JP5319208B2 - Piezoelectric ceramic and piezoelectric element using the same - Google Patents
Piezoelectric ceramic and piezoelectric element using the same Download PDFInfo
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- 239000000919 ceramic Substances 0.000 title claims description 66
- 239000002245 particle Substances 0.000 claims description 64
- 230000010287 polarization Effects 0.000 claims description 31
- 239000000203 mixture Substances 0.000 claims description 29
- 229910052797 bismuth Inorganic materials 0.000 claims description 15
- 229910052744 lithium Inorganic materials 0.000 claims description 10
- 229910052758 niobium Inorganic materials 0.000 claims description 10
- 229910052700 potassium Inorganic materials 0.000 claims description 10
- 229910052708 sodium Inorganic materials 0.000 claims description 10
- 239000000463 material Substances 0.000 claims description 7
- 230000002269 spontaneous effect Effects 0.000 claims description 4
- 229910052573 porcelain Inorganic materials 0.000 claims description 2
- 239000011734 sodium Substances 0.000 description 34
- 230000005684 electric field Effects 0.000 description 22
- 230000008859 change Effects 0.000 description 13
- 239000000843 powder Substances 0.000 description 12
- 230000007704 transition Effects 0.000 description 11
- 239000003513 alkali Substances 0.000 description 9
- 238000003917 TEM image Methods 0.000 description 6
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 6
- 239000000758 substrate Substances 0.000 description 6
- 230000008878 coupling Effects 0.000 description 5
- 238000010168 coupling process Methods 0.000 description 5
- 238000005859 coupling reaction Methods 0.000 description 5
- 239000002994 raw material Substances 0.000 description 5
- 239000013078 crystal Substances 0.000 description 4
- 238000010304 firing Methods 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910015902 Bi 2 O 3 Inorganic materials 0.000 description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 3
- 229910052783 alkali metal Inorganic materials 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 3
- HFGPZNIAWCZYJU-UHFFFAOYSA-N lead zirconate titanate Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ti+4].[Zr+4].[Pb+2] HFGPZNIAWCZYJU-UHFFFAOYSA-N 0.000 description 3
- 229910052451 lead zirconate titanate Inorganic materials 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 150000001340 alkali metals Chemical class 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000002789 length control Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 229910002651 NO3 Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000003916 acid precipitation Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- NKZSPGSOXYXWQA-UHFFFAOYSA-N dioxido(oxo)titanium;lead(2+) Chemical compound [Pb+2].[O-][Ti]([O-])=O NKZSPGSOXYXWQA-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012776 electronic material Substances 0.000 description 1
- 238000010828 elution Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000005469 granulation Methods 0.000 description 1
- 230000003179 granulation Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000011268 mixed slurry Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- UKDIAJWKFXFVFG-UHFFFAOYSA-N potassium;oxido(dioxo)niobium Chemical compound [K+].[O-][Nb](=O)=O UKDIAJWKFXFVFG-UHFFFAOYSA-N 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- UYLYBEXRJGPQSH-UHFFFAOYSA-N sodium;oxido(dioxo)niobium Chemical compound [Na+].[O-][Nb](=O)=O UYLYBEXRJGPQSH-UHFFFAOYSA-N 0.000 description 1
- 230000007480 spreading Effects 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000012856 weighed raw material Substances 0.000 description 1
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Description
本発明は、圧電磁器および圧電素子に関し、位置決め、光学装置の光路長制御、流量制御用バルブ、超音波モータあるいは自動車のブレーキ装置等に使用されるアクチュエータなどに好適に用いられる圧電磁器および圧電素子に関するものである。 TECHNICAL FIELD The present invention relates to a piezoelectric ceramic and a piezoelectric element. The piezoelectric ceramic and the piezoelectric element are preferably used for positioning, an optical path length control of an optical device, a flow control valve, an ultrasonic motor, an actuator used in an automobile brake device, or the like. It is about.
圧電磁器を利用した製品としては、例えば、フィルタ、位置決め、光学装置の光路長制御、流量制御用バルブ、超音波モータあるいは自動車のブレーキ装置等に使用されるアクチュエータなどがある。 Examples of products using piezoelectric ceramics include filters, positioning, optical path length control of optical devices, flow rate control valves, ultrasonic motors, actuators used in automobile brake devices, and the like.
従来、アクチュエータとしては、圧電性の高い、ＰＺＴ（チタン酸ジルコン酸鉛）系材料やＰＴ（チタン酸鉛）系材料が使用されていた。しかしながら、ＰＺＴ系材料やＰＴ系材料は、鉛を約６０質量％の割合で含有しているため、酸性雨により鉛の溶出が起こり、環境汚染を招く危険性が指摘されている。そこで、鉛を含有しない圧電材料へ高い期待が寄せられている。 Conventionally, PZT (lead zirconate titanate) -based materials and PT (lead titanate) -based materials having high piezoelectricity have been used as actuators. However, since PZT-based materials and PT-based materials contain lead in a proportion of about 60% by mass, the elution of lead due to acid rain has been pointed out as a risk of causing environmental pollution. Therefore, high expectations are placed on piezoelectric materials that do not contain lead.
そのような非鉛圧電材料としては、ニオブ酸カリウム（ＫＮｂＯ３）とニオブ酸ナトリウム（ＮａＮｂＯ３）とを主成分とした圧電磁器が提案されている（例えば特許文献１を参照。）。
しかしながら、ＫＮｂＯ３やＮａＮｂＯ３といったニオブ酸アルカリを主成分とした圧電磁器は、比較的高い圧電定数を示すものの、圧電磁器として使用する前の分極処理時に飽和分極とするために高い強度の電界を印加する必要があり、その際に発生する圧電磁器の絶縁破壊により、圧電磁器の歩留りが低いという問題があった。また、そのために圧電素子の歩留りが悪いという問題があった。 However, although piezoelectric ceramics mainly composed of alkali niobate such as KNbO 3 and NaNbO 3 exhibit a relatively high piezoelectric constant, a high-intensity electric field is required for saturation polarization during polarization processing before use as a piezoelectric ceramic. There is a problem in that the yield of the piezoelectric ceramic is low due to the dielectric breakdown of the piezoelectric ceramic generated at that time. In addition, for this reason, there is a problem that the yield of the piezoelectric element is poor.
したがって、本発明は、分極処理時に飽和分極に達する電界強度を低くできる非鉛の圧電磁器およびそれを用いた圧電素子を提供することを目的とする。 Accordingly, an object of the present invention is to provide a lead-free piezoelectric ceramic that can reduce the electric field strength that reaches saturation polarization during polarization processing, and a piezoelectric element using the same.
本発明の圧電磁器は、Ｎａ、Ｋ、Ｌｉ、ＮｂおよびＢｉを含み、組成式で（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９と表したとき、Ｎａ、Ｋ、Ｌｉ、ＮｂおよびＢｉの元素の割合が０．３８≦ａ≦０．６２、０．００≦ｂ≦０．０８、０．００１≦ｘ≦０．００５の関係を満足するとともに、前記Ｂｉを含む粒子のうち、内部に自発分極の方向が９０度違うドメインが交互に並んで形成されたド
メインウォールが、略平行である粒子の割合が８０％以上であることを特徴とする。また、前記Ｂｉを含む粒子の平均粒子径が２μｍ以下であることが好ましい。
The piezoelectric ceramic of the present invention contains Na, K, Li, Nb, and Bi, and has a composition formula of (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5 ) Bi 2. When expressed as Nb 2 O 9 , the ratio of Na, K, Li, Nb, and Bi elements is 0.38 ≦ a ≦ 0.62, 0.00 ≦ b ≦ 0.08, 0.001 ≦ x ≦ 0. .005, and among the particles containing Bi, a domain in which domains having spontaneous polarization directions differing by 90 degrees are alternately formed.
The main wall is characterized in that the proportion of particles substantially parallel is 80% or more . The average particle size of the particles containing the Bi is preferably a 2μm or less der Turkey.
またさらに、前記組成式でｘが０．００１≦ｘ≦０．００２５である成分１００質量部に対して、ＭｎをＭｎＯ２換算で０．０５〜２質量部含有することが好ましい。 Furthermore, it is preferable to contain 0.05 to 2 parts by mass of Mn in terms of MnO 2 with respect to 100 parts by mass of the component where x is 0.001 ≦ x ≦ 0.0025 in the composition formula.
さらにまた、前記組成式でｂが０．０４≦ｂ≦０．０６である成分１００質量部に対して、ＭｎをＭｎＯ２換算で０．０５〜２質量部含有することが好ましい。 Furthermore, it is preferable to contain 0.05 to 2 parts by mass of Mn in terms of MnO 2 with respect to 100 parts by mass of the component in which b is 0.04 ≦ b ≦ 0.06 in the composition formula.
本発明の圧電素子は、前記圧電磁器からなる基体の対向する一対の表面に電極を備えたことを特徴とする。 The piezoelectric element of the present invention is characterized in that electrodes are provided on a pair of opposing surfaces of a base body made of the piezoelectric ceramic.
本発明の圧電磁器は、Ｎａ、Ｋ、Ｌｉ、ＮｂおよびＢｉを含み、組成式で（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９と表したとき、Ｎａ、Ｋ、Ｌｉ、ＮｂおよびＢｉの元素の割合が０．３８≦ａ≦０．６２、０．００≦ｂ≦０．０８、０．００１≦ｘ≦０．００５の関係を満足するとともに、前記Ｂｉを含む粒子のうち、内部に自発分極の方向が９０度違うドメインが交互に並んで形成されたドメインウォールが、略平行である粒子の割合が８０％以上であることにより、ドメインサイズが小さく、かつ粒子内のドメインウォールが１方向に整列している粒子の割合が高いため、低い電界強度で分極処理を行なうことができる。
The piezoelectric ceramic of the present invention contains Na, K, Li, Nb, and Bi, and has a composition formula of (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5 ) Bi 2. When expressed as Nb 2 O 9 , the ratio of Na, K, Li, Nb, and Bi elements is 0.38 ≦ a ≦ 0.62, 0.00 ≦ b ≦ 0.08, 0.001 ≦ x ≦ 0. The ratio of particles that satisfy the relationship of .005 and the domain wall in which domains having spontaneous polarization directions of 90 degrees are alternately formed in the Bi-containing particles is approximately parallel is 80%. As described above, since the ratio of the particles having a small domain size and the domain walls in the particles being aligned in one direction is high, the polarization treatment can be performed with a low electric field strength.
また、前記組成式でｘが０．００１≦ｘ≦０．００２５である成分１００質量部に対して、ＭｎをＭｎＯ２換算で０．０５〜２質量部含有する場合、室温付近（−２０〜１００℃）の圧電特性の温度に対する変化が緩やかになる。 When 100 parts by mass of the component having x of 0.001 ≦ x ≦ 0.0025 in the composition formula is contained in an amount of 0.05 to 2 parts by mass in terms of MnO 2 , near room temperature (−20 to 20 (100 ° C.) The change in the piezoelectric characteristics with respect to temperature becomes gradual.
またさらに、前記組成式でｂが０．０４≦ｂ≦０．０６である成分１００質量部に対して、ＭｎをＭｎＯ２換算で０．０５〜２質量部含有する場合、圧電定数をより高くできる。 Furthermore, when 100 parts by mass of the component in which b is 0.04 ≦ b ≦ 0.06 in the composition formula is contained in an amount of 0.05 to 2 parts by mass in terms of MnO 2 , the piezoelectric constant is higher. it can.
さらにまた、前記組成式の成分１００質量部に対して、ＭｎをＭｎＯ２換算で０．０５〜２質量部含有するとともに、０．０４≦ｂ≦０．０６である場合、圧電定数をより高くできる。 Furthermore, with respect to 100 parts by mass of the component of the composition formula, when Mn is contained in an amount of 0.05 to 2 parts by mass in terms of MnO 2 and 0.04 ≦ b ≦ 0.06, the piezoelectric constant is higher. it can.
本発明の圧電素子によれば、前記圧電磁器からなる基体の対向する一対の表面に電極を備えたことを特徴とするにより、圧電素子の製造工程中で、圧電素子に欠けや割れなどが生じにくく、それらに起因する不良が少なくなり、歩留りの良い圧電素子ができる。 According to the piezoelectric element of the present invention, the piezoelectric element is provided with electrodes on a pair of opposing surfaces of the base made of the piezoelectric ceramic, so that the piezoelectric element is chipped or cracked during the manufacturing process of the piezoelectric element. It is difficult to reduce the number of defects resulting from them, and a piezoelectric element with a good yield can be obtained.
ここで、ニオブ酸アルカリを主成分とするとは、化学量論的なニオブ酸アルカリ、すなわちＭをアルカリ金属元素としたときにＭＮｂＯ３の比率で含まれるＭ（アルカリ金属元素）、ＮｂおよびＯの割合が、全体の８０質量％以上、または９０質量％以上、さらには９５質量％以上であることをいう。また、圧電磁器にはビスマスが含まれる。ビスマスはこれに限定されるわけではないが、概ねＢｉ２Ｏ３の組成比でＯを伴って含まれる。これ以外に含まれるものとしては、ＭｎＯ２やＣｒ２Ｏ３などの焼結助剤、不純物、化学量論的な比率からずれたアルカリ金属元素、Ｎｂなどが挙げられる。 Here, the alkali niobate is the main component when the stoichiometric alkali niobate, that is, M (alkali metal element), Nb, and O contained in a ratio of MNbO 3 when M is an alkali metal element. It means that the ratio is 80% by mass or more, 90% by mass or more, and further 95% by mass or more. The piezoelectric ceramic includes bismuth. Bismuth is not limited to this, but is generally included with O at a composition ratio of Bi 2 O 3 . In addition to this, sintering aids such as MnO 2 and Cr 2 O 3 , impurities, alkali metal elements deviating from the stoichiometric ratio, Nb, and the like are included.
本発明の圧電磁器に含まれる、前記ニオブ酸アルカリを主成分とするとともに前記ビスマスを含む粒子の平均粒子径は２μｍ以下である。詳細は後述するが、これにより粒子に含まれるドメインウォールの方向が一方方向に揃っているものが多くなり、分極処理時に飽和分極に達する電界強度を低くするができる。また、平均粒子径が小さくなるとドメインのサイズが小さくなり、圧電特性を向上させることができる。なお、後述の９０度ドメインの集合が効率よく形成されるためには、平均粒子径は０．１μｍ以上であるのが好ましく、焼成後の粒子が原料の粉末より大きくなることを考えれば、原料の取りあつかいを容易にするため、０．３μｍ以上であるのが好ましい。
圧電磁器に含まれる粒子の平均粒子径は、例えば、後述のように、圧電磁器の断面を研磨して、走査型電子顕微鏡（ＳＥＭ）で観察し、インターセプト法により求めることができる。
The average particle diameter of the particle | grains which are contained in the piezoelectric ceramic of this invention and which contain the said alkali niobate as a main component and contain the said bismuth is 2 micrometers or less. As will be described in detail later, the number of domain walls contained in the particles is often aligned in one direction, and the electric field intensity reaching saturation polarization during the polarization treatment can be reduced. Further, when the average particle size is reduced, the domain size is reduced, and the piezoelectric characteristics can be improved. In order to efficiently form a set of 90-degree domains described later, the average particle size is preferably 0.1 μm or more, and considering that the particles after firing are larger than the raw material powder, In order to facilitate handling, it is preferable that the thickness is 0.3 μm or more.
The average particle diameter of the particles contained in the piezoelectric ceramic can be determined by, for example, an intercept method after polishing the cross section of the piezoelectric ceramic, observing with a scanning electron microscope (SEM), as will be described later.
本発明の圧電磁器に含まれるニオブ酸アルカリを主成分とするとともにビスマスを含む粒子の８０％以上は、粒子内部に存在するドメインウォールが略平行になっている。これは、粒子内にドメインの自発分極の方向が９０度違うドメインが交互に並んでおり（これを９０度ドメインという）、その交互に並んだドメインの集合体が粒子内にひとつであるため、ドメインの境界であるドメインウォールが略平行になっているということである。このような状態のドメインウォールは分極電圧が加わった際に、粒子内に複数の方向のドメインウォールが存在するいわゆるマルチドメインのものに比べ、印加される電界によりドメインウォールが揃いやすく、そのような粒子は低い電界強度で飽和分極に達する。なお、ドメインウォールは基本的に平行に移動するため、分極処理を施した後の粒子のドメインウォールも略平行になっている。 In 80% or more of particles containing alkali niobate contained in the piezoelectric ceramic of the present invention and containing bismuth, the domain walls existing inside the particles are substantially parallel. This is because the domains in which the direction of spontaneous polarization of domains is 90 degrees are alternately arranged in a particle (this is called a 90-degree domain), and the aggregate of the alternating domains is one in the particle. This means that domain walls that are domain boundaries are substantially parallel. When domain voltage in such a state is applied with a polarization voltage, the domain wall is more easily aligned by the applied electric field than the so-called multi-domain domain in which there are domain walls in a plurality of directions in the particle. The particles reach saturation polarization with low electric field strength. Since the domain wall basically moves in parallel, the domain wall of the particle after the polarization treatment is also substantially parallel.
このように低い電界強度で飽和分極に達する粒子、すなわち粒子内部に存在するドメインウォールが略平行になっている粒子が８０％以上であることにより圧電磁器全体としても低い電界強度で飽和分極に達する。ドメインウォールが略平行になっていない粒子が８０％より少ない、つまりドメインウォールが略平行になっていない粒子、すなわち次に説明するマルチドメインの粒子の割合が高いと、それらの粒子ではドメインウォールが移動して飽和分極に達する電界強度が高いため、圧電磁器全体としても高い強度の電界を加えないと飽和分極に達しない。 Thus, the saturation polarization is reached with a low electric field strength as a whole of the piezoelectric ceramic because the particles reaching saturation polarization with a low electric field strength, that is, particles having domain walls substantially parallel to each other inside the particle are 80% or more. . If the number of particles whose domain walls are not substantially parallel is less than 80%, that is, the proportion of particles whose domain walls are not substantially parallel, that is, the multi-domain particles described below, is high, Since the electric field strength that moves and reaches saturation polarization is high, the entire piezoelectric ceramic cannot reach saturation polarization unless a high-intensity electric field is applied.
１つの粒子内のドメインウォールが略平行になっている場合、すなわち９０度ドメインの集合体が１つの粒子内に１つである場合に対して、１つの粒子内に９０度ドメインが複数ある場合、それぞれの９０度ドメインの集合体内部のドメインウォールは略平行になるが、異なる９０度ドメインの集合体の間ではドメインウォールが違った方向に形成され、また、９０度ドメインの集合体同士の間にもドメインウォールが存在する、いわゆるマルチドメイン構造を呈する。そのためこのような粒子の中には方向の異なるドメインウォールが存在し、このため、あるいは９０度ドメインの集合体の間のドメインウォールも移動させるエネルギーが必要になるため、分極する際に飽和分極に達するまでに高い電界が必要になる。このような構造はマルチドメインといわれる。 When the domain walls in one particle are substantially parallel, that is, when there are one 90 ° domain aggregate in one particle, there are multiple 90 ° domains in one particle The domain walls inside each 90-degree domain aggregate are substantially parallel, but the domain walls are formed in different directions between different 90-degree domain aggregates. It has a so-called multi-domain structure with domain walls in between. For this reason, there are domain walls with different directions in such particles. For this reason, or because the energy required to move the domain walls between 90-degree domain aggregates is also necessary, saturation polarization occurs during polarization. A high electric field is required to reach. Such a structure is called multi-domain.
上述のドメインの構造は、圧電磁器を薄片に加工し、透過型電子顕微鏡（ＴＥＭ）で観察することで確認できる。図１（ａ）は、本発明の一実施例である圧電磁器のＴＥＭ像であり、後述の実施例の試料Ｎｏ．３を観察したものある。組成としては（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９と表したとき、ｘ＝０．００２５、ａ＝０．５、ｂ＝０．０５である主成分１００質量部に対して、ＭｎＯ２を０．５質量部含有するものである。図１（ｂ）は、図１（ａ）のＴＥＭ像の中の粒子１と粒子１内に観察されるドメインウォール２を模式的に表したものである。なお、図１（ｂ）に示したドメインウォール２を表す破線は、ドメインウォール２の観察される範囲と方向を模式的に示したもので、図１（ａ）のドメインウォール２の１つ１つとは必ずしも一致しない。 The domain structure described above can be confirmed by processing a piezoelectric ceramic into a thin piece and observing it with a transmission electron microscope (TEM). FIG. 1A is a TEM image of a piezoelectric ceramic according to an embodiment of the present invention. 3 is observed. As a composition, when expressed as (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 , x = 0.0025, a = 0. 5 and 0.5 parts by mass of MnO 2 with respect to 100 parts by mass of the main component of b = 0.05. FIG. 1B schematically shows the particle 1 in the TEM image of FIG. 1A and the domain wall 2 observed in the particle 1. The broken line representing the domain wall 2 shown in FIG. 1B schematically shows the observed range and direction of the domain wall 2, and each of the domain walls 2 shown in FIG. Does not necessarily match.
図１（ａ）、（ｂ）では粒子１内の１ａの付近に９０度ドメインの集合体があり、ドメインウォール２が略平行に存在しているのが観察できる。図１（ａ）、（ｂ）では、１ｂ付近には明確なドメインウォールが見えないが、試料の角度を変えて観察すると、１ｂ付近にも１ａ付近のドメインウォール２と略平行なドメインウォール２が確認できる。同様に、図１（ａ）、（ｂ）では粒子１の左右および下に位置する粒子にドメインウォール２が見えないが、それらの粒子にも略平行なドメインウォールが存在している。なお、圧電特性を高くするにはドメインウォールの効果をより導入するためにドメイン密度を向上させた方がよいため、ドメインのサイズ（ドメインウォール２の間隔）は狭い方が好ましく、５０ｎｍ以下であることが好ましい。 In FIGS. 1 (a) and 1 (b), it can be observed that there is a 90 ° domain aggregate in the vicinity of 1a in the particle 1 and the domain wall 2 exists substantially in parallel. In FIGS. 1A and 1B, a clear domain wall cannot be seen in the vicinity of 1 b, but when observed by changing the angle of the sample, a domain wall 2 substantially parallel to the domain wall 2 in the vicinity of 1 a is also observed in the vicinity of 1 b. Can be confirmed. Similarly, in FIGS. 1A and 1B, the domain wall 2 is not visible in the particles located on the left and right and below the particle 1, but there are also substantially parallel domain walls in these particles. In order to enhance the piezoelectric characteristics, it is better to improve the domain density in order to introduce the effect of the domain wall. Therefore, the domain size (interval between the domain walls 2) is preferably narrow, and is 50 nm or less. It is preferable.
図２（ａ）は、本発明の範囲外の圧電磁器のＴＥＭ像であり、後述の実施例の試料Ｎｏ．１を観察したものある。組成としては（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３と表したとき、ａ＝０．５、ｂ＝０．０５である主成分１００質量部に対して、ＭｎＯ２を０．５質量部含有するものである。図２（ｂ）は、図２（ａ）のＴＥＭ像の中の粒子５と粒子５内に観察されるドメインウォール６を模式的に表したものである。なお、図２（ｂ）に示したドメインウォール６を表す破線は、ドメインウォール６の観察される範囲と方向を模式的に示したもので、図２（ａ）のドメインウォール６の１つ１つとは必ずしも一致しない。 FIG. 2A is a TEM image of a piezoelectric ceramic outside the scope of the present invention. 1 is observed. As a composition, when expressed as (Na a K 1-a ) 1-b Li b NbO 3 , MnO 2 is set to 0. It contains 5 parts by mass. FIG. 2B schematically shows the particle 5 in the TEM image of FIG. 2A and the domain wall 6 observed in the particle 5. 2B schematically shows the observed range and direction of the domain wall 6, and each broken line representing the domain wall 6 shown in FIG. Does not necessarily match.
図２（ａ）、（ｂ）では粒子５の中に９０度ドメインの集合体が複数存在する。そのうちの２つの９０度ドメインの集合体５ａ、５ｂを観察すると、それぞれの中に存在するドメインウォール６は略平行であるが、９０度ドメインの集合体５ａ内のドメインウォール６と９０度ドメインの集合体５ｂ内のドメインウォール６とは異なる角度になっている。また、９０度ドメインの集合体５ａと９０度ドメインの集合体５ｂの間にもドメインウォール６があり、このドメインウォール６は、９０度ドメインの集合体５ａ内のドメインウォール６および９０度ドメインの集合体５ｂ内のドメインウォール６と違う角度になっている。 2A and 2B, a plurality of 90-degree domain aggregates exist in the particle 5. In FIG. When two of the 90-degree domain aggregates 5a and 5b are observed, the domain walls 6 existing in each of the 90-degree domain aggregates 5a and 5b are substantially parallel to each other. The angle is different from that of the domain wall 6 in the aggregate 5b. There is also a domain wall 6 between the 90 ° domain aggregate 5a and the 90 ° domain aggregate 5b. The domain wall 6 is composed of the domain wall 6 in the 90 ° domain aggregate 5a and the 90 ° domain aggregate 5a. The angle is different from that of the domain wall 6 in the aggregate 5b.
なお、本発明の圧電磁器は、典型的には、断面において各粒子１内のほぼ全体にドメイン（９０度ドメイン）が観察されるが、組成によっては、ドメインの存在する領域が少なくなっている場合もある。その場合は、断面において、１つの粒子１内でドメインの存在する領域が半分以上となっているものについて、ドメインウォール６が略平行になっているか調べ、ドメインウォール６が略平行になっている粒子が粒子全体の８０％以上かどうかで判定すればよい。 In the piezoelectric ceramic according to the present invention, typically, domains (90-degree domains) are observed almost entirely in each particle 1 in a cross section, but depending on the composition, there are fewer domains. In some cases. In that case, in the cross section, the domain wall 6 is approximately parallel by checking if the domain wall 6 is approximately parallel for the region where the domain exists in one particle 1 is more than half. What is necessary is just to judge by whether a particle | grain is 80% or more of the whole particle | grain.
図３は、後述の実施例の試料Ｎｏ．３の圧電磁器および試料Ｎｏ．１の圧電磁器に分極処理を行なった際の、加えた電界と圧電定数ｄ３３の関係を示したグラフである。いずれの試料も加わる電界が高くなるとともに圧電定数ｄ３３が大きくなっていくが、しだいに圧電定数ｄ３３の変化は少なくなり、飽和する。本発明の一実施例の圧電磁器である試料Ｎｏ．３では、４ＭＶ／ｍの電界で飽和するのに対して、本発明の範囲外の圧電磁器である試料Ｎｏ．１では９ＭＶ／ｍまで電界を加えないと飽和しない。試料Ｎｏ．１のように高い電界を加えた場合、圧電磁器が絶縁破壊を起こしてしまうことがあり、分極時飽和電界強度は６ＭＶ／ｍ以下であることが好ましい。 FIG. 3 shows a sample No. of Example described later. 3 and sample no. At the time of performing polarized in the first piezoelectric ceramic is a graph showing the relationship between the electric field and the piezoelectric constant d 33 was added. In any sample, the electric field applied increases and the piezoelectric constant d 33 increases, but the change in the piezoelectric constant d 33 gradually decreases and becomes saturated. Sample No. which is a piezoelectric ceramic according to an embodiment of the present invention. 3 saturates at an electric field of 4 MV / m, whereas sample No. 3 which is a piezoelectric ceramic outside the scope of the present invention. In 1, it is not saturated unless an electric field is applied up to 9 MV / m. Sample No. When a high electric field is applied as in 1, the piezoelectric ceramic may cause dielectric breakdown, and the saturation saturation electric field strength is preferably 6 MV / m or less.
また、圧電磁器はＮａ、Ｋ、Ｌｉ、ＮｂおよびＢｉを含み、これらの元素の割合が、組成式（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９で表したとき、０．４２≦ａ≦０．５８、０．０３≦ｂ≦０．０６、０．００１≦ｘ≦０．００５であることが好ましい。 The piezoelectric ceramic contains Na, K, Li, Nb, and Bi, and the ratio of these elements is expressed by the composition formula (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0. 5 ) When expressed as Bi 2 Nb 2 O 9 , it is preferable that 0.42 ≦ a ≦ 0.58, 0.03 ≦ b ≦ 0.06, 0.001 ≦ x ≦ 0.005.
組成式で（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３、ａ＝０．５、ｂ＝０．０５で表される圧電磁器はペロブスカイト構造をもち、室温付近の結晶構造は斜方晶であり、１００℃程度での結晶構造は正方晶である。そのため、室温から１００℃程度の間にある相転移点で圧電特性、例えば、圧電定数に急激な変化がある。この相転移点は、Ｎａ、Ｋ、Ｌｉの元素比率を少し変えても、室温付近になり、やはり圧電特性の急激な変動を生じる。また、前述のａ＝０．５、ｂ＝０．０５の元素比率は、圧電定数の高くなる、いわゆるＭＰＢ（Morphotoropic Phase Boundary）領域となる比率であり、この組成の近傍である０．４２≦ａ≦０．５８、０．０３≦ｂ≦０．０６の範囲では高い圧電特性を示す。例えば、Ｌｉの比率を高くすることにより相転移点を低くすることはできるが、ａ＝０．５、ｂ＝０．０８程度にしても相転移点は０℃あるいはこれを少し下回る程度であり、この比率では圧電定数はあまり高くはならない。 The piezoelectric ceramic represented by the composition formula (Na a K 1-a ) 1-b Li b NbO 3 , a = 0.5, b = 0.05 has a perovskite structure, and the crystal structure near room temperature is oblique The crystal structure at about 100 ° C. is tetragonal. Therefore, there is a rapid change in piezoelectric characteristics, for example, the piezoelectric constant, at a phase transition point between room temperature and about 100 ° C. This phase transition point is close to room temperature even if the element ratio of Na, K, and Li is slightly changed, and suddenly changes in piezoelectric characteristics are caused. The element ratio of a = 0.5 and b = 0.05 described above is a ratio that becomes a so-called MPB (Morphotoropic Phase Boundary) region where the piezoelectric constant is high, and is in the vicinity of this composition of 0.42 ≦ High piezoelectric characteristics are exhibited in the range of a ≦ 0.58 and 0.03 ≦ b ≦ 0.06. For example, the phase transition point can be lowered by increasing the ratio of Li, but even if a = 0.5 and b = 0.08, the phase transition point is 0 ° C. or slightly below this. At this ratio, the piezoelectric constant does not become so high.
これに対して、（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３組成に対して（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９を添加することにより、斜方晶から正方晶への相転移が緩慢になる。具体的には、組成比を（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９と表したとき、０．００１≦ｘ≦０．００５とすれば、室温付近（−２０〜８０℃）での圧電特性の急激な変動を抑制できるので好ましい。また、ａおよびｂについては、前述したように圧電特性の高くなるＭＰＢの近傍領域である０．４２≦ａ≦０．５８、０．０３≦ｂ≦０．０６であることが好ましい。 On the other hand, by adding (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 to the (Na a K 1-a ) 1-b Li b NbO 3 composition, The phase transition to tetragonal becomes slow. Specifically, when the composition ratio is expressed as (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 , 0.001 ≦ x If it is set to ≦ 0.005, it is preferable because rapid fluctuations in piezoelectric characteristics around room temperature (-20 to 80 ° C.) can be suppressed. Further, as described above, it is preferable that a and b are 0.42 ≦ a ≦ 0.58 and 0.03 ≦ b ≦ 0.06, which are regions in the vicinity of MPB where the piezoelectric characteristics are enhanced.
図４（ａ）は、後述の実施例の試料Ｎｏ．１の圧電磁器と試料Ｎｏ．３の圧電磁器の共振周波数の温度依存性を測定した結果である。共振周波数の温度変化は圧電磁器の弾性定数の変化により起こるものであり、５０℃付近に存在する共振周波数の谷間は、結晶構造の相転移により弾性定数が変わることに起因している。試料Ｎｏ．１と３とでは相転移温度自体に大きな差はないが、試料Ｎｏ．３では温度変化率が低くなっている。これは、構造相転移が緩慢となっていることを示している。 FIG. 4A shows a sample No. in Examples described later. No. 1 piezoelectric ceramic and sample no. It is the result of having measured the temperature dependence of the resonant frequency of 3 piezoelectric ceramics. The temperature change of the resonance frequency is caused by the change of the elastic constant of the piezoelectric ceramic, and the valley of the resonance frequency existing around 50 ° C. is caused by the change of the elastic constant due to the phase transition of the crystal structure. Sample No. Although there is no significant difference in the phase transition temperature itself between 1 and 3, sample no. In 3, the temperature change rate is low. This indicates that the structural phase transition is slow.
図４（ｂ）は、同試料の径方向広がり振動の電気機械結合係数Ｋｒの温度依存性を測定した結果である。圧電磁器の共振周波数の温度依存性の変化に対応して電気機械結合係数Ｋｒの温度依存性が小さくなっていることがわかる。つまり、（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３組成に対して（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９を０．００１≦ｘ≦０．００５の範囲で添加することにより、圧電定数を低くすることなく、室温付近の圧電特性の温度依存性を少なくすることができる。添加量を０．００１≦ｘ≦０．００２５の範囲にすれば、圧電定数を高くすることができるため、より好ましい。 4 (b) is a result of measuring the temperature dependence of the electromechanical coefficient K r of the radial extent vibrations of the same sample. It can be seen that the temperature dependence of the electromechanical coefficient K r corresponding to the temperature dependence of the change in resonance frequency of the piezoelectric ceramic is small. That is, (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 is in the range of 0.001 ≦ x ≦ 0.005 with respect to the (Na a K 1-a ) 1-b Li b NbO 3 composition. By adding it, it is possible to reduce the temperature dependence of the piezoelectric characteristics near room temperature without lowering the piezoelectric constant. If the amount of addition is in the range of 0.001 ≦ x ≦ 0.0025, the piezoelectric constant can be increased, which is more preferable.
また、上述の組成式（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９の成分１００質量部に対して、ＭｎＯ２およびＣｒ２Ｏ３から選ばれる少なくとも１種を合量で０．０５〜２質量部含有すると圧電磁器が緻密になり圧電定数も高くなるためより好ましい。ただし、含有する量が２質量部を超えると、絶縁性が低くなることがある。なお、同量の含有量の場合ＭｎＯ２の方が圧電磁器が緻密になるため添加するのはＭｎＯ２が好ましい。 In addition, with respect to 100 parts by mass of the component of the above composition formula (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 , MnO 2 and When at least one selected from Cr 2 O 3 is contained in a total amount of 0.05 to 2 parts by mass, it is more preferable because the piezoelectric ceramic becomes dense and the piezoelectric constant increases. However, when the content exceeds 2 parts by mass, the insulating property may be lowered. Note that to add because towards the case of the MnO 2 content of the same amount piezoelectric ceramic becomes dense the MnO 2 is preferred.
そして、ＭｎＯ２およびＣｒ２Ｏ３から選ばれる少なくとも１種を合量で０．０５〜２質量部含有して、圧電磁器が緻密になった状態では、ｘの範囲を０．００１≦ｘ≦０．００２５とすることにより、より圧電定数を高くできる。 In the state where 0.05 to 2 parts by mass of the total amount of at least one selected from MnO 2 and Cr 2 O 3 is contained and the piezoelectric ceramic becomes dense, the range of x is 0.001 ≦ x ≦ By setting it to 0.0025, the piezoelectric constant can be further increased.
また、ＭｎＯ２およびＣｒ２Ｏ３から選ばれる少なくとも１種を合量で０．０５〜２質量部含有して、圧電磁器が緻密になった状態では、ｂの範囲を０．０４≦ｂ≦０．０６とすることにより、圧電定数をより高くすることができる。 In addition, when the total amount of at least one selected from MnO 2 and Cr 2 O 3 is 0.05 to 2 parts by mass and the piezoelectric ceramic becomes dense, the range of b is set to 0.04 ≦ b ≦ By setting it to 0.06, the piezoelectric constant can be further increased.
本発明の圧電磁器は、粉砕時のＺｒＯ２ボールからＺｒ等が混入する場合もあるが、微量であれば特性上問題ない。組成式（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９の成分、ＭｎＯ２およびＣｒ２Ｏ３が合計で９９質量％以上を占め、それ以外の組成は１質量％未満、より好ましくは０．５質量％未満であるのがよい。 In the piezoelectric ceramic according to the present invention, Zr or the like may be mixed from the ZrO 2 ball at the time of pulverization. Composition formula (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 component, MnO 2 and Cr 2 O 3 in total 99 mass% The other composition is less than 1% by mass, more preferably less than 0.5% by mass.
本発明の圧電磁器は、例えば、原料として、Ｎａ２ＣＯ３、Ｋ２ＣＯ３、Ｌｉ２ＣＯ３、Ｎｂ２Ｏ５、Ｂｉ２Ｏ３、ＭｎＯ２、Ｃｒ２Ｏ３からなる各種酸化物あるいはその塩を用いることができる。原料はこれに限定されず、焼成により酸化物を生成する炭酸塩、硝酸塩等の金属塩を用いても良い。 The piezoelectric ceramic of the present invention includes, for example, various oxides made of Na 2 CO 3 , K 2 CO 3 , Li 2 CO 3 , Nb 2 O 5 , Bi 2 O 3 , MnO 2 , Cr 2 O 3 as raw materials. The salt can be used. A raw material is not limited to this, You may use metal salts, such as carbonate and nitrate which produce | generate an oxide by baking.
これらの原料を、ニオブ酸アルカリが主成分となりビスマスを含む所望の割合で秤量し、混合後の平均粒度分布（Ｄ５０）が０．３〜１μｍの範囲になるように粉砕する。この混合物を８５０〜１０００℃で仮焼し、仮焼後の平均粒度分布（Ｄ５０）が０．３〜１μｍの範囲になるように粉砕し、再度所定の有機バインダを加え湿式混合し造粒する。 These raw materials are weighed at a desired ratio containing alkali niobate as a main component and containing bismuth, and are pulverized so that the average particle size distribution (D 50 ) after mixing is in the range of 0.3 to 1 μm. This mixture is calcined at 850 to 1000 ° C., pulverized so that the average particle size distribution (D 50 ) after calcining is in the range of 0.3 to 1 μm, and a predetermined organic binder is added again to perform wet mixing and granulation. To do.
このようにして得られた粉体を、公知のプレス成形等により所定形状に成形し、大気中等の酸化性雰囲気において１０００〜１２００℃の温度範囲で２〜５時間焼成し、本発明の圧電磁器が得られる。 The powder thus obtained is molded into a predetermined shape by known press molding or the like, and baked in an oxidizing atmosphere such as the atmosphere at a temperature range of 1000 to 1200 ° C. for 2 to 5 hours. Is obtained.
図５（ａ）に、本発明の圧電素子の実施形態の一例であるアクチュエータの概略縦断面図を示す。このアクチュエータは、上述の圧電磁器からなる６つの圧電基体１１が積層されている。各圧電基体１１の一方の主面に電極１２が形成され、他方の主面には電極１３が形成されている。アクチュエータ内で電極１２、１３は積層方向に交互に形成されている。分極は各圧電基体１１の主面に垂直に電極１３から電極１２の方向に施してある。このようなアクチュエータは、電極１２と電極１３との間に電圧を加えることにより圧電基体１１がＰ方向に変位する、すなわち、厚みが変化する方向に変形し、アクチュエータとして働く。
FIG. 5A shows a schematic longitudinal sectional view of an actuator which is an example of an embodiment of the piezoelectric element of the present invention. In this actuator, six piezoelectric substrates 11 made of the above-described piezoelectric ceramic are laminated. An electrode 12 is formed on one main surface of each piezoelectric substrate 11, and an electrode 13 is formed on the other main surface. The electrodes 12 and 13 are alternately formed in the stacking direction in the actuator. Polarization is performed in the direction from the electrode 13 to the electrode 12 perpendicular to the main surface of each piezoelectric substrate 11. In such an actuator, when a voltage is applied between the electrode 12 and the electrode 13, the piezoelectric substrate 11 is displaced in the P direction, that is, deformed in a direction in which the thickness changes, and acts as an actuator.
図５（ｂ）に、本発明の圧電素子の実施形態の一例である圧力センサ素子の概略斜視図を示す。この圧力センサは、上述の圧電磁器からなる圧電基体２１の対向する一対の主面に、それぞれに電極２２、２３を形成され、互いに対向させた一対の電極２２、２３を備えている。また、分極は主面と垂直な方向に施してある。このような圧力センサでは、主面間に加わる圧力により、各主面に電荷が生じるため、この電荷を測定することにより、主面間に加わっている圧力を測定することができる。 FIG. 5B is a schematic perspective view of a pressure sensor element which is an example of an embodiment of the piezoelectric element of the present invention. This pressure sensor is provided with a pair of electrodes 22 and 23 which are formed on a pair of opposing main surfaces of the piezoelectric substrate 21 made of the above-described piezoelectric ceramic, respectively, and are opposed to each other. Polarization is performed in a direction perpendicular to the main surface. In such a pressure sensor, electric charges are generated on the main surfaces due to the pressure applied between the main surfaces. Therefore, the pressure applied between the main surfaces can be measured by measuring the electric charges.
出発原料として純度９９．９％のＮａ２ＣＯ３粉末、Ｋ２ＣＯ３粉末、Ｌｉ２ＣＯ３粉末、Ｎｂ２Ｏ５粉末、Ｂｉ２Ｏ３粉末を、モル比による組成式（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９と表したとき、ｘ、ａ、ｂが表１に示す量の成分と、この成分１００質量部に対して、ＭｎＯ２粉末を表１に示す質量部となるように秤量し混合した。なお、アルカリ炭酸塩は通常の大気中の環境では、吸湿した状態になるので正確に秤量ができないため、高温下で水分を飛ばした後、ドライ窒素ブース内で手早く秤量した。
炭酸アルカリは常温常湿の環境下では、吸湿した状態になるため、高温化で水分を飛ばした後、湿度を低く保ったブース内で手早く秤量した。
As a starting material, Na 2 CO 3 powder with a purity of 99.9%, K 2 CO 3 powder, Li 2 CO 3 powder, Nb 2 O 5 powder, Bi 2 O 3 powder, a composition formula (Na a K 1 -a) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5) when expressed as Bi 2 Nb 2 O 9, the amount of components showing x, a, b are shown in Table 1, the component 100 MnO 2 powder was weighed and mixed so as to be the mass parts shown in Table 1 with respect to the mass parts. In addition, since the alkali carbonate is in a moisture absorption state in a normal atmospheric environment and cannot be accurately weighed, it was quickly weighed in a dry nitrogen booth after water was blown off at a high temperature.
Since alkali carbonate is in a state of absorbing moisture in an environment of normal temperature and humidity, after water was removed at a high temperature, it was quickly weighed in a booth kept at a low humidity.
秤量した原料粉末を、純度９９．９％のＺｒＯ２ボール、イオン交換水と共に５００ｍｌポリポットに投入し、１６時間回転ミルで混合した。 The weighed raw material powder was put into a 500 ml polypot together with ZrO 2 balls having a purity of 99.9% and ion-exchanged water, and mixed in a rotary mill for 16 hours.
混合後のスラリーを大気中で乾燥し、＃４０メッシュを通し、その後、大気中９００℃、３時間保持して仮焼し、この合成粉末を純度９９．９％のＺｒＯ２ボールとイオン交換水と共に５００ｍｌポリポットに投入し、２０時間粉砕して評価粉末を得た。 The mixed slurry is dried in the air, passed through a # 40 mesh, and then calcined at 900 ° C. for 3 hours in the air, and this synthetic powder is mixed with 99.9% purity ZrO 2 balls and ion-exchanged water. Together with this, it was put into a 500 ml polypot and pulverized for 20 hours to obtain an evaluation powder.
この粉末に適量の有機バインダを添加して造粒し、金型プレスで１５０ＭＰａの圧力で成形し、大気中において３時間本焼成し、直径１３ｍｍ、厚み２ｍｍの円柱状の圧電磁器を得た。焼成では、焼成ピーク温度を１０４０から１１６０℃まで間２０℃毎に７条件で焼成して圧電磁器を作製し、後述の評価では圧電定数ｄ３３のもっとも高い圧電磁器の結果を示した。 An appropriate amount of an organic binder was added to the powder, granulated, molded with a mold press at a pressure of 150 MPa, and finally fired in air for 3 hours to obtain a cylindrical piezoelectric ceramic having a diameter of 13 mm and a thickness of 2 mm. In firing, a piezoelectric ceramic was produced by firing at a firing peak temperature of 1040 to 1160 ° C. under 20 conditions every 20 ° C., and in the evaluation described later, the result of the piezoelectric ceramic having the highest piezoelectric constant d 33 was shown.
圧電磁器は、厚さ１．５ｍｍに研磨した後、両主面（円柱の上下面）にＡｇ電極を形成して、１００℃で厚み方向に分極処理を行ない、圧電素子を得た。分極をする際には、加えた電界と圧電定数ｄ３３との関係を測定しながら行ない、分極が飽和する際の電界強度を測定した。 After the piezoelectric ceramic was polished to a thickness of 1.5 mm, Ag electrodes were formed on both main surfaces (upper and lower surfaces of the cylinder), and polarization treatment was performed in the thickness direction at 100 ° C. to obtain a piezoelectric element. When the polarization is carried out while measuring the relationship between the electric field and the piezoelectric constant d 33 was added to measure the electric field strength when the polarization is saturated.
得られた測定用素子はｄ３３メーターで圧電定数ｄ３３を測定した。また、圧電素子を恒温槽に入れ、温度を変化させながら静電容量、広がり振動モードの共振周波数、反共振周波数、共振抵抗、反共振抵抗を測定した。続いて、共振周波数、反共振周波数より日本電子材料工業会標準規格ＥＭＡＳ−６１００に準拠して、電気機械結合定数ｋｒを算出した。 The resulting measurement device measured the piezoelectric constant d 33 with d 33 meter. Further, the piezoelectric element was placed in a thermostatic chamber, and the capacitance, the resonance frequency of the spreading vibration mode, the anti-resonance frequency, the resonance resistance, and the anti-resonance resistance were measured while changing the temperature. Subsequently, the electromechanical coupling constant kr was calculated from the resonance frequency and the anti-resonance frequency in accordance with the Japan Electronic Materials Industry Association Standard EMA-6100.
また、圧電磁器は断面を研磨して、粒径に応じて１０００〜１００００倍のＳＥＭで観察し、インターセプト法により平均粒子径を算出した。さらに、圧電磁器を薄片に加工し、粒径に応じて１０００〜１００００倍のＴＥＭで観察し、任意に選んだ粒子２０個について観察し、１つの粒子内に存在するドメインウォールが略平行にないっている粒子の割合を評価した。なお、この際には、粒子内のドメインを見逃さないよう試料の角度を調整しながら観察した。なお、全ての試料において、観察されたドメインはほとんど９０度ドメインであった。以上の結果を表１示す。 Moreover, the cross section of the piezoelectric ceramic was polished and observed with an SEM of 1000 to 10,000 times according to the particle diameter, and the average particle diameter was calculated by the intercept method. Furthermore, the piezoelectric ceramic is processed into a thin piece, and is observed with a TEM of 1000 to 10000 times according to the particle diameter, and 20 arbitrarily selected particles are observed, and domain walls existing in one particle are not substantially parallel. The percentage of particles that were falling was evaluated. At this time, the observation was performed while adjusting the angle of the sample so as not to miss the domains in the particles. In all samples, the observed domain was almost 90 degree domain. The results are shown in Table 1.
表１から明らかなように、本発明の範囲内の試料Ｎｏ．２〜４および６〜２３の圧電磁器は、ニオブ酸アルカリを主成分とするとともにビスマスを含み、平均粒子径が２μｍ以下であり、かつ内部に存在するドメインウォールが略平行である粒子の割合が全体の８０％以上であるため、分極処理時の電界強度を６ＭＶ／ｍ以下と低くなった。 As is apparent from Table 1, sample nos. 2 to 4 and 6 to 23 piezoelectric ceramics are composed of alkali niobate as a main component, bismuth, an average particle diameter of 2 μm or less, and a ratio of particles in which domain walls existing inside are substantially parallel. Is 80% or more of the whole, and the electric field strength during the polarization treatment was as low as 6 MV / m or less.
また、試料Ｎｏ．２〜４、７〜１０、１３〜１５および１８〜２３の圧電磁器は、Ｎａ、Ｋ、Ｌｉ、ＮｂおよびＢｉを含み、組成式で（ＮａａＫ１−ａ）１−ｂＬｉｂＮｂＯ３＋ｘ（Ｎａ０．５Ｂｉ０．５）Ｂｉ２Ｎｂ２Ｏ９と表したとき、Ｎａ、Ｋ、Ｌｉ、ＮｂおよびＢｉの元素の割合が０．４２≦ａ≦０．５８、０．０３≦ｂ≦０．０６、０．００１≦ｘ≦０．００５の関係を満足することにより、−２０〜＋８０℃の範囲での電気機械結合定数ｋｒの変化率が１０％以下と低くなった。 Sample No. Piezoelectric ceramics of 2 to 4, 7 to 10, 13 to 15, and 18 to 23 include Na, K, Li, Nb, and Bi, and (Na a K 1-a ) 1-b Li b NbO 3 in the composition formula + X (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 , the ratio of Na, K, Li, Nb and Bi elements is 0.42 ≦ a ≦ 0.58, 0.03 ≦ by satisfying the relation of b ≦ 0.06,0.001 ≦ x ≦ 0.005, the rate of change of the electromechanical coupling constant k r in the range of -20 to + 80 ° C. is lower than 10%.
またさらに、試料Ｎｏ．２〜３、７〜１０、１３〜１５および１９〜２３の圧電磁器は、ｘが０．００１≦ｘ≦０．００２５である前記組成式の成分１００質量部に対して、ＭｎをＭｎＯ２換算で０．０５〜２質量部含有することにより、圧電定数ｄ３３が１３２ｐＣ／Ｎ以上と高くなった。 Furthermore, sample no. In the piezoelectric ceramics of 2-3, 7-10, 13-15, and 19-23, x is MnO 2 conversion with respect to 100 parts by mass of the component of the composition formula in which 0.001 ≦ x ≦ 0.0025. in by containing 0.05 to 2 parts by weight, the piezoelectric constant d 33 was as high as 132pC / N or more.
さらにまた、試料Ｎｏ．２〜３、７〜１０、１４、１５および１９〜２３の圧電磁器は、さらに０．０４≦ｂ≦０．０６であることにより、圧電定数ｄ３３が１４１ｐＣ／Ｎ以上と高くなった。 Furthermore, sample no. Piezoelectric ceramic 2～3,7～10,14,15 and 19-23, by still more 0.04 ≦ b ≦ 0.06, the piezoelectric constant d 33 was as high as 141pC / N or more.
これに対して、本発明の範囲外の試料Ｎｏ．１、５および２４〜２６では、ドメインウォールが略平行である粒子の割合が全体の８０％に達していないか、平均粒径が大きいため、分極処理時の電界強度が６ＭＶ／ｍより高くなったか、分極中に絶縁破壊し分極が十分できなかった。 On the other hand, sample no. In 1, 5 and 24-26, the ratio of the particles whose domain walls are substantially parallel does not reach 80% of the total, or the average particle size is large, so that the electric field strength during the polarization treatment is higher than 6 MV / m. Or, dielectric breakdown occurred during polarization, and polarization was not sufficient.
なお、本発明の範囲外の試料Ｎｏ．１は、ｘ＜０．００１であるため、電気機械結合定数ｋｒの変化率が−１６％と大きくなった。これは、この試料の相転移点が約５０℃にあり、この相転移点付近での急激な結晶構造変化により電気機械結合定数ｋｒが変わるためである。このため変化率が高温側で大きくなった。 Note that sample No. Since 1 was x <0.001, the rate of change of the electromechanical coupling constant k r was as large as −16%. This phase transition point of the sample is in approximately 50 ° C., because the electromechanical coupling constant k r is changed due to rapid crystal structure changes in the vicinity the phase transition point. For this reason, the rate of change increased on the high temperature side.
また、本発明の範囲外の試料Ｎｏ．２５および２６は、ｘ＜０．００１であるため、電気機械結合定数ｋｒの変化率が２０％以上と大きくなった。これは、これら試料の相転移点がＬｉの添加により低温側に移動し、低温側の変化率が大きくなってためである。図６に、これらの試料の電気機械結合係数Ｋｒの温度依存性を示す。 In addition, the sample no. 25 and 26 are the x <0.001, the rate of change of the electromechanical coupling constant k r is as large as 20% or more. This is because the phase transition point of these samples moves to the low temperature side due to the addition of Li, and the rate of change on the low temperature side increases. Figure 6 shows the temperature dependence of the electromechanical coefficient K r of these samples.
また、実施例で作製した試料を、蛍光Ｘ線分析装置で組成分析した。その結果、各試料の磁器の組成は、調合した原料組成と同じであった。 In addition, the composition of the sample prepared in the example was analyzed with a fluorescent X-ray analyzer. As a result, the composition of the porcelain of each sample was the same as the prepared raw material composition.
１、５・・・粒子
２、６・・・ドメインウォール
１１、２１・・・圧電基体（圧電磁器）
１２、１３、２２、２３・・・電極
Ｐ・・・分極方向
1, 5 ... Particles 2, 6 ... Domain walls 11, 21 ... Piezoelectric substrate (piezoelectric ceramic)
12, 13, 22, 23 ... Electrode P ... Polarization direction
Claims (5)
前記Ｂｉを含む粒子のうち、内部に自発分極の方向が９０度違うドメインが交互に並んで形成されたドメインウォールが、略平行である粒子の割合が８０％以上であることを特徴とする圧電磁器。 It contains Na, K, Li, Nb and Bi, and is expressed as (Na a K 1-a ) 1-b Li b NbO 3 + x (Na 0.5 Bi 0.5 ) Bi 2 Nb 2 O 9 in the composition formula. When the ratio of the elements Na, K, Li, Nb and Bi satisfies the relationship of 0.38 ≦ a ≦ 0.62, 0.00 ≦ b ≦ 0.08, 0.001 ≦ x ≦ 0.005 With
A piezoelectric material characterized in that, among the particles containing Bi, a domain wall in which domains having spontaneous polarization directions of 90 degrees are alternately arranged in the inside has a ratio of particles that are substantially parallel to 80% or more. porcelain.
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