INCOMMENSURATELY MODULATED POLAR STRUCTURES IN ANTIFERROELECTRIC TIN-MODIFIED LEAD-ZIRCONATE-TITANATE - II, DEPENDENCE OF STRUCTURE-PROPERTY RELATIONS ON TIN CONTENT

Studies of the structure-property relations in Pb0.98Nb0.02-[(Zr1-xSnx )(0.97)Ti-3](1-z)O-3 (PZST x/3/2) were performed for 0 < x < 0.50 by t ransmission electron microscopy, dielectric spectroscopy, and electric ally induced polarization and strain methods. As the tin content incre ased, a general sequence of changes in phase stability was observed, i ncluding (i) a ferroelectric rhombohedral (FEr) phase (x < 0.15), (ii) a coexistence of FEr and antiferroelectric incommensurate (AFE(in)) s tates (x = 0.15), and (iii) an AFE(in) state (x > 0.15), Evidence will be presented that incommensurately modulated structures become pinned into long-lived metastable states by quenched tin impurities, rather than evolving toward a commensurate phase. Maximum electrically induce d strains (epsilon) and polarizations (P) were found in the compositio nal range of x approximate to 0.15, where FEr and AFE(in) regions coex isted, Values of epsilon as large as 0.5% were found at field strength s of <80 kV/cm, In addition, these studies demonstrated evidence for t wo electrically induced phase transitions (x = 0.15): (i) an antiferro electric-ferroelectric (AFE-FE) transition near 40 kV/cm, and (ii) a s econdary ferroelectric-ferroelectric (FE-FE) transition near 60-80 kV/ cm, The dominate contribution to epsilon was associated with the secon dary transition, whereas the dominate contribution to P was associated with the first. For x < 0.15, evidence of an induced FE-FE transition was found, For x > 0,15, an induced AFE-FE transition was evident, Ho wever, no indications of a secondary FE-FE transition were observed. L arge epsilon values were not induced until field levels significantly greater than that required to induced polarization saturation were obt ained, which indicates a decoupling of epsilon and P.