CA1100750A - Piezoelectric ceramic composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A piezoelectric ceramic composition comprising a perovskite structure having the formula:

Pbl-ACdA(Ni1/3Nb2/3)xTiyZrzO3 where x is in the range from 0.05 to 0.25 y is in the range from 0.30 to 0.95 z is in the range from 0 to 0.65 and x + y + z = 1 in which the Pb is partially replaced by Cd in the crystal such that A is in the range from 0.005 to 0.02, said composition further including at least one additional element said addi-tional element being cadmium, manganese or tungsten, the amount of , cadmium calculated as CdCO3 being from 0.7 to 1.5 weight % of the perovskite structure including the amount of A, the amount of manganese calculated as MnO2, being in the range from 0 to 1.5 weight % of the perovskite structure, and the amount of tungsten, calculated as WO3 being in the range from 0 to 1.0 weight % of said perovskite structure.

-i-

Description

110()750 13r/\CKGRC)UND OF Tl~ INVENTION
Field of the Invention Tllis invention is in the field of piezoelectric ceramic compositions of perovskite crystalline structure, said compositions being suitable for use as surface acoustic wave filters or the like.
DESCRIPTION OF THE PRIOR ART
There is a piezoelectric ceramic composition already known having the formula:
Pb(N i 1/3Nb2/3)xTiyzrz 3 where x + y + z = l~ Examples of similar compositions are PbTixZryO3, and Pb(Mg] /3Nb2/3)xTiyZrzO3. These materials, however, have very high sintering temperatures so that they cannot be conveniently produced despite their excellent piezoelectric properties.
Prior art perovskite piezoelectric ceramic materials which contain lead oxide (PbO) as their main component are low in price and relatively easy to produce as compared with single crystal piezoelectric materials, In addition, there are various characteristics, for example7 such as electro-mechanical coupllng factor (Kp) dielectric constant (~ ) and the like can be adjusted by proper selection of the composition.
These materials are widely utilized for ignition elements, filters, pick-ups, and the like. Such commercial materials, however, contain a substantial quantity of PbO in their compositions. Consequently, when the material is fired at a sintering temperature in the range of about 1250 to 1350~C, PbO is violently vaporized to cause the generation of pores and a variation in the composition with the result that a uniform, fine ceramic composi~ion cannot be obtained. If the firing temperature is lowered in order to suppress the vaporization of PbO, a gas remains , .

llV()7SO

in the cer~llnic comlx)sition clue to the imperfect reaction, to produce a number of la rge pores. ~ccordingly, the ceramic cornpositions being produced in this area have a density which is substantially lower than the theoretical density. The commercial materials average about 95 to 967~ of the theoretical density.
As will be described later, as tbe density becomes lower than the theoretical density, the piezoelectric modulus becomes more irregular. Consequentlywhen such a ceramic composition is used as a high frequency vibrating source of more than 10 MHz, its characteristics are very irregular and its propagation loss is great due to the presence of pores each having a diameter of several tens of microns. When this ceramic composition is attached to a comb-like electrode, each tooth of which is less than 50 microns wide, to provide a surface acoustic wave -Eilter, ~iscontinuous portions appear in the electrode resulting in the deterioration of the element in its performance.
In the prior art, PbO, Bi203 or the like have been added in substantial amounts in order to lower the sintering temperature. In such case, however, these materials deposit in the grain boundaries and in forming a surface acoustic wave filter device, the PbO or Bi203 in such boundaries is dissolved away when the sureace is chemically washed. This etching of the grain boundaries by the cleansing liquid spoils the desired polished surface of,the material.
SUMMARY OF T~!E Il~IVENTION
The present invention provides a piezoelectric ceramic composition which is free from the above-described defects of the prior art. It provides a piezoelectric ceramic composition which has a high sintering density and has stabLe characteristics.

11()(~750 According to the present invention, the lead in the prior art materials is partially replaced by cadmium. The piezoelectric composition of the present invention has a perovskite structure having the formula:

Pbl ACdA (Nil/3Nb2/3) xTiyZrz3 where x is in the range from 0.05 to 0.25 y is in the range from 0.30 to 0.95 z is in the range from 0 to 0.65 and x ~ y + z = 1 in which the Pb is partially replaced by Cd in the crystal such that A is in the range from 0.005 to 0.02 and includes at least one additional element, the additional element being cadmium, manganese or tungsten. In the case of cadmium, I can add an amount of from 0.7 to 1.5 weight %, calculated as CdCO3 of the perovskite structure and including the amount specified in A.
The amount of manganese, calculated as MnO2 is in the range from 0 to 1.5 weight % of the perovskite structure. The amount of tungsten, calculated as WO3 is in the range from 0 to 1.0 weight % of the perovskite structure.

BRIEF DESC~IPTION OF THE DRAWINGS

Figure 1 is a ternary system diagram of the system l-A A ( 1/3Nb2/3) - (Pbl_ACdA) TiO3 - (Pb Cd ) ZrO

11~(J750 I~`igllre 2 is a graph showing the relationship between the cellter frequency of an acoustic surface wave filter manufactured by using a ceramic composition as its substrate and sintering density thereof; and Figure 3 is a chart showing the center frequency distribu-tion s~f the acoustic surface wave filter using the ceramic composition produced according to the present invention as its s ubstrate .
DESCRIPTION O~ THE PREFERRED EMBODIMENTS
A description will first be given on the preparation of a ceramic composition according to this invention, In the first step, the materials are mixed and ground in the same manner as used in the preparation of prior art piezoelectric ceramic materials. That is, predetermined amounts of PbO, ~rO2, WO3, NiO, Nb2O5, TiO2, CdCO3, and MnO2 are weighed out to form the composition and are mixed together by either the wet or dry process. The calcination is then carried out at a temperature of 800~C to 850C according to the nature of the composition. Then, grinding is carried out either by wet or dry process. The thus obtained calcined powder is molded in a press at a pressure of 1 metric ton/cm2 and then fired for 1 to 3 hours at a predetermined firing temperature while oxygen gas is supplied at a rate of 1 to 5 litres per minute. This rate of oxygen flow is used when the molded element is located in a cover having a cavity of 1 litre. As the capacity of the cover is increased, the flow rate must accordingly be increased.
Table 1 sets forth a series of measurements of sintering temperatures, sintering density and porosity relative to variations in composition in the ceramic element according to this invention.

J~ --u~ ~ ~ ~ ~ Lt~ u~ ~ C~ ~D ~ 0 u~ ~ ~ r~ ~D ~ I~ ~ U~ ~O U~ ~ ~D ~ ~ ~ ~
~ o o o o o o o o o o o o o o o P~
b~ _ _ _ _ _ ._ _ _ ~ 4 C) ,_1 O u~ ~ C5~ ~ Ci~ 00 1~ Cl~ O C~l O~ ~1 a~
~ O ~0 ~0 ~ O ~0 O O Co CO~I C`oJ O ~0 Co`l o a ~, bt co _ _ __ 00 __ _ 00 00 00 Oo _ 00 _ -b~ `_ _ _ _. ~ . _ _ ~. . '.
~ ~ O O O 0 O ~ O O O O O O O O O
4 aJ o ~O Lrl L~ If~ Ir~ Lo L~l Ll') O O 1~ O Lr~ O L~
~ ' 1_l ~ ~1 ~ ~1 ~1 c:: ~_~ ~1 o r-l ~1 0~ ~ O
U~
4 oC~ O u) u-) O u~ u~ O In 1~ O u~ u) O Ir~ O
,- O O O O O 5~ _ 0_ C~ _ ~ _ . ' -q oC~I Lr~ o In, u~ O u~ Lr~ O u~) U~ O u~ In ~ Ir~ ~ :
O O O O O O C;~ O O O O
~4 _ .. _ _ _._ _ . _ __ .
~ ~ ~O~ u~ In u~ In u~ u~ O O O Lr u~ u~ O O u'1r-l ~ ~ O O O O O O ~i ,_i r~ O O O O
~ r~l~ -O __ O _ ~ u~ ~ _ ~ ~ _~ ~ __ ~ ~ .
g~O ~ I~ u~ L~ ~D ~O ~ ~0 ~ ~ ~ ~0 ~ ~0 ~ O
.. . _ _ _ __ _ . _ ~ ~, u~ L~ u~ u~ u) u~ u~ . u~ u~ n u, u~ u~ u~
c~O ~ ~ C~l C`l C~l C~l C~l C~l C~l ~ C~l C~ ~ C~l C~ C`~
. ~ _ __ .
Oo O O ~ .~ ~1 ~ O O O O ~ ~ O C~ ~
_~ O O O O O O O O O O O O O O O
. __ .. u~ u~ ~ _ _ _ .._ ~ ~ ~ a~ c~ o~ a~ ~ cr o~ o~ ~ c~ o~ oO ~
,n ~o a~ ~ cs~ o~ ~ a~ ~ ~ c~ ~ ~ o~ a~ o~ ~
O O O O O O O O O O O O O O O
., _ _ _ _ .. ___ _ .~ c~
.. _ ~1~0750 ~_. _ ~ ~ ~ ~D 00 C~ _ a~ o~ ~r~ u~ O .
h--' ¦
bO _ _ _ _ _ _ _ _ _ h-rl CJ o o O o 3 o o o o o o o o o o o G oo oo cooO ~ oo oo co oo oo oo oo co co oo oO
Q _ _ _ _ . _ _ _ _ .~. . . .
h ~ ~ O O o O ,O o O o O O O O o O O O
~ au ~ O O ~ ~ ~ ~ ~ u~ O ~ O O ~ O ~ u~
C~l U~ _ _ _ _ ._ _ _ b~ ~ ~ u~ u~ O u~ u~ O u~ u~ O ~ u~ O ul ~ O u~
0~ C`~ O O O O . O O _ O O_ _O O _ O
l ~_ O O U~ Ll'~ O Ir~ U') O ~, Lr~ O U~ 1~ O U) U~) O, t'~ ~ ~ O O O O O O O O _Q Q_ ~ ~ 3 ~o~ u~ In L~l n Ln n u~ u~ Lr~ ul 1~ ul 1~ u~ 1~ L~
H ¢ ~ O O O O O O O O O O O O O O O O .
O 0~ Ir~ Ir~ O O O O O O 1~ U~ 1~ 1~ U~ n o o ,~ ~ .~ ~ __ c~ c~ ~. ~ _~ ~ ~ n u~ __ _, o~ ~ O O U~ L~l U~ ~ ~ U) U~ L~ U~ O ~ O U~ U~
R --' ~ ~) 00 a:) 00 ~ ~ ~ _ ~ ~ ~) _ ~ ~) ~ ~
¢ o ~ u~ n ~, u~) u, n u~ u~ O O O u~ ~r, u~ Ul u E-~ ~:) _ ~I c~l ~1 ,_, ~1 ,-1 ~-1 r-l .-1 1-~ ~1 ~1 ~1 ~1 a) ___ _ .. __ . __ _ O ~/ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ O O O O O O O O O O O O O O O O O
C~ R
. __ _ __ _ ____ _ _ ___ _.
a~ ~ a~ ~ ~ ~ ~ cs~ cs~ c~ ~ ~ cs~ ~ ~ o~
O .~ ~ o~ ~ ~ cr~ ~ cr~ O~ c~ ~ ~ ~ cr ~ ~ cs~
~E3 o o o o o o o o o o o o o o o o 'r~'- __ _ _ _ __ ~i . . ._._. O _ _ 0 -11007S~

~ _ _ _ _ _ __., ~r~ ci~ O~ ~ O CO ~ 00 00 C~ r~ o~ ~ ~ o u~
~0 ~ ~ u~ 1 ~ ~O ~ u~ u~ ~D u~ u~ ~D u~ ~ ~ . ' o o o o o o o o o o C o o o o o bO~- _ _ _ _ __ _ _ ~' O C~l C~ C~l C~ C~l C~3 0 ~'ta o o o o o o o o o o o ~ o o o ~ ~ ~ oo oo o~ co co oo oo oo o~ oo ~ co oo oo . . . _. . _ _ _ - --- 1-: ----.~b, .- '.'--~ ~ ~ o o o o o o . o o o o o o o o o .
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~l U~ ~ ~ ~
U~ _ _ _ -l _ _ Q) ~J ~ I~ ~ O Il~ In O ".,, 11~ G Lf~ ul o ~ 1~ O
t~ ~o o _ o o o o o o 1 o o l ¢_ ~ L~ ~ o u~ u~ o u~ u~ o u~ u~ 1 u~ 1~
P~ ~3 0~ O O O O _O O . O ~ ~ ~
H ¢ ~ Ir~ ~ f~ 1~ Lr~ In 1--) ~ 1~ In ¦ o ¦ o O ¦ u~ .
E-l _ ~ _ O O O O O O O I I ~ . ~ I ~L--. co, g~ o o o o u~, Ln, L~ ~ ~ ~ ~ 1 , ~
_~ l rl N C~l c~ C~l c~J C~l C`] I I ~ I ~ ~ I ~ ~ I
~ _~ . _ _ _ _ _. I _ . I ~ , .
rl a) ~ ~ u~ ~ ~ u~ u~ o o I o I u~ u~ I LQ LQ I - - ' c~t r~ r` I` I~ 1~ ~ ~ ~ I ~ I c~ c~ I ~ ~ I
~ la~E~ ~ _ ~O ~ ~ ~ n ~ ~
x u~ u~ u~ u~ In In u~ u~ Lr~ u~ u~ I
~ aJ-- _ _ _. -~ ~ ~
I oO ~ ~ ~ o ~ ~ lo ~ ~ o lo o 1~ ~ I
~, o o o 1 1 lo lo 1 I I
_ _t - I I 1- ~
~ ~ ~ I ~ ~ ~ ~ I ~ ~ ~ 1 ~ 1 ~ 1 ~ ~ ~ ~ ~ ~ ~
I ~ ~ ~ ~ 1 ' ~ ~ ' 1 ~ ~ ~ ~ 1 ~ a~ I I
I ~ o o 1 o o o 1 1 1 ' o 1 I ~
1~- 1 ~--t--1 ~ 1 _~
I ~z 1~ ~ 1~ ~
1, ~ _ 1 ..

..

.,~--oo ~ , U~ ~ oo C~ ~ ~
O ~ u~ u~ ~ u~ u~ u~ u~ u~ ~D ~ I~ r-~o~ ~ o o o o o o o o o o o o ~ _ : _ __ __ __ _ _ ~ ~ o~ o ~ ~ C~ ~ C~ ~ ~ ~ o ~
a~'~ o o o o o o o o o o o o o ~ Uoo 0 oo oo oo oo ~o oo oo CO oo CO
~ ___ t_ ___ _ .,.,.o o o .~. o o o o o o o o o h ~ ~ O O ~1 O O ~1 o O r I O O ~1 o ~1 ~. ~1 ~1 ~ ~1 ~1 ~1 r-l ~1 Q) ~ ~ ~ o o - o o o o o ~o o o o o--~_ ~ u~ Ltl O u~ u~ O u~ U~ O 'U~ u~ O n ::

H ~ ~: O 1~ In u~ u ) L~ L~ u ) u~ Ir~ Ll 1 r~
z ¢ ~, o o 1 1 N ~ ~ ~ . ~:) Lrl O O . O O --~1 ~ _ _ ~ ~ - ~ o ~ ~ o o E~ ~ ~ u~ ~ u~ u~ u~ u~

'`3 1'`' ~ o ~ ~I ~I
~,~ o 1 111 ----- -~ 1- 1 1 __ a~ ~ oo I o~ oO I ~ I ~ a~ a~ ~ o~ oo oO .
O ~ ~ ~ ~ I ~ I ~ I ~ ci~ ~ cs~ ~ ~ a~
.~ o olo olololo o o o o o o ~o l 1~ t~ ~ _ ~ ~ _ .

il~)O75Q
In I able 1, X is P,b,~dfl(Nil/3 Nb2/3)03, Y is (PbCdA) '~q 6 TiO3, and Z; is (PbCd~ZrO3.

Aswillbe noted from Table 1,dependin~on the composi-tion, the sintering temperature is lowered by 200 to 300C as com-pared witll prior art sintering temperatures which occurred in the range of 1250C to 1350C. Accordingly, a high sintering density is obtained. The theoretical density is about 7.9 to 8. 1 which differs depending on the composition, but the sintering density o~ the composi-tions produced according to the present invention is very close to the theoretical density.
Figure 1 illustrates a ternary system diagram of (Pbl-A C~dA) (Nil/3Nb2/3)3 - (Pbl A CdA) -rio3 - (Pbl A CdA) ZrO3, in which the compositions of samples 1 to 19 of Table 1 are repre-sented by re~erence numerals 1 to l9, respectively. The composition according to the present invention is circumscribed by the lines a b c d a o~ Figure 1. The composition in the area above the line ab of F igure 1 has a very low Curie point so that its temperature charac-teristics deteriorate and also does not have the proper perovskite structure. The composition in the area at the ri~ht of the line bc has a low Curie point which, as mentioned, causes a deterioration in its temperature characteristic, and a composition in the area below the A~ ~ q ~ 3 line cd has low ~:rys-t~lfi~abi=~ ' Table 2 shows a series of measured results o~ sintering tempera~ure, sintering density and porosity relative to adding various amounts o~ CdC03, MnO2 and W03, to the composition Pb1 -A CdA (Ni1 /3Nh2 /3)xTiyZrz 3 .

_ . _ _ J~
., ,~ ~ ~ ~ ,~ ~ C~1 U~ ~ C~
O ~ u~ ~ u~ ~D u~ r~ u~ ~ u~
~D O O O u~ O O O O O
. . __ _ _ ,~ ~ ~n ,~ ~ ,~ c~l ~ oo u~
, o~ o ~ o o~ o ~o ~ ~ ~o , r~ oo 0~ 00 1~ oo c~ o~ oo 00 _ ____ __ .~. .
s~ ~ ~ o o o o . o o o o o o a~ c~ u~ u~ u~ u, u~ u~ u~ u~ u~ u~
J~ aJ o ~1 ~ ~ ~ ~ ~ ~ ~ ~ ,~
__ J ~ O O O O ~ O O O O O
~ ~C~J _ ~,` ~ U~ Ul' U~ U~ U~ o ,~ ~ ~ o ~ _ r O O O O O O O ~ ~
O ~ ~) ~ ~ O O C`~ ~ O U~ U~ Ul U~ U~ U~
c~ d ~::1 o o ,~ I ~ o o o . o o _ _ _ . _ _ = , . ~ g~o ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ C~ ~ ~ ~ ~ ~ `J ~ ~ ~ ~
J~ ~ __ .. . . _ __ o o ~ u~- u~ L~ ~ u~ ~ u~ u~ n u~
__ _ _ __ u~ Ll~ v~ ,Lr) u~ n u~ u~ u~ L~
~- __ _ ___ o ~ ,~ ~ ~ ~ ~ ~ ~ ,~ ."~ ,1 o o o o o o o o o o o t~ o o o o o o o o o o __ __ __ _ __ ~
a) ~ C5~ c~ ~ ~ ~ ~ ~ ~ cs~
O r~ cr~ ~ a~ ~ ~ ~ a~ cs~ ~ ~
P~ E3 o o o o o o o o o o . ~o ~ . . ._. __ .. _ ..
~ ,,,, . . __. ____ _.

, :

~__ . _ __ .~ oo ~.` o ~ ~ ,~ o C~l h _~ ~D ~ r~ r~ ~D ~ o~ ~
O O u~ O O O O O ~
~1:4 -- - - --~, ~ ~ ~ n I~ u~ C5~ ~-S~ ~0 ~ O O O O O
00 1~ 00 ~ ~0 C~ o~
__ ~ _ _ , ~rJ . O O -O O O O O O
h ~ ~ ~ ~1 u~, ~n ~1 ~ u~ ,~
~ o ~1 ~1 ~1 ~1 ~1 -l rl c~l a) _ _ _ _ o o o ~ ~ u~ o u :~ ~ ~ _ o o o _~ ~
u~ o o o o o o o ~ ~ u _ ~ . .
H ~ O In u~ u~ ul In Lf) ~ Ir~
Z ~ ra C' O _ _ _ .
~) ~U~ LQ O O O O O O
c~l rl ~ ~ , ~ ~ u~ u~ u) u~ u~ ~
~r~ O L~ It~ In In U~ n n u~
~1 u~ ~( C~r c~
r~ o o ~ ~ n ¢ ~ ~3 __ ___ _ E~ v X u~ u~ u~ u~ u~ .u~ u~ u~
_ _ __ ._ ~ r-l~1 ~1 ~ ~1r-l ~1 r-l O~ O O O O O O O O
O . . . . . . .
~ O O O O O O O O
- ~_ . , ___ ., âJ c;~ cr~ c~ o~ ~ ~ o~
~o a~ ~ a~ ~ c~ G~ CS~ a~
P~ O O O O O O O O

r~l . _ _ _ _ !~ oc) __ _ ~ _ -LL .

11~)()'7SO

In I able 2, ~ is PhCd(Nil~3N~2~3)03, Y is (PbC,d)TiO3 and ~ is (PbCd)7rO3.
It will be noted from Table 2 that where the manganese dioxide is constant, and tungsten oxide is not added7 if the total amount of cadmium, including the amount used in replacing the lead as well as the additional ~f~a~ amounts is less than 0. 7 weight ~
calculated as CdCO3, or higher than 1. 5 weight ~, the sintering density is lowered and the porosity is substantially increased.
In the case where the amount of CdCO3 was constant and WO3 was not added, if the additional amount of MnO2 was 1~ 5 weight % or less, good sintering occurred but if the additional amount of MnO2 exceeded 1. 5 weight ~, the sintering was deteriorated.
When MnO2 was adcled in more than 1 5 weight ~, its accumulation at the grain boundaries becomes great enough to increase the instability.
In the case where the amount of CdCO3 was constant and MnO2 was not added, sintering proceeded well when the added amount of WO3 was 1 0 weight % or less, but the sintering deteriorated and the porosity increased when the amount of WO3 exceeded 1.0 weight 7~. For these reasons, the amount of Cd calculated as CdCO3 should be confined to a range from 0.7 to 1.5 weight 7~, the amount of Mn, calculated as MnO2 should be in the range from 0 to 1. 5 weight 7~, and the weight of W, calculated as WO3 should be in the range from 0 to 1.0 weight ~.
Table 3 sets forth a series of measured values of di-electric constant (~), dielectric loss (tan~), electro-mechanical coupling factor (Kp), frequency constant (fR) and mechanical Q value 1~0~50 (QM) in the SitU~tiOIl where the ~mounts of CdC~3, MnC)2 and W03 are va r ied .

~1~)()7SO

~ .
__ __ _ o o oo o ~ o L~ CO C~ 00 ~ 0~ O U~ O ~
~o ~ ~ ~ o~ c~ a~ o oo ,, . ~ _~ _ ~ ~ ~, o ~ ~ oo ,` ,, ~ C~ oo U~
~: . C~ ~ oo ,~ C~l ~ ~ ,~
, ,~ ~ ~ o ,~ ,~ ,~
N c~ tN C~l ~N C`l ~_1 C~l C~ C~l C~
~ __ __ I~ ~ ~ ~ ~ ~ U~ I~ O
~o~_ 1~ U~ ~ r-l L~ ~ U~ ~1 ~1 C`l . ~ _ _ __ ~0~ (:~ ~ 00 C~l I~ 00 it ~:) a~
~_~ O ~ O ~ O O O O O O
-- _ __ ~ __ `~ O O ~ ~ ~ ~ ~ C~ Lr~
C~ ~ ~ C~ ~1 ~ `;t 1~ ~D
tr) . _ _ I~ C~l ~I ~`I N r-l C`l N
~ ~ ~ O O O _ O O ~, O _ O

. fi~ oC`' Lr) I~ Il~ U~ U~ O U) Ir~ 1~ Lr~
t~O~ ~ O` O O O O O O O O ~:
~ _ _ _, _ _ _ ' .
¢ O U~ u~ U~ u~ u~ ~ Lr~ u~ u~ U~
~ O O O O O O O O O O
W _ _ __ _ __ __ ~.
~0 O - ,0 O ~0 O O ~0 ~0 ~0 ~0 O O O O O O O O O O
_ __, _ _ _ _ __ . .
~i æ ~ ~ , ~ ~
~ . ~ .
_ ~ _ 1~0750 . _ . ~ ~ , oo o o~
,_ ~ ~ ~ u, a~ u~ ~ ~ u~ ~
~, O ~D /o O O G~ ~ CO ~ co . ~ ~
. ___ . _ _ ~; I ~ o , ~ u~ a~ u~ oO u~ O
~ U~ I~ U) ~ ~ ~ U~ ~ ~ ~
~ I~ I ~ ~ I~ I~ I r- I~ I~
f ~ C`l C~ c~ ~ C~l C~ C~ C`l C`l C~l _ . ., _ _ .
~ ~ o~ o ~ L~ U~ ~ ~ C~ U~
C`l ~, ~ ~ ~ C~ ~ C~l C~l C`~ C~ C`l a) . . _ __ . ~o ~ ~D ~ 1~ O ~ 03 O~ ~ CO
, ~, __ o o o ~ o o o o o ~^ ~ .
:, ~ ~ o~ o~ ~ C~l ~ ~ ~ ~ o ~; ~ GO ~ CO. ~ ~ ~ ~ ~ ~ ~
H ~ ~ C`l ~ ~t) ~ ~f) t') ~ t') .
O _ . _ . . - _ _ _ _ 0~ Ul O U') O U') Ln O Ul O U-~
lJ ~rz O O O O O O
~ ~ .... . _ _ _ __ ~ ~0 ~
U~ U~ U~ U~ O Ul U~ O U) . U~ .
bO~ O O O O O O O O ....
~ _ _ . _ . __ . ¢ O Lr~) 1~ u~ ~ 1~ ~_ u~ ~ u~ C~`l C~l . ~d O O O O O O o o o o _ . __ _ _ . _ . ~
.~ ~ U~ U~ U~
O ~ ~ - ~ C~ C~ O O O ~ ' ~ C`l C`l : ~O O O O O O O O O O O
~ 3 o o o o o ' o o o o o .- _ _ _ _ ._ ~0 ~ .
. _ _ _ .

11()0750 _ _ o ~ ~ ~ ~ ,~ ~ ~ o ~ o o a~ ~D 0~ a~ ~ ~ ~ ' ~
U~ o U~ oo ~ U~ U~ ~ C~
. _ ~ ~ ~_ . ~ ~ _ ~ _ ~ o o o o ~ ~ ~ r~ o P~ I ~ ~ ~ ~ In ~ o ,~ n u~
~H I~ I~ ~D u~ ~ ~ O O
N C~l c~ ~1 ~c~ ~ c~l C~l ~ c~
~ .
_ _ _ _ ~
:
o~ ~ ~ O I~ c~l ~ a~ ~ u~
C~ ~ ~ ~ U~ U~ ~D ~ ~ c~
.. _ _ _ _ _ . ._.
'O~ ~ t- I_ ~ o~ ~0 CS~ CS~ C~
b~~ . . . . . . . . . .
~ ~ O O O O O O O O ~ O
~ . __ _ _ ___ ~ ~ ~ ~ r` o oo ~O O O ~ C~
\ ~1 ~ ~'1 ~1 1~ C~ ~D a~ r-~ ~tl H J~, ~ ~ ~5) 1~ ~1 O u~) ~1 Z __ _ . _ ___ ',: -O 0~ O U~ O U~ O O U~ U~ O U~
_~ ~ ~:3 O O O O O
~ ~ _ _ . . __ '.'' ~ ~ O Ln, U~ U~ U) U~ O O U~ U~ U~
i~ ~ ~ ~1 o o o o o ~i o o o ~3 _ _ _ . - _ _ _ ¢ cO~ u, L~ u~ u~l u~ u~ n u~ u~ ~
~a o o o o o o o o o o ___ _ _ ___ _ 00 .
.
~ 1 ~ ~ ~ ~ ~ ~ ~ ~ ~
O O O O O O O O O O O O
~¢ ~ O O O O O O O O O O
P~
. _ ___ _ - _ . ~Z; ~ `D _ - . _ .

.

` 110()750 From Table 3 it will be understood that the piezoelectric characteristics of Kp,~ and QM can be controlled by composite addition of CdCO3 and MnO2; CdCO3 and WO3; and CdCO3; MnO2 and WO3. Sample numbers in Table 3 correspond to the points illustrated in Figure 1 of the drawings.
In Table 4 there is shown a comparison between a piezo-electric ceramic element whose composition is Pb(Nil/3Nb2/3)0 1-Tio 45ZrO 453 and that of Sample No. 13-3 of Table 1 according to the present invention, with respect to pore size and porosity.

Table 4 Size of pore, Number of pores (microhs) Element on the market Sample No. 13-3 0 - 5 1~4 105 Porosity (~) 15.1 0.58 From Table 4, it will be evident that in the ceramic element according to the present invention there are no large ~-pores present, and the porosity is decreased by a factor of about 30. In the above Table, the pores are measured by a microscope with respect to a ceramic element having an area of 300 microns by 300 microns, and the surface being polished to a mirror finish.

11~)(~750 l~ig~lr~ 2 shows the relationship between the sintering density and the center frequency fO with respect to surface acoustic wave filters made of materials of the same composition but with various sintering density. According to Figure 2, assuming that the sintering density of a ceramic element is 7.72 g/cc and varied + 0.2%
at the minimum, the center frequency fO would vary + 60 kHz as indicated by ~ f2 in Figure 2. Since the ceramic composition of this invention has a sintering density more than 8.00 g/cc, however, the center frequency fO varies only about + 10 kHz as indicated by ~ f even when the density is varied + 0.2%~ ~hus, with the ceramic compositions according to the present invention, their piezoelectric constants are less dependent on sintering density.
A surface acoustic wave filter of 10. 7 MHz was formed from Sample No. 14 according to the present invention and the dis-tribution of the center frequency fO was displayed by the dots shown in l~igure 3. Samples of two lots, each having 3 blocks, were used to form 54 elements. In this case, only 2 elements were out of the range of + 0 27~, and 96.3% of the total elements were included in the range of + ~%, 77.8% of the elements being in the range of + 0.15% In this connection, the catalog value of a filter on the market using a prior art ceramic material is 10.7 MHz + 0.13 MHz which represents a scattering of about + 1.2%. With such a large scattering, it will cost a considerable amount of labor to sort the filter elements, thus creating a higher price. In addition, several types of specifications are necessary for tuners to be used and the like. According to the present invention, however, the scattering can be controlled to about + 0.2% and this defect can be avoided.

., 110~7so In accordance with the present invention, the sintering temperature of the material is lowered and the sintering density is improved. The scattering of the center frequency is decreased, and the fineness of the product is increased. Consequently, the charac~
teristics of the ceramic material are standardized, the reproducilibity is improved, and the propagation efficiency is enhanced. In addition, the discontinuous portions of electrodes can be prevented from being formed, thereby increasing the yield. In producing a ceramic element according to this invention, if the sintering is carried out in an oxygen containing gas, the vaporization of PbO can be effectively suppressed.
Further, according to the invention, since a portion of the Pb is replaced by Cd, the ceramic composition of this invention is chemically stable even when the ceramic surface is washed or an acid etchant is used with photoetching for selective formation of an electrode on the ceramic surface.
It will be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention,

Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A piezoelectric ceramic composition comprising a perovskite structure having the formula:
Pbl-ACdA (Ni1/3Nb2/3)XTiyZrzO3 where x is in the range from 0.05 to 0.25 y is in the range from 0.30 to 0.95 z is in the range from 0 to 0.65 and x + y + z = 1 in which the Pb is partially replaced by Cd such that A is in the range from 0.005 to 0.02, said composition further including at least one additional element, said additional element being cadmium, manganese, or tungsten, the amount of cadmium calculated as CdCO3 being from 0.7 to 1.5 weight % of the perovskite structure, including the amount of A, the amount of manganese calculated as MnO2 being in the range from 0 to 1.5 weight % of the perovskite structure, and the amount of tungsten, calculated as WO3, being in the range from 0 to 1.0 weight % of said perovskite structure.

2. A ceramic composition as claimed in claim 1 which includes from 0.2 to 1.0% by weight cadmium calculated as CdCO3, from 0 to 1.5% by weight manganese calculated as MnO2 and from 0 to 1.0% by weight tungsten, calculated as WO3.