DIELECTRIC INORGANIC COMPOSITION

Abstract

Provided is a dielectric body having a high dielectric constant and a change rate of the dielectric constant of 30% or less, in a temperature range from −50° C. to 350° C.

An inorganic substance contains an oxide crystal including A and M (the A being one or more of P, Ge, and V, and the M being one or more of Nb and Ta), wherein the dielectric constant is 500 or more. In the inorganic substance, the oxide crystal is one or more of PNb.sub.9O.sub.25, P.sub.2.5Nb.sub.18O.sub.50 and GeNb.sub.9O.sub.25, GeNb.sub.18O.sub.47, GeNb.sub.19.144O.sub.50, VNb.sub.9O.sub.25, VNb.sub.9O.sub.24.9, PTa.sub.9O.sub.25, GeTa.sub.9O.sub.25, VTa.sub.9O.sub.25, and solid solutions thereof.

Claims

1. An inorganic substance containing an oxide crystal including A and M (the A being one or more of P, Ge, and V, and the M being one or more of Nb and Ta), wherein a ratio of the A and the M is in a range from 0.01 to 1.00, and a dielectric constant is 500 or more.

2. The inorganic substance according to claim 1, wherein a change rate of the dielectric constant relative to a temperature range from −50° C. to 350° C. is 30% or less.

3. The inorganic substance according to claim 1, wherein the oxide crystal is one or more of PNb.sub.9O.sub.25, P.sub.2.5Nb.sub.18O.sub.50 and GeNb.sub.9O.sub.25, GeNb.sub.18O.sub.47, GeNb.sub.19.144O.sub.50, VNb.sub.9O.sub.25, VNb.sub.9O.sub.24.9, PTa.sub.9O.sub.25, GeTa.sub.9O.sub.25, VTa.sub.9O.sub.25, and solid solutions thereof.

4. The inorganic substance according to claim 2, wherein the oxide crystal is one or more of PNb.sub.9O.sub.25, P.sub.2.5Nb.sub.18O.sub.50 and GeNb.sub.9O.sub.25, GeNb.sub.18O.sub.47, GeNb.sub.19.144O.sub.50, VNb.sub.9O.sub.25, VNb.sub.9O.sub.24.9, PTa.sub.9O.sub.25, GeTa.sub.9O.sub.25, VTa.sub.9O.sub.25, and solid solutions thereof.

5. A dielectric body including the inorganic substance according to any one of claims 1 to 4.

6. The dielectric body according to claim 5, wherein the dielectric body is a ferroelectric body.

7. A condensor including the dielectric body according to claim 5 or 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a graph showing XRD-patterns of Examples 1 and 2.

[0020] FIG. 2 is a graph showing a relationship between a dielectric constant and a frequency in Examples 1 and 2.

[0021] FIG. 3 is a graph showing a relationship between a dielectric constant and a temperature in Example 4.

[0022] FIG. 4 is a graph showing a hysteresis curve of Example 4.

[0023] FIG. 5 is a graph showing a relationship between a dielectric constant and a frequency in Example 5.

[0024] FIG. 6 is a graph showing a relationship between a dielectric constant and a temperature in Example 5.

[0025] FIG. 7 is a graph showing a relationship between a dielectric constant and a frequency in Example 6.

[0026] FIG. 8 is a graph showing a relationship between a dielectric constant and a temperature in Example 6.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0027] <Dielectric Body According to Present Disclosure>

[0028] An inorganic composition according to the present disclosure will be described.

[0029] The inorganic composition according to the present disclosure is useful as a dielectric body, and is a ceramic containing oxide crystals including A and M (the A being one or more of P, Ge, and V, and the M being one or more of Nb and Ta). If a ratio of the A and the M is adjusted, it is possible to realize an inorganic composition having characteristics in which the dielectric constant is 500 or more and the dielectric constant varies little over a wide temperature range from −50 to 350° C. In order to obtain excellent dielectric properties, the ratio of the A and the M is preferably in a range from 0.01 to 1.00, more preferably in a range from 0.03 to 0.50, and most preferably in a range from 0.04 to 0.20. Among the oxide crystals including the A and the M, in particular, PNb.sub.9O.sub.25, P.sub.2.5Nb.sub.18O.sub.50 and GeNb.sub.9O.sub.25, GeNb.sub.18O.sub.47, GeNb.sub.19.144O.sub.50, VNb.sub.9O.sub.25, VNb.sub.9O.sub.24.9, PTa.sub.9O.sub.25, GeTa.sub.9O.sub.25, VTa.sub.9O.sub.25, and solid solutions thereof have excellent characteristics and thus are preferably included in the inorganic composition.

[0030] In addition to the components mentioned above, for example, SiO.sub.2, GeO.sub.2, B.sub.2O.sub.3, Al.sub.2O.sub.3, ZnO, Bi.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, V.sub.2O.sub.5, Ta.sub.2O.sub.5, WO.sub.3, alkali metal oxides, alkaline earth metal oxides, rare earth oxides, and transition metal oxides may be included in the inorganic composition according to the present disclosure. These components act as sintering aids and may exist alone, or may be dissolved as solid solutions in the above-mentioned crystals, or may form new crystals with the elements constituting the above-mentioned crystals. If these sintering aids are introduced, the firing temperature is lowered or a solid solution is formed, and thus, it is possible to improve the dielectric properties.

[0031] Glass may be added to the inorganic composition according to the present disclosure. Glass acts as a sintering aid and has an effect of lowering the firing temperature.

[0032] The inorganic composition according to the present disclosure can form a composite with other dielectric crystals, such as tungsten bronze type crystals, perovskite type crystals, CaZrO.sub.3 crystals, SrZrO.sub.3 crystals, BaTi.sub.2O.sub.5 crystals, and CaTi.sub.2O.sub.5 crystals. With a composite with these dielectric bodies, it may be possible to obtain dielectric properties as designed. Note that the above-mentioned tungsten bronze type crystals particularly preferably include one or more selected from the group consisting of MNb.sub.2O.sub.6(M: Ca, Sr, Ba), M.sub.2RNb.sub.5O.sub.15 (M: Ca, Sr, Ba; R: Na, K), and K.sub.2LnNb.sub.5O.sub.15 (Ln: Y, Ce, Sm, Eu, La, Gd, Tb, Dy, Ho, Bi) crystals and solid solutions thereof. The above-mentioned perovskite type crystals particularly preferably include one or more selected from the group consisting of RNbO.sub.3, RTaO.sub.3, (Bi.sub.0.5, R.sub.0.5)TiO.sub.3 (R: Na, K), and MTiO.sub.3 (M: Ca, Sr, Ba) crystals and solid solutions thereof.

[0033] The inorganic composition according to the present disclosure preferably has a dielectric constant of 500 or more, more preferably 650 or more, still more preferably 800 or more, and most preferably 900 or more, at a frequency of from 1 kHz to 100 kHz.

[0034] In the inorganic composition according to the present disclosure, a change rate of the dielectric constant relative to a temperature range from −50° C. to 350° C. at 1 kHz and/or 100 kHz is preferably 30% or less, more preferably 20% or less, still more preferably 15% or less, and most preferably 10% or less, in the temperature range from −50° C. to 350° C.

[0035] Note that, in the present disclosure, the dielectric constant and the dielectric loss are measured over a frequency of from 100 Hz to 1 MHz by using an LRC meter (4274A, manufactured by Keysight Technologies) or an impedance analyzer (for example, SI1260, manufactured by Solartron), and the values at 1 kHz or 100 kHz are used as the dielectric constant and the dielectric loss in the present disclosure.

[0036] If the inorganic composition according to the present disclosure is a dielectric ceramic, the inorganic composition has a high relative dielectric constant and the dielectric constant has good temperature characteristics in a wide temperature range from −50° C. to 350° C. Therefore, the inorganic composition according to the present disclosure can be suitably used as a high-temperature condensor. Specific examples of the high-temperature condensor include electronic components used in high-temperature environments, such as electronic components used for operating power devices including SiC or GaN as a base material, which are anticipated as vehicle-mounted devices, or for removing noise in the engine room of automobiles.

[0037] Further, a dielectric body using the inorganic composition according to the present disclosure is a ferroelectric body and is also expected to have good piezoelectric characteristics (for example, piezoelectric constant: d, electromechanical coupling coefficient: k), and thus, can also be suitably used for a piezoelectric element.

[0038] <Manufacturing Method>

[0039] A method of manufacturing the inorganic composition according to the present disclosure will be described.

[0040] Firstly, raw materials for each component constituting the inorganic composition according to the present disclosure are prepared. The raw materials of each component are not particularly limited, and may be appropriately selected from oxides and composite oxides of the components mentioned above, or various types of compounds resulting in these oxides or composite oxides obtained by firing, such as carbonates, nitrates, hydroxides, fluorides, and organic metal compounds.

[0041] Next, the prepared raw materials are weighed and mixed so as to obtain a predetermined composition ratio, to acquire a raw material mixture. Examples of the mixing method include wet mixing using a ball mill and dry mixing using a dry mixer.

[0042] The obtained raw material mixture may be granulated by adding a binder resin, to form a granulated product, or may be added with a binder resin or a solvent to form a paste to obtain a slurry. Further, the raw material mixture may be calcined before being formed into the granulated product or the slurry.

[0043] A method for forming the granulated product or the slurry is not particularly limited, but examples thereof include a sheet method, a printing method, dry forming, wet forming, and extrusion forming. For example, if dry forming is employed, the granulated product is filled in a mold and then compressed and pressed to obtain a formed body. The shape of the formed body is not particularly limited and may be appropriately determined according to application.

[0044] The obtained formed body can be fired, as needed, by any method including pressureless sintering, hot-pressing sintering, hot isostatic pressing sintering, spark plasma sintering, and microwave sintering, to obtain a ceramic dielectric body. The firing conditions may be appropriately determined according to the firing method, composition, and the like, but the firing temperature is preferably from 800° C. to 1400° C., and the holding time is preferably from several minutes to 24 hours.

[0045] The fired ceramic dielectric body may be heat-treated in air, oxygen, or a reducing atmosphere, as needed. The heat treatment reduces defects and improves the dielectric properties of the dielectric body. The temperature of the heat treatment is preferably in a range from 700° C. to 1200° C., and the treatment time is preferably in a range from 1 to 24 hours.

[0046] The ceramic dielectric body including the inorganic composition according to the present disclosure thus manufactured is suitably used for electronic components such as condensors.

[0047] In the above, a method for producing a ceramic dielectric body including a disk-shaped inorganic composition according to the present disclosure is described. However, ceramic condensors for forming the dielectric layers of multilayer type electronic components can also be produced by the green sheet method or the like. That is, powder of the dielectric body according to the present disclosure is formed into a paste, dielectric green sheet layers are formed on a carrier film by a doctor blade method or the like, and a paste for an internal electrode layer is printed on the dielectric green sheet layers in a predetermined pattern. After that, the printed green sheet layers are peeled one by one and then laminated, and then, the laminated printed green sheet layers are applied with pressure to be integrally formed, and the resultant product is fired at a temperature of about 800° C. to 1200° C. to produce the ceramic condensor.

[0048] Further, the inorganic composition according to the present disclosure can be produced as a thin film dielectric body by using a normal thin film forming method. For example, the thin film dielectric body can be formed by using a vacuum vapor deposition method, a high frequency sputtering method, a pulsed laser deposition (PLD) method, a metal organic chemical vapor deposition (MOCVD) method, a metal organic decomposition (MOD) method, a sol-gel method, a hydrothermal method, and the like.

[0049] Therefore, the inorganic composition according to the present disclosure may be employed for electronic components such as single-plate condensors, may be employed for electronic components such as multilayer type condensors, and may be employed for thin-film electronic components. Alternatively, the inorganic composition according to the present invention may be employed for a piezoelectric element.

EXAMPLES

[0050] Hereinafter, the present disclosure will be described in more detail with reference to Examples, but the present disclosure is not limited to these Examples.

Production of Example 1-4

[0051] An inorganic composition containing oxide crystals including P and Nb was produced by spark plasma sintering according to the following procedure. Firstly, powders of NH.sub.4H.sub.2PO.sub.4 and Nb.sub.2O.sub.5 as raw materials were blended at a predetermined ratio (P/Nb=0.11), filled into a polypot together with zirconia balls having a diameter of 2 mm and ethanol, mixed for 24 hours, and then, dried for 24 hours. The dried mixed powders were calcined at 1000° C. for 2 hours. The obtained calcined product was mixed, pulverized, and dried under conditions similar to that described above to obtain a dielectric powder including the inorganic composition. 4 g of this dielectric powder was taken, filled into a graphite die having an inner diameter of 20 mm, and heated at 1050° C. to 1200° C. for 5 to 12 minutes while being applied with pressure of 35 MPa in the vertical direction in a vacuum atmosphere by a spark plasma sintering device (SPS625, manufactured by Sumitomo Coal Mining Co., Ltd.), to obtain a disk-shaped dielectric body. After both sides of the obtained disk-shaped dielectric body were polished, the dielectric body was subjected to a heat treatment at 1000° C. for 4 hours while passing oxygen at 1 L/min, to be used as a sample for evaluating the physical properties. Table 1 shows the production conditions and various physical properties of the Examples.

[0052] FIG. 1 shows XRD-patterns of Examples 1 and 2. All diffraction peaks can be attributed to PNb.sub.9O.sub.25, and thus, it was clarified that the present ceramic dielectric body was formed of PNb.sub.9O.sub.25 crystals. Note that the XRD-patterns were measured using an X-ray diffractometer (manufactured by Philips, trade name: X′Pert-MPD).

[0053] FIG. 2 shows the frequency dependence of the dielectric constant in Examples 1 and 2. Note that, after gold electrodes were vapor-deposited on both sides of the sample, the dielectric constant and the dielectric loss was measured at room temperature (25° C.) by using an impedance analyzer (SI1260, manufactured by Solartron). From FIG. 2, it can be understood that the dielectric constant is 900 or more in the frequency range (100 Hz to 10.sup.6 Hz) used for measurement and does not vary significantly with the frequency. Further, in checking the dielectric loss, the dielectric loss as small as 5% or less was found in the above-mentioned frequency range.

[0054] The temperature dependence of the dielectric properties was measured by using an LCR meter in a temperature range from −30° C. to 350° C. over frequencies from 100 Hz to 100 kHz. FIG. 3 shows measurement results for Example 4 as a representative example. In FIG. 3, the dielectric constant at a frequency of 100 kHz is plotted relative to a temperature. From FIG. 3, it can be understood that the dielectric constant of the dielectric body according to the present disclosure has high values and does not vary significantly in a temperature range from −30° C. to 350° C.

[0055] To calculate a change rate (ε.sub.T) of the dielectric constant relative to a temperature, the following equation was used to obtain how much the dielectric constant varies at each temperature, using the dielectric constant at 25° C. as a reference.

ε.sub.T(%)=[(dielectric constant at target temperature−dielectric constant at 25° C.)/dielectric constant at 25° C.]×100%

[0056] The change rate (ε.sub.T) of the dielectric constant of Example 4 obtained from the above-mentioned equation is shown in FIG. 3. From FIG. 3, it can be understood that the change rate of the dielectric constant was 25% or less in the temperature range from −30° C. to 350° C., and 10% or less in a temperature range from −30° C. to 250° C.

TABLE-US-00001 TABLE 1 Examples 1 2 3 4 Composition 0.1 P.sub.2O.sub.5 and 0.1 P.sub.2O.sub.5 and 0.1 P.sub.2O.sub.5 and 0.1 P.sub.2O.sub.5 and 0.9 Nb.sub.2O.sub.5 0.9 Nb.sub.2O.sub.5 0.9 Nb.sub.2O.sub.5 0.9 Nb.sub.2O.sub.5 Sintering Temperature 1100 1150 1130 1150 conditions (° C.) Time 10 10 5 5 (Min.) Annealing Temperature 1100 1100 1000 1000 conditions (° C.) (in oxygen) Time (h) 4 4 4 4 Crystal phase PNb.sub.9O.sub.25 PNb.sub.9O.sub.25 PNb.sub.9O.sub.25 PNb.sub.9O.sub.25 Dielectric constant (100 kHz) 1162 1916 1205 1286 Dielectric loss (100 kHz) 0.03 0.05 0.04 0.04

[0057] FIG. 4 shows an electric field-polarization curve of Example 4. From FIG. 4, it was clarified that the present dielectric body was a ferroelectric body.

Production of Example 5

[0058] An inorganic composition containing oxide crystals including Ge and Nb was produced by a spark plasma sintering method according to the following procedure. Firstly, powders of GeO.sub.2 and Nb.sub.2O.sub.5 as raw materials were blended at a predetermined ratio (Ge/Nb=0.11), filled into a polypot together with zirconia balls having a diameter of 2 mm and ethanol, mixed for 24 hours, and then, dried for 24 hours. The dried mixed powders were calcined at 950° C. for 2 hours. The obtained calcined product was mixed, pulverized, and dried under conditions similar to that described above to obtain a dielectric powder including the inorganic composition. 2.5 g of this dielectric powder was taken, filled into a graphite die having an inner diameter of 15 mm, and heated at 900° C. for 5 minutes while being applied with pressure of 50 MPa in the vertical direction in a vacuum atmosphere by a spark plasma sintering device, to obtain a disk-shaped dielectric body. After both sides of the obtained disk-shaped dielectric body were polished, the dielectric body was subjected to a heat treatment at 850° C. for 4 hours while passing oxygen at 2 L/min, to be used as a sample for evaluating the physical properties.

[0059] From the analysis of the XRD-pattern, it is assumed that a GeNb.sub.19.144O.sub.50 crystal phase or a GeNb.sub.9O.sub.25 crystal phase is produced. The diffraction peaks of GeNb.sub.19.144O.sub.50 and GeNb.sub.9O.sub.25 overlap, and thus, the two crystals may coexist at the same time.

[0060] FIG. 5 shows the frequency dependence of the dielectric constant in Example 5. It can be understood that the dielectric constant is as high as 4000 to 5000 in the frequency range used for measurement. From the relationship between the dielectric properties and the temperature characteristics in FIG. 6, it can be confirmed that the dielectric constant varies little and the change rate of the dielectric constant is 15% or less at high temperatures of 250° C. or higher.

Production of Example 6

[0061] An inorganic composition containing oxide crystals including Ge and Nb was produced by a normal sintering method according to the following procedure. Firstly, powders of GeO.sub.2 and Nb.sub.2O.sub.5 as raw materials were blended at a predetermined ratio (Ge/Nb=0.11), filled into a polypot together with zirconia balls having a diameter of 2 mm and ethanol, mixed for 24 hours, and then, dried for 24 hours. The dried mixed powders were calcined at 950° C. for 2 hours. The obtained calcined product was mixed, pulverized, and dried under conditions similar to that described above to obtain a dielectric powder including the inorganic composition. 2.0 g of this dielectric powder was taken, filled into a mold having an inner diameter of 20 mm, molded into pellets by a biaxial press, and then sintered in air at 1170° C. for 4 hours in an electric furnace. The XRD of the obtained disk-shaped dielectric body was measured, and then, the dielectric constant was measured.

[0062] The XRD-pattern was the same as in Example 5, and thus, it was clarified that the dielectric body had a similar crystal phase.

[0063] FIG. 7 shows the frequency dependence of the dielectric constant in Example 6. It can be understood that the dielectric constant is substantially constant at about 700 in the frequency range used for measurement. From the relationship between the dielectric properties and the temperature characteristics in FIG. 8, it was confirmed that the change rate of the dielectric constant was as low as 15% or less and the dielectric loss was 0.5 or less at high temperatures of 200° C. or higher.