Composition design and high electromechanical effect in the PNN-based ceramics

Abstract

Relaxor-type ferroelectric perovskite Pb(Ni_1/3Nb_2/3)O₃ (PNN) could be synthesized through a two-steps process consisting of heat treatment at high temperatures and then acetic acid treatment of oxide mixture containing PbO in amount greater than in the perovskite composition, though until now it is very difficult to obtain its single phase. This made possible to open a new route of actuator materials in the combination of PNN and other kinds of perovskite compounds. In this paper, an investigation was undertaken for the combinations with perovskites PbTiO₃ (PT), PbZrO₃ (PZ) and Pb(Sc_1/2Nb_1/2)O₃ (PSN), such as PNN-PT, PNN-PZ-PT, PNN-PSN and PNN-PSN-PT, to search compositions giving higher electric field-induced strain. In order to obtain higher strain, it was essential to bring close the composition near the morphotropic phase boundary (MPB) from rhombohedral to tetragonal symmetry. For the PNN-based ceramics showing higher strain, the potentiality as actuator was discussed.