【発明の詳細な説明】
この発明は、TiO2−MgO−CuO−CaO系より
なる磁器組成物に係り、比誘電率εｒが大きく、
高周波帯における誘電損失角tan δが小さく、
誘電率の温度係数が組成により−150〜
200ppm／℃程度まで広範囲に制御できる磁器組
成物に関する。
近年、マイクロ波帯域での共振器などに高誘電
率で低損失な誘電体磁器材料が積極的に用いら
れ、機器の安定化、小型化が計られている。従
来、これらの誘電体材料としては、CaO−MgO
−TiO2系の３元器気組成物やこの３元系に添加
物を加えたものが検討されていた。
ところが、CaO−MgO−TiO2系磁器は誘電率
の温度係数と誘電損失角tan δが共に小さくと
れる組成範囲が狭く、組成比を変えると比誘電率
とその温度係数が同時に変化するため、例えばこ
れらの材料をマイクロ波用共振器等に応用する際
には、共振器の挿入損失を最少にでき、かつ共振
器の温度特性を最少にするために用いられる誘電
体磁器の誘電損失角tan δが最少で比誘電率の
温度係数が±0ppm／℃付近の値が得られるよう
に考慮してCaO−MgO−TiO2系で検討すると、
このような条件を満足する組成での比誘電率εｒ
値は15〜22程度であり、これ以上の大きな比誘電
率を得ることが困難であつた。
しかし、共振器の小型化にはさらに比誘電率の
大きな材料が必要であり、このためCaO−MgO
−TiO2系にLa2O3，Al2O3，Gd2O3等の添加が検
討されてきた。添加物としてLa2O3を用いる場
合、大気中のCO2と反応して炭酸塩となりやす
く、そのために組成変動の原因となり、厳密な組
成制御を必要とするこれら材料の量産化、工業化
に際して障害となつていた。また、Al2O3や
Gd2O3を添加する場合は、焼結温度が1400〜1500
℃付近の高温度が必要となり、コスト高となる等
の欠点があつた。
発明者らは上述した問題を解消し、すぐれた高
誘電率かつ低誘電損失を有する磁器組成物につい
て種々検討した結果、TiO2−MgO−CaO系磁器
に特定量のCuOを含有させることにより、比誘
電率が大きく、高周波帯域での誘電損失角tan
δが小さく、誘電率の温度係数が組成により広範
囲に制御できる磁器組成物が得られることを知見
した。
すなわち、この発明は、TiO2，MgO，CuO及
びCaOよりなる磁器組成物であつて、その成分の
組成範囲を
XTiO2・YMgO・ZCuO・UCaO
で表わしたときＸ，Ｙ，Ｚ，Ｕが、
24≦Ｘ≦70 mol％
22≦Ｙ≦70 mol％
０＜Ｚ≦５ mol％
０＜Ｕ≦10 mol％
を満足ることを特徴とする磁器組成物である。
この発明による磁器組成物の各組成を限定した
理由は以下の通りである。
TiO2が70mol％を超え、MgOが70mol％を超
え、CaOが10mol％を超えると、誘電率の温度係
数が急激に負へと増大るため、組成変動による特
性の変化が大となり、実用上不適である。
また、TiO2が24mol％未満、MgOが22mol％未
満では、焼結磁器の誘電損失角tan δが劣化す
ると同時に焼結後の収縮によつて磁器素材にクラ
ツクが生じやすく、実用に供するには困難があ
る。
また、CuOが5mol％を超えると、誘電率の温
度係数は急激に負へと増大し、組成変動による特
性の変化が大となり、又誘電損失角tan δが劣
化すると共に焼結後の収縮によつて、磁器素材に
クラツクが発生すやすくなる。
以下に、この発明を実施例に基づいて説明す
る。
原料粉末に純度99.9％以上のTiO2，MgO，
CuO，CaCO3の各粉末を用い、第１表に示す所
定の組成となるよう秤量し、ボール・ミルで純水
とともに湿式混合した。次いで、この混合物を乾
燥した後空気中において900℃の温度で２時間仮
焼した。
この仮焼物を再びボール・ミルで湿式粉砕して
平均粒子径が１〜２μｍとした後、脱水乾燥し
た。この粉末にバインダーとして濃度８％のポリ
ビニルアルコール溶液を約5wt％添加して造粒
し、34メツシユのふるいを通して整粒したものと
を金型と油圧プレスを用いて100Kg／cm2の成型圧
力で40mm×25mm×15mmのブロツクに加圧成型し
た。成型体はその組成に応じて空気中で1150℃〜
1380℃の範囲の温度で２時間保持して焼成した。
得られた磁器組成物を厚み１mmに切断し、その
両面に市販の銀電極ペーストを焼付けて電極を形
成した後、デジタルLCRメータにより1KHz〜
10MHzの周波数で静電容量（Ｃ）と誘電体損失
（Ｄ）を測定し、各々の磁器寸法より比誘電率ε
ｒを求めた。
また、比誘電率の温度係数（τｋ ppm／
℃）は、−40℃〜＋100℃の温度範囲における静電
容量の変化をLC共振回路を用いて共振周波数の
変化（τ ppm／℃）として求め、下記(1)式
よりτｋを求めた。これの試験結果を第１表に示
す。
τ＝1/2τｋ−α …(1)式
ただし τ：共振周波数の温度係数
τｋ：誘電率の温度係数
α ：磁器の熱膨張係数
なお、第１表において、試料番号２，３，６，
８，９，11の試料はこの発明による限定外の組成
からなる磁器であり、試料番号19，20，21，22の
ものは比較例であり、これら以外の試料はこの発
明の実施例である。
第１表に示した試料結果より明らかなように、
この発明による磁器は高周波領域において比誘電
率εｒが大きく、誘電損失が小であることがわか
る。さらに、本発明磁器はその組成によつて比誘
電率の温度係数を広範囲にわたつて変化させるこ
とができ、工業上のその利用範囲並びに価値が極
めて大きい材料であることがわかる。
【表】DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic composition composed of TiO 2 -MgO-CuO-CaO system, which has a large relative dielectric constant εr,
The dielectric loss angle tan δ in the high frequency band is small,
The temperature coefficient of dielectric constant varies from −150 to −150 depending on the composition.
This invention relates to a porcelain composition that can be controlled over a wide range up to about 200 ppm/°C. In recent years, dielectric ceramic materials with high permittivity and low loss have been actively used for resonators in the microwave band, etc., in an effort to stabilize and downsize devices. Conventionally, these dielectric materials include CaO−MgO
-TiO 2 -based ternary compositions and additives added to this ternary system have been studied. However, in CaO-MgO-TiO 2 ceramics, the composition range in which both the temperature coefficient of permittivity and the dielectric loss angle tan δ can be kept small is narrow, and when the composition ratio is changed, the relative permittivity and its temperature coefficient change at the same time. When applying these materials to microwave resonators, etc., the dielectric loss angle tan δ of the dielectric ceramic used is used to minimize the insertion loss of the resonator and the temperature characteristics of the resonator. When considering the CaO-MgO-TiO 2 system, taking into consideration that the temperature coefficient of the relative dielectric constant can be obtained at a value around ±0 ppm/℃ with the minimum value,
The relative dielectric constant εr for a composition that satisfies these conditions
The value was about 15 to 22, and it was difficult to obtain a larger dielectric constant. However, miniaturization of the resonator requires a material with an even higher dielectric constant, so CaO−MgO
The addition of La 2 O 3 , Al 2 O 3 , Gd 2 O 3 , etc. to the -TiO 2 system has been studied. When La 2 O 3 is used as an additive, it easily reacts with CO 2 in the atmosphere to form carbonates, which causes compositional fluctuations and poses an obstacle to the mass production and industrialization of these materials, which require strict compositional control. It was becoming. Also, Al 2 O 3 and
When adding Gd2O3 , the sintering temperature is 1400-1500
This method requires a high temperature around ℃, which has disadvantages such as high cost. The inventors solved the above-mentioned problems and conducted various studies on ceramic compositions having excellent high dielectric constant and low dielectric loss. As a result, by incorporating a specific amount of CuO into TiO 2 -MgO-CaO ceramic, The relative dielectric constant is large, and the dielectric loss angle tan in the high frequency band is
It has been found that a ceramic composition can be obtained in which δ is small and the temperature coefficient of dielectric constant can be controlled over a wide range by composition. That is, the present invention provides a ceramic composition consisting of TiO 2 , MgO, CuO, and CaO, in which when the composition range of the components is expressed as XTiO 2・YMgO ・ZCuO ・UCaO, The present invention is a porcelain composition that satisfies the following: 24≦X≦70 mol%, 22≦Y≦70 mol%, 0<Z≦5 mol%, and 0<U≦10 mol%. The reasons for limiting each composition of the porcelain composition according to the present invention are as follows. When TiO 2 exceeds 70 mol%, MgO exceeds 70 mol%, and CaO exceeds 10 mol%, the temperature coefficient of dielectric constant rapidly increases to a negative value, resulting in large changes in properties due to compositional fluctuations, making it impractical for practical use. Not suitable. Furthermore, if TiO 2 is less than 24 mol% and MgO is less than 22 mol%, the dielectric loss angle tan δ of the sintered porcelain deteriorates, and at the same time cracks are likely to occur in the porcelain material due to shrinkage after sintering, making it difficult to put it into practical use. There are difficulties. Furthermore, when CuO exceeds 5 mol%, the temperature coefficient of the dielectric constant rapidly increases to a negative value, the change in properties due to composition fluctuation becomes large, the dielectric loss angle tan δ deteriorates, and shrinkage after sintering increases. Therefore, cracks are more likely to occur in the porcelain material. The present invention will be explained below based on examples. TiO 2 , MgO, with a purity of 99.9% or more is added to the raw material powder.
Each powder of CuO and CaCO 3 was weighed to give the prescribed composition shown in Table 1, and wet mixed with pure water in a ball mill. Next, this mixture was dried and then calcined in air at a temperature of 900° C. for 2 hours. This calcined product was wet-milled again in a ball mill to have an average particle size of 1 to 2 μm, and then dehydrated and dried. Approximately 5 wt% of polyvinyl alcohol solution with a concentration of 8% as a binder was added to this powder, and the powder was granulated, passed through a 34-mesh sieve, and sized at a molding pressure of 100 kg/cm 2 using a mold and hydraulic press. It was pressure molded into a 40mm x 25mm x 15mm block. The molded body can be heated up to 1150℃ in air depending on its composition.
It was fired by holding at a temperature in the range of 1380°C for 2 hours. The resulting porcelain composition was cut to a thickness of 1 mm, and a commercially available silver electrode paste was baked on both sides to form electrodes.
The capacitance (C) and dielectric loss (D) were measured at a frequency of 10MHz, and the relative permittivity ε was determined from the dimensions of each porcelain.
I found r. Also, the temperature coefficient of relative permittivity (τk ppm/
.degree. C.) was determined by using an LC resonant circuit to determine the change in capacitance in the temperature range of -40.degree. C. to +100.degree. C. as a change in resonance frequency (.tau. ppm/.degree. C.), and .tau.k was determined from the following equation (1). The test results are shown in Table 1. τ=1/2τk−α …Equation (1) where τ: Temperature coefficient of resonance frequency τk: Temperature coefficient of permittivity α: Coefficient of thermal expansion of porcelain In Table 1, sample numbers 2, 3, 6,
Samples Nos. 8, 9, and 11 are porcelains with compositions other than those specified by this invention, sample numbers 19, 20, 21, and 22 are comparative examples, and the other samples are examples of this invention. . As is clear from the sample results shown in Table 1,
It can be seen that the ceramic according to the present invention has a large relative dielectric constant εr and a small dielectric loss in the high frequency range. Furthermore, the temperature coefficient of the dielectric constant of the porcelain of the present invention can be varied over a wide range depending on its composition, and it can be seen that it is a material with an extremely large range of industrial application and value. 【table】