Dielectric porcelain composition and dielectric element having the same

Abstract

A dielectric porcelain composition with a sintering density of 93% or above, is expressed by the composition formula below: 100[1x(0.94Bi.sub.1/2Na.sub.1/2TiO.sub.30.06BaTiO.sub.3)xK.sub.0.5Na.sub.0.5NbO.sub.3]+CuO+LiF (wherein x is between 0.14 and 0.28, and and meet either (I) is between 0.4 and 1.5, and is between 0 and 2.4, or (II) is between 0 and 1.5, and is between 0.2 and 2.4). The dielectric porcelain composition is Pb-free and can be sintered at low temperature, as well as a dielectric element having such composition.

Claims

1. A dielectric porcelain composition with a sintering density of 93% or above, expressed by a composition formula below: 100[1x(0.94Bi.sub.1/2Na.sub.1/2TiO.sub.30.06BaTiO.sub.3)xK.sub.0.5Na.sub.0.5NbO.sub.3]+CuO+LiF (wherein x is from 0.14 and 0.28, and and meet either (I) is from 0.4 to 1.5 and is from 0 to 2.4, or (II) is from 0 to 1.5 and is from 0.2 to 2.4).

2. A dielectric element of laminated type having a laminate constituted by dielectric layers made of a dielectric porcelain composition according to claim 1 and internal electrode layers made of silver palladium alloy, wherein a composition of silver palladium alloy is 65 to 90 percent by weight of silver and palladium accounting for the remainder.

3. A dielectric element according to claim 2 whose C.sub.400 C./C.sub.25 C. is 30% or below and whose C.sub.peak/C.sub.25 C. is 50% or below, wherein C.sub.400 C./C.sub.25 C. is a value obtained by dividing a difference between a capacitance at 400 C. and a capacitance at 25 C., by the capacitance at 25 C., and C.sub.peak/C.sub.25 C. is a value obtained by dividing a difference between a maximum value of capacitance at 55 to 400 C. and a capacitance at 25 C., by the capacitance at 25 C.

4. A dielectric element according to claim 3 whose time constant RC measured at 150 C., electric field intensity of 5 kV/mm, and capacitance of 1 V, is 200 to 350 sec.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

(1) The dielectric porcelain composition proposed by the present invention has a composition expressed by the general formula (1) above.

(2) x, which is a value reflecting the ratio of BNT-BT and KNN, is between 0.14 and 0.28 under the present invention.

(3) and are values reflecting the amount of CuO and LiF added, respectively. Only one of CuO and LiF needs to be contained, and is zero when CuO is not contained, and is zero when LiF is not contained.

(4) If LiF is not contained (i.e., =0), the minimum value of is 0.4 or more. The maximum value of is 1.5 regardless of whether or not LiF is contained. If CuO is not contained (i.e., =0), the minimum value of is 0.2 or more. The maximum value of is 2.4 regardless of whether or not CuO is contained. By summarizing the above, the condition (I) or (II) below is derived regarding and :

(5) Condition (I): is between 0.4 and 1.5, and is between 0 and 2.4.

(6) Condition (II): is between 0 and 1.5, and is between 0.2 and 2.4.

(7) The sintering density improves when CuO or LiF exists or the two coexist in a manner meeting the ranges of and above.

(8) The dielectric porcelain composition proposed by the present invention has a sintering density of 93% or above. The measuring method for sintering density is described in the section of Examples. Ways to improve the sintering density normally include raising the sintering temperature, but under the dielectric porcelain composition proposed by the present invention, the aforementioned sintering density can be achieved by performing sintering at such sintering temperatures as below 1050 C., which is a great advantage.

(9) The manufacturing method is explained and embodiments of the dielectric porcelain composition proposed by the present invention are cited below. It should be noted that the following manufacturing method is only an example and is not intended to limit in any way the method in which the dielectric porcelain composition proposed by the present invention is manufactured.

(10) First, material powders containing the respective metal elements are prepared as the starting materials for producing a dielectric porcelain composition. The material powders include powders of oxides and carbonates of the respective metal elements, such as powders of bismuth oxide (Bi.sub.2O.sub.3), sodium carbonate (Na.sub.2CO.sub.3), potassium carbonate (K.sub.2CO.sub.3), barium carbonate (BaCO.sub.3), titanium oxide (TiO.sub.2), niobium oxide (Nb.sub.2O.sub.5), copper oxide (CuO), lithium fluoride (LiF), and the like.

(11) These material powders are weighed to match the composition of the dielectric porcelain composition (sintered body) finally targeted. Next, the weighed material powders are wet-mixed in a ball mill, etc. Then, the mixture obtained through the wet-mixing is calcined to obtain a calcined product. Here, calcination is normally performed in air. Also, preferably the calcination temperature is 850 to 900 C., and preferably the calcination time is 1 to 8 hours.

(12) The obtained calcined product is wet-pulverized in a ball mill, etc., and then dried to obtain a calcined powder. Next, the obtained calcined powder is pressed after adding a small amount of binder (acryl monomer) to it, to obtain a compact. Here, preferably the compacting pressure is approx. 4 to 6 t/cm.sup.2, although the specific pressure varies depending on the state of the powder. The shape of the compact is not limited in any way, and it may be a disk-shaped compact with a flat area diameter of 12 mm and thickness of 1 mm or so, for example.

(13) Then, the obtained compact is sintered to obtain a sample of dielectric porcelain composition. Here, sintering is normally performed in air. Also, the sintering temperature is below 1050 C., or preferably 960 to 1040 C., and the sintering time is preferably 2 to 10 hours. At this time, a compact with a sintering density of 93% or above must be obtained.

(14) Silver or other metal electrodes may be formed on both sides of the obtained sample of dielectric porcelain composition. The electrode forming method is not limited in any way, and examples include vapor deposition, baking and electroless plating, among others.

(15) The dielectric porcelain composition proposed by the present invention may have a dielectric element as dielectric layers, and such dielectric element also constitutes an embodiment of the present invention. As an example of the dielectric element proposed by the present invention, a laminated dielectric element is explained, along with its manufacturing method. This dielectric element has a laminate of rectangular solid shape, as well as a pair of terminal electrodes formed on the opposing end faces of this laminate, respectively.

(16) The laminate comprises, among others, a base body constituted by dielectric layers and internal electrode layers (electrode layers) stacked alternately with each other, and a pair of protective layers provided in a manner sandwiching the base body from both its end faces in the stacking direction (vertical direction).

(17) The dielectric layers are layers made of the aforementioned dielectric porcelain composition. The thickness of one dielectric layer is arbitrary, but examples include 0.1 to 100 m.

(18) The internal electrode layers are provided in parallel with each other. In the base body, internal electrode layers formed in such a way that one end is exposed at one end of the laminate, and internal electrode layers formed in such a way that one end is exposed at the other end of the laminate, are provided alternately in parallel.

(19) For the material of internal electrode layers, silver palladium alloy is used. Under the present invention, silver palladium alloy consists of 65 to 90 percent by weight of silver, and palladium accounting for the rest. The higher content of silver provides cost advantage.

(20) The ends of the internal electrode layer exposed on one end face and the other end face of the laminate are connected to the respective terminal electrodes. This way, the terminal electrodes are electrically connected to the internal electrode layers, respectively. These terminal electrodes are not limited in their material in any way, and may be constituted by any conductive material whose primary component is Ag, Au, Cu, etc. The thickness of the terminal electrodes is set as deemed appropriate according to the application, size of the laminated dielectric element, etc., and may be 10 to 50 m, for example.

(21) With the dielectric element, preferably the rate of change in capacitance at high temperature is 30% or below for C.sub.400 C./C.sub.25 C., and 50% or below for C.sub.peak/C.sub.25 C.

(22) The rate of change due to temperature C.sub.400 C./C.sub.25 C. is a value obtained by dividing the difference between the capacitance at 400 C. and capacitance at 25 C., by the capacitance at 25 C. The rate of change due to temperature C.sub.peak/C.sub.25 C. is a value obtained by dividing the difference between the maximum value of capacitance at 55 to 400 C. and capacitance at 25 C., by the capacitance at 25 C. To be specific, when the capacitance at 400 C. is given by C.sub.400 C., capacitance at 25 C. (room temperature) is given by C.sub.25 C., and maximum value of capacitance in a measurement range of 55 to 400 C. is given by C.sub.peak, each rate of change due to temperature is calculated as follows based on the measured values of these capacitances:
C.sub.400 C./C.sub.25 C.=(C.sub.400 C.C.sub.25 C.)/C.sub.25 C.
C.sub.peak/C.sub.25 C.=(C.sub.peakC.sub.25 C.)/C.sub.25 C.

(23) These capacitances are measured for the dielectric element on which the electrodes have been formed as described above, using an LCR meter (Hewlett Packard 4192A or Agilent E4980A). The measurement frequency is 1 kHz, and the measurement temperature range is 55 to 400 C.

(24) Preferably time constant RC of the dielectric element at high temperature (such as 150 C.) is 200 to 350 sec. The time constant was evaluated at 150 C. The impression voltage was impressed so that the electric field intensity would become 5 kV/mm. The capacitance was measured at 1 V.

(25) The foregoing explained the dielectric porcelain composition and dielectric element in this embodiment, and because this dielectric porcelain composition exhibits good DC bias properties when high electric field is impressed, it can be favorably used for medium to high-voltage capacitors whose rated voltage is relatively high, for example. Also, it should be noted that the present invention is not limited to the aforementioned embodiment. The dielectric element proposed by the present invention only needs to have a laminate structure constituted by dielectric layers made of the aforementioned dielectric porcelain composition and internal electrode layers made of silver palladium of the aforementioned composition, and prior art may be referenced as deemed appropriate for its specific shape, manufacturing method, etc.

EXAMPLES

(26) The present invention is explained more specifically below using examples. It should be noted, however, that the present invention is not limited to the embodiments described in these examples.

(27) To produce a dielectric porcelain composition, powders of bismuth oxide (Bi.sub.2O.sub.3), sodium carbonate (Na.sub.2CO.sub.3), potassium carbonate (K.sub.2CO.sub.3), barium carbonate (BaCO.sub.3), titanium oxide (TiO.sub.2), niobium oxide (Nb.sub.2O.sub.5), copper oxide (CuO), and lithium fluoride (LiF) were prepared as the starting materials.

(28) Then, the material powders were weighed so that the sintered dielectric porcelain composition (sintered body) would meet the general formula (1) above.

(29) Next, the weighed material powders were wet-mixed in a ball mill. Then, the mixture obtained through the wet-mixing was calcined at 900 C. for 3 hours to obtain a calcined product.

(30) The obtained calcined product was wet-pulverized in a ball mill and then dried to obtain a calcined powder. Next, the obtained calcined powder was pressed after adding a small amount of binder to it, to obtain a disk-shaped compact with a diameter of 12 mm and thickness of 1 mm (Manufacturing Examples 1 to 13).

(31) Then, the obtained compact was sintered for 3 hours in air at the sintering temperature below, to obtain a sample of a dielectric porcelain composition. The obtained sample of dielectric porcelain composition was measured for sintering density. The sintering density was measured according to JIS R 1634:1998.

(32) The composition, sintering temperature, and sintering density of each sample were as follows (shown in Table 1 below). It is required that a composition with a sintering density of 93% or above be obtained at a sintering temperature below 1050 C. It should be noted that the manufacturing example numbers preceded by an asterisk (*) represent comparative examples of the present invention.

(33) TABLE-US-00001 TABLE 1 Sintering Sintering x temperature density % * Manufacturing Example 1 0.10 0 0 1100 C. 94.3 * Manufacturing Example 2 0.12 0 0 1100 C. 94.1 * Manufacturing Example 3 0.14 0 0 1100 C. 94.5 * Manufacturing Example 4 0.18 0 0 1100 C. 94.9 * Manufacturing Example 5 0.24 0 0 1130 C. 93.0 * Manufacturing Example 6 0.12 1 0 1000 C. 97.2 Manufacturing Example 7 0.14 1 0 1000 C. 96.3 Manufacturing Example 8 0.18 1 0 1000 C. 95.5 Manufacturing Example 9 0.24 1 0 1000 C. 97.3 * Manufacturing Example 10 0.12 0 1 1040 C. 93.0 Manufacturing Example 11 0.14 0 1 1040 C. 93.3 Manufacturing Example 12 0.18 0 1 1040 C. 93.2 Manufacturing Example 13 0.24 0 1 1040 C. 93.1

(34) Next, laminated dielectric elements having the dielectric porcelain composition proposed by the present invention were manufactured (Manufacturing Examples 14 to 34). The dielectric elements each have a laminate of rectangular solid shape, as well as a pair of terminal electrodes formed on the opposing end faces of this laminate, respectively.

(35) The laminate was comprised of: a base body constituted by internal electrode layers (electrode layers) stacked alternately with dielectric layers in such a way that a dielectric layer was present between each pair of internal electrode layers, and a pair of protective layers provided in a manner sandwiching this base body from the both end faces in the stacking direction (vertical direction). In the base body, the dielectric layers and internal electrode layers were stacked alternately with each other. Here, a dielectric porcelain composition meeting the general formula (1) above was used for the dielectric layers.

(36) The thickness of one dielectric layer was set to 8 m, and ten layers were stacked in these manufacturing examples. As for the internal electrode layers, those formed in such a way that one end was exposed at one end of the laminate, and others formed in such a way that one end was exposed at the other end of the laminate, were provided alternately in parallel. In these manufacturing examples, silver palladium alloy (70 percent by weight of silver, plus palladium accounting for the rest) was used for the material of internal electrode layers.

(37) At both ends of the laminate, terminal electrodes were formed in a manner contacting the ends of the aforementioned internal electrode layers, respectively. This way, the terminal electrodes and internal electrode layers were electrically connected. In these manufacturing examples, silver was used for the material of the terminal electrodes. The thickness of the terminal electrodes was set to 100 m.

(38) A laminated dielectric element was manufactured to the aforementioned design. It was manufactured by preparing a slurry containing the aforementioned calcined powder, using this slurry to prepare green sheets, separately preparing a paste containing internal electrode material, and then printing this paste onto the green sheets. The printed green sheets were stacked, pressure-welded and cut, and then sintered for 2 hours in air at the specified sintering temperature. Thereafter, silver paste was baked to form terminal electrodes. A dielectric element was thus obtained.

(39) The sintering temperature was as follows.

(40) It was 1100 C. in Manufacturing Examples 14 to 20 where ==0, 1000 C. in Manufacturing Examples 21 to 27 where =1 and =0, and 1040 C. in Manufacturing Examples 28 to 34 where =0 and =1. By sintering at these temperatures, all dielectric layers, or dielectric porcelain compositions, exhibited a sintering density of 93% or above, except in Manufacturing Example 20. In Manufacturing Example 20, a sintering density high enough to justify measuring the following electrical properties was not reached.

(41) The obtained dielectric elements were measured for the rate of change in capacitance due to temperature and the time constant.

(42) The composition of each manufacturing example and its rate of change in capacitance due to temperature were as follows (shown in Table 2 below). C.sub.400 C./C.sub.25 C. and C.sub.peak/C.sub.25 C. were measured as the rates of change in capacitance due to temperature. Results consisting of a sintering temperature of below 1050 C., and rates of change due to temperature C.sub.400 C./C.sub.25 C. (referred to as T1 below) of 30% or below, and C.sub.peak/C.sub.25 C. (referred to as T2 below) of 50% or below, are required. Also, the time constant (RC constant, in units of sec) of each manufacturing example was measured and the following results were obtained. Desirably the RC constant is 200 to 350 sec.

(43) TABLE-US-00002 TABLE 2 x T1 (%) T2 (%) RC * Manufacturing 0.10 0 0 0.1 47.6 245 Example 14 * Manufacturing 0.12 0 0 3.2 40.0 220 Example 15 * Manufacturing 0.14 0 0 6.5 35.1 198 Example 16 * Manufacturing 0.18 0 0 9.2 31.3 181 Example 17 * Manufacturing 0.24 0 0 48.4 20.0 63 Example 18 * Manufacturing 0.28 0 0 20.1 17.3 52 Example 19 * Manufacturing 0.30 0 0 Could not be measured 45 Example 20 due to low density. * Manufacturing 0.10 1 0 8.2 123.0 340 Example 21 * Manufacturing 0.12 1 0 5.7 109.7 387 Example 22 * Manufacturing 0.14 1 0 10.2 49.2 349 Example 23 * Manufacturing 0.18 1 0 25.0 45.8 331 Example 24 * Manufacturing 0.24 1 0 27.5 44.9 280 Example 25 * Manufacturing 0.28 1 0 1.8 35.2 244 Example 26 * Manufacturing 0.30 1 0 Could not be measured 226 Example 27 due to production of abnormal phase. * Manufacturing 0.10 0 1 9.5 119.3 390 Example 28 * Manufacturing 0.12 0 1 6.2 111.9 340 Example 29 * Manufacturing 0.14 0 1 15.6 10.9 304 Example 30 * Manufacturing 0.18 0 1 25.2 25.2 289 Example 31 * Manufacturing 0.24 0 1 28.5 42.6 243 Example 32 * Manufacturing 0.28 0 1 2.3 33.9 210 Example 33 * Manufacturing 0.30 0 1 Could not be measured 180 Example 34 due to production of abnormal phase.

(44) In the above, the abnormal phase is a type of secondary phase which is abnormal to the extent that measurement of T1 and T2 is hindered.

(45) Table 3 below is a table combining the results shown in Tables 1 and 2 and shows the evaluation of each formula of the composition (* indicates unsatisfactory examples). As can be seen from Table 3, when x was in a range of 0.14 to 0.28, and at least one of and was not zero (in some embodiments, at least one of and is 10.5), regardless of the sintering temperature (i.e., even at a low sintering temperature such as 1000 C.), all of the sintering density, T1, T2, and R C were satisfactory.

(46) TABLE-US-00003 TABLE 3 Sin- Sin- tering tering Dielectric element of Formula (1) Temp. Density laminated type Ex. X ( C.) (%) T1 (%) T2 (%) R C *1, * 14 0.10 0 0 1100 94.3 0.1 47.6 245 *2, *15 0.12 0 0 1100 94.1 3.2 40.0 220 *3, *16 0.14 0 0 1100 94.5 6.5 35.1 198 *4, *17 0.18 0 0 1100 94.9 9.2 31.3 181 *5 0.24 0 0 1130 93.0 *18 0.24 0 0 1100 93 48.4 20.0 63 *19 0.28 0 0 1100 93 20.1 17.3 52 *20 0.30 0 0 1100 93> Could not be 45 measured due to low density *21 0.10 1 0 1000 93 8.2 123.0 340 *6, *22 0.12 1 0 1000 97.2 5.7 109.7 387 7, 23 0.14 1 0 1000 96.3 10.2 49.2 349 8, 24 0.18 1 0 1000 95.5 25.0 45.8 331 9, 25 0.24 1 0 1000 97.3 27.5 44.9 280 26 0.28 1 0 1000 93 1.8 35.2 244 *27 0.30 1 0 1000 93 Could not be 226 measured due to production of abnormal phase *28 0.10 0 1 1040 93 9.5 119.3 390 *10, * 29 0.12 0 1 1040 93.0 6.2 111.9 340 11, 30 0.14 0 1 1040 93.3 15.6 10.9 304 12, 31 0.18 0 1 1040 93.2 25.2 25.2 289 13, 32 0.24 0 1 1040 93.1 28.5 42.6 243 33 0.28 0 1 1040 93 2.3 33.9 210 *34 0.30 0 1 1040 93 Could not be 180 measured due to production of abnormal phase

(47) In the present disclosure where conditions and/or structures are not specified, a skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, in the present disclosure including the examples described above, any ranges applied in some embodiments may include or exclude the lower and/or upper endpoints, and any values of variables indicated may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, a may refer to a species or a genus including multiple species, and the invention or the present invention may refer to at least one of the embodiments or aspects explicitly, necessarily, or inherently disclosed herein. The terms constituted by and having refer independently to typically or broadly comprising, comprising, consisting essentially of, or consisting of in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

(48) The present application claims priority to Japanese Patent Application No. 2015-130140, filed Jun. 29, 2015, and No. 2016-082482, filed Apr. 15, 2016, each disclosure of which is incorporated herein by reference in its entirety including any and all particular combinations of the features disclosed therein.

(49) It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention.