Effects of aging and annealing on the polar and antiferrodistortive components of the antiferroelectric transition inPbZr1−xTixO3

Abstract

The antipolar and antiferrodistortive (AFD) components of the antiferroelectric (AFE) transition in PbZr1−xTixO3 (x ≤ 0.054) can occur separately and with different kinetics, depending on the sample history, and are accompanied by elastic softening and stiffening, respectively. Together with the softening that accompanies octahedral tilting in the fraction of phase that is not yet transformed into AFE, they give rise to a variety of shapes of the curves of the elastic compliance versus temperature. All such anomalies found in samples with x = 0.046 and 0.054, in addition to those already studied at x = 0.050, can be fitted consistently with a phenomenological model based on the simple hypothesis that each of the polar and AFD transitions produces a step in the elastic modulus, whose position in temperature and width reflect the progress of each transition. The slowing of the kinetics of the transformations is correlated with the formation of defect structures during aging in the ferroelectric (FE) or AFE state, which are also responsible for a progressive softening of the lattice with time and thermal cycling, until annealing at high temperature recovers the initial conditions.

Separate Kinetics of the Polar and Antiferrodistortive Order Parameters in the Antiferroelectric Transition of PbZr1-xTixO3 and the Influence of Defects

“…Below ∼6% Ti the low-T phase is O-AFE, with a tilt pattern a − a − c 0 where the rotation about the pseudocubic c axis is absent. The anelastic spectra show that the T T line continues into the region of coexistence of the R-FE and O-AFE phases [3,4]. The crossing of all these phase borders can be revealed as more or less broadened steps in the elastic compliance s'(T ), and generally also in the Q −1 = s /s , but we will consider the losses only when dealing with the relaxations at high T .…”

“…It has been recognized that this transition may have extremely large thermal hysteresis and slow kinetics, partially attributed to the stabilization of the FE phase by charged defects [2], but a recent combined anelastic, dielectric and X-ray diffraction study on PZT with x(Ti) = 0.05 revealed additional unexpected features [3], further studied in connection with the effect of aging and high temperature annealing [4].…”

Elastic aging from coexistence and transformations of ferroelectric and antiferroelectric states in PZT

“…Aging and thermal cycling through the AFE/FE transition may also cause outstanding softenings of the Young's modulus and splitting of the antipolar and octahedral tilt modes involved in the AFE/FE transition, which however can be fully recovered with mild annealing 10,11,12 . In order to better understand the nature of these phenomena in PbZrO 3 -based materials, and in particular whether the orthorhombic AFE phase itself plays a particular role, we study here the effect of La doping on the elastic aging.…”

“…The jump in ε ′ is due to the first order nature of the transition, though the thermal hysteresis is only 2.5 K. Notice the logarithmic scale of ε ′ in order to put in evidence the anomalies at the AFE transitions. The transition between the R-FE and the orthorhombic (O) AFE phase has a large thermal hysteresis, and the susceptibility curves during cooling may strongly depend on the cooling rate and state of the sample 10,11 . For this reason, the two temperatures T c AF from the s and ε curves are different, and the anomaly in ε ′ has not the same shape as during heating.…”

“…2 for the lack of a spike, which appeared in the fourth cycle (not shown). The shape of the elastic anomaly at T AF depends on the sample and its history and can be fitted with the superposition of two steps of opposite signs corresponding to the transitions in the polar and octahedral tilt modes; apparently, the transition kinetics of these modes may be differently affected by aging and fatigue, resulting in a variety of shapes 10,11 . The spike arises from a slight shift in T of the centers of the two opposite steps.…”