JP5349146B2 - Dielectric ceramics and dielectric resonator - Google Patents

Description

  The present invention relates to a dielectric ceramic having a high relative dielectric constant εr (ratio to the dielectric constant εo of vacuum) and a sharpness of resonance (quality factor) Q value in a high frequency region including microwaves and / or millimeter waves, and the like. The present invention relates to a dielectric resonator.

  A resonator is incorporated in a mobile phone relay base station or BS antenna. Dielectric ceramics are used at the core of the resonator. Characteristics required for this dielectric ceramic include a relative dielectric constant εr, a Q value obtained as an inverse of dielectric loss, and a temperature coefficient τf of a resonance frequency. Due to differences in the design of resonators used in base stations such as mobile phones and BS antennas, the dielectric constant required for dielectric ceramics varies, and in particular for dielectric ceramics having a relative dielectric constant of about 45, a high Q is required. The demand for a good value and a good temperature coefficient τf of the resonance frequency has increased.

  As such dielectric ceramics having a relative dielectric constant εr of about 45, Patent Document 1 contains Ln, Al, Ca and Ti, and SrO and / or BaO added (Ln is at least one kind or more) Rare earth elements) have been proposed.

Japanese Patent No. 3274950

  In recent years, there has been an increasing demand for dielectric ceramics having a relative dielectric constant εr of about 45, with a further improvement in Q value and a temperature coefficient of resonance frequency approaching 0 ppm / ° C. As a dielectric ceramic having such characteristics, a La-Al-Ca-Ti system using La as a rare earth element described in Patent Document 1 can be considered, but a desired dielectric ceramic can be obtained. It wasn't.

  An object of the present invention is to add a suitable amount of BaO to a La—Al—Ca—Ti system to obtain a dielectric constant εr and a high Q value in the vicinity of 45, and a temperature coefficient of resonance frequency close to 0 ppm / ° C. It is to obtain a body ceramic and to obtain a resonator using this.

The dielectric ceramic according to one embodiment of the present invention has a composition formula of αLa ₂ O _x · βAl ₂ O ₃ ·
When expressed as γCaO · δTiO ₂ (where 3 ≦ x ≦ 4), the barium content is converted to oxide with respect to 100 mol parts of the components whose molar ratios α, β, γ, and δ satisfy the following formula: in not more than 0.001 parts by mole or more 0.009 mol part, and characterized in that it comprises a single CaTiO ₃ crystals.

0.16 ≦ α ≦ 0.21
0.16 ≦ β ≦ 0.22
0.29 ≦ γ ≦ 0.36
0.29 ≦ δ ≦ 0.37
(However, α + β + γ + δ = 1)
A dielectric resonator according to an aspect of the present invention is characterized in that the dielectric ceramic is used as a dielectric material.

  According to the dielectric ceramics and dielectric resonator of the present invention, the relative dielectric constant εr shows a value around 45, a high Q value is obtained, and the temperature coefficient of the resonance frequency in the temperature range of −40 to 85 ° C. Can be brought close to 0 ppm / ° C., and good performance can be stably maintained over a long period even in a place where the temperature difference is severe.

It is a partial sectional view showing typically an example of a dielectric resonator concerning one form of the present invention.

The dielectric ceramic according to one embodiment of the present invention will be described below. This dielectric ceramic contains La, Al, Ca, and Ti. When the composition formula is expressed as αLa ₂ O _x · βAl ₂ O ₃ · γCaO · δTiO ₂ (where 3 ≦ x ≦ 4), The ratios α, β, γ, and δ satisfy the following formula. 0.16 ≦ α ≦ 0.21, 0.16 ≦ β ≦ 0.22, 0.29 ≦ γ ≦ 0.36, 0.29 ≦ δ ≦ 0.37 and α + β + γ + δ = 1 are satisfied. Furthermore, with respect to 100 mol parts of this component, the barium content is not less than 0.001 mol parts and not more than 0.009 mol parts in terms of oxide, and contains a single crystal of CaTiO ₃ .

Here, regarding the temperature coefficient τf of the resonance frequency, 0.001 mol part or more of barium in terms of oxide is 0 with respect to 100 mol part of the La—Al—Ca—Ti dielectric ceramic which is the main component of the composition range. It is optimized to be less than 0.009 mole part and less than the conventional barium addition amount, and CaTiO ₃ crystals are precipitated in the dielectric ceramic.

  With this configuration, the dielectric ceramic of the present embodiment has a relative dielectric constant εr of around 45, and a high Q value and a temperature coefficient τf of 0 ppm / ° C. or a resonance frequency close to this value. That is, the temperature coefficient of the resonance frequency close to 0 ppm / ° C. or this value in the temperature range of −40 to 85 ° C. can be obtained. In addition, if such a dielectric ceramic is used as a resonator in, for example, a mobile phone base station or a BS antenna, the performance change can be minimized even in a place where the temperature changes rapidly. It becomes possible.

As described above, the reason why the temperature coefficient τf of the resonance frequency close to 0 ppm / ° C. can be obtained is that the amount of barium that easily forms a compound in the dielectric ceramic sintered body is reduced to suppress the formation of a different phase. This is because a CaTiO ₃ crystal having a temperature coefficient τf of a positive resonance frequency is precipitated in the dielectric ceramics, and the temperature coefficient τf is adjusted. Moreover, if CaTiO ₃ crystal is precipitated, the temperature coefficient τf up to −40 to 25 ° C. and the temperature coefficient τf up to 25 to 85 ° C. can be brought to 0 ppm / ° C. or close to this value under any conditions. Thus, a dielectric ceramic having a substantially constant temperature coefficient of resonance frequency in the range of −40 to 85 ° C. can be obtained.

In the conventional La—Al—Ca—Ti dielectric ceramic sintered body, both the LaAlO ₃ raw material and the CaTiO ₃ raw material are finely pulverized and used as fine powder having an average particle diameter of about 1 μm. For this reason, CaTiO ₃ and LaAlO ₃ are uniformly solid-solved with each other, and the precipitation of CaTiO ₃ crystals alone in the sintered body is suppressed.

In this embodiment, the CaTiO ₃ material was finely pulverized to an average particle size of about 1 [mu] m, relative to the total weight of CaTiO ₃ material the CaTiO ₃ raw material consisting of another average particle diameter 3μm or more coarse particles previously prepared were the finely pulverized Then, a CaTiO ₃ raw material that is added and mixed in a proportion of 10 to 40% and is distributed is used. Thereby, a part of solid solution of CaTiO ₃ and LaAlO ₃ is suppressed, and CaTiO ₃ crystals are precipitated in the La—Al—Ca—Ti based dielectric ceramic sintered body. When the average particle diameter of the coarse CaTiO ₃ raw material is 3 μm or more, CaTiO ₃ crystals are easily precipitated in the sintered body, and a temperature coefficient τf of a resonance frequency near 0 ppm / ° C. is easily obtained.

  Here, the reason why the molar ratios α, β, γ, and δ of each component are limited to the above ranges is as follows.

  First, 0.16 ≦ α ≦ 0.21 is set because the relative permittivity (εr) is large, the Q value is high, and the absolute value of the temperature coefficient τf of the resonance frequency can be reduced within this range. is there. In particular, the lower limit of α is preferably 0.17, and the upper limit of α is preferably 0.20.

  Further, the reason why 0.16 ≦ β ≦ 0.22 is set is that, if it is within this range, the relative dielectric constant (εr) is large, the Q value is high, and the absolute value of τf can be decreased. In particular, the lower limit of β is preferably 0.17, and the upper limit of β is preferably 0.20.

  Further, the reason why 0.29 ≦ γ ≦ 0.36 is set is that if it is within this range, the relative dielectric constant (εr) is large, the Q value is high, and the absolute value of τf can be small. In particular, the lower limit of γ is preferably 0.30, and the upper limit of γ is preferably 0.35.

  Further, the reason why 0.29 ≦ δ ≦ 0.37 is set is that the relative permittivity (εr) is large, the Q value is high, and the absolute value of τf can be decreased within this range. In particular, the lower limit of δ is preferably 0.30, and the upper limit of δ is preferably 0.35.

  The addition amount of barium to 0.001 mol part or more and 0.009 mol part or less in terms of oxide with respect to 100 mol parts of the main component is effective in improving the relative dielectric constant εr and Q value. This is because the sinterability does not deteriorate. When the amount exceeds 0.009 mole part, the added barium component tends to form a compound that is different from the impurities in the dielectric ceramic, and the values of the relative dielectric constant εr, the Q value, and the temperature coefficient τf of the resonance frequency. Reduce.

  As for the amount of barium in the dielectric ceramic, a part of the dielectric ceramic is pulverized, and the obtained powder is dissolved in a solution such as hydrochloric acid, and then an IPC emission spectroscopic analyzer (manufactured by Shimadzu Corporation: ICPS-8100). ) To measure the amount of Ba and convert it to oxide. The error of the measuring device is n ± √n where n is the analysis value.

Whether or not the CaTiO ₃ crystal is present alone in the dielectric ceramic is determined using, for example, a wavelength dispersive X-ray microanalyzer device (JXA-8100 manufactured by JEOL Ltd.), on any surface of the dielectric ceramic. This can be confirmed by examining the distribution of Ca and Ti elements. CaTiO ₃ crystals are present in portions where the detection ratio of Ca and Ti elements is higher than that of other surfaces.

Further, the ratio of CaTiO ₃ crystals on the surface of the dielectric ceramic is 3% or more and 15% or less in terms of area ratio. If the ratio of the CaTiO ₃ crystal is within the above range in terms of area ratio, the absolute value can be within the range of the temperature coefficient of the resonance frequency of 0 to 2 ppm / ° C., which is closer to 0 pp m / ° C. it can.

Here, as a method of measuring the area ratio of the ratio of CaTiO ₃ crystal on an arbitrary surface, for example, with a wavelength dispersion X-ray microanalyzer device (JXA-8100 manufactured by JEOL Ltd.) used in the confirmation of the CaTiO ₃ crystal. Measure the distribution state of Ca and Ti elements in an area of 100 μm × 100 μm on any surface of dielectric ceramics at two or more locations, and the area with respect to the total measurement area of the portion where the detection ratio of Ca and Ti elements is higher than other surfaces It is possible to measure by calculating the ratio, adding up and dividing by the number of measurement points.

Further, in the dielectric ceramic of the present embodiment, the lattice constant a of the CaTiO ₃ crystal calculated by the Rietveld method is 5.409 or more and 5.415 or less, b is 5.408 or more and 5.416 or less, and c is 7 .643 or more and 7.656 or less. Thereby, the solid solution state of barium is stabilized, and it becomes possible to obtain a dielectric ceramic exhibiting more excellent dielectric properties.

The Rietveld method is a method of refining the crystal structure parameters from the X-ray diffraction pattern of the substance. By giving the measured X-ray diffraction pattern and crystal structure data as inputs, and moving the structure parameters, This is a method of refinement so that the calculated diffraction intensity and the measured diffraction intensity match as much as possible. In the present embodiment, analysis software RIETON is used, for example, as a crystal structure model (Ca _0.7 Nd _0.3 ) (Ti _0.7 Al _0.3 ) O ₃ (crystal system: orthohombic, space group: No. 62). , Lattice constant: a = 5.3803Å, b = 5.4003Å, c = 7.614), and the lattice constant can be calculated. The X-ray diffraction chart is measured with, for example, an X-ray diffractometer (X'Pert PRO manufactured by PANalytical), measurement range: 2θ = 10 ° to 100 °, radiation source: CuKα ₁ , output voltage, current: 45 kV, 40 mA. It is possible to measure under the following conditions.

  In addition, the dielectric ceramic of the present embodiment is characterized in that the void ratio is 4% or less. Thereby, since dielectric ceramic is densified more, the fall of mechanical characteristics, such as intensity | strength and hardness, can be suppressed. Therefore, the dielectric ceramics are less likely to be broken, broken, damaged, etc. due to an impact or the like during handling, dropping, mounting in the resonator, or after installation in each mobile phone base station or the like. More preferably, the void ratio is 3% or less.

  The void ratio is measured, for example, as follows. First, several portions of the ceramic surface and internal cross section of dielectric ceramics are photographed or photographed with a metal microscope or SEM adjusted to an arbitrary magnification so that a range of 100 μm × 100 μm can be observed. Then, by analyzing this photograph or image with an image analysis device, it is possible to calculate several void ratios and obtain this average value. As an image analysis apparatus, for example, LUZEX-FS manufactured by Nireco Corporation may be used.

  Further, the dielectric ceramic of the present embodiment may contain Fe, Sr, Na, Ca, K, Si, Pb, Ni, Cu or Mg as inevitable impurities in total of 1% by mass or less in terms of oxides. Thereby, it is suppressed that the value of various dielectric characteristics falls, and the fall of the mechanical characteristics as a sintered compact is suppressed.

  Next, the manufacturing method of the dielectric ceramic of this embodiment is demonstrated. For example, the following steps (1) to (7) are performed.

(1) As starting materials, high purity lanthanum oxide (La ₂ O ₃ ), high purity aluminum oxide (Al ₂ O ₃ ), calcium carbonate (CaCO ₃ ) and titanium oxide (TiO ₂ ) powders are prepared. . Thereafter, La ₂ O ₃ and Al ₂ O ₃ are first weighed to a desired ratio, then pure water is added, and zirconia balls are added for 1 to 100 hours until the average particle size of the mixed raw material becomes 2.0 μm or less. Etc. to obtain a mixture by wet mixing and pulverization with a ball mill using the like. In parallel with this, CaCO ₃ and TiO ₂ are also subjected to the same process to obtain a mixture (primary preparation).

(2) This mixture is dried and calcined at 1100 to 1300 ° C. for 1 to 10 hours, respectively, to obtain a calcined product of LaAlO ₃ and CaTiO ₃ .

(3) The obtained calcined product is wet pulverized with a ball mill or the like until the average particle size becomes 1 to 2 μm, and the resulting mixture is transferred to a stainless steel container, dried, mesh-passed, and LaAlO ₃ , CaTiO _3. Get the ingredients. As for the CaTiO ₃ raw material, in order to precipitate CaTiO ₃ crystals in the dielectric ceramic after firing, a CaTiO ₃ raw material having an average particle diameter of 3 μm or more consisting of coarse particles is prepared in advance, and the crushed CaTiO ₃ is prepared. Those added at a rate of 10 to 40% by mass with respect to the _three raw materials are used.

(4) Each raw material of LaAlO ₃ and CaTiO ₃ is weighed in a desired ratio, and BaTiO ₃ having a high purity and an average particle size of 0.5 to ₃ μm is added thereto, and the barium content is 0.001 mol part in terms of oxide. After weighing and mixing so as to be 0.009 mol part or less and adding pure water, wet mixing is performed by a ball mill using zirconia balls or the like (secondary preparation).

  (5) 3-10 mass% binder is added and then dehydrated, and then granulated or sized by, for example, a spray drying method, and the resulting granulated product or sized powder is subjected to, for example, a die press It is formed into an arbitrary shape by a method such as a cold isostatic pressing method or an extrusion molding method. The form of the granulated body or the sized powder may be not only a solid such as a powder but also a solid such as a slurry or a liquid mixture. In this case, the liquid may be a liquid other than water, for example, IPA (isopropyl alcohol), methanol, ethanol, toluene, acetone or the like.

  (6) The obtained molded body is fired at 1500 ° C. to 1700 ° C. in the air for 5 to 10 hours. More preferably, baking is performed at 1550 to 1650 ° C.

  (7) The obtained fired body is heat-treated at a temperature of 1500 to 1700 ° C. and a pressure of 300 to 3000 atm for 1 minute to 100 hours in a gas containing 5 to 30% by volume of oxygen. More preferably, heat treatment is performed at a temperature of 1550 to 1650 ° C. and a pressure of 1000 to 2500 atmospheres for 20 minutes to 3 hours.

  Next, an example of a dielectric resonator using the dielectric ceramic of the present embodiment will be described below. As shown in FIG. 1, a TE mode type dielectric resonator 1 includes an input terminal 3 and an output terminal 4 on opposite sides of an inner wall of a metal case 2 made of a lightweight metal such as aluminum. It is provided. A dielectric ceramic 5 using the above-described dielectric ceramics as a filter is arranged between the input / output terminal 3 and the output terminal 4 at a predetermined position on the mounting table 6. In such a dielectric resonator 1, millimeter wave and / or microwave high frequency is input from the input terminal 3, and the high frequency is confined in the dielectric ceramic 5 by reflection at the boundary between the dielectric ceramic 5 and the free space. Resonance occurs at a specific frequency. This signal is then electromagnetically coupled to the output terminal 4 and output. As described above, the dielectric ceramic of the present embodiment can be suitably used as various resonator materials used for mobile phone base stations and BS antennas.

  The dielectric ceramic of the present embodiment is not limited to the above, and the input terminal 3 and the output terminal 4 may be directly provided on the dielectric ceramic 5. The dielectric porcelain 5 is a resonance medium having a predetermined shape made of the dielectric ceramic of the present embodiment, and the shape thereof is a rectangular parallelepiped, a cube, a plate, a disk, a cylinder, a polygonal column, or other resonance. Any three-dimensional shape is possible. The frequency of the input high frequency signal is about 500 MHz to 500 GHz, and the resonance frequency is preferably about 2 GHz to 80 GHz in practice.

  Further, the dielectric ceramic of the present embodiment may be used as a dielectric substrate material for MIC (Monolithic IC), a dielectric waveguide material, or a dielectric material of a multilayer ceramic capacitor in addition to various resonator materials. Good.

  Next, examples will be described.

  Samples were prepared by changing the molar ratios α, β, γ and δ of the La—Al—Ca—Ti-based material and the amount of barium added, and the relative permittivity εr, Q value and temperature coefficient of the resonance frequency were measured. did. Details of the manufacturing method and the characteristic measuring method will be described below.

La ₂ O ₃ , Al ₂ O ₃ , CaCO ₃ and TiO ₂ having a purity of 99.5% by mass or more were prepared as starting materials.

After weighing each material to the ratio shown in Table 1, La ₂ O ₃ and Al ₂ O ₃ were mixed, and CaCO ₃ and TiO ₂ were added to each other in a separate ball mill, and mixed. The mixture was wet-mixed and pulverized by a ball mill using zirconia balls until the average particle size of the raw material became 2 μm or less, and primary mixing was performed to obtain two types of mixtures.

After drying each mixture to obtain a calcined LaAlO _3, CaTiO ₃ precalcination at 1200 ° C..

The obtained two types of calcined products are wet pulverized and pulverized using a ball mill so that both LaAlO ₃ and CaTiO ₃ calcined products have an average particle diameter of 1 to 2 μm to obtain LaAlO ₃ raw materials and CaTiO ₃ raw materials. It was. Note that the CaTiO _3, and a total mass with respect to the addition and mixing of CaTiO ₃ raw material having an average particle diameter of 3μm consisting previously prepared coarse in a ratio of 30 mass% CaTiO ₃ raw material after milling.

  Then, both are mixed, and as a barium component, a commercially available barium carbonate having an average particle diameter of 1 μm is added, pure water is added, and wet mixing is performed by a ball mill using zirconia balls or the like for 1 to 100 hours to obtain a secondary preparation. Several types of slurry were obtained.

  Next, 1 to 10% by mass of a binder was further added to the slurry and mixed for a predetermined time, followed by dehydration, and the slurry was spray granulated with a spray dryer to obtain a secondary material. This secondary material was molded into a cylindrical body having a diameter of 20 mm and a height of 15 mm by a die press molding method to obtain a molded body.

  The obtained molded body was held in the atmosphere at 1500 ° C. to 1700 ° C. for 10 hours and fired. 1-27 were obtained. In addition, after baking, these samples grind | polished upper and lower surfaces and a part of side surface, and ultrasonically cleaned in acetone.

As a comparative example, the sample No. manufactured in the same process as described above except that no barium component was added. 28 were also prepared. As another comparative example, a sample except without the addition of CaTiO ₃ raw material consisting of coarse particles having an average particle size of 3μm in CaTiO ₃ raw material after pulverization manufactured through the same processes No. 29 was also prepared.

  Next, these sample Nos. Dielectric characteristics were measured for 1 to 29. The dielectric properties were measured by measuring the relative dielectric constant εr and Q values at a measurement frequency of 3.5 to 4.5 GHz by a cylindrical resonator method. The Q value was converted to a Q value at 1 GHz from the general relationship (Q value) × (measurement frequency f) = constant that is generally established in a microwave dielectric.

Also, the presence of CaTiO ₃ crystal, using wavelength dispersive X-ray microanalyzer apparatus (JEOL JXA-8100), of any surface of the sample Ca, check the distribution of Ti element, the other The confirmation was carried out on the assumption that CaTiO ₃ crystals exist in the portion where the detection ratio of Ca and Ti elements is higher than the surface.

  Table 1 shows the results showing the critical significance of the composition range and the amount added in the comparative example and the La—Al—Ca—Ti-based material containing barium of the present embodiment. In addition, the addition amount (= content) of barium was converted into BaO which is an oxide.

  In Table 1, the relative permittivity εr is in the range of 40.0 to 48.0, the Q value is 30000 or more, the temperature coefficient τf of the resonance frequency is in the range of −10 to +10, 25 to 85 ° C., and −40 The difference in temperature coefficient within each temperature range of ˜25 ° C. was an absolute value of 2 or less, which was regarded as a good range.

  As shown in Table 1, the sample No. For 1 and 6, the relative dielectric constant εr was outside the range of 40 to 48, and the temperature coefficient of the resonance frequency was also outside the range of −10 to +10.

  In particular, the sample No. whose β value is not within the preferred range. 7 and 10, the relative dielectric constant εr was outside the range of 40.0 to 48.0, and the temperature coefficient of the resonance frequency was outside the range of −10 to +10.

  In addition, the sample No. whose γ value is not within the preferred range. For sample No. 11, the Q value is 30000 or less, and similarly, the sample No. For No. 17, the relative dielectric constant εr was outside the range of 40.0 to 48.0, the Q value was 30000 or less, and the temperature coefficient of the resonance frequency was outside the range of −10 to +10.

  In addition, the sample No. where the value of δ is not in the preferred range. For 18, the relative dielectric constant εr was outside the range of 40.0 to 48.0, and the Q value was 30000 or less. Similarly, the sample No. whose δ value is not in the preferred range. For No. 21, the temperature coefficient of the resonance frequency was outside the range of −10 to +10.

In addition, Sample No. in which the barium component is not in a suitable range. For No. 22 , the absolute value difference of the temperature coefficients of the resonance frequencies of 25 to 85 ° C. and −40 to 25 ° C. exceeds 2, and sample no. For No. 27, the temperature coefficient of the resonance frequency was outside the range of −10 to +10.

  In addition, sample No. manufactured as a comparative example. For No. 28, since it did not contain a barium component, the sinterability was lowered and the dielectric ceramic could not be sufficiently densified, and both the relative permittivity εr and Q values were low.

In Sample No. I was not used CaTiO ₃ material arranged grain without adding CaTiO ₃ raw material coarse particles was prepared as a comparative example For No. 29, the temperature coefficient of the resonance frequency shows a value outside the range of −10 to +10, and the absolute value difference of the temperature coefficient of the resonance frequency of 25 to 85 ° C. and −40 to 25 ° C. shows a value exceeding 2. It was.

  Compared with these samples, sample Nos. Within the scope of the present invention. 2 to 5, 8, 9, 12 to 16, 19, 20, 23 to 26, the relative permittivity εr, the Q value, the temperature coefficient of the resonance frequency, the resonance frequency of 25 to 85 ° C. and the resonance frequency of −40 to 25 ° C. The absolute value difference of temperature coefficient was within the range.

From the above results, the molar ratios α, β, γ, and δ (rounded to the third decimal place) are 0.16 ≦ α ≦ 0.21, 0.16 ≦ β ≦ 0.22, 0.29 ≦ γ. ≦ 0.36, 0.29 ≦ δ ≦ 0.37 and α + β + γ + δ = 1 (rounded to the nearest decimal place), and barium is 0.001 mol part or more and 0.009 mol part or less in terms of oxide, and It has been found that it is preferable to include CaTiO ₃ crystals.

Next, samples in which the area ratio of the CaTiO ₃ crystal was variously changed were prepared, and a test for measuring the temperature coefficient of the resonance frequency was performed.

The prepared samples are α, β, γ, δ, and the amount of barium added. 14 except that the amount of coarse CaTiO ₃ raw material (shown as CaTiO ₃ coarse particles in the table) was changed as shown in Table 2 and the composition ratio was the same as that of Example 1. ing.

  Then, the temperature coefficient of the resonance frequency was measured by the same method as in Example 1.

  The results are shown in Table 2.

From Table 2, sample No. 2 with a low CaTiO ₃ coarse grain addition amount of 5% by mass and a CaTiO ₃ area ratio of less than 3% and 2% is low. For 30, the temperature coefficient τf itself was within the range of −10 to +10 ppm / ° C., but the absolute value difference between the temperature coefficients of the resonance frequencies of 25 to 85 ° C. and −40 to 25 ° C. was as high as 2 ppm / ° C.

In addition, the amount of CaTiO ₃ coarse particles added was as high as 45% by mass, and the area ratio of CaTiO ₃ exceeded 15% and was as high as 20%. Regarding No. 35, since the addition amount of CaTiO ₃ coarse particles was too large, the sinterability was lowered and the mechanical strength was lowered, and the temperature coefficient τf of the resonance frequency was also increased.

  Compared to these, sample No. As for 31 to 34, there was no decrease in sinterability, and an excellent temperature coefficient τf and an absolute value difference in temperature coefficients of resonance frequencies of 25 to 85 ° C. and −40 to 25 ° C. were shown.

1: Dielectric resonator 2: Metal case 3: Input terminal 4: Output terminal 5: Dielectric porcelain 6: Mounting table

Claims (5)

When the composition formula is expressed as αLa ₂ O _x · βAl ₂ O ₃ · γCaO · δTiO ₂ (where 3 ≦ x ≦ 4), the molar ratio α, β, γ, δ satisfies the following formula: 100 mol A dielectric ceramic characterized in that the content of barium is 0.001 mol part or more and 0.009 mol part or less in terms of oxide with respect to parts, and contains a single CaTiO ₃ crystal.
0.16 ≦ α ≦ 0.21
0.16 ≦ β ≦ 0.22
0.29 ≦ γ ≦ 0.36
0.29 ≦ δ ≦ 0.37
(However, α + β + γ + δ = 1) 2. The dielectric ceramic according to claim 1, wherein a ratio of the CaTiO ₃ crystal on the surface is 3% or more and 15% or less in terms of area ratio. The dielectric ceramic according to claim 1 or 2, wherein the lattice constants a, b, and c of the CaTiO ₃ crystal calculated by a Rietveld method satisfy the following formula.
5.409 ≦ a ≦ 5.415
5.408 ≦ b ≦ 5.416
7.643 ≦ c ≦ 7.656   4. The dielectric ceramic according to claim 1, wherein a void ratio is 4% or less.   5. A dielectric resonator comprising the dielectric ceramic according to claim 1 as a dielectric material.

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