High-Temperature Synchrotron X-Ray Powder Diffraction Study of the Orthorhombic–Tetragonal Phase Transition in La_0.63(Ti_0.92,Nb_0.08)O₃

Author： Ali R. Yashima M. Tanaka M. Yoshioka H. Mori T. Sasaki S.

Publisher： Academic Press

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.164, Iss.1, 2002-02, pp. : 51-59

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

The crystal structure of La_0.63(Ti_0.92,Nb_0.08)O₃ has been refined by the Rietveld analysis of CuKα X-ray powder diffraction data collected at 23°C. This material was confirmed to have an A-site deficient orthorhombic perovskite-type structure with double ideal perovskite ABO₃ units along the c-axis (space group Pmmm, Z=2, a=3.86036(5) Å, b=3.87222(5) Å, c=7.82609(9) Å). Lattice parameters of the same sample have been investigated in situ in the temperature range from 25°C to 496°C by 1.37873(3) Å synchrotron X-ray powder diffraction. The synchrotron X-ray powder diffraction technique was found to be very powerful to determine precise lattice parameters around a phase transition temperature. This compound exhibited a reversible phase transition between the orthorhombic and tetragonal phases at around 370°C. (1) The lattice parameters increased continuously with temperature, while the b/a ratio decreased continuously with temperature and became unity at the orthorhombic–tetragonal transition point. (2) No hysteresis was observed in the lattice parameter values between heating and cooling. These results of (1) and (2) suggest that the orthorhombic–tetragonal phase transition is continuous. © 2002 Elsevier Science (USA).