【発明の詳細な説明】
本発明は、電気機械結合係数が大きく、誘電率
が小さく周波数定数が大きく、さらに結晶粒子径
が小さくて均一で微細な磁器組織を持ち、かつ圧
電性を得るのに必要な分極処理が容易である、高
周波での電気機械変換素子として有用な圧電性磁
器に関する。
従来、圧電性磁器としてチタン酸バリウム系磁
器ジルコン・チタン酸鉛系磁器が知られている。
特にジルコン・チタン酸鉛系磁器は電気機械結合
係数（Ｋ）、誘電率（ε）が大きく、電気機械変
換素子として多方面で実用されている。
ところで最近電子回路の発達から高周波域特に
数ＭHz以上で使用できる電気機械変換素子の出現
が強く要望されている。従来のチタン酸バリウム
系磁器、ジルコン・チタン酸鉛系磁器では誘電率
が大きい為にかかる高周波域では損失が大きくな
る。又、周波数定数が小さい為にかかる高周波域
で実用する場合、素子の厚味を極く薄くする等非
常な小寸法の素子とすることが必要となり、実用
上良好な結果を得ていない。
これらの点を解決する組成物としてNaNbO3
−LiNbO3系固溶体が見出されている。これらの
組成物は誘電率が小さく、周波数定数が大きい特
徴を有している。しかし、これらの組成物は磁器
組織として微細で均一なものが得難い。すなわ
ち、焼結に適する温度範囲が狭く、かつ異状粒成
長が起きやすく、結晶粒子径が大きくかつ不均一
となりさらに気孔を多く残存させる。
ところで高周波域では、これらの磁器組織の不
均一性は電気機械変換素子としての性能を著るし
く低下させ、さらに結晶粒子径が大きいことが素
子としての強度、特にかかる高周波用として必要
な小寸法での強度を極めて低下させ、これらのこ
とが実用上大きな障害となつている。
これらの点を解決する方法として特殊な製造方
法、例えばホツトプレス法による焼結等が見い出
されているが、それでも焼結温度等の条件範囲は
狭くて充分な結果は得られず、かつ製造方法を複
雑にすることから実用上好ましくない。
又、NaNbO3−LiNbO3系磁器は、圧電性を得
るのに必要な分極処理において、従来のチタン酸
バリウム系磁器およびジルコン・チタン酸鉛系磁
器と比較して２倍又はそれ以上の高い印加電圧を
必要とする為、分極処理中にかかる磁器が絶縁破
壊の為、破損する確率が大きく、実用上大きな障
害となつていた。
本発明は上記の様な従来のものの欠点を除去
し、高周波用電気機械変換子として利用できる全
く新しい圧電性磁器を提供するものである。即
ち、本発明は一般式
（Na1-x、Lix）z（Nb1-y、Sby）O3 〔１〕
で示され、ｘ、ｙの値が0.03ｘ0.14、0.001
ｙ0.03 0.980ｚ＜１の範囲の組成を有する圧
電性磁器である。
本発明による圧電性磁器は、通常の焼成方法に
よつて結晶粒子径の小さい、均一微細な磁器組織
が得られかつ、分極処理における破損が少くさら
に電気機械結合係数が大きく、誘電率が小さく周
波数定数が大きい特徴を有し、高周波域特に数Ｍ
Hz以上での電気機械変換素子として実用するに好
適な材料である。
本発明における組成限定の理由はｘ＜0.03では
分極処理に要する印加電圧が極めて大きくなり、
実用に供することは難しい。他方ｘ＞0.14では単
一相からなる焼結体が得られず混相となり、所定
の圧電特性を示さない。又、ｙ＜0.001では焼結
が極めて進みやすく焼結過程において結晶粒の成
長が進展して結晶粒子径が10μを超えて、さらに
異常粒成長を起す為通常の焼成方法では均一な磁
器組成が得られない。他方ｙ＞0.03では、ｙ＜
0.001と同様に均一な磁器組織が得られない。ｚ
＝１では、十分な密度の焼結体を得る為に、高い
焼結温度が必要で、かつ分極処理において、高電
圧印加中に磁器が絶縁破壊によつて破損すること
が多い。
0.98ｚ＜１では十分な密度の焼結体を得るの
に必要な焼結温度がｚ＝１に比較して10〜70℃程
度低く、かつ、分極処理における磁器の破損が少
ない。ｚ＜0.98では十分な密度を得るのに必要な
焼結温度がさらに低いが均一な磁器組織が得られ
ない。
本発明の圧電性磁器を製造するには、例えば
Na2CO3、Li2CO3、Nb2O5、Sb2O3の様な成分原
料を所定量、秤量、混合しその混合物を800〜
1000℃で２〜８時間仮焼する。仮焼物を粉砕後、
成形し、次いで成形物を1130〜1300℃で焼結して
磁器を得る。この磁器に所定の方法で分極処理を
施し、圧電特性を持たせる。
実施例
出発原料粉末としてNa2CO3、Li2CO3、
Nb2O5、Sb2O3を用いた。純度は炭酸塩で99.5％
以上Nb2O5、Sb2O3は共に99.9％以上である。
これらの原料を所定量、秤量し、エタノールに
よるボールミルで湿式混合した後混合物を乾燥し
た。得られた混合粉末を850〜900℃で４時間空気
中で仮焼した。得られた仮焼物を粉砕後厚さ２
mm、直径25mmの円板に500〜600Kg／cm2の圧力で加
圧成形した。この円板試料を1150℃ないし1280℃
のある温度で空気中で焼結させた。得られた磁器
の嵩比重、真比重を測定し、又磁器組織の観察に
よつて結晶粒子径の測定を行つた。磁器組織の観
察は、まず得られた円板磁器の円面を鏡面研磨
し、次にこの面は1050℃で15分間程度空気中加熱
することにより熱エツチさせ、この面を顕微鏡観
察する方法によつて行つた。
次に圧電特性については、得られた円板磁器を
厚さ１mm、直径18mmの円板に成形研磨し、この円
板の両面にAg電極を焼きつけて100℃のシリコン
オイル中に入れて両電極間に５ないし6KV／mm
のある直流電圧を20分間印加して分極処理を施し
た。このとき、分極処理を施した磁器の全数と、
その内、分極処理中に絶縁破壊による破損が起き
なかつた磁器の数とを計数し、いわゆる分極成功
率を測定した。
分極した試料を24時間放置した後、圧電特性を
評価する為、径方向振動における電気機械結合係
数（Kp）及び周波数定数（NP：共振周波数×直
径）を測定した。測定はI.R.E.の標準回路の方法
に従い、Kpの算出は共振及び反共振周波数から
算出した。さらに、誘電率（ε／ε0）を1KHzの
周波数で測定した。第１表に、この様にして得ら
れた種々の組成の試料における特性を一般式
（Na1-x、Lix）z（Nb1-y、Sby）O3におけるｘ、ｙ
及びｚの値と共に示した。
なお、分極成功率は、分数の形で表わし、分母
に分極処理を施した磁器の数、分子には、その内
絶縁破壊による破損が起きなかつた磁器の数を示
した。
又、誘電率、電気機械結合係数は、これら分極
処理において破損が起きなかつた磁器内での平均
値で示した。
表１で＊印で示したものは、比較例である。第
１表に示した試料は全て比重は真比重の97％以上
であり、又周波数定数は3.55−3.77（ＫHz・ｍ）
の範囲にある。
第１表及び上記の特性から明らかな様に、本発
明による圧電性磁器は結晶子径が小さく均一であ
り、かつ分極処理における破損が少く、さらに大
きい電気機械結合係数（Kp）を有し、誘電率
（ε／ε0）が小さいという特徴を有し、さらに周
波数定数が大きいので高周波での電気機械変換素
子用の圧電性磁器として好適である。
【表】Detailed Description of the Invention The present invention has a large electromechanical coupling coefficient, a small dielectric constant, a large frequency constant, a small crystal grain size, a uniform and fine porcelain structure, and a method for obtaining piezoelectricity. The present invention relates to piezoelectric porcelain useful as an electromechanical transducer at high frequencies, which is easy to perform necessary polarization processing. BACKGROUND ART Barium titanate-based porcelain and zircon/lead titanate-based porcelain are conventionally known as piezoelectric porcelain.
In particular, zircon-lead titanate-based porcelain has a large electromechanical coupling coefficient (K) and dielectric constant (ε), and is used in many fields as an electromechanical transducer. Recently, with the development of electronic circuits, there has been a strong demand for an electromechanical transducer that can be used in a high frequency range, particularly at several MHz or higher. Conventional barium titanate-based porcelain and zircon-lead titanate-based porcelain have large dielectric constants, resulting in large losses in such high frequency ranges. Furthermore, since the frequency constant is small, when it is put to practical use in such a high frequency range, it is necessary to make the element very small in size, such as by making the thickness of the element extremely thin, and good results have not been obtained in practice. NaNbO 3 as a composition that solves these points
-LiNbO 3 solid solution has been discovered. These compositions are characterized by a low dielectric constant and a large frequency constant. However, with these compositions, it is difficult to obtain a fine and uniform porcelain structure. That is, the temperature range suitable for sintering is narrow, abnormal grain growth is likely to occur, the crystal grain size is large and non-uniform, and many pores remain. By the way, in the high frequency range, the non-uniformity of these porcelain structures significantly reduces the performance as an electromechanical transducer, and the large crystal grain size also reduces the strength of the element, especially the small size required for such high frequencies. These problems pose a major obstacle in practical use. Special manufacturing methods such as hot press sintering have been found to solve these problems, but the range of conditions such as sintering temperature is narrow and satisfactory results cannot be obtained. This is not practical because it complicates the process. In addition, NaNbO 3 -LiNbO 3 based porcelain has a polarization treatment that is required to obtain piezoelectricity, and can be applied twice or more compared to conventional barium titanate based porcelain and zircon/lead titanate based porcelain. Since voltage is required, there is a high probability that the porcelain will be damaged due to dielectric breakdown during the polarization process, which has been a major obstacle in practical use. The present invention eliminates the above-mentioned drawbacks of the conventional piezoelectric ceramics and provides a completely new piezoelectric ceramic that can be used as a high frequency electromechanical transducer. That is, the present invention is represented by the general formula (Na 1-x , Li x ) z (Nb 1-y , Sb y )O 3 [1], and the values of x and y are 0.03x0.14 and 0.001.
It is a piezoelectric ceramic having a composition in the range of y0.03 0.980z<1. The piezoelectric porcelain according to the present invention can obtain a uniform fine porcelain structure with a small crystal grain size by a normal firing method, has little damage during polarization treatment, has a large electromechanical coupling coefficient, has a small dielectric constant, and has a low frequency It is characterized by a large constant, especially in the high frequency range
This material is suitable for practical use as an electromechanical transducer at frequencies above Hz. The reason for the composition limitation in the present invention is that when x<0.03, the applied voltage required for polarization treatment becomes extremely large.
It is difficult to put it into practical use. On the other hand, when x>0.14, a sintered body consisting of a single phase cannot be obtained, but a mixed phase is obtained, and the desired piezoelectric properties are not exhibited. In addition, when y < 0.001, sintering progresses extremely easily, and the growth of crystal grains progresses during the sintering process, resulting in a crystal grain size exceeding 10μ, which further causes abnormal grain growth, making it difficult to achieve a uniform porcelain composition with normal firing methods. I can't get it. On the other hand, for y>0.03, y<
Similar to 0.001, a uniform porcelain structure cannot be obtained. z
When =1, a high sintering temperature is required to obtain a sintered body with sufficient density, and in the polarization process, the porcelain is often damaged due to dielectric breakdown during high voltage application. When 0.98z<1, the sintering temperature required to obtain a sintered body with sufficient density is about 10 to 70°C lower than when z=1, and there is less damage to the porcelain during the polarization process. When z<0.98, the sintering temperature required to obtain sufficient density is lower, but a uniform porcelain structure cannot be obtained. In order to manufacture the piezoelectric porcelain of the present invention, for example,
Mix a predetermined amount of component raw materials such as Na 2 CO 3 , Li 2 CO 3 , Nb 2 O 5 , and Sb 2 O 3 by weight, and make the mixture 800~
Calcinate at 1000℃ for 2 to 8 hours. After crushing the calcined material,
The molded product is then sintered at 1130-1300°C to obtain porcelain. This porcelain is polarized using a predetermined method to give it piezoelectric properties. Examples Na 2 CO 3 , Li 2 CO 3 ,
Nb 2 O 5 and Sb 2 O 3 were used. Purity is 99.5% carbonate
Both Nb 2 O 5 and Sb 2 O 3 are 99.9% or more. A predetermined amount of these raw materials was weighed, wet mixed in a ball mill using ethanol, and then the mixture was dried. The obtained mixed powder was calcined in air at 850 to 900°C for 4 hours. After crushing the obtained calcined product, the thickness is 2
mm, and was press-molded into a disc with a diameter of 25 mm at a pressure of 500 to 600 Kg/cm 2 . This disk sample was heated to 1150℃ to 1280℃.
sintered in air at a certain temperature. The bulk specific gravity and true specific gravity of the obtained porcelain were measured, and the crystal grain size was also measured by observing the porcelain structure. To observe the porcelain structure, we first mirror-polish the circular surface of the obtained disc porcelain, then heat-etch this surface by heating it in the air at 1050℃ for about 15 minutes, and then observe this surface with a microscope. I waded over. Next, regarding piezoelectric properties, the obtained disk porcelain was molded and polished into a disk with a thickness of 1 mm and a diameter of 18 mm, Ag electrodes were baked on both sides of this disk, and the electrodes were placed in silicone oil at 100°C. 5 to 6KV/mm between
A certain DC voltage was applied for 20 minutes to perform polarization treatment. At this time, the total number of porcelains that have been polarized,
Among them, the number of porcelains that were not damaged due to dielectric breakdown during the polarization treatment was counted, and the so-called polarization success rate was measured. After leaving the polarized sample for 24 hours, the electromechanical coupling coefficient (Kp) and frequency constant (NP: resonance frequency x diameter) in radial vibration were measured in order to evaluate the piezoelectric properties. The measurements were carried out according to the IRE standard circuit method, and Kp was calculated from the resonance and anti-resonance frequencies. Furthermore, the dielectric constant (ε/ε 0 ) was measured at a frequency of 1 KHz. Table 1 shows the characteristics of samples with various compositions obtained in this way using the general formula (Na 1-x , Li x ) z (Nb 1-y , Sb y )O 3 x, y
and z values. The polarization success rate is expressed in the form of a fraction, with the denominator representing the number of porcelains subjected to polarization treatment, and the numerator representing the number of porcelains that were not damaged due to dielectric breakdown. In addition, the dielectric constant and electromechanical coupling coefficient are shown as average values within the porcelain in which no damage occurred during these polarization treatments. Those marked with * in Table 1 are comparative examples. The specific gravity of all the samples shown in Table 1 is 97% or more of the true specific gravity, and the frequency constant is 3.55-3.77 (KHz・m)
within the range of As is clear from Table 1 and the above characteristics, the piezoelectric porcelain according to the present invention has a small and uniform crystallite diameter, less damage during polarization treatment, and a large electromechanical coupling coefficient (Kp). It is characterized by a low dielectric constant (ε/ε 0 ) and a large frequency constant, so it is suitable as a piezoelectric ceramic for electromechanical transducers at high frequencies. 【table】