Emeritus Professor Mike Glazer

Abstract:

PbZr1-x Tix O3 (PZT) ceramics made by mixed-oxide and sol-gel routes within the rhombohedral region of the phase diagram have been prepared, and their structures determined by Rietveld refinement using high-resolution time-of-flight neutron diffraction. Different structural models have been used but the best fits have been found using a mixture of rhombohedral R3c (C 3v 6) and monoclinic Cm (Cs3) across the whole rhombohedral range with the proportion of monoclinic phase increasing continuously with composition x toward the morphotropic phase boundary. Some differences are found between the ceramics prepared by the two routes, especially with respect to the diffraction peak widths, suggesting that the precise structural arrangements in these materials depend on the method of preparation. The results show that PZT ceramics made in this region always consist of mixed phases and this accounts for the fact that no phase boundary has been discovered in the PZT phase diagram between the monoclinic and rhombohedral phases. © 2009 The American Physical Society.

Abstract:

The phase diagram of lead-free piezoelectric Kx Na1-x NbO3 has been studied, with particular focus on the proposed morphotropic phase boundaries, by powder and single crystal x-ray diffraction. The tilt system and cation displacement has been mapped out as a function of temperature and composition, highlighting changes in the oxygen octahedra at x=0.2 and x=0.4 at room temperature. The orthorhombic to monoclinic boundary at x=0.5 has been investigated, with a subtle change in the structure observed. The conclusion is that Kx Na1-x NbO3 does not display a morphotropic phase boundary comparable with that in lead zirconate titanate, and that the most significant structural change as a function of composition occurs at x=0.2 because of the change of the tilt system. © 2009 American Institute of Physics.

Abstract:

Rietveld refinement using neutron powder diffraction data is reported for the potential lead-free piezoelectric material K(x)Na(1-x)NbO3 (x = 0.05, x = 0.3) at low temperatures. The structures were determined to be of rhombohedral symmetry, space group R3c, with the tilt system a(-)a(-)a(-) for both compositions. It was found that some of the structural parameters differ significantly in the two structures, and particularly the NbO6 octahedral strains as a function of temperature. The 300 K profile for K(0.05)Na(0.95)NbO3 shows the coexistence of rhombohedral and monoclinic phases, which indicates that the phase boundary is close to room temperature; the phase boundary for K(0.30)Na(0.70)NbO3 is found to be at approximately 180 K.

Abstract:

The structure of the A-site substituted perovskite K x Na1 - x NbO3, x = 0.24-0.36, where a phase boundary was previously reported, has been determined by high-resolution X-ray powder and neutron powder diffraction studies. The structure of the x = 0.3 compound was refined in the monoclinic space group Pm at 293 K and in P4mm at 523 K. The Glazer tilt system of the room-temperature monoclinic phase is a 0 b + c 0, which has implications for the nature of the next symmetry change with composition towards pure potassium niobate. A phase-coexistence region at the transition between monoclinic and tetragonal phases was also identified, consistent with a first-order phase boundary. There is also evidence for an intermediate oxygen-octahedra tilted tetragonal phase. © 2009 International Union of Crystallography Printed in Singapore - all rights reserved.