INCOMMENSURATELY MODULATED POLAR STRUCTURES IN ANTIFERROELECTRIC SN-MODIFIED LEAD-ZIRCONATE-TITANATE - THE MODULATED STRUCTURE AND ITS INFLUENCES ON ELECTRICALLY-INDUCED POLARIZATIONS AND STRAINS

Tin-modified lead zirconate titanate ceramics, Pb-(0.99)Nb-0.02-[(Zr0. 55Sn0.45)(0.98)Ti-y]O-3 (PZST 45/y/2), have been studied by hot-stage transmission electron microscopy (TEM), dielectric spectroscopy. Sawye r-Tower polarization (P-E) measurements, and electrically induced stra in (epsilon-E) techniques. The compositional range chosen for investig ation was 0 < y < 0.09. Electron diffraction confirmed the existence o f 1/x[110] superlattice reflections in the previously designated antif erroelectric tetragonal state. For PZST 45/0/2, the room-temperature m odulated structure was found to be commensurate with the lattice and i somorphous with the antiferroelectric orthorhombic phase of PbZrO3. Wi th increasing Ti content, the modulation wavelength (lambda) increased and became incommensurate. At high temperatures, lambda was found to be incommensurate for all compositions. A model is discussed which sug gests that the origin of incommensuration is due to a competition betw een antiferroelectric and ferroelectric tendencies. P-E studies reveal ed antiferroelectric-ferroelectric (AFE-FE) polarization curves which possessed no hysteresis in the incommensurate region, indicating a the rmally reversible AFE-FE transformation. On cooling, strong hysteresis developed as the incommensurate structure became metastably locked. I nvestigations then revealed that the electrically induced strain assoc iated with the AFE-FE transformation was not realized until field stre ngths were attained significantly above that required for polarization saturation. It is believed that the electrically induced strain is de coupled from the polarization due to AFE-FE switching by the field mod ulation of the incommensurately modulated polar structure.