Effect of the M3+ cation size on the structural and high temperature phase transitions in Sr2 MSbO6 (MÂ =Â Ln, Y) double perovskites

We present a rigorous study of the crystal structures at room temperature of Sr2MSbO6 (M= Ln and Y) compounds by using Synchrotron and laboratory XRPD. An in situ high-temperature measurements show the existence of two temperature driven phase-transitions: a discontinuous one, from the RT symmetry P21/n to R3¯ and a continuous one from the latter symmetry to the highest one, the cubic Fm3¯m. The physics behind the origin of the phase-transition sequence observed in the antimony materials is discussed. The phase transition temperatures are correlated to the M3+ cation size. The analysis of the phase transitions and the structural refinements was done using a novel tool: the symmetry-adapted modes instead of the conventional atomic coordinate method. A step forward in these analysis consisting of parametrization of the refinements by fixing a selected common direction in the sub-space spanned by X5+, this parametrization is confirmed by energy calculations (to be published) that has given us more physical arguments that corroborate the main conclusions of the workflow we are developing.90