The transition from the rhombohedral ferroelectric (FE) to the lower temperature orthorhombic antiferroelectric (AFE) phase in Zr-rich PZT involves two order parameters (OPs): 1) the polar OP responsible for the change from a prevalent FE <111> displacement of the Ti cations to the prevalent AFE <110> displacement of Pb; 2) an antiferrodistortive (AFD) OP responsible for tilting of the ZrO6 octahedra. It has been known that this transition may have extremely large thermal hysteresis and slow kinetics, partially attributed to the stabilisation of the FE phase by charged defects, but a recent combined anelastic, dielectric and X-ray diffraction study on PZT with x(Ti) = 0.05 revealed additional unexpected features [1]. The two OPs act together only in quasistatic experiments, while at cooling rates of 0.5 K/min or faster the polar component remains frozen and only the AFD transition is observable as a steplike softening in the Young's modulus. The latter transition remains rather sharp, but its temperature is lowered by an increased cooling rate. New measurements on compositions x ~ 0.05, close to the border to the FE phase, show that also the opposite behavior of the AFE component occurring in advance of octahedral tilting. In addition, the kinetics of the transition becomes slower with ageing, presumably due to clustering of O vacancies at the domain and twin walls. Such defect structures are probably at the origin of intense thermally activated relaxation processes observed above TC in the dielectric and anelastic spectra, and can be annealed out at >800 K, allowing the AFE transition to recover a fast kinetics. Depending on the temperature rate and sample history, a great variety of curves of the elastic compliance vs T is found, but all of them can be fitted very well fitted both for cooling and heating as superpositions of broadened steps for each of the following transformations: 1) AFE cation, 2) tilt to the orthorhombic AFE phase and 3) tilt within the non-transformed rhombohedral FE phase, the latter always sharp and with small thermal hysteresis.
Separate kinetics of the polar and antiferrodistortive order parameters in the antiferroelectric transition of PbZr1-xTixO3 and the influence of defects
F Cordero;C Galassi
2014
Abstract
The transition from the rhombohedral ferroelectric (FE) to the lower temperature orthorhombic antiferroelectric (AFE) phase in Zr-rich PZT involves two order parameters (OPs): 1) the polar OP responsible for the change from a prevalent FE <111> displacement of the Ti cations to the prevalent AFE <110> displacement of Pb; 2) an antiferrodistortive (AFD) OP responsible for tilting of the ZrO6 octahedra. It has been known that this transition may have extremely large thermal hysteresis and slow kinetics, partially attributed to the stabilisation of the FE phase by charged defects, but a recent combined anelastic, dielectric and X-ray diffraction study on PZT with x(Ti) = 0.05 revealed additional unexpected features [1]. The two OPs act together only in quasistatic experiments, while at cooling rates of 0.5 K/min or faster the polar component remains frozen and only the AFD transition is observable as a steplike softening in the Young's modulus. The latter transition remains rather sharp, but its temperature is lowered by an increased cooling rate. New measurements on compositions x ~ 0.05, close to the border to the FE phase, show that also the opposite behavior of the AFE component occurring in advance of octahedral tilting. In addition, the kinetics of the transition becomes slower with ageing, presumably due to clustering of O vacancies at the domain and twin walls. Such defect structures are probably at the origin of intense thermally activated relaxation processes observed above TC in the dielectric and anelastic spectra, and can be annealed out at >800 K, allowing the AFE transition to recover a fast kinetics. Depending on the temperature rate and sample history, a great variety of curves of the elastic compliance vs T is found, but all of them can be fitted very well fitted both for cooling and heating as superpositions of broadened steps for each of the following transformations: 1) AFE cation, 2) tilt to the orthorhombic AFE phase and 3) tilt within the non-transformed rhombohedral FE phase, the latter always sharp and with small thermal hysteresis.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
