Lead calcium titanate piezoelectric ceramic element

An improved lead calcium titanate piezoelectric sintered body is produced by sintering in air at 1000.degree. C.-1200.degree. C. a calcined mixture of oxides or oxide compounds in amounts adapted to form a composition of the formula Pb.sub.1-x Ca.sub.x Ti.sub.1-y (Co.sub.1/2 W.sub.1/2).sub.y O.sub.3 +0.005-0.02(A) where A is at least one of MnO, MnO.sub.2, NiO and Nb.sub.2 O.sub.3, wherein x=0.3-0.4 and 0.04<y.ltoreq.0.06.

BACKGROUND OF THE INVENTION 
This invention relates to new and improved piezoelectric sintered bodies of 
the lead calcium titanate type. 
Articles by Y. Yamashita, K. Tokoyama et al, Japan. J. Appl. Phys. 20, 
Suppl. 20-4, 183 (1981), Y. Yamashita, S. Yoshida et al, Proc. FMA 4, 
Kyoto, Japan, 25 (1983) and S. Jyomura et al, J. Appl. Phys. 52, 4472 
(1981) disclose sintered lead titanate piezoelectric ceramics exhibit 
characteristics making these useful for ceramic ultrasonic transducers. 
However, the piezoelectric ceramics disclosed in these references while 
showing properties that render these materials useful in some aspects 
exhibit other properties that make these materials less useful for use in 
ultrasonic transducers and for similar uses. 
While the Yamashita et al 1981 article shows piezoelectric compositions 
exhibiting a relatively high thickness mode coupling (k.sub.t) to planar 
mode coupling (k.sub.p) ratio, it has been found that the piezoelectric 
constant (d.sub.33) is not sufficiently high for some purposes. 
It is highly desirable for many purposes that the piezoelectric constant 
d.sub.33 be increased as far as possible while the ratio of k.sub.t 
/k.sub.p be maintained as high as possible. Additionally, it is also 
desired that the dielectric constant K be maintained as high as possible 
while the dissipation factor D be maintained as low as possible. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a sintered lead titanate body 
which exhibits a high k.sub.t /k.sub.p ratio a high piezoelectric constant 
(d.sub.33), a high dielectric constant (K) and a low dissipation factor 
(D). 
According to one aspect of the invention, it has been found that a novel 
sintered lead calcium titanate of the formula Pb.sub.1-x Ca.sub.x 
Ti.sub.1-y (Co.sub.1/2 W.sub.1/2).sub.y O.sub.3 +0.005-0.02(A) where A is 
at least one of MnO, MnO.sub.2, NiO or Nb.sub.2 O.sub.3 and wherein 
x=0.3-0.4 and 0.04&lt;y.ltoreq.0.06 exhibit an improved combination of a high 
piezoelectric constant d.sub.33, a high k.sub.t /k.sub.p coupling ratio, a 
low dissipation factor D and a high dielectric constant K. 
According to another aspect of the invention, a new and novel method has 
been developed for producing the novel piezoelectric bodies of the 
invention. 
In this method of the invention the novel piezoelectric bodies are produced 
by calcining a mixture of PbO, CaO, TiO, CO(OH).sub.2, WO.sub.3 and at 
least one of MnO, MnO.sub.2, NiO or Nb.sub.2 O.sub.3 the precursors of 
these materials and then sintering the resultant calcined mixture in an 
atmosphere consisting essentially of 10 to 20% of oxygen and 90-80% of 
nitrogen at a temperature of 1000.degree. C.-1200.degree. C. for a period 
of approximately 1-50 hours.

DETAILED DESCRIPTION OF THE INVENTION 
While improved results are achieved with the piezoelectric bodies of the 
invention having calcium content of 30-40 at.%, it has been found that 
even more improved results are achieved when the content of calcium is 
within 34-36 at.% inclusive. 
According to the novel method of the invention, the piezoelectric bodies 
may be prepared while calcining the ground mixture of the oxides PbO, CaO, 
TiO, CoO, WO.sub.3 and at least one of MnO, MnO.sub.2, NiO and Nb.sub.2 
O.sub.3 or of the precursors of these oxides such as the hydroxides, 
carbonates or acetates, all in amounts adapted to form piezoelectric 
bodies of the composition of the invention and sintering the resultant 
calcined mixture in an atmosphere consisting essentially of 10-20% of 
oxygen and 90-80% of nitrogen at a temperature of 1000.degree. 
C.-1200.degree. C. at a period of 1-50 hours. 
Calcining is carried out preferably at a temperature of 925.degree. 
C.-975.degree. C. It has been found that the best results are achieved 
when the sintering is carried out in air at a temperature of 1100.degree. 
C.-1150.degree. C. for a period of 5 hours to 30 hours. 
For a more complete understanding of the invention, operation of preferred 
embodiments of the invention will now be described in greater detail with 
reference to the following example. 
EXAMPLE 
Compositions of several variations of x and y in the formula 
EQU Pb.sub.1-x Ca.sub.x Ti.sub.1-y (Co.sub.1/2 W.sub.1/2).sub.y O.sub.3 
+0.01MnO 
were prepared from the raw materials: PbO, CaO or CaCO.sub.3, TiO.sub.2, 
Co(OH).sub.2, WO.sub.3 and MnO in the amounts as shown in the following 
Table 1. 
TABLE 1 
______________________________________ 
Material weight for 
Pb.sub.1-X Ca.sub.X Ti.sub.1-Y (Co.sub.1/2 W.sub.1/2).sub.Y O.sub.3 + 
0.01 MnO system 
Material Weight for 
X = 0.34 X = 0.34 X = 0.36 
X = 0.38 
1 Mole (g) Y = 0.04 Y = 0.06 Y = 0.04 
Y = 0.04 
______________________________________ 
Raw Materials 
PbO (223.19) 
147.3054 147.3054 142.8416 
138.3778 
CaO (56.08) 19.0672 -- -- 21.3104 
CaCO.sub.3 (100.0912) 
-- 34.0310 36.0328 
-- 
TiO.sub.2 (79.90) 
76.7040 75.1060 76.7040 
76.7040 
Co(OH).sub.2 (92.933) 
1.8587 2.7880 1.8587 1.8587 
WO.sub.3 (231.85) 
4.6370 6.9555 4.6370 4.6370 
MnO (70.938) 
0.7094 0.7094 0.7094 0.7094 
2% extra PbO 
4.4638 4.4638 4.4638 4.4638 
Evaporation 
CO.sub.2 (44.0112) 
-- -14.9638 -15.8440 
-- 
H.sub.2 O (18.0000) 
-0.3600 -0.5400 -0.3600 
-0.3600 
2% extra PbO 
-4.4638 -4.4638 -4.4638 
-4.4638 
Composition 249.6016 251.3915 246.5795 
242.9172 
Weight (g) 
______________________________________ 
After being weighed, the mixtures of these raw materials were prepared by 
mixing in a plaster bottle with zirconic balls and alcohol. 
The resultant mixtures were then ball milled for 24 hours, dried at 
120.degree. C., crushed and calcined in an aluminum crucible at 
950.degree. C. for 2 hours. 
The resultant calcined lumps were then crushed and ground in a mortar, 
sieved to pass 50 mesh, and ground again with a few weight % of deionized 
water. The wet calcined mixture was then pressed at 1.times.10.sup.8 
N/m.sup.2 (1000 Kg/cm.sup.2) in a die of 1.905 cm in diameter into green 
discs. 
The green discs were positioned between two platinum sheets to decrease Pb 
evaporation, and sintered in a covered crucible at 
1100.degree.-1120.degree. C. for 1, 5 or 30 hours. 
The sintered discs were lapped to a thickness of 0.9-1.3 mm. Both surfaces 
of the discs were then polished to a high brightness. 
Gold electrodes were then provided on both surfaces of the discs by 
sputtering. 
The gold-electroded discs were then poled in an oil bath at an elevated 
temperature in an electric field of 50 kV/cm for 5 minutes. 
The dielectric constant K, the thickness coupling factor k.sub.t, the 
planar coupling factor k.sub.p, the dissipation factor D and the 
piezoelectric constant of d.sub.33 were then determined for the resultant 
sintered discs. 
The dielectric constant K, the coupling factors k.sub.t and k.sub.p, the 
piezoelectric constant d.sub.33 and the dissipation factor D as a function 
of x amounts of Ca for bodies of the system Pb.sub.1-x Ca.sub.x 
Ti.sub.0.96 (Co.sub.1/2 W.sub.1/2).sub.0.04 O.sub.3 +0.01MnO are shown in 
the graph of FIG. 1. 
These are also shown as a function of y amounts of (Co.sub.1/2 W.sub.1/2) 
for the bodies of the system. Pb.sub.0.66 Ca.sub.0.34 Ti.sub.1-y 
(Co.sub.1/2 W.sub.1/2).sub.y O.sub.3 +0.01MnO in the graph of FIG. 2. 
The effect of sintering time on these for bodies of the system Pb.sub.0.66 
Ca.sub.0.34 Ti.sub.0.94 (Co.sub.1/2 W.sub.1/2).sub.0.06 O.sub.3 +0.01MnO 
are shown in the graph of FIG. 3. 
Additionally the dielectric constant K, and the coupling factors k.sub.p 
and k.sub.t as a function of x amounts of Ca for bodies of the system 
Pb.sub.1-x Ca.sub.x Ti.sub.0.96 (Co.sub.1/2 W.sub.1/2).sub.0.04 O.sub.3 
+0.3wt% MnO+0.4wt%NiO as described in Yamashita and Yokoyama et al, 1981 
are shown in the graph of FIG. 4. 
As will be noted from a comparison of the graphs of FIGS. 1, 2 and 3 with 
the graph of FIG. 4, the sintered lead calcium titanate piezoelectric 
bodies of the invention exhibit significantly higher k.sub.t /k.sub.p 
ratios particularly when sintered from 5 to 30 hours. 
The sintered lead calcium titanate piezoelectric bodies of the invention 
have the additional advantage of exhibiting a significantly higher 
piezoelectric constant.