Nb, selected from among Ta and Sb in stably present in valence 3+, can take a coordination number of 4, the ion radius in this state is about 0.3 and at least one element selected Ga in the range of ～0.6A, from among Al and Fe, Ca 3 Ga 2 constituted by four or more different cations and oxygen ions consisting of the other elements in the compounds of Ge 4 O 14 type crystal structure, Ge content of 0 or 8.70 tm% or less, the piezoelectric material content of at least one element selected from among Ca, Ba and Sr and Pb is made from those being in the range of 4.35 ~13.04 atm% Is provided.
[0009]
The compound having the Ca 3 Ga 2 Ge 4 O 14 type crystal structure is composed of at least four kinds of 23 different cation atoms and 23 different anion oxygen atoms. Two or less thereof, ie, 8.70 atm% or less, is Ge, and at least one selected from Ca, Ba, Sr, and Pb is one or more, ie, 4.35 atm% or more, preferably two or more, 8.70 atm% or more . When the number is three, it is 13.04 atm%.
[0010]
The cation atoms other than Ge, Ca, Ba, Sr and Pb are not particularly limited as long as they can be substituted in the Ca 3 Ga 2 Ge 4 O 14 type crystal structure. Thus, those usable as the piezoelectric material of the present invention, for example formula M 1 x M 2 3-x M 3 M 4 3 + x M 5 2-x O 14 (I)
(Where M 1 is at least one atom selected from La, Pr, Nd and Bi, M 2 is at least one atom selected from Ca, Sr, Ba and Pb, M 3 Is at least one atom selected from Nb, Ta, and Sb; M 4 is at least one atom selected from Ga, Al, and Fe; and M 5 is Si, Ge, Ti, Sn, Zr. And at least one atom selected from Hf, and x is a number satisfying 0 ≦ x ≦ 2)
And a compound having a Ca 3 Ga 2 Ge 4 O 14 type crystal structure having a composition represented by the following formula: X in this general formula is preferably a number from 0 to 1, and most preferably 0.
[0011]
In this general formula (I), the atoms represented by M 1 and M 2 are both stably present with valences of 3+ and 2+, can take a coordination number of 8, and the ionic radius in this state is about 1.1 to 1.4 °. Furthermore, atom represented by M 3 are both stably present in valence 5+ may take a coordination number of 6, the ion radius in this state is in the range of about 0.6~0.7Å Things. Next, the atoms represented by M 4 and M 5 are stably present with valences of 3+ and 4+, can assume a coordination number of 4, and have an ionic radius of about 0.3 to 0.6 ° in this state. Are in range.
[0012]
The ionic radius referred to herein means an effective ionic radius described in "Acta Crystallographica", 1976, Vol. A32, pp. 751-767. .
Ge, which is an atom that hinders the practical use of Sr 3 Ga 2 Ge 4 O 14 and Ba 3 Ga 2 Ge 4 O 14 , is stable at a valence of 4+, and has a coordination number of 4 and therefore, M 5. However, this Ge can be replaced with an atom other than Ge in M 4 or M 5. Therefore, if this is positively performed, the cost can be reduced and the crystal can be easily grown. Therefore, practical use becomes possible.
[0013]
The piezoelectric material of the present invention forms a stable Ca 3 Ga 2 Ge 4 O 14 type crystal structure, and this Ca 3 Ga 2 Ge 4 O 14 type crystal structure is applied to an ASTM (JCPDS) card 36-0098. FIG. 1 is a plan view schematically showing this known crystal structure. In the figure, (a) shows the position of the B-site, (d) shows the C-site, (e) shows the A-site (f) shows the position of the cation of the D-site.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The compound constituting the piezoelectric material of the present invention is obtained, for example, by mixing oxides or carbonates of the elements constituting the general formula (I) in a powder form so as to have a predetermined atomic ratio, and compression-molding the mixture into a columnar shape. After that, it is sintered at 1000 to 1500 ° C. in the air and melted in a nitrogen pulling apparatus containing a small amount of oxygen in a crystal pulling apparatus which is kept airtight, and is subjected to a conventional method such as a Czochralski method. Can be produced by crystal growth. The growth conditions at this time are generally a crystal rotation speed of 1 to 100 rpm, preferably 5 to 50 rpm, and a seed crystal pulling rate of 0.1 to 10 mm / hr, preferably 0.5 to 5 mm / hr. Thus, a colorless and transparent single crystal having a diameter of about 25 mm and a length of about 70 mm can be obtained. The identification of the crystal can be performed by crushing a part thereof, performing X-ray powder diffraction, and comparing the diffraction peaks.
The single crystal thus obtained had a small weight change rate (ΔW / W 1 ) of 0.4% or less and a large electromechanical coupling coefficient (k 12 ) of 0.17 or more.
[0015]
【Example】
Next, the present invention will be described in more detail with reference to examples. The weight change rate and the electromechanical coupling coefficient in each example were determined by the following methods.
[0016]
(1) were weighed crucible weight in a state in which the weight change ratio crystal growth immediately before the material is filled, which is referred to as W 1. Immediately after the completion of the crystal growth then, the raw material is weighed crucible weight while remaining This is referred to as W 2. When the weight of the crystal obtained by crystal growth and W 3, the amount ΔW of raw material vaporized during crystal growth is as follows.
ΔW = W 1 − (W 2 + W 3 )
Therefore, the weight change rate W (%) is
W (%) = ΔW / W 1 × 100
Is required.
[0017]
(2) Electromechanical Coupling Coefficient A plate having a size of 15 × 2.5 × 0.5 mm was prepared from a single crystal, and aluminum was deposited on a surface of 15 × 2.5 mm to form an electrode surface. The electrode face was parallel to the x-plane of the crystal orientation, and the plate was cut out so that the longitudinal direction was parallel to the y-axis of the crystal orientation. Then, this sample electrode surface by applying an alternating electric field, the a standard circuit method according resonant frequency of the IRE (omega R) and the anti-resonance frequency (omega A) was measured to obtain the electromechanical coupling factor k 12 from the following equation Was.
[0018]
(Equation 1)
Example 1
SrCO 3 , Ta 2 O 5 , Ga 2 O 3, and SiO 2 having a purity of 99% or more are mixed in an atomic ratio such that Sr: Ta: Ga: Si becomes 3: 1: 3: 2, and this is circled. It was compressed into a columnar shape and sintered at about 1450 ° C. in an air atmosphere. This sintered body was placed in an iridium crucible having a diameter of 50 mm, a height of 50 mm, and a thickness of 1.5 mm, and was subjected to induction heating in a nitrogen pulling apparatus containing 2 vol% of oxygen in an airtight crystal pulling apparatus. Melted. The crystal growth process is performed by a known method by the Czochralski method, and a colorless and transparent single crystal having a length of 68 mm and a diameter of 24 mm is obtained at a crystal rotation speed of 5 rpm and a seed crystal pulling speed of 1.5 mm / hr. Was.
As a result of performing phase identification by powder X-ray diffraction by crushing a part of the crystal, all diffraction peaks can be indexed as a phase having a Ca 3 Ga 2 Ge 4 O 14 structure, and no other heterophase peaks are observed. It was confirmed that it was a single phase.
The surface condition of the crystal is smooth and glossy without any roughening or attachment of foreign substances. No macroscopic defects such as bubbles, cracks and inclusions were found in the crystal, and it was found from an orthoscopic image by a polarizing microscope that the crystal was a uniform single crystal. This single crystal has almost the same hardness as quartz and is chemically and physically stable around room temperature. In addition, it was found that under normal processing conditions used for quartz and the like, there was no problem such as crack generation, crystal cutting and polishing could be performed, and crystal handling was easy. Weight change ratio [Delta] W / W 1 in the crystal growth before and after this compound, 0.1%, the electromechanical coupling factor k 12 was 0.25.
[0020]
Example 2
BaCO 3 , Ta 2 O 5 , Ga 2 O 3, and SiO 2 having a purity of 99% or more are mixed at an atomic ratio of Ba: Ta: Ga: Si of 3: 1: 3: 2, and this is mixed with a circle. It was compressed into a columnar shape and sintered at about 1300 ° C. in an air atmosphere. Crystal growth was performed under the same conditions as in Example 1 to obtain a colorless and transparent single crystal having a length of 33 mm and a diameter of 25 mm.
This crystal is a single phase having a Ca 3 Ga 2 Ge 4 O 14 structure, has no roughness on its surface, has no foreign substances attached thereto, and is smooth and glossy. No macroscopic defects such as bubbles, cracks and inclusions were found in the crystal, and it was confirmed that the crystal was a uniform single crystal. The weight change rate [Delta] W / W 1 before and after crystal growth is 0.4%, transpiration during growth was little. Further, the electromechanical coupling coefficient k 12 of this material showed a large value of 0.29.
[0021]
Example 3
La: Sr: Ta: Ga: Si having an atomic ratio of La 2 O 3 , SrCO 3 , Ta 2 O 5 , Ga 2 O 3, and SiO 2 having a purity of 99% or more is 1: 2: 1: 4: 1. The resulting mixture was compressed into a columnar shape and sintered at about 1300 ° C. in an air atmosphere. Crystal growth was carried out under the same conditions as in Example 1 to obtain a slightly yellow transparent single crystal having a length of 39 mm and a diameter of 22 mm.
This crystal is a single phase having a Ca 3 Ga 2 Ge 4 O 14 structure, has no roughness on its surface, has no foreign substances attached thereto, and is smooth and glossy. No macroscopic defects such as bubbles, cracks and inclusions were found in the crystal, and it was confirmed that the crystal was a uniform single crystal. The weight change rate [Delta] W / W 1 before and after the crystal growth was 0.2%. Further, the electromechanical coupling coefficient k 12 of this material was 0.20.
[0022]
Example 4
La 2 O 3 , SrCO 3 , Ta 2 O 5, and Ga 2 O 3 having a purity of 99% or more are mixed at an atomic ratio of La: Sr: Ta: Ga of 2: 1: 1: 5. Was compressed into a columnar shape and sintered at about 1300 ° C. in an air atmosphere. Crystal growth was performed under the same conditions as in Example 1 to obtain a colorless and transparent single crystal having a length of 34 mm and a diameter of 23 mm.
This crystal is a single phase having a Ca 3 Ga 2 Ge 4 O 14 structure, has no roughness on its surface, has no foreign substances attached thereto, and is smooth and glossy. No macroscopic defects such as bubbles, cracks and inclusions were found in the crystal, and it was confirmed that the crystal was a uniform single crystal. The weight change rate [Delta] W / W 1 before and after the crystal growth was 0.3%. Further, the electromechanical coupling coefficient k 12 of this material was 0.17.
[0023]
Comparative Example SrCO 3 , Ga 2 O 3, and GeO 2 having a purity of 4N were mixed in an atomic ratio of Sr: Ga: Ge of 3: 2: 4, and this was sintered at about 1300 ° C. in an oxygen atmosphere. . The sintered body was placed in a platinum crucible having a diameter of 50 mm, a height of 50 mm and a thickness of 1.5 mm, and was melted by induction heating in a crystal pulling apparatus. The crystal growth process was performed by a known method using the Czochralski method, and an oxygen atmosphere was selected for the purpose of suppressing the evaporation of GeO 2 . A slightly yellowish crystal having a length of 32 mm and a diameter of 18 mm was obtained at a crystal rotation speed of 10 rpm and a seed crystal pulling speed of 1 mm / hr.
The surface state of the crystal was entirely roughened in the form of wrinkles, and deposits considered to be black granular platinum were observed. In particular, there are many macroscopic defects such as cracks and inclusions in the latter half of the crystal. A sample for measuring the piezoelectric characteristics having the size shown in Example 1 could not be prepared from this crystal.
Weight change ratio [Delta] W / W 1 before and after crystal growth is 2.6%, the raw material transpiration of growing was very large.
[0024]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the usage-amount of expensive Ge is small, crystal growth can be performed easily, and the piezoelectric material which can be used practically and has excellent piezoelectric characteristics is provided.
[Brief description of the drawings]
FIG. 1 is a plan view of a model of a Ca 3 Ga 2 Ge 4 O 14 type crystal structure.
Claims (4)
Ｍ１ ｘＭ２ ３−ｘＭ３Ｍ４ ３＋ｘＭ５ ２−ｘＯ１４
（式中のＭ１はＬａ、Ｐｒ、Ｎｄ及びＢｉの中から選ばれた少なくとも１種の原子、Ｍ２はＣａ、Ｂａ、Ｓｒ及びＰｂの中から選ばれた少なくとも１種の原子、Ｍ３はＮｂ、Ｔａ及びＳｂの中から選ばれた少なくとも１種の原子、Ｍ４はＧａ、Ａｌ及びＦｅの中から選ばれた少なくとも１種の原子、Ｍ５はＳｉ、Ｇｅ、Ｔｉ、Ｓｎ、Ｚｒ及びＨｆの中から選ばれた少なくとも１種の原子であり、ｘは０≦ｘ≦２の数である）
で表わされる組成をもつＣａ３Ｇａ２Ｇｅ４Ｏ１４型結晶構造の化合物からなる圧電体材料。Formula M 1 x M 2 3-x M 3 M 4 3 + x M 5 2-x O 14
(Wherein M 1 is at least one atom selected from La, Pr, Nd and Bi, M 2 is at least one atom selected from Ca, Ba, Sr and Pb, M 3 Is at least one atom selected from Nb, Ta, and Sb; M 4 is at least one atom selected from Ga, Al, and Fe; and M 5 is Si, Ge, Ti, Sn, Zr. And at least one atom selected from Hf, and x is a number satisfying 0 ≦ x ≦ 2)
A piezoelectric material comprising a compound having a Ca 3 Ga 2 Ge 4 O 14 type crystal structure having a composition represented by the following formula:
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| JP33415497A JP3562947B2 (en) | 1997-12-04 | 1997-12-04 | Piezoelectric material |
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| US6413442B2 (en) | 2000-05-22 | 2002-07-02 | Tdk Corporation | Method of producing single crystal and piezoelectric element |
| JP4748170B2 (en) * | 2008-02-08 | 2011-08-17 | Ｔｄｋ株式会社 | Piezoelectric single crystal material and piezoelectric device using the piezoelectric single crystal material |
| JP6369977B2 (en) * | 2014-05-07 | 2018-08-08 | 株式会社Ｐｉｅｚｏ Ｓｔｕｄｉｏ | Piezoelectric vibrator |
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