Effects of fluorine-oxygen substitution on the dielectric and electromechanical properties of lead zirconate titanate ceramics

In this study, a fluorine-oxygen substitution in lead zirconate titanate (PZT) ceramics with a nominal composition of Pb-0.89(Ba, Sr)(0.11)(Zr0.52Ti0.48)O-3 (PZT) doped with 1% MgO is proposed. The evolution of four dielectric and electromechanical coefficients-epsilon(r), tg delta, d(33), and Q(m)-with increasing fluorine concentration showed that (MgO and F)-doped PZT ceramics are harder than only MgO-doped PZT (0 at. % F). The influence of the F-O substitution on the temperature dependence of the frequency constant N-33 and the stress dependence of the piezoelectric coefficient d(33) was investigated. A hysteretic free response of N-33 and the lowest stress dependence of d(33) were obtained for the (MgO and 4 at. % F)-doped PZT specimen. This material also exhibits the highest Q(m) in the (MgO and F)-doped PZT family and seems to be stoichiometric and without oxygen vacancies. For comparison, both the temperature and stress dependences of two commercial PZT ceramics are shown. The study of the influence of the Zr/Ti ratio on the temperature dependence of N-33 revealed that fluorine stabilizes the rhombohedral phase/tetragonal phase interface. Both types of stability, versus temperature and uniaxial mechanical stress, may be linked to the domain wall configuration stabilization by Mg2+-F- dipoles which are less mobile than Mg2+-V-O ones. (C) 1999 American Institute of Physics. [S0021-8979(99)00822-1].