Method for producing piezoelectric ceramics

Claim 1

A method for producing a piezoelectric ceramic of a system Pb(Sn.sub.α Sb 1- α)O 3 -PbTiO 3 -PbZrO 3 , which comprises (a) preparing a mixture of raw materials selected from the group consisting of oxides and materials which produce oxides by calcination, to provide a piezoelectric ceramic composition expressed by the general formula xPb(Sn.sub.α Sb 1- α)O 3 -yPbTiO 3 -zPbZrO 3 wherein subscrips α, x, y and z are mole fractions of the respective components and wherein x+y+z=1.00, 1/4≦α≦3/4, said composition falling within a polygonal area defined by the points A, B, C, D and E in FIG. 3 (except the compositions defined by a line connecting the points A and E), the sets of mole fractions of the three components at said points being as follows: ______________________________________ x y z ______________________________________ A 0.01 0.99 0.00 B 0.01 0.04 0.95 C 0.04 0.01 0.95 D 0.40 0.01 0.59 E 0.40 0.60 0.00 ______________________________________ (b) calcining said mixture and grinding the calcined body, (c) forming the resultant powder into forming bodies, and (d) sintering the forming bodies by firing them at a temperature of 1100°to 1350° C. in an oxygen atmosphere containing not less than 80 vol% of oxygen so as to produce an intermediate pyrochlore phase of Pb 2 Sn 2 α Sb 2-2 α O 7- α with oxygen defects at the grain boundaries of the forming bodies during the sintering process which promotes transfer of oxygen ions at said boundaries and effects the production of a fine, dense ceramic; said pyrochlore phase being converted into a perovskite phase Pb(Sn 60 Sb 1- α)O 3 at the end of the firing.

Claim 2

A method for producing a piezoelectric ceramic of a system Pb(Sn.sub.α Sb 1- α)O 3 -PbTiO 3 -PbZrO 3 , which comprises (a) preparing a mixture of raw materials selected from the group consisting of oxides and materials which produce oxides by calcination, to provide a piezoelectric ceramic composition expressed by the general formula xPb(Sn.sub.α Sb 1- α)O 3 -yPbTiO 3 -zPbZrO 3 wherein subscrips α, x, y and z are mole fractions of the respective components and wherein x+y+z=1.00, 1/4≦α≦3/4, said composition falling within a polygonal area defined by the points A, B, C, D and E in FIG. 3 (except the compositions defined by a line connecting the points A and E), the sets of mole fractions of the three components at said points being as follows: ______________________________________ x y z ______________________________________ A 0.01 0.99 0.00 B 0.01 0.04 0.95 C 0.04 0.01 0.95 D 0.40 0.01 0.59 E 0.40 0.60 0.00 ______________________________________ (b) calcining said mixture and grinding the calcined body, (c) forming the resultant powder into forming bodies, and (d) sintering the forming bodies by firing them at a temperature of 1100°to 1350° C. in an oxygen atmosphere containing not less than 80 vol% of oxygen so as to produce an intermediate pyrochlore phase of Pb 2 Sn 2 α Sb 2-2 α O 7- α with oxygen defects at the grain boundaries of the forming bodies during the sintering process which promotes transfer of oxygen ions at said boundaries and effects the production of a fine, dense ceramic; said pyrochlore phase being converted into a perovskite phase Pb(Sn 60 Sb 1- α)O 3 at the end of the firing.