JP2004002051A

JP2004002051A - Piezoelectric ceramic composition, piezoelectric ceramic element, and method of producing the piezoelectric ceramic composition

Info

Publication number: JP2004002051A
Application number: JP2002132653A
Authority: JP
Inventors: Masahiko Kimura; 木村　雅彦; Akira Ando; 安藤　陽; Tomoyuki Ogawa; 小川　智之
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2001-05-29
Filing date: 2002-05-08
Publication date: 2004-01-08
Anticipated expiration: 2022-05-08
Also published as: JP3864840B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition which contains, as a main component, a compound mainly composed of the elements of Na, Li, Nb and O, expressed by compositional formula: (Na<SB>1-x</SB>Li<SB>x</SB>)NbO<SB>3</SB>, and having a perovskite structure, and which has improved mechanical quality factor Qm. <P>SOLUTION: The piezoelectric ceramic composition contains, as the main component, the compound having the perovskite structure and composed mainly of the elements comprising Na, Li, Nb and O. The crystal system of the main component is different from a crystal system originally stable in room temperature and originally stable in a temperature range higher than room temperature, and becomes a metastable state in room temperature. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
この発明は圧電磁器組成物、圧電セラミック素子および圧電磁器組成物の製造方法に関し、特にたとえば、圧電セラミックフィルタ、圧電セラミック発振子および圧電セラミック振動子などの圧電セラミック素子などの材料として有用な圧電磁器組成物およびそれを用いた圧電セラミック素子などに関する。
【０００２】
【従来の技術】
圧電セラミックフィルタ、圧電セラミック発振子および圧電セラミック振動子などの圧電セラミック素子に用いられる圧電磁器組成物として、従来、チタン酸ジルコン酸鉛（Ｐｂ（Ｔｉ_ｘＺｒ_１−ｘ）Ｏ_３）またはチタン酸鉛（ＰｂＴｉＯ_３）を主成分とする圧電磁器組成物が広く用いられている。しかしながら、チタン酸ジルコン酸鉛またはチタン酸鉛を主成分とする圧電磁器組成物では、その組成中に鉛を多量に含有するため、製造過程において鉛酸化物の蒸発のため製品の均一性が低下するという問題があった。製造過程における鉛酸化物の蒸発による製品の均一性の低下を防止するためには、組成中に鉛をまったく含まないまたは少量のみ含む圧電磁器組成物が好ましい。
これに対して、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３で表される一連の化合物を主成分とする圧電磁器組成物では、その組成中に鉛酸化物を含有しないため、上記のような問題は生じない。
【０００３】
【発明が解決しようとする課題】
ところが、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３で表される一連の化合物を主成分とする圧電磁器組成物では、機械的品質係数Ｑ_ｍが比較的小さい。このため、このような圧電磁器組成物では、たとえば圧電セラミックフィルタなどのように高い機械的品質係数Ｑ_ｍが要求される用途に対しては対応が困難であるという問題があった。
また、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３で表される一連の化合物を主成分とする圧電磁器組成物では、比較的低温で、室温において安定な結晶系から室温より高温域において安定な結晶系に相転移してしまい、その結果、相転移温度において共振周波数が大きく変化するという問題点がある。
【０００４】
それゆえに、この発明の主たる目的は、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３で表されるようなＮａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物を主成分とし、機械的品質係数Ｑ_ｍを向上させた圧電磁器組成物を提供することである。
この発明の他の目的は、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３で表されるようなＮａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物を主成分とし、機械的品質係数Ｑ_ｍを向上させた圧電磁器組成物を用いた圧電セラミック素子を提供することである。
この発明のさらに他の目的は、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３で表されるようなＮａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物を主成分とし、機械的品質係数Ｑ_ｍを向上させた圧電磁器組成物の製造方法を提供することである。
【０００５】
【課題を解決するための手段】
この発明にかかる圧電磁器組成物は、Ｎａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物を主成分とする圧電磁器組成物において、主成分の結晶系は、本来室温において安定な結晶系とは異なり、本来室温より高い温度域で安定な結晶系が室温において準安定状態となっているものであることを特徴とする、圧電磁器組成物である。
この発明にかかる圧電磁器組成物において、本来室温において安定な結晶系は、たとえば菱面体晶であり、本来室温より高い温度域で安定な結晶系はたとえば単斜晶である。
この発明にかかる圧電磁器組成物では、主成分となる化合物が、たとえば組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３（ただし、０．０２≦ｘ≦０．３０）で表される。
また、この発明にかかる圧電磁器組成物では、主成分となる化合物が、たとえば組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３（ただし、０．０８≦ｘ≦０．１８）で表される。
さらに、この発明にかかる圧電磁器組成物では、主成分となる化合物が、たとえば組成式（１−ｎ）［（Ｎａ_１−ｘＬｉ_ｘ）_１−ｙＫ_ｙ］（Ｎｂ_１−ｚＴａ_ｚ）Ｏ_３−ｎＭ１Ｍ２Ｏ_３（ただし、０．０２≦ｘ≦０．３０、０≦ｙ≦０．２、０≦ｚ≦０．２、０≦ｎ≦０．１、Ｍ１は２価の金属元素、Ｍ２は４価の金属元素）で表される。この場合、Ｍ１は、たとえばＭｇ、Ｃａ、ＳｒおよびＢａからなる群から選ばれた少なくとも１種であり、Ｍ２は、たとえばＴｉ、Ｚｒ、ＳｎおよびＨｆからなる群から選ばれた少なくとも１種である。
また、この発明にかかる圧電セラミック素子は、この発明にかかる圧電磁器組成物からなる圧電磁器と、圧電磁器に形成される電極とを含む、圧電セラミック素子である。
この発明にかかる圧電磁器組成物の製造方法は、この発明にかかる圧電磁器組成物を製造する方法であって、圧電磁器組成物に分極処理を施した後に、結晶系が安定状態である温度かそれ以上の温度でかつ主成分となる化合物が強誘電性を失う温度未満に圧電磁器組成物を加熱することを特徴とする、圧電磁器組成物の製造方法である。
この発明にかかる圧電磁器組成物の製造方法では、圧電磁器組成物を加熱する温度が、たとえば２５０℃から４００℃の範囲内である。
【０００６】
この発明では、Ｎａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物を主成分とする圧電磁器組成物において、主成分の結晶系は、本来室温において安定な結晶系とは異なり、本来室温より高い温度域で安定な結晶系が室温において準安定状態となっているものであるようにする。ここで準安定状態とは、ある物質において、その温度を変えていくとき、相転移点で本来安定であるはずの結晶相に移らず、もとの結晶相が非常に長い非平衡状態としてそのまま続くような状態を指す。たとえば、チタン酸バリウム（ＢａＴｉＯ_３）は、通常、室温では正方晶が安定であるが、１４６０℃以上の高温から急冷することによって、室温で六方晶のものを得ることが可能であることが知られている。ここでいう準安定状態とは、室温での六方晶のチタン酸バリウムと同様な状態を言う。また、この準安定状態は、低温から高温への温度変化に伴って生じるものではなく、高温から低温への温度変化に伴って生じるものであること、すなわち、より高温で本来安定であるはずの結晶相を低温で示す場合を指す。
こうすることによって、たとえば円板状の圧電セラミック振動子の厚み縦振動の機械的品質係数Ｑ_ｍについて言うと、Ｎａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物を主成分とする圧電磁器組成物において、たとえば、機械的品質係数Ｑ_ｍが５００程度かそれ以下であったものが１０００以上に向上する。
さらに、この発明にかかる圧電磁器組成物は、本来室温より高い温度域で安定な結晶系が室温において準安定状態となっているので、本来の相転移温度になっても相転移が生じず、共振周波数が大きく変化することがない。
この発明にかかる圧電磁器組成物の主成分、すなわち、Ｎａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物としては、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３（ただし、０．０２≦ｘ≦０．３０）で表される化合物であることが、この発明の効果が顕著となり好ましい。また、このうち０．０８≦ｘ≦０．１８の場合には、この発明の効果が特に顕著となりさらに好ましい。また、この発明は、組成式（１−ｎ）［（Ｎａ_１−ｘＬｉ_ｘ）_１−ｙＫ_ｙ］（Ｎｂ_１−ｚＴａ_ｚ）Ｏ_３−ｎＭ１Ｍ２Ｏ_３（ただし、０．０２≦ｘ≦０．３０、０≦ｙ≦０．２、０≦ｚ≦０．２、０≦ｎ≦０．１、Ｍ１は２価の金属元素、Ｍ２は４価の金属元素）で表される化合物が主成分となる圧電磁器組成物についても効果がある。この場合、Ｍ１は、Ｍｇ、Ｃａ、ＳｒおよびＢａからなる群から選ばれた少なくとも１種であり、Ｍ２は、Ｔｉ、Ｚｒ、ＳｎおよびＨｆからなる群から選ばれた少なくとも１種であることが好ましい。
また、この発明にかかる圧電磁器組成物では、たとえば、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３と記述した場合にはおよそ（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３の組成式で表されておればよく、Ｎａ、Ｌｉ、ＮｂまたはＯの比が化学量論組成から５％程度ずれていても特に差し支えない。また、この発明にかかる圧電磁器組成物には、Ａｌ、Ｍｎ、Ｆｅ、Ｓｉ、Ｃｏ、Ｐｂなどが数パーセント程度混入されていても問題ない。
また、この発明にかかる圧電磁器組成物を製造する一方法としては、圧電磁器組成物に分極処理を施した後に、結晶系が安定状態である温度かそれ以上の温度でかつ主成分となる化合物が強誘電性を失う温度未満に圧電磁器組成物を加熱する方法が有効である。このとき、圧電磁器組成物を加熱する温度は、２５０℃から４００℃の範囲内であることが好ましい。
【０００７】
この発明の上述の目的、その他の目的、特徴および利点は、図面を参照して行う以下の発明の実施の形態の詳細な説明から一層明らかとなろう。
【０００８】
【発明の実施の形態】
（実施例）
まず、出発原料として、Ｎａ_２ＣＯ_３、Ｌｉ_２ＣＯ_３、Ｋ_２ＣＯ_３、Ｎｂ_２Ｏ_５、Ｔａ_２Ｏ_５、ＣａＣＯ_３、ＢａＣＯ_３、ＴｉＯ_２およびＺｒＯ_２を用意し、これらを組成式（１−ｎ）［（Ｎａ_１−ｘＬｉ_ｘ）_１−ｙＫ_ｙ］（Ｎｂ_１−ｚＴａ_ｚ）Ｏ_３−ｎＭ１Ｍ２Ｏ_３（ただし、０．０１≦ｘ≦０．３５、０≦ｙ≦０．２５、０≦ｚ≦０．２５、０≦ｎ≦０．２、Ｍ１はＣａまたはＢａ、Ｍ２はＴｉまたはＺｒ）となるように秤取して、ボールミルを用いて約１６時間湿式混合して、混合物を得た。得られた混合物を乾燥した後、７００〜９００℃で仮焼して、仮焼物を得た。それから、この仮焼物を粗粉砕した後、有機バインダを適量加えてボールミルを用いて１６時間湿式粉砕し、４０メッシュのふるいを通して粒度調整を行った。次に、これを１５００ｋｇ／ｃｍ^２の圧力で直径１２ｍｍ、厚さ０．６ｍｍの円板に成型し、これを大気中で１０００〜１３００℃で焼成することによって、円板状の磁器を得た。この磁器の表面（両主面）に、通常の方法により銀ペーストを塗布し焼付けて銀電極を形成した後、１００〜２５０℃の絶縁オイル中で３〜１０ｋＶ／ｍｍの直流電圧を３０〜６０分間印加して分極処理を施し、圧電磁器（試料）を得た。そして、これらの試料を１５０〜５００℃に加熱（熱処理）した。
【０００９】
図１（ａ）には、試料Ｎｏ．７などのように組成式（Ｎａ_０．８７Ｌｉ_０．１３）ＮｂＯ_３で表される円板状の試料を電極を形成する前（未分極）に粉砕して得た粉末試料の室温でのＸ線回折プロファイルを示す。また、図１（ｂ）には、同組成の円板状の試料に電極を形成し、分極を施した後、電極を除去し、粉砕して得た粉末試料の室温でのＸ線回折プロファイルを示す。図１（ａ）に示すプロファイルおよび図１（ｂ）に示すプロファイルは、ほぼ同様のプロファイルと考えられる。発明者らが分析を行った結果では、図１（ａ）に示すプロファイルおよび図１（ｂ）に示すプロファイルは、菱面体晶を示しているものと思われる。次に、同組成の円板状の試料に電極を形成し、分極を行った後に３５０℃に加熱した後、室温に戻して電極を取り除き、粉砕して得た粉末試料の室温でのＸ線回折プロファイルを図１（ｃ）に示す。図１（ｃ）に示すプロファイルは、図１（ａ）に示すプロファイルおよび図１（ｂ）に示すプロファイルとは明らかに異なる。特に、２θが３５〜４５°付近において、それらのプロファイルには大きな相違がみられる。発明者らが分析を行った結果では、図１（ｃ）に示すプロファイルは、単斜晶のプロファイルであるものと思われる。同組成の円板状の試料を電極を形成する前（未分極）に粉砕して得た粉末試料のＸ線回折を温度を変化させて行ったところ、図１（ｃ）に見られるプロファイルは、２００〜３５０℃付近の高温領域で安定な結晶相のプロファイルと一致することが明らかになった。分極処理の直後には、室温で菱面体晶と思われる結晶構造を示していた試料が、３５０℃の熱処理後には室温で単斜晶と思われる結晶構造を示した。分極後に熱処理を行うことによって本来高温で安定な結晶相が室温で準安定状態として実現されていることが明らかである。分極後に熱処理を施した試料を２ヶ月間放置し、再び同様のＸ線回折分析を行ったが同様の結果が得られた。
【００１０】
同様に、組成式（１−ｎ）［（Ｎａ_１−ｘＬｉ_ｘ）_１−ｙＫ_ｙ］（Ｎｂ_１−ｚＴａ_ｚ）Ｏ_３−ｎＭ１Ｍ２Ｏ_３（ただし、Ｍ１は２価の金属元素、Ｍ２は４価の金属元素）で表される本発明の範囲内の他の試料について熱処理前後の結晶系の調査を行ったが、いずれの試料でも同様の関係が見られた。また、本発明におけるＱ_ｍの向上効果は、準安定状態である結晶相が実現した場合にのみ現われることが明らかになった。
【００１１】
次に、これらの試料について、熱処理前後の円板状の圧電セラミック振動子の厚み縦振動基本波の電気機械結合係数ｋ_ｔおよび機械的品質係数Ｑ_ｍを測定した。それらの結果を表１および表２に示す。
【００１２】
【表１】

【００１３】
【表２】

【００１４】
表１および表２に示す値は、同じ組成の試料のうち、最も大きな機械的品質係数Ｑ_ｍが得られた条件（仮焼温度、焼成温度、分極時の絶縁オイルの温度、直流電圧）の場合の値である。
なお、表１中の試料Ｎｏ．５は、熱処理温度が高すぎるため強誘電性および圧電性を失っており、本発明の範囲外である。また、表１中の試料Ｎｏ．１０は、熱処理温度が低すぎるために、すなわち高温結晶相が安定となる温度に達していないために、結晶形が変化しておらず、本発明の範囲外である。
それに対して、表１および表２に示すように、本発明の範囲内にある試料については、いずれも機械的品質係数Ｑ_ｍが大幅に向上しており、特に、圧電セラミックフィルタ、圧電セラミック発振子、圧電セラミック振動子などの圧電セラミック素子などの材料として有用な圧電磁器組成物であることが明らかである。
【００１５】
また、試料Ｎｏ．１〜２８の各試料について、熱処理前および熱処理後において、−４０℃〜４００℃と条件を変動させたときの拡がり振動の共振周波数をインピーダンスアナライザを用いて測定し、共振周波数の大幅な変化（相転移の発生）がないかどうかを調べた。それらの結果を表３に示す。また、特に試料Ｎｏ．６を用いた圧電セラミック振動子について、熱処理前後において、温度と拡がり振動の共振周波数との関係をグラフにし、図２に示した。
【００１６】
【表３】

【００１７】
表３および図２に示す結果から明らかなように、熱処理前においては、全ての試料について共振周波数の大幅な変化（相転移の発生）が確認され、熱処理後においては、試料Ｎｏ．５が脱分極により測定不可で、試料Ｎｏ．１０が共振周波数の大幅な変化（相転移の発生）が確認されている。
それに対して、本発明の範囲内にある試料については、いずれも共振周波数の大幅な変化（相転移の発生）が確認されていない。
【００１８】
一例として、図２に示すグラフより、熱処理前の試料Ｎｏ．６の共振周波数の温度変化が非直線的であるのに対して、熱処理後の試料Ｎｏ．６の共振周波数の温度変化は直線的であることが分かる。圧電セラミックフィルタ、圧電セラミック発振子および圧電セラミック振動子などにおいては、しばしば共振周波数の温度変化率が小さいことが要求される。このような場合に共振周波数の温度変化が直線的な挙動であれば、補正によって変化率を小さく抑えることが比較的容易に行える。それに対して、共振周波数の温度変化が非直線的の場合には、補正によって変化率を抑えることが困難である。さらに、熱処理前の試料Ｎｏ．６では、共振周波数の温度変化が、昇温時、降温時の別で、または、昇降温の速度によって変化する。すなわち、共振周波数の温度変化が履歴を持つ。一方、熱処理後の試料Ｎｏ．６においては、通常の使用温度である−４０〜１２５℃の温度範囲でほとんど履歴が見られない。
【００１９】
なお、この発明にかかる圧電磁器組成物は上記の実施例の組成に限定されるものではなく、発明の要旨の範囲内であれば有効である。
【００２０】
また、上述の実施例では機械的品質係数Ｑ_ｍは円板状の圧電セラミック振動子の厚み縦振動についての例を示したが、本発明の効果は、円板状の圧電セラミック振動子の厚み縦振動に限定されず、拡がり振動、厚みすべり振動や厚み縦振動の高調波など、他の圧電セラミック素子として特にたとえば圧電セラミック発振子などに利用される他の振動モードにおいても、厚み縦振動の場合と同様に有効である。
【００２１】
さらに、上述の実施例では周波数の温度変化は円板状の圧電セラミック振動子の拡がり振動についての例を示したが、本発明の効果は、円板状の圧電セラミック振動子の拡がり振動に限定されず、厚み縦振動や厚みすべり振動など、他の圧電セラミック素子としても同様に有効である。
【００２２】
図３はこの発明にかかる圧電セラミック振動子の一例を示す斜視図であり、図４はその断面図解図である。図３および図４に示す圧電セラミック振動子１０は、たとえば直方体状の圧電磁器１２を含む。圧電磁器１２は、２枚の圧電磁器層１２ａおよび１２ｂを含む。これらの圧電磁器層１２ａおよび１２ｂは、上述のこの発明にかかる圧電磁器組成物からなり、積層されかつ一体的に形成される。また、これらの圧電磁器層１２ａおよび１２ｂは、図４の矢印で示すように、同じ厚み方向に分極されている。
【００２３】
圧電磁器層１２ａおよび１２ｂの間には、その中央にたとえば円形の振動電極１４ａが形成され、その振動電極１４ａから圧電磁器１２の一端面にわたってたとえばＴ字形の引出電極１６ａが形成される。また、圧電磁器層１２ａの表面には、その中央にたとえば円形の振動電極１４ｂが形成され、その振動電極１４ｂから圧電磁器１２の他端面にわたってたとえばＴ字形の引出電極１６ｂが形成される。さらに、圧電磁器層１２ｂの表面には、その中央にたとえば円形の振動電極１４ｃが形成され、その振動電極１４ｃから圧電磁器１２の他端面にわたってたとえばＴ字形の引出電極１６ｃが形成される。
【００２４】
そして、引出電極１６ａにはリード線１８ａを介して一方の外部端子２０ａが接続され、引出電極１６ｂおよび１６ｃには別のリード線１８ｂを介して他方の外部端子２０ｂが接続される。
【００２５】
なお、この発明は、上述の圧電セラミック振動子１０以外の圧電セラミック振動子、圧電セラミックフィルタおよび圧電セラミック発振子などの他の圧電セラミック素子にも適用される。
【００２６】
【発明の効果】
この発明によれば、組成式（Ｎａ_１−ｘＬｉ_ｘ）ＮｂＯ_３で表されるようなＮａ、Ｌｉ、ＮｂおよびＯの元素で主に構成され、ぺロブスカイト構造を有する化合物を主成分とし、機械的品質係数Ｑ_ｍを向上させ、鉛または鉛化合物をまったく含まないまたは少量のみ含む、圧電セラミックフィルタ、圧電セラミック発振子および圧電セラミック振動子などの圧電セラミック素子などの材料として有用な圧電磁器組成物およびそれを用いた圧電セラミック素子が得られる。
また、この発明にかかる圧電磁器組成物は、本来室温より高い温度域で安定な結晶系が室温において準安定状態となっているので、本来の相転移温度になっても相転移が生じず、共振周波数が大きく変化することがない。
【図面の簡単な説明】
【図１】組成式（Ｎａ_０．８７Ｌｉ_０．１３）ＮｂＯ_３で表される試料のＸ線回折プロファイルである。
【図２】組成式（Ｎａ_０．８７Ｌｉ_０．１３）ＮｂＯ_３で表される試料Ｎｏ．６を用いた熱処理前後の圧電セラミック振動子の拡がり振動の共振周波数の温度変化を示すグラフである。
【図３】この発明にかかる圧電セラミック振動子の一例を示す斜視図である。
【図４】図３に示す圧電セラミック振動子の断面図解図である。
【符号の説明】
１０　圧電セラミック振動子
１２　圧電磁器
１２ａ、１２ｂ　圧電磁器層
１４ａ、１４ｂ、１４ｃ　振動電極
１６ａ、１６ｂ、１６ｃ　引出電極
１８ａ、１８ｂ　リード線
２０ａ、２０ｂ　外部端子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a piezoelectric ceramic composition, a piezoelectric ceramic element, and a method for producing the piezoelectric ceramic composition, and particularly to a piezoelectric ceramic useful as a material for a piezoelectric ceramic element such as a piezoelectric ceramic filter, a piezoelectric ceramic oscillator, and a piezoelectric ceramic oscillator. The present invention relates to a composition and a piezoelectric ceramic element using the composition.
[0002]
[Prior art]
The piezoelectric ceramic filter, a piezoelectric ceramic composition used for the piezoelectric ceramic element such as a piezoelectric ceramic oscillator and a piezoelectric ceramic oscillator, conventionally, lead zirconate titanate _{(Pb (Ti x Zr 1-} x) O 3) or titanate Piezoelectric ceramic compositions containing lead (PbTiO ₃ ) as a main component are widely used. However, in piezoelectric ceramic compositions containing lead zirconate titanate or lead titanate as a main component, the composition contains a large amount of lead, and the uniformity of the product is reduced due to evaporation of lead oxides in the manufacturing process. There was a problem of doing. A piezoelectric ceramic composition containing no or only a small amount of lead in its composition is preferred in order to prevent a reduction in product uniformity due to evaporation of lead oxides during the production process.
On the other hand, a piezoelectric ceramic composition containing a series of compounds represented by the composition formula (Na _1-x Li _x ) NbO ₃ as a main component does not contain a lead oxide in the composition, and therefore, as described above. Problems do not arise.
[0003]
[Problems to be solved by the invention]
However, in the piezoelectric ceramic composition mainly composed of a series of compounds represented by the composition formula _{_{(Na 1-x Li x)}} NbO 3, a relatively small mechanical quality factor _{Q m.} Therefore, in such a piezoelectric ceramic composition, there is a problem that correspondence is difficult for applications for example a high mechanical quality factor Q _m, such as a piezoelectric ceramic filter is required.
Further, in a piezoelectric ceramic composition containing a series of compounds represented by the composition formula (Na _1-x Li _x ) NbO ₃ as a main component, a crystal system that is relatively low in temperature and stable at room temperature is stable in a region higher than room temperature. However, there is a problem that the resonance frequency greatly changes at the phase transition temperature.
[0004]
Therefore, a main object of the present invention is to provide a compound having a perovskite structure which is mainly constituted by elements of Na, Li, Nb and O represented by a composition formula (Na _1-x Li _x ) NbO _3. as a main component, is to provide a piezoelectric ceramic composition with improved mechanical quality factor Q _m.
Another object of the present invention is to provide a compound mainly composed of elements of Na, Li, Nb and O represented by a composition formula (Na _1-x Li _x ) NbO ₃ and having a perovskite structure as a main component. and then, it is to provide a piezoelectric ceramic element using the piezoelectric ceramic composition with improved mechanical quality factor Q _m.
Still another object of the present invention is to provide a compound mainly composed of elements of Na, Li, Nb and O represented by a composition formula (Na _1-x Li _x ) NbO ₃ and having a perovskite structure. and component is to provide a method for manufacturing a piezoelectric ceramic composition with improved mechanical quality factor Q _m.
[0005]
[Means for Solving the Problems]
The piezoelectric ceramic composition according to the present invention is mainly composed of elements of Na, Li, Nb and O. In the piezoelectric ceramic composition mainly composed of a compound having a perovskite structure, the crystal system of the main component is originally A piezoelectric ceramic composition characterized in that, unlike a crystal system stable at room temperature, a crystal system originally stable in a temperature range higher than room temperature is in a metastable state at room temperature.
In the piezoelectric ceramic composition according to the present invention, the crystal system originally stable at room temperature is, for example, rhombohedral, and the crystal system originally stable at a temperature higher than room temperature is, for example, monoclinic.
In the piezoelectric ceramic composition according to the present invention, the compound serving as the main component is represented, for example, by the composition formula (Na _1-x Li _x ) NbO ₃ (where 0.02 ≦ x ≦ 0.30).
In the piezoelectric ceramic composition according to the present invention, the compound serving as the main component is represented, for example, by the composition formula (Na _1-x Li _x ) NbO ₃ (where 0.08 ≦ x ≦ 0.18).
Furthermore, in the piezoelectric ceramic composition according to the present invention, a compound as a main component is, for example, the composition formula _{_{_{(1-n) [(Na}}} 1-x Li x) 1-y K y] (Nb 1-z Ta z) O ₃ -nM1M2O ₃ (where 0.02 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2, 0 ≦ n ≦ 0.1, M1 is a divalent metal element, M2 is a tetravalent metal element). In this case, M1 is at least one selected from the group consisting of, for example, Mg, Ca, Sr and Ba, and M2 is at least one selected from the group consisting of, for example, Ti, Zr, Sn and Hf. .
Further, a piezoelectric ceramic element according to the present invention is a piezoelectric ceramic element including a piezoelectric ceramic comprising the piezoelectric ceramic composition according to the present invention, and electrodes formed on the piezoelectric ceramic.
The method for producing a piezoelectric ceramic composition according to the present invention is a method for producing the piezoelectric ceramic composition according to the present invention, wherein after subjecting the piezoelectric ceramic composition to a polarization treatment, the temperature at which the crystal system is in a stable state is determined. A method for producing a piezoelectric ceramic composition, comprising heating the piezoelectric ceramic composition at a temperature higher than that and below a temperature at which the compound serving as a main component loses ferroelectricity.
In the method for producing a piezoelectric ceramic composition according to the present invention, the temperature at which the piezoelectric ceramic composition is heated is, for example, in the range of 250 ° C to 400 ° C.
[0006]
According to the present invention, in the piezoelectric ceramic composition mainly composed of elements of Na, Li, Nb and O and having a perovskite structure as a main component, the crystal system of the main component is a crystal system which is originally stable at room temperature. Unlike this, a crystal system that is originally stable in a temperature range higher than room temperature is in a metastable state at room temperature. Here, a metastable state means that when a temperature of a certain substance is changed, it does not shift to a crystal phase that should be originally stable at a phase transition point, and the original crystal phase remains in a very long non-equilibrium state. Refers to a state that continues. For example, it is known that barium titanate (BaTiO ₃ ) is generally tetragonal at room temperature, but can be hexagonal at room temperature by rapidly cooling from a high temperature of 1460 ° C. or higher. Have been. Here, the metastable state means a state similar to hexagonal barium titanate at room temperature. In addition, this metastable state does not occur with a temperature change from a low temperature to a high temperature, but occurs with a temperature change from a high temperature to a low temperature, that is, it should be originally stable at a higher temperature. It refers to the case where the crystal phase is shown at a low temperature.
By doing so, for example, say the mechanical quality factor Q _m of the thickness longitudinal vibration of the disk-shaped piezoelectric ceramic vibrator, Na, Li, mainly consists of elements Nb and O, a compound having a perovskite structure the in piezoelectric ceramic composition mainly, for example, those mechanical quality factor Q _m was 500 degrees or less is improved over 1000.
Further, the piezoelectric ceramic composition according to the present invention has a crystal system which is originally stable in a temperature range higher than room temperature, is in a metastable state at room temperature, so that no phase transition occurs even at the original phase transition temperature, The resonance frequency does not change significantly.
As a main component of the piezoelectric ceramic composition according to the present invention, that is, a compound mainly composed of elements of Na, Li, Nb and O and having a perovskite structure, a compound having a composition formula (Na _1-x Li _x ) NbO ₃ (However, a compound represented by 0.02 ≦ x ≦ 0.30) is preferable because the effects of the present invention are remarkable. When 0.08 ≦ x ≦ 0.18, the effect of the present invention is particularly remarkable, which is more preferable. Further, the present invention is a composition formula _{_{_{_{(1-n) [(Na}}}} 1-x Li x) 1-y K y] (Nb 1-z Ta z) O 3 -nM1M2O 3 ( however, 0.02 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2, 0 ≦ n ≦ 0.1, M1 is a divalent metal element, and M2 is a tetravalent metal element. The piezoelectric ceramic composition as a main component is also effective. In this case, M1 is at least one selected from the group consisting of Mg, Ca, Sr and Ba, and M2 is at least one selected from the group consisting of Ti, Zr, Sn and Hf. preferable.
Further, in the piezoelectric ceramic composition according to the present invention, for example, represented by the composition formula of the composition formula _{_{(Na 1-x Li x)}} NbO 3 and when description is approximately _{_{(Na 1-x Li x)}} NbO 3 It is sufficient that the ratio of Na, Li, Nb or O deviates from the stoichiometric composition by about 5%. Further, there is no problem even if Al, Mn, Fe, Si, Co, Pb, and the like are mixed in the piezoelectric ceramic composition according to the present invention by about several percent.
Further, as one method of producing the piezoelectric ceramic composition according to the present invention, after subjecting the piezoelectric ceramic composition to a polarization treatment, a compound which is a main component at a temperature at which the crystal system is in a stable state or higher or higher. The method of heating the piezoelectric ceramic composition to a temperature lower than the temperature at which the material loses ferroelectricity is effective. At this time, the temperature at which the piezoelectric ceramic composition is heated is preferably in the range of 250 ° C to 400 ° C.
[0007]
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example)
First, as starting materials, Na ₂ CO ₃ , Li ₂ CO ₃ , K ₂ CO ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , CaCO ₃ , BaCO ₃ , TiO _2, and ZrO ₂ are prepared, and these are represented by the composition formula. _{_{_{_{(1-n) [(Na}}}} 1-x Li x) 1-y K y] (Nb 1-z Ta z) O 3 -nM1M2O 3 ( however, 0.01 ≦ x ≦ 0.35,0 ≦ y ≦ 0.25, 0 ≦ z ≦ 0.25, 0 ≦ n ≦ 0.2, M1 is Ca or Ba, M2 is Ti or Zr) and wet mixed using a ball mill for about 16 hours Thus, a mixture was obtained. After drying the obtained mixture, it was calcined at 700 to 900 ° C. to obtain a calcined product. Then, after roughly pulverizing the calcined product, an appropriate amount of an organic binder was added, and the mixture was wet-pulverized using a ball mill for 16 hours, and the particle size was adjusted through a 40-mesh sieve. Next, this was molded into a disk having a diameter of 12 mm and a thickness of 0.6 mm at a pressure of 1500 kg / cm ² and fired at 1000 to 1300 ° C. in the atmosphere to obtain a disk-shaped porcelain. . A silver paste is applied to the surface (both main surfaces) of the porcelain by a usual method and baked to form a silver electrode. Then, a DC voltage of 3 to 10 kV / mm is applied in an insulating oil of 100 to 250 ° C. for 30 to 60 kV / mm. For a minute, polarization treatment was performed to obtain a piezoelectric ceramic (sample). Then, these samples were heated (heat treated) to 150 to 500 ° C.
[0009]
FIG. At room temperature of a powder sample obtained by grinding a disc-shaped sample represented by a composition formula (Na _0.87 Li _0.13 ) NbO ₃ such as 7 before forming an electrode (unpolarized). 3 shows an X-ray diffraction profile. FIG. 1B shows an X-ray diffraction profile at room temperature of a powder sample obtained by forming an electrode on a disk-shaped sample having the same composition, applying polarization, removing the electrode, and pulverizing the electrode. Is shown. The profile shown in FIG. 1A and the profile shown in FIG. 1B are considered to be substantially the same. As a result of the analysis performed by the inventors, it is considered that the profile shown in FIG. 1A and the profile shown in FIG. 1B show rhombohedral crystals. Next, an electrode was formed on a disk-shaped sample having the same composition, polarized, heated to 350 ° C., returned to room temperature, and the electrode was removed. The diffraction profile is shown in FIG. The profile shown in FIG. 1C is clearly different from the profile shown in FIG. 1A and the profile shown in FIG. In particular, when 2θ is around 35 to 45 °, there is a great difference between the profiles. According to the results of the analysis performed by the inventors, the profile shown in FIG. 1C is considered to be a monoclinic profile. X-ray diffraction of a powder sample obtained by pulverizing a disc-shaped sample of the same composition before forming an electrode (unpolarized) at various temperatures was performed, and the profile shown in FIG. , In the high-temperature region around 200 to 350 ° C. Immediately after the polarization treatment, the sample which had a crystal structure considered to be rhombohedral at room temperature showed a crystal structure considered to be monoclinic at room temperature after heat treatment at 350 ° C. It is clear that the heat treatment after the polarization realizes a crystal phase which is originally stable at a high temperature as a metastable state at room temperature. The sample subjected to the heat treatment after the polarization was allowed to stand for two months, and the same X-ray diffraction analysis was performed again, but the same result was obtained.
[0010]
Similarly, composition formula _{_{_{_{(1-n) [(Na}}}} 1-x Li x) 1-y K y] (Nb 1-z Ta z) O 3 -nM1M2O 3 ( however, M1 is a bivalent metal element, M2 The crystal system before and after the heat treatment was examined for other samples within the scope of the present invention represented by (a tetravalent metal element), and the same relationship was found in any of the samples. Moreover, the effect of improving the Q _m in the present invention was found to appear only when the crystalline phase is a metastable state has been achieved.
[0011]
Next, these samples were measured electromechanical coupling factor k _t and the mechanical quality factor Q _m of the thickness longitudinal vibration fundamental wave of the disk-shaped piezoelectric ceramic vibrator before and after the heat treatment. The results are shown in Tables 1 and 2.
[0012]
[Table 1]

[0013]
[Table 2]

[0014]
Values shown in Table 1 and Table 2 are of the same composition of the sample, the greatest mechanical quality factor Q _m are obtained conditions (calcination temperature, firing temperature, temperature of the polarization at the time of the insulating oil, DC voltage) of The value of the case.
The sample No. in Table 1 was used. Sample No. 5 loses ferroelectricity and piezoelectricity because the heat treatment temperature is too high, and is outside the scope of the present invention. Further, the sample No. in Table 1 was used. Sample No. 10 is out of the scope of the present invention because the heat treatment temperature is too low, that is, the temperature at which the high-temperature crystal phase is not stable has not changed the crystal form.
In contrast, as shown in Table 1 and Table 2, for the samples that are within the scope of the present invention, both the mechanical quality factor Q _m have been greatly improved, in particular, piezoelectric ceramic filters, piezoelectric ceramic oscillation It is clear that the piezoelectric ceramic composition is useful as a material for a piezoelectric ceramic element such as a piezoelectric element and a piezoelectric ceramic vibrator.
[0015]
Further, the sample No. For each of Samples 1 to 28, before and after the heat treatment, the resonance frequency of the spread vibration was measured using an impedance analyzer when the conditions were varied from -40 ° C to 400 ° C. Phase transition). Table 3 shows the results. In particular, the sample No. FIG. 2 is a graph showing the relationship between the temperature and the resonance frequency of the spreading vibration before and after the heat treatment for the piezoelectric ceramic vibrator using No. 6 shown in FIG.
[0016]
[Table 3]

[0017]
As is clear from the results shown in Table 3 and FIG. 2, before the heat treatment, a significant change in the resonance frequency (occurrence of phase transition) was confirmed for all the samples. 5 cannot be measured due to depolarization, and In No. 10, a significant change in the resonance frequency (the occurrence of a phase transition) was confirmed.
On the other hand, no significant change in the resonance frequency (the occurrence of phase transition) was confirmed for any of the samples within the scope of the present invention.
[0018]
As an example, from the graph shown in FIG. While the temperature change of the resonance frequency of the sample No. 6 was non-linear, the sample No. It can be seen that the temperature change of the resonance frequency of No. 6 is linear. In piezoelectric ceramic filters, piezoelectric ceramic oscillators, piezoelectric ceramic oscillators, and the like, it is often required that the rate of temperature change of the resonance frequency be small. In such a case, if the temperature change of the resonance frequency is a linear behavior, it is relatively easy to suppress the rate of change by correction. On the other hand, when the temperature change of the resonance frequency is non-linear, it is difficult to suppress the change rate by correction. Further, Sample No. before heat treatment was used. In 6, the temperature change of the resonance frequency changes depending on whether the temperature rises or falls, or according to the speed of the temperature rise or fall. That is, the temperature change of the resonance frequency has a history. On the other hand, the sample No. In No. 6, almost no history is seen in the temperature range of -40 to 125 ° C, which is the normal use temperature.
[0019]
The piezoelectric ceramic composition according to the present invention is not limited to the composition of the above-described embodiment, but is effective as long as it is within the scope of the invention.
[0020]
Although in the above embodiment the mechanical quality factor Q _m shows an example of the thickness extensional vibration of the disk-shaped piezoelectric ceramic vibrator, the effect of the present invention, a disk-shaped thickness of the piezoelectric ceramic oscillator It is not limited to longitudinal vibration, but also in other vibration modes used for other piezoelectric ceramic elements, such as, for example, piezoelectric ceramic oscillators, such as spread vibration, thickness shear vibration, and harmonics of thickness longitudinal vibration. It is just as effective.
[0021]
Further, in the above-described embodiment, the example of the temperature change of the frequency regarding the spread vibration of the disc-shaped piezoelectric ceramic vibrator has been described, but the effect of the present invention is limited to the spread vibration of the disc-shaped piezoelectric ceramic vibrator. However, other piezoelectric ceramic elements such as thickness longitudinal vibration and thickness shear vibration are also effective.
[0022]
FIG. 3 is a perspective view showing an example of the piezoelectric ceramic vibrator according to the present invention, and FIG. 4 is a schematic sectional view thereof. The piezoelectric ceramic vibrator 10 shown in FIGS. 3 and 4 includes, for example, a rectangular parallelepiped piezoelectric ceramic 12. The piezoelectric ceramic 12 includes two piezoelectric

ceramic layers

12a and 12b. These piezoelectric

ceramic layers

12a and 12b are made of the above-described piezoelectric ceramic composition according to the present invention, and are laminated and integrally formed. Further, these piezoelectric

ceramic layers

12a and 12b are polarized in the same thickness direction as shown by arrows in FIG.
[0023]
Between the piezoelectric

ceramic layers

12a and 12b, for example, a circular vibration electrode 14a is formed at the center thereof, and, for example, a T-shaped extraction electrode 16a is formed from the vibration electrode 14a to one end surface of the piezoelectric ceramic 12. On the surface of the piezoelectric ceramic layer 12a, for example, a circular vibration electrode 14b is formed at the center thereof, and, for example, a T-shaped extraction electrode 16b is formed from the vibration electrode 14b to the other end surface of the piezoelectric ceramic 12. Further, on the surface of the piezoelectric ceramic layer 12b, for example, a circular vibration electrode 14c is formed at the center thereof, and, for example, a T-shaped extraction electrode 16c is formed from the vibration electrode 14c to the other end surface of the piezoelectric ceramic 12.
[0024]
The extraction electrode 16a is connected to one external terminal 20a via a lead wire 18a, and the

extraction electrodes

16b and 16c are connected to the other external terminal 20b via another lead wire 18b.
[0025]
The present invention is also applicable to other piezoelectric ceramic elements such as a piezoelectric ceramic oscillator other than the above-described piezoelectric ceramic oscillator 10, a piezoelectric ceramic filter, and a piezoelectric ceramic oscillator.
[0026]
【The invention's effect】
According to the present invention, a compound mainly composed of elements of Na, Li, Nb and O represented by a composition formula (Na _1-x Li _x ) NbO ₃ and having a perovskite structure is used as a main component, the mechanical quality factor Q _m improves, containing a small amount or do not contain lead or lead compounds at all only, piezoelectric ceramic filter, useful piezoelectric ceramic composition as a material such as a piezoelectric ceramic element such as a piezoelectric ceramic oscillator and a piezoelectric ceramic oscillator An article and a piezoelectric ceramic element using the same are obtained.
In addition, the piezoelectric ceramic composition according to the present invention is such that a crystal system which is originally stable in a temperature range higher than room temperature is in a metastable state at room temperature, so that no phase transition occurs even at the original phase transition temperature, The resonance frequency does not change significantly.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction profile of a sample represented by a composition formula (Na _0.87 Li _0.13 ) NbO ₃ .
FIG. 2 shows a sample No. represented by a composition formula (Na _0.87 Li _0.13 ) NbO ₃ . 6 is a graph showing the temperature change of the resonance frequency of the spreading vibration of the piezoelectric ceramic vibrator before and after the heat treatment using No. 6;
FIG. 3 is a perspective view showing an example of a piezoelectric ceramic vibrator according to the present invention.
4 is an illustrative sectional view of the piezoelectric ceramic vibrator shown in FIG. 3;
[Explanation of symbols]
10 Piezoelectric ceramic vibrator 12

Piezoelectric ceramics

12a, 12b Piezoelectric

ceramic layers

14a, 14b,

14c Vibrating electrodes

16a, 16b,

16c Leading electrodes

18a,

18b Lead wires

20a, 20b External terminals

Claims

In a piezoelectric ceramic composition mainly composed of elements of Na, Li, Nb and O, and mainly containing a compound having a perovskite structure,
The crystal system of the main component is different from a crystal system that is originally stable at room temperature, and a crystal system that is originally stable in a temperature range higher than room temperature is in a metastable state at room temperature. Porcelain composition.

The piezoelectric ceramic composition according to claim 1, wherein the crystal system originally stable at room temperature is rhombohedral, and the crystal system stable at a temperature region higher than room temperature is monoclinic. .

The piezoelectric ceramic composition according to claim 1, wherein the compound serving as the main component is represented by a composition formula (Na _1-x Li _x ) NbO ₃ (where, 0.02 ≦ x ≦ 0.30). object.

The main component and comprising compounds formula _{_{(Na 1-x Li x)}} NbO 3 ( however, 0.08 ≦ x ≦ 0.18) represented by a piezoelectric ceramic composition according to claim 3.

The main component and comprising compounds formula _{_{_{_{(1-n) [(Na}}}} 1-x Li x) 1-y K y] (Nb 1-z Ta z) O 3 -nM1M2O 3 ( however, 0.02 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2, 0 ≦ n ≦ 0.1, M1 is a divalent metal element, M2 is a tetravalent metal element), The piezoelectric ceramic composition according to claim 1 or 2.

The M1 is at least one member selected from the group consisting of Mg, Ca, Sr and Ba, and the M2 is at least one member selected from the group consisting of Ti, Zr, Sn and Hf. 6. The piezoelectric ceramic composition according to 5.

A piezoelectric ceramic element comprising a piezoelectric ceramic comprising the piezoelectric ceramic composition according to any one of claims 1 to 6, and an electrode formed on the piezoelectric ceramic.

A method for producing the piezoelectric ceramic composition according to any one of claims 1 to 6, wherein
After subjecting the piezoelectric ceramic composition to a polarization treatment, the piezoelectric ceramic composition at a temperature at which the crystal system is in a stable state or higher and at a temperature lower than the temperature at which the compound serving as the main component loses ferroelectricity. A method for producing a piezoelectric ceramic composition by heating.

The method for producing a piezoelectric ceramic composition according to claim 8, wherein the temperature at which the piezoelectric ceramic composition is heated is in the range of 250C to 400C.