Study of the antiferrodistortive (AFD) phase transition and the ground state of (Pb0.94Sr0.06) (Zrxt1-x)O3 (PSZT) in and around the Morphotropic Phase Boundary (MPB) region

PZT has been extensively exploited in a wide variety of commercial sensor and actuator device applications, but the physics behind the high piezoelectric response at the MPB and the ground state of PZT in and Zr-rich side of the MPB are still under intense debate. The ground state of PZT in the MPB region and Zr-rich side is the result of a competition between ferroelectric and AFD instabilities associated with zone centre Γ-4 and zone boundary R+4 optical phonons of the paraelectric phase. Present work was undertaken to settle the controversies about the space group of the ground state of PZT in and Zr-rich side of the MPB. To achieve this objective, (i) we doped PZT with smaller radius ion Sr2+ at Pb2+-site that will increase the tilt angle and thereby the intensity of the AFD superlattice reflections and (ii) we used high wavelength neutrons to increase the angular resolution of the superlattice peaks from the nearby perovskite peaks. The neutron diffraction data collected at 4K at ECHIDNA diffractometer, ANSTO, Australia on PSZT530 and at 12K at SPODI diffractometer, FRMII, Germany on PSZT550 clearly show that the peak position of (5/2 1/2 1/2) pseudocubic superlattice reflection cannot be accounted well by the R3c space group. To confirm the symmetry, we carried out Rietveld refinement, which shows that Cc is the correct space group of the ground state of PSZT for the MPB and Zr-rich compositions. (author)