Structural transformations and phase transition froodite (α–PdBi2) — urvantsevite (β–PdBi2) at high temperature

The phase transition in the structure of the PdBi2 compound was studied using high-temperature in-situ methods (differential thermal analysis, high-temperature single-crystal X-ray diffraction). The structures of PdBi2 polymorphic modifications were refined at temperatures of 300, 373, 473, 573 and 637 K based on the high-temperature single-crystal X-ray diffraction data. A low-temperature modification of α-PdBi2 is monoclinic, space group C2/m (a = 12.726(1)A, b = 4.2605(4)A, c = 5.5668(5)A, β = 102.51(1) °, V = 299.95(5)A3, Z = 2). It is stable in the temperature range from 300K (27 °C) to 573K (300 °С) and is corresponding to the mineral froodite. A high-temperature modification of β-PdBi2 was fixed at the temperature 673K (400 °C). The phase β-PdBi2 is structural analogue of the mineral urvancevite: it’s tetragonal, space group I4/mmm (a = 3.3876(3) A, c = 13.092(2) A, V = 150.24(4) A3, Z = 1). The phase transition refers to a type I and is a reconstructive polymorphic transformation with a rearrangement of the first coordination sphere.