Merging of the polar and tilt instability lines near the respective morphotropic phase boundaries of PbZr_(1-x)Ti_xO_3

摘要

We present the results of anelastic and dielectric spectroscopy measurements performed on large-grain, ceramic PbZr_(1-x)Ti_xO_3 (PZT) compositions located near the two morphotropic phase boundaries (MPBs) that separate the ferroelectric (FE) rhombohedral (R) phase from the Zr-rich antiferroelectric and Ti-rich FE tetragonal phases. Additional evidence is provided of the existence of a temperature T_(IT), which we interpret as the onset of the tilt instability in the R phase, where tilting is initially frustrated by lattice disorder but achieves long-range order at the lower temperature T_T.The T_(IT)(x) line is observed for x < 0.17, beginning at the T_T(x) line at the point where T_T (x) drops abruptly and then continuing up to the T_C (x) line. If T_(IT) (x) indeed signals the onset of short-range ordered tilting, then it follows that the tilt instability lines should tend to be attracted and merge with those of the polar instabilities. Not only does the T_(IT) (x) line bend toward and then merge with the T_C(x) line but, in our series of samples, the temperature T_(MPB) defined by the dielectric and anelastic maxima at the rhombohedral/tetragonal MPB does not cross the T_ T(x) line. Instead it gradually bends downward to become parallel to, and possibly merges with, the T_T (x)line. An abrupt change is found in the shape of the anelastic anomaly at T_T when x passes from 0.465 to 0.48, possibly indicative of a rhombohedral/monoclinic boundary.