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 La 0.63 (Ti 0.92 ,Nb 0.08 )O 3 by three X-ray powder diffractometers with different Δ d / d resolutions of 0.03%, 0.06% and 0.10%. The d and Δ d denote the λ /(2·sin θ ) and peak width where λ and θ are wavelength of X-ray and Bragg angle. Only the highest-resolution diffractometer of Δ d / 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 Δ d / 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 Δ d / d value.