Piezoelectric ceramic composition and piezoelectric ceramic device using the same

A lead-free piezoelectric ceramic composition is composed of a main component represented by the general formula (Sr.sub.1-x M1.sub.x)Bi.sub.2 (Nb.sub.1-y W.sub.y).sub.2 O.sub.9, wherein M1 is one of divalent metals other than Sr and trivalent metals other than Bi, 0<x.ltoreq.0.3, and 0<y.ltoreq.0.3. Examples of the divalent metals and trivalent metals include Ca, Ba, Mg, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y. The piezoelectric ceramic composition can be sintered at a relatively low temperature of 1,100.degree. C. or less, and has an electromechanical coupling coefficient kt which is at a practical level. The piezoelectric ceramic composition may be used in piezoelectric ceramic filters, piezoelectric ceramic oscillators and piezoelectric ceramic vibrators.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to piezoelectric ceramic compositions and
 piezoelectric ceramic devices using the same. In particular, the present
 invention relates to piezoelectric ceramic compositions, which are useful
 as materials for piezoelectric ceramic filters, piezoclectric ceramic
 oscillators and piezoelectric ceramic vibrators, and relates to
 piezoelectric ceramic devices using the same.
 2. Description of the Related Art
 Piezoelectric ceramic compositions comprising lead titanate zirconate
 (Pb(Ti.sub.x Zr.sub.1-x)O.sub.3) or lead titanate (PbTiO.sub.3) as main
 components are extensively used in piezoclectric ceramic filters,
 piezoelectric ceramic oscillators, and piezoelectric ceramic vibrators. In
 piezoelectric ceramic compositions comprising lead titanate zirconate or
 lead titanate as the main components, lead oxide is generally used. Lead
 oxide, however, requires facilities such as filters for removing powdered
 lead oxide, which is scattered by vaporization during the production
 steps. Such facilities incur increased production costs. In addition, the
 vaporization of the lead oxide causes deterioration of the uniformity of
 product quality.
 On the other hand, piezoelectric ceramic compositions comprising bismuth
 layered compounds such as (Sr.sub.1-x M.sub.x)Bi.sub.2 Nb.sub.2 O.sub.9 as
 main components and Mn as an optional component do not contain lead oxide
 and do not cause the above problems. These piezoelectric ceramic
 compositions, however, must be sintered at high temperatures of at least
 1,250.degree. C. in order to obtain piezoelectric ceramics having
 electromechanical coupling coefficients kt of at least 10%, which are at
 practical levels. Thus, these piezoelectric ceramic compositions require
 sintering furnaces which withstand such high-temperature sintering.
 Moreover, setters and the like for containing the piezoelectric ceramic
 compositions during sintering have short service lives in high-temperature
 operation, resulting in increased production costs.
 SUMMARY OF THE INVENTION
 Accordingly, it is an object of the present invention to provide a
 piezoelectric ceramic composition which can be sintered at a temperature
 of 1,100.degree. C. or less, does not contains lead or lead compounds, and
 exhibits a practical level of electromechanical coupling coefficient kt at
 such a low sintering temperature. The piezoelectric ceramic composition is
 useful as materials for piezoelectric ceramic filters, piezoelectric
 ceramic oscillators and piezoelectric ceramic vibrators.
 It is another object of the present invention to provide a piezoelectric
 ceramic device using the piezoelectric ceramic composition.
 According to a first aspect of the present invention, a piezoelectric
 ceramic composition comprises a main component represented by the general
 formula SrBi.sub.2 (Nb.sub.1-x W.sub.y).sub.2 O.sub.9, wherein
 0&lt;y.ltoreq.0.3.
 According to second aspect of the present invention, a piezoelectric
 ceramic composition comprises a main component represented by the general
 formula (Sr.sub.1-x M1.sub.x)Bi.sub.2)Nb.sub.1-y W.sub.y).sub.2 O.sub.9,
 wherein M1 is one of divalent metals other than Sr and trivalent metals
 other than Bi, 0&lt;x .ltoreq.0.3, and 0&lt;y .ltoreq.0.3. The M1 in the general
 formula may be at least one element selected from the group consisting of
 Ca, Ba, Mg, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
 According to a third aspect of the present invention, a piezoelectric
 ceramic composition comprises a main component represented by the general
 formula (Sr.sub.1-x M2.sub.2x/3)Bi.sub.2 (Nb.sub.1-y W.sub.y).sub.2
 O.sub.9, wherein M2 is a trivalent metal other than Bi, 0&lt;x .ltoreq.0.45,
 and 0&lt;y .ltoreq.0.3. The M2 in the general formula may be at least one
 element selected from the group consisting of La, Ce, Pr, Nd, Sm, Gd, Dy,
 Er, Yb, Sc and Y.
 According to a fourth aspect of the present invention, a piezoelectric
 ceramic composition comprises a main component represented by the general
 formula SrBi.sub.2 Nb.sub.2 O.sub.9 and more than 0 to about 0.3 mole of W
 with respect to 1 mole of Bi in the main component. This piezoelectric
 ceramic composition may further comprise one of divalent metals other than
 Sr and trivalent metals other than Bi in an amount of more than 0 to about
 0.15 mole with respect to 1 mole of Bi in the main component. The divalent
 metal or the trivalent metal may be at least one element selected from the
 group consisting of Ca, Ba, Mg, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and
 Y.
 The piezoelectric ceramic compositions according to the first to fourth
 aspects may further comprise manganese as an auxiliary component in an
 amount of more than 0 to about 1.0 percent by weight calculated as
 MnCO.sub.3.
 According to a fifth aspect of the present invention, a piezoelectric
 ceramic device comprises a piezoelectric ceramic comprising the
 piezoelectric ceramic composition according to one of the first to fourth
 aspects, and electrodes.
 The above objects, other objects, features and advantages of the present
 invention will be further apparent from the following preferred
 embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The piezoelectric ceramic composition in accordance with the present
 invention is composed of a main component represented by the general
 formula (Sr.sub.1-x M.sub.x)Bi.sub.2 Nb.sub.2 O.sub.9 wherein M is a
 divalent metal element other than Sr or a trivalent metal element other
 than Bi, and 0&lt;x .ltoreq.0.3. Alternatively, the piezoelectric ceramic
 composition in accordance with the present invention is composed of a main
 component represented by the formula SrBi.sub.2 Nb.sub.2 O.sub.9.
 In the piezoelectric ceramic composition comprising a main component
 represented by the general formula (Sr.sub.1-x M1.sub.x)Bi.sub.2
 (Nb.sub.1-y W.sub.y).sub.2 O.sub.9, the subscript x indicating the M1
 content lies in a range of 0&lt;x .ltoreq.0.3. At an M1 content outside this
 range, the electromechanical coupling coefficient kt does not reach a
 practical level.
 In the piezoelectric ceramic composition comprising a main component
 represented by the general formula (Sr.sub.1-x M2.sub.2x/3)Bi.sub.2
 (Nb.sub.1-y).sub.2 O.sub.9, the subscript x indicating the M2 content lies
 in a range of 0&lt;x.ltoreq.0.45. At an M2 content outside this range, the
 electromechanical coupling coefficient kt does not reach a practical
 level.
 In the piezoelectric ceramic compositions in accordance with the present
 invention, the subscript y indicating the W content lies in a range of 0
 &lt;y &lt;0.3. When the piezoelectric ceramic composition does not contain W
 (y=0), this piezoelectric ceramic composition is not sufficiently sintered
 at a temperature of 1,100.degree. C. or less and is not polarized. When
 the subscript y exceeds 0.3, the electromechanical coupling coefficient kt
 does not reach a practical level.
 In the piezoelectric ceramic composition comprising a main component
 represented by the general formula SrBi.sub.2 Nb.sub.2 O.sub.9 and W as an
 additional component, the W content lies in a range of more than 0 to
 about 0.3 mole respect to 1 mole of Bi in the main component. When the W
 content is 0, the piezoelectric ceramic composition is not sufficiently
 sintered at a temperature of 1,100.degree. C. or less and is not
 polarized. When the W content exceeds about 0.3 mole, the
 electromechanical coupling coefficient kt does not reach a practical
 level.
 This piezoelectric ceramic composition may further comprises one of
 divalent metals other than Sr and trivalent metals other than Bi in an
 amount of more than 0 to about 0.15 mole with respect to 1 mole of Bi in
 the main component. When the content of the divalent or trivalent metal
 exceeds about 0.15 mole, the electromechanical coupling coefficient kt
 does not reach a practical level.
 The piezoelectric ceramic composition in accordance with the present
 invention preferably further comprises manganese as an auxiliary component
 in an amount of more than 0 to about 1.0 percent by weight as MnCO.sub.3.
 The addition of manganese contributes to improved sintering
 characteristics. When the manganese content exceeds about 1.0 percent by
 weight as MnCO.sub.3, the piezoelectric ceramic composition is not
 polarized.
 The advantages in the present invention are particularly noticeable when
 the MI is at least one element selected from the group consisting of Ca,
 Ba, Mg, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
 Also, the advantages in the present invention are particularly noticeable
 when the M2 is at least one element selected from the group consisting of
 La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
 Moreover, the advantages in the present invention are particularly
 noticeable when the divalent metal other than Sr or trivalent metal other
 than Bi is at least one element selected from the group consisting of Ca,
 Ba, Mg, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
 FIG. 1 is an isometric view of an exemplary piezoelectric ceramic vibrator
 in accordance with the present invention, and FIG. 2 is a schematic
 cross-sectional view of the piezoelectric ceramic vibrator. A
 piezoelectric ceramic vibrator 10 includes, for example, a rectangular
 piezoelectric ceramic 12. The piezoelectric ceramic 12 has two
 piezoelectric ceramic layers 12a and 12b. These piezoelectric ceramic
 layers 12a and 12b are composed of the piezoelectric ceramic composition
 of the present invention, and are laminated.
 Moreover, the piezoelectric ceramic layers 12a and 12b are polarized in the
 same thickness direction, as shown by the arrows in FIG. 2.
 A circular vibrating electrode 14a is formed between the piezoelectric
 ceramic layers 12a and 12b, and an extraction electrode 16a having a
 T-shape extends from the vibrating electrode 14a to one end face of the
 piezoelectric ceramic 12. Another circular vibrating electrode 14b is
 formed on the piezoelectric ceramic layer 12a, and another extraction
 electrode 16b having a T-shape extends from the vibrating electrode 14b to
 the other end face of the piezoelectric ceramic 12. In addition, a third
 circular vibrating electrode 14c is formed on the piezoelectric ceramic
 layer 12b, and an extraction electrode 16c having a T-shape extends from
 the vibrating electrode 14c to the other end face of the piezoelectric
 ceramic 12.
 The extraction electrode 16a is connected to an external terminal 20a via a
 lead line 18a, whereas the extraction electrodes 16b and 16c are connected
 to another external terminal 20b via another lead line 18b.
 The present invention is not limited to the device configuration shown by
 the piezoelectric ceramic vibrator 10, and is applicable to other device
 configurations and other piezoelectric ceramic devices, such as
 piezoelectric ceramic vibrators using vibrational modes (for example,
 thickness shear vibration or thickness third harmonic waves),
 piezoelectric filters and piezoelectric ceramic oscillators.
 EXAMPLES
 As starting materials, SrCO.sub.3, Bi.sub.2 O.sub.3, Nb.sub.2 O.sub.5,
 CaCO.sub.3, BaCO.sub.3, La.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Sm.sub.2
 O.sub.3, Y.sub.2 O.sub.3, WO.sub.3 and MnCO.sub.3 were prepared. These
 materials were weighed and mixed by a wet process in a ball mill for
 approximately 4 hours so as to have a composition (Sr.sub.1-x
 M1.sub.x)Bi.sub.2 (Nb.sub.1-y W.sub.y).sub.2 O.sub.9 +z percent by weight
 of MnCO.sub.3, wherein M1 is one of divalent metals other than Sr and
 trivalent metals other than Bi0.ltoreq.x.ltoreq.0.35,
 0.ltoreq.y.ltoreq.0.35, and 0.ltoreq.z.ltoreq.1.1, or to have a
 composition (Sr.sub.1-x M2.sub.2x/3)Bi.sub.2 (Nb.sub.1-y W.sub.y).sub.2
 O.sub.9 +z percent by weight of MnCO.sub.3, wherein M2 is a trivalent
 metal other than Bi, 0.ltoreq.x.ltoreq.0.5, 0.ltoreq.y.ltoreq.0.35, and
 0.ltoreq.z.ltoreq.1.1. The mixture was dried and calcined at 700 to
 900.degree. C. The calcined mixture was roughly pulverized and finely
 pulverized together with a proper amount of organic binder by a wet
 process for 4 hours. The pulverized powder was screened using a 40-mesh
 sieve to adjust the particle size. The powder was pressed under a pressure
 of 1.000 kg/cm.sup.2 to form a disk with a diameter of 12.5 mm and a
 thickness of1 mm. The disk was sintered at 900 to 1,250.degree. C. in the
 air to form a disk ceramic. A silver paste was applied onto both main
 faces of the disk ceramic to form silver electrodes. A DC voltage of 5 to
 10 kV/mm was applied between the silver electrodes for 10 to 30 minutes in
 an insulating oil at 150 to 200.degree. C. for polarization. A
 piezoelectric ceramic sample was thereby prepared. Similarly,
 piezoelectric ceramic samples were prepared in which the types of the M1
 or M2, the M1, the M2 contents (x or k) and the W contents (y) were
 different.
 A half of the subscript x in the above formula (Sr.sub.1-x
 M1.sub.x)Bi.sub.2 (Nb.sub.1-y W.sub.y).sub.2 O.sub.9 correspond to the
 content of the divalent or trivalent metal with respect to 1 mole of Bi in
 the above formula fourth aspect. Similarly, one-third of the subscript x
 in the above formula (Sr.sub.1-x M1.sub.x)Bi.sub.2 (Nb.sub.1-y
 W.sub.y).sub.2 O.sub.9 corresponds to the content of the divalent or
 trivalent metal with respect to 1 mole of Bi in the main component in the
 fourth aspect.
 The density, resistivity and electromechanical coupling coefficient kt of
 each sample were measured. Table 1 to 3 show these results, in addition to
 the type of the M1 or M2, x or k, y, the MnCO.sub.3 content and the
 sintering temperature. In Tables 1 to 3, a Sample No. with an asterisk
 indicates a sample outside the ranges of the present invention.
 TABLE 1
 Sintering
 Sample MnCO.sub.3 Temp. Density Resistivity kt
 No. M1 x y (wt %) (.degree. C.) (g/cm.sup.3) (.OMEGA.
 .multidot. cm) (%)
 1* -- 0 0 0 1,100 5.70 5.0 .times. 10.sup.8
 Unpolarized
 2 -- 0 0.1 0 1,100 6.85 3.0 .times. 10.sup.12
 13.1
 3 -- 0 0.3 0 1,100 6.96 4.0 .times. 10.sup.12
 11.8
 4* -- 0 0.35 0 1,100 6.80 3.0 .times. 10.sup.12
 8.8
 5* -- 0 0 0.5 1,250 6.96 6.0 .times. 10.sup.12
 17.6
 6* -- 0 0 0.5 1,100 6.05 2.0 .times. 10.sup.9
 Unpolarized
 7 -- 0 0.05 0.5 1,100 6.98 8.0 .times. 10.sup.12
 17.9
 8 -- 0 0.1 0.5 1,100 7.01 6.0 .times. 10.sup.12
 17.3
 9 -- 0 0.1 0.5 1,000 6.99 8.0 .times. 10.sup.11
 16.0
 10 -- 0 0.3 0.5 1,100 7.02 5.0 .times. 10.sup.12
 15.7
 11* -- 0 0.35 0.5 1,100 6.98 2.0 .times. 10.sup.12
 8.1
 12* -- 0 0.35 0.5 1,000 6.65 2.0 .times. 10.sup.10
 6.5
 13* -- 0 0.35 0.5 900 5.65 5.0 .times. 10.sup.8
 Unpolarized
 14* -- 0 0 1.0 1,100 5.98 1.0 .times. 10.sup.9
 Unpolarized
 15 -- 0 0.3 1.0 1,100 6.97 4.0 .times. 10.sup.12
 14.6
 16* -- 0 0.35 1.0 1,100 6.84 2.0 .times. 10.sup.12
 8.0
 17 -- 0 0.1 1.1 1,100 6.96 7.0 .times. 10.sup.9
 11.8
 18 -- 0 0.3 1.1 1,100 6.95 5.0 .times. 10.sup.9
 10.8
 19* Ca 0.1 0 0.5 1,100 6.07 4.0 .times. 10.sup.9
 Unpolarized
 20 Ca 0.1 0.1 0.5 1,100 7.05 6.0 .times. 10.sup.12
 18.3
 21 Ca 0.1 0.3 0.5 1,100 7.07 6.0 .times. 10.sup.12
 16.6
 22* Ca 0.1 0.35 0.5 1,100 6.98 2.0 .times. 10.sup.12
 9.1
 23* Ca 0.3 0 0.5 1,100 6.07 2.0 .times. 10.sup.13
 Unpolarized
 24 Ca 0.3 0.1 0.5 1,100 7.07 2.0 .times. 10.sup.13
 20.9
 25 Ca 0.3 0.3 0.5 1,100 7.07 1.0 .times. 10.sup.13
 19.1
 TABLE 1
 Sintering
 Sample MnCO.sub.3 Temp. Density Resistivity kt
 No. M1 x y (wt %) (.degree. C.) (g/cm.sup.3) (.OMEGA.
 .multidot. cm) (%)
 1* -- 0 0 0 1,100 5.70 5.0 .times. 10.sup.8
 Unpolarized
 2 -- 0 0.1 0 1,100 6.85 3.0 .times. 10.sup.12
 13.1
 3 -- 0 0.3 0 1,100 6.96 4.0 .times. 10.sup.12
 11.8
 4* -- 0 0.35 0 1,100 6.80 3.0 .times. 10.sup.12
 8.8
 5* -- 0 0 0.5 1,250 6.96 6.0 .times. 10.sup.12
 17.6
 6* -- 0 0 0.5 1,100 6.05 2.0 .times. 10.sup.9
 Unpolarized
 7 -- 0 0.05 0.5 1,100 6.98 8.0 .times. 10.sup.12
 17.9
 8 -- 0 0.1 0.5 1,100 7.01 6.0 .times. 10.sup.12
 17.3
 9 -- 0 0.1 0.5 1,000 6.99 8.0 .times. 10.sup.11
 16.0
 10 -- 0 0.3 0.5 1,100 7.02 5.0 .times. 10.sup.12
 15.7
 11* -- 0 0.35 0.5 1,100 6.98 2.0 .times. 10.sup.12
 8.1
 12* -- 0 0.35 0.5 1,000 6.65 2.0 .times. 10.sup.10
 6.5
 13* -- 0 0.35 0.5 900 5.65 5.0 .times. 10.sup.8
 Unpolarized
 14* -- 0 0 1.0 1,100 5.98 1.0 .times. 10.sup.9
 Unpolarized
 15 -- 0 0.3 1.0 1,100 6.97 4.0 .times. 10.sup.12
 14.6
 16* -- 0 0.35 1.0 1,100 6.84 2.0 .times. 10.sup.12
 8.0
 17 -- 0 0.1 1.1 1,100 6.96 7.0 .times. 10.sup.9
 11.8
 18 -- 0 0.3 1.1 1,100 6.95 5.0 .times. 10.sup.9
 10.8
 19* Ca 0.1 0 0.5 1,100 6.07 4.0 .times. 10.sup.9
 Unpolarized
 20 Ca 0.1 0.1 0.5 1,100 7.05 6.0 .times. 10.sup.12
 18.3
 21 Ca 0.1 0.3 0.5 1,100 7.07 6.0 .times. 10.sup.12
 16.6
 22* Ca 0.1 0.35 0.5 1,100 6.98 2.0 .times. 10.sup.12
 9.1
 23* Ca 0.3 0 0.5 1,100 6.07 2.0 .times. 10.sup.13
 Unpolarized
 24 Ca 0.3 0.1 0.5 1,100 7.07 2.0 .times. 10.sup.13
 20.9
 25 Ca 0.3 0.3 0.5 1,100 7.07 1.0 .times. 10.sup.13
 19.1
 TABLE 3
 Sintering
 Sample MnCO.sub.3 Temp. Density Resistivity kt
 No. M.sub.2 x' y (wt %) (.degree. C.) (g/cm.sup.3) (.OMEGA.
 .multidot. cm) (%)
 49* La 0.15 0 0.5 1,100 6.01 2.0 .times. 10.sup.9
 Unpolarized
 50 La 0.15 0.1 0.5 1,100 6.87 4.0 .times. 10.sup.12
 15.8
 51 La 0.15 0.3 0.5 1,100 6.75 4.0 .times. 10.sup.12
 14.3
 52* La 0.15 0.35 0.5 1,100 6.52 5.0 .times. 10.sup.11
 7.2
 53* La 0.45 0 0.5 1,100 5.99 1.0 .times. 10.sup.9
 Unpolarized
 54 La 0.45 0.1 0.5 1,100 6.75 4.0 .times. 10.sup.12
 14.7
 55 La 0.45 0.3 0.5 1,100 6.76 4.0 .times. 10.sup.12
 13.9
 56* La 0.45 0.35 0.5 1,100 6.29 4.0 .times. 10.sup.11
 6.6
 57 La 0.5 0.1 0.5 1,100 6.50 4.0 .times. 10.sup.9
 10.4
 58* Nd 0.15 0 0.5 1,100 5.98 2.0 .times. 10.sup.9
 Unpolarized
 59 Nd 0.15 0.1 0.5 1,100 6.90 4.0 .times. 10.sup.12
 15.9
 60 Nd 0.15 0.3 0.5 1,100 6.86 4.0 .times. 10.sup.12
 14.7
 61* Nd 0.15 0.35 0.5 1,100 6.59 5.0 .times. 10.sup.11
 7.9
 As shown in Tables 1 to 3, the samples in accordance with the present
 invention have electromechanical coupling coefficients kt which are at
 practical levels when the samples are sintered at a temperature of
 1,100.degree. C. or less.
 The piezoelectric ceramic composition in accordance with the present
 invention is not limited to the above EXAMPLES and may have other
 formulations within the scope of the present invention.
 While preferred embodiments of the invention have been disclosed, various
 modes of carrying out the principles disclosed herein are contemplated as
 being within the scope of the following claims. Therefore, it is
 understood that the scope of the invention is not to be limited except as
 otherwise set forth in the claims.