JPH0228909B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ferroelectric ceramic composition, and particularly to a ferroelectric ceramic composition having a low mechanical quality factor and high stability of properties. In recent years, there has been a growing tendency to emphasize sound quality in AM radio, FM radio, and other audio communication equipment, and ceramic filters with extremely low phase distortion are now required to be used in these equipment. Ta. Therefore, ferroelectric ceramic materials for ceramic filters are required to have a low mechanical quality factor (hereinafter referred to as Qm) and stable characteristics. Conventionally, ferroelectric ceramic materials with low Qm are
Lead zircon titanate (Pb(Zr,Ti)O ₃ ) in which part of the Pb is replaced with divalent elements such as Ba, Sr, Ca, etc., or lead zircon titanate with Nb ₂ O ₅ ,
Those to which oxides such as Sb ₂ O ₃ and La ₂ O ₃ are added are known. However, these porcelain materials
When the composition has a low value of Qm of 80 to 200, the electromechanical coupling coefficient Kp and the relative dielectric constant ε _T33 /ε ₀ become large values of 60 to 70% and 1500 to 2500, respectively, making it possible to create a narrow band ceramic filter. In manufacturing, polarization must be controlled, resulting in large variations, making it difficult to mass-produce ceramic filters with stable characteristics. Moreover, the stability of the center frequency was poor, making it difficult to put it to practical use as a ceramic filter, and the high sintering temperature of 1,250 to 1,300°C caused a large amount of lead to evaporate during firing, resulting in poor reproducibility. . The present invention was made to solve this problem, and an object of the present invention is to provide a ferroelectric ceramic composition that has a low Qm and high stability of characteristics and can be used to manufacture a narrow band ceramic filter. shall be. Another object of the present invention is to provide a ferroelectric ceramic composition that has applications in ultrasonic vibrators, ceramic disc liminators, piezoelectric transformers, piezoelectric ignition elements, and other piezoelectric transducers. The ferroelectric ceramic composition according to the present invention has the general formula: xPb(Y _1/2 Sb _1/2 )O ₃ −yPbTiO ₃ −zPbZrO ₃ (where x, y, and z are the molar ratios of each component, x+
y+z=1.00, 0.005≦x≦0.200, 0.140≦y≦
Satisfies 0.620, 0.350≦z≦0.830. ), and the polygon shown in Figure 1
It has a composition within a range surrounded by ABCDEF, and is characterized in that the composition at each vertex of the polygon is as shown below. x y z A 0.200 0.450 0.350 B 0.030 0.620 0.350 C 0.005 0.615 0.380 D 0.005 0.165 0.830 E 0.030 0.140 0.830 F 0.200 0.270 0 .530 The composition of the ferroelectric ceramic composition according to the present invention is
The reason why we limited the compositions to those within the range surrounded by the polygon ABCDEF in the figure is because compositions outside this range would have an electromechanical coupling coefficient of 20% or less, and the characteristics would change significantly due to thermal aging. . Also,
When the molar ratio x of Pb(Y _1/2 Sb _1/2 ) O ₃ becomes smaller than 0.005, the firing temperature increases to 1270-1300℃, and the electromechanical coupling coefficient (Kp) and relative dielectric constant (ε _T33 / The reproducibility of electrical characteristics such as ε ₀ ), Qm, and frequency constant (frD) deteriorates, and when it exceeds 0.200,
Volume resistivity decreases and polarization becomes difficult.
In addition, the molar ratio y of PbTiO ₃ is less than 0.140 or 0.620
If it exceeds , the electromechanical coupling coefficient (Kp) will be less than 20%, making it impossible to obtain a value sufficient for practical use.
If the molar ratio z of PbZrO ₃ is less than 0.350 or more than 0.830, the electromechanical coupling coefficient (Kp) will be less than 20%,
Practically sufficient values cannot be obtained. The ferroelectric ceramic composition can be manufactured by a conventionally known method, but since it is sintered at a firing temperature of 1210 to 1250°C, which is relatively lower than conventional methods, the amount of lead evaporated during firing is small. Since the ratio deviation is controlled, reproducibility is good, and therefore mass production is excellent. In addition, by selecting the composition within the range of the polygon, any low Qm within the range of 90 to 300 can be obtained.
At the same time, the electromechanical coupling coefficient (Kp) and relative permittivity (ε _T33 /ε ₀ ) are 20 to 55%, respectively.
It is possible to obtain porcelain exhibiting low values in the range 300-1500. Therefore, ceramic filters of various bands can be manufactured using porcelain of the same composition, which is extremely useful industrially. Furthermore, when a ceramic filter is manufactured using this porcelain, the stability of the characteristics of the porcelain is good, so a filter with very good center frequency stability can be obtained. Examples of the present invention will be described below. Examples PbO or Pb ₃ O ₄ , Y ₂ O ₃ as raw materials,
Sb ₂ O ₃ , TiO ₂ and ZrO ₂ were weighed and mixed to have the composition shown in Table 1, and then mixed in a pot mill to approx.
After wet mixing for 20 hours, drying and then 850
Calcinate at ~950℃ for 2 hours. After pulverizing the calcined raw material, an appropriate amount of a known binder is added, wet-mixed in a pot mill for about 10 hours, and granulated through an 80-mesh sieve. The powder thus obtained was molded into a disk with a diameter of 22 mm and a thickness of 1.1 mm at a pressure of 700 to 1000 Kg/cm ² and fired at the firing temperature shown in Table 1 for 2 hours to produce ferroelectric porcelain. Obtain a sample of Silver electrodes were baked on both surfaces of this sample, and a DC electric field of 1.0 to 3.0 KV/mm was applied in insulating oil at 80° C. to polarize the sample, and its electrical characteristics were measured. The results obtained are shown in Table 1. The piezoelectric properties of the sample were measured using an IRE standard circuit, and the dielectric constant was measured using a capacitance bridge. In Table 1, * indicates a composition outside the scope of the present invention, and symbols A, B, C, D, E, and F correspond to the same symbols in FIG. 1, respectively. From the results in Table 1, the ferroelectric ceramics according to the present invention have a low Qm of 90 to 300, a Kp of 20 to 55%, and a specific dielectric constant of any value within the range of 300 to 1500. You can see what you can get.

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[Table] Next, 0.04Pb(Y _1/2 Sb _1/2 )O ₃ −0.53PbZrO ₃ −
_0.43PbTiO3 , and 0.02Pb(Y1 _/ 2Sb1 _/2 ) _O3−
Samples with each composition of _{0.51PbZrO3 −0.47PbTiO3} ,
141 and 142 and for comparison (Pb _0.96
Sr _0.04 ) (Zr _0.05 Ti _0.46 ) O ₃ + 0.03 mol% Sb ₂ O ₃ and (Pb _0.92 Sr _0.08 ) (Zr _0.52 Ti _0.48 ) O ₃ + 0.03 mol%
Comparative samples 1 and 2 having respective compositions of Nb ₂ O ₅ were prepared in the same manner as in the examples, and each of the obtained ceramics was used to obtain an energy trapping type ceramic filter with a center frequency of 10.7 MHz. Figure 2 shows the attenuation characteristics of the filter of sample 141. Thermal cycle tests were repeated for each of the obtained filters in the temperature range of -55°C to +85°C, and changes in the center frequency, 3 dB pass band width, and 20 dB pass band width were examined. In this thermal cycle test, each filter was first cooled to -55°C and held for several minutes, then heated to +85°C in a few seconds, held at the same temperature for several minutes, and then cooled to -55°C in a few seconds.
The cooling process is repeated as one cycle. The results are shown in FIGS. 3 to 5. As can be seen from the results shown in Figures 3 to 5, even after repeating the thermal cycle test 100 times, the product using the porcelain according to the present invention has a higher center frequency and 3 dB passthrough than the conventional comparative example using porcelain. Changes in bandwidth and 20dB passband width are extremely small, and the characteristics are extremely stable.

[Brief explanation of drawings]

FIG. 1 is a triangular diagram showing the composition range of the ferroelectric ceramic composition of the present invention, FIG. 2 is a graph showing the attenuation characteristics of a ceramic filter using the ferroelectric ceramic according to the present invention, and FIG. 3 is a graph showing the composition range of the ferroelectric ceramic composition of the present invention. Graphs showing changes in center frequencies of ceramic filters using ferroelectric ceramics according to the invention and conventional ferroelectric ceramics due to thermal cycle tests. Figures 4 and 5 show their 3 dB passband width and 20 dB passband, respectively. It is a graph showing a change in width due to a thermal cycle test.

Claims (1)

[Claims] 1 General formula: xPb(Y _1/2 Sb _1/2 )O ₃ −yPbTiO ₃ −zPbZrO ₃ (where x, y, and z are the molar ratios of each component, and x+
y+z=1.00, 0.005≦x≦0.200, 0.140≦y≦
Satisfies 0.620, 0.350≦z≦0.830. ) and has a composition within the range surrounded by the polygon ABCDEF shown in Figure 1,
A ferroelectric ceramic composition in which the composition at each vertex of the polygon is as shown below. x y z A 0.200 0.450 0.350 B 0.030 0.620 0.350 C 0.005 0.615 0.380 D 0.005 0.165 0.830 E 0.030 0.140 0.830 F 0.200 0.270 0 .530