| Large diameter (80 mmf) piezoelectric single crystals
of lead magnesium niobate/lead titanate (PMN-PT) grown by the one-batch melt
Bridgman method display an inhomogeneous distribution of the titanium (Ti) concentration
in the growth direction. This is an inevitable result of Ti segregation. Making
positive use of this phenomenon, the distribution of the Ti concentration in
single crystals and the dependence of dielectric/piezoelectric properties on
Ti concentration were investigated. As properties of PMN-PT, it is possible to
obtain a piezoelectric constant and electromechanical coupling coefficient with
far higher conversion efficiency than with the conventional lead zirconium titanate
(PZT: Pb(Zr,Ti)O3) ceramics. However, strong dependence of these properties
on the Ti concentration is also recognized. Moreover, even with the same Ti concentration,
significant variations exist in dielectric/piezoelectric properties. It is pointed
out that the establishment of a continuous feeding growth of crystal method is
needed in order to achieve a homogeneous Ti composition, and optimization of
poling conditions and the development of a domain control technique are needed
to control dielectric/piezoelectric properties within the desirable range. |
