Space group symmetries of the phases of (Pb0.94Sr0.06)(ZrxTi1-x)O3 across the antiferrodistortive phase transition in the composition range 0.620<x<0.940

TL;DR

This study clarifies the space group symmetries of Pb(ZrxTi1-x)O3 across the antiferrodistortive transition, resolving controversies with detailed diffraction analysis and proposing a comprehensive phase diagram for compositions 0.40<x<0.90.

Contribution

It provides definitive symmetry assignments for phases in PSZT near the AFD transition, using combined diffraction and dielectric measurements, and refines the phase diagram for these compositions.

Findings

Rietveld analysis rejects rhombohedral phases above and below TAFD.

Monoclinic symmetries Cc and Cm are confirmed below and above TAFD.

A phase diagram for 0.40<x<0.90 is proposed, showing stability fields of various phases.

Abstract

The existing controversies about the space group symmetries of Pb(ZrxTi1-x)O3 (PZT) above and below antiferrodistortive (AFD) phase transition temperature (TAFD) in the Zr4+- rich (0.620<x<0.940) compositions are addressed using the results of dielectric, synchrotron x-ray powder diffraction (SXRPD) and neutron powder diffraction (NPD) studies. These compositions undergo an AFD phase transition above room temperature due to tilting of oxygen octahedral leading to a superlattice phase of PZT. We have substituted 6% Sr2+ at Pb2+-site to enhance the tilt angle and thereby the intensity of the superlattice peaks. The real and imaginary parts of complex dielectric permittivity have been used to locate the paraelectric to ferroelectric and ferroelectric to AFD phase transitions. Rietveld analysis of SXRPD and NPD profiles unambiguously reject the rhombohedral phases in R3c and R3m space groups below and above TAFD, respectively, with or without a coexisting monoclinic phase in Cm space group, and confirm that the true symmetries are monoclinic in Cc and Cm space groups below and above TAFD, respectively. Based on these and previous findings a phase diagram of PSZT for 0.40<x<0.90 showing stability fields of monoclinic Cc and monoclinic Cm, tetragonal P4mm and cubic Pm3m phases has also been presented.