HOT-STAGE TRANSMISSION ELECTRON-MICROSCOPY STUDIES OF PHASE-TRANSFORMATIONS IN TIN-MODIFIED LEAD-ZIRCONATE-TITANATE

The temperature dependence of phase stability for tin-modified lead zirconate titanate solid solution ceramics Pb(0.98)Nb0.02[(Zr1-x,Snx)1-yTiy]1-zO3 (PZST) was investigated by hot-stage transmission electron microscopy. Compositions studied included, a material that was antiferroelectric (AFE) at room temperature with x=0.42 and y=0.04, and a material that was ferroelectric (FE) at room temperature with x=0.43 and y=0.08 (abbreviated as PZST 42/4/2 and 43/8/2, respectively). PZST 42/4/2 was found to exhibit a sequence of phase transformations on heating of AFE-multicell cubic (MCC)-simple cubic (SC), whereas PZST 43/8/2 had a sequence of FE-AFE-MCC-SC. Previously referred to F spots (i.e., 1/2[111] superlattice spots) were observed in all four phases. The diffraction intensities for the F spots decreased with increasing temperature, and eventually disappeared above 300-degrees-C. Electron diffraction confirmed the presence of the MCC phase which was characterized by the existence of weak 1/2[110] superlattice spots in the temperature region between the AFE and SC phases. In each composition the AFE phase was characterized by arrays of one-dimensional antiphase domain boundaries and (1/x)[110] superlattice spots. The modulation wavelength for the superlattice spots was found to be a strong function of temperature and was incommensurate with the lattice. The thermal stability of phases in the crystalline solution PZST system is discussed in terms of the observed microstructural features.