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Monday, August 29, 2016
Abstract-Lattice dynamics and domain wall oscillations of morphotropic Pb(Zr,Ti)O3 ceramics
E. Buixaderas, V. Bovtun, M. Kempa, D. Nuzhnyy, M. Savinov, P. Vanek, I. Gregora, and B. Malic
Phys. Rev. B 94, 054315 – Published 29 August 2016
The temperature dependence of the optical phonons and high-frequency microwave excitations of morphotropic Pb(Zr1−xTix)O3 (PZT) ceramics with compositions PZT 52/48 and 53/47 were studied by a broadband spectroscopy approach, using Raman, far-infrared, time-domain terahertz (THz), and microwave spectroscopies. A careful evaluation of the evolution of phonon parameters with temperature clearly revealed only two macroscopic phase transitions of intrinsic origin, driven by phonons: the ferroelectric one at high temperatures near 650 K (driven by an anharmonic soft mode at THz frequencies coupled to a weak component at higher frequencies, ω∼70cm−1) and a transition to an antiferrodistortive phase around 400 K, signaled by a new peak (ω∼60cm−1) that appeared in the infrared and Raman spectra. This peak confirmed the onset of the antiphase tilt of the oxygen octahedra and the doubling of the unit cell, as well as the splitting of the B1−E doublet in the Raman spectra. No indications of an additional phase transition were found by these techniques down to 20 K. On the other hand, dielectric measurements below the phonon frequencies showed anomalies at lower temperatures; however, they had extrinsic character and were not related to the atomic vibrations. An excitation in the gigahertz range displayed a softening towards 270 K, in agreement with a maximum in the low-frequency dielectric loss spectra. The quantitative analysis of this excitation revealed the presence of two contributions assigned to piezoelectric resonances in grains and domain wall oscillations, which, together, satisfactorily explain the dielectric anomaly below room temperature, without taking into account another transition to a lower-symmetry phase.