Roushown Ali

Structural Disorder and Diffusional Pathway of Oxide Ions in a Doped Pr2NiO4-Based Mixed Conductor

MEM nuclear density analysis from neutron diffraction data measured in situ at 1015.6 degrees C has indicated the two-dimensional network of curved O2-O3-O2 oxide-ion diffusion paths on the (Pr,La)-O layer in a K2NiF4-type structured oxide-ionic and electronic mixed conductor (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+delta.

High-temperature X-ray diffraction study of the lanthanum aluminium titanate perovskite La0.683Ti0.95Al0.05O3

Abstract High-temperature X-ray powder diffraction experiments have been performed to investigate precisely the lattice parameters of an ionic conducting material La 0.683 Ti 0.95 Al 0.05 O 3 perovskite. This material was orthorhombic (space group P/mmm) at 29 and 192°C, while it was tetragonal (space group P4/mmm) from 392 to 1402°C. The orthorhombic–tetragonal phase transition is a possible explanation for the change in the temperature dependence of ionic conductivity around 400°C.

High-temperature synchrotron X-ray powder diffraction study of the orthorhombic–tetragonal phase transition in lanthanum titanate perovskite La0.68(Ti0.95,Al0.05)O3

Abstract We have investigated in situ an orthorhombic ( o )–tetragonal ( t ) phase transition of double perovskite-structured La 0.68 (Ti 0.95 ,Al 0.05 )O 3 by high-resolution ( Δd / d ≈0.0002) synchrotron powder diffraction technique. The unit-cell parameters increased continuously with temperature also near the o – t transition point. Good agreement was obtained in the unit-cell parameter values between heating and cooling. These results indicate that the o – t phase transition occurs reversibly and continuously at T c =350±2 °C. We demonstrate that the present synchrotron X-ray powder diffraction technique is very powerful to determine both the transition temperature of a continuous transformation and precise unit-cell parameters even near the continuous transition point.

Dependence of the accuracy of a continuous phase transition temperature on angular resolution in powder diffractometry

Abstract We have investigated in situ a continuous transition between the orthorhombic and tetragonal phases in perovskite-structured La0.63(Ti0.92,Nb0.08)O3 by three X-ray powder diffractometers with different Δd/d resolutions of 0.03%, 0.06% and 0.10%. The d and Δd denote the λ/(2·sinθ) and peak width where λ and θ are wavelength of X-ray and Bragg angle. Only the highest-resolution diffractometer of Δd/d=0.03% was able to detect the peak splitting between 400 and 040 reflections in the temperature range of 327–339°C. It was found that the accuracy of the transition temperature is considerably improved with decreasing of Δd/d value. The maximum temperature where the peak splitting between 400 and 040 reflections is detectable increases, while the transition temperature determined by a power law decreases with decreasing of Δd/d value.

Lattice parameters and structural phase transition of lanthanum titanate perovskite, La0.68(Ti0.95,Al0.05)O3

Lattice parameters and the structural phase transition of La(0.68)(Ti(0.95),Al(0.05))O(3) have been investigated in situ in the temperature range 301-689 K by the synchrotron radiation powder diffraction (SR-PD) technique. High-angular-resolution SR-PD is confirmed to be a powerful technique for determining precise lattice parameters around a phase-transition temperature. The title compound exhibits a reversible phase transition between orthorhombic and tetragonal phases at 622.3 +/- 0.6 K. The following results were obtained: (i) 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; (ii) no hysteresis was observed between the lattice-parameter values measured on heating and on cooling. Results (i) and (ii) indicate that the orthorhombic-tetragonal phase transition is continuous and reversible. The b/a ratio is found to exhibit a more continuous temperature evolution than does the order parameter for a typical second-order phase transition based on Landau theory.