Structural Transformations and Froodite (α-PdBi2)–Urvantsevite (β-PdBi2) Phase Transition at High Temperatures

The phase transition in structure of the PdBi2 compound has been studied using high-temperature in-situ methods (differential thermal analysis and high-temperature single-crystal X-ray diffraction). The structures of PdBi2 polymorphic modifications are refined at temperatures of 300, 373, 473, 573, and 637 K based on high-temperature single-crystal X-ray diffraction data. A low-temperature modification of α-PdBi2 corresponding to froodite occurs in a temperature range from 300K (27°C) to 573K (300°С) and is characterized by monoclinic syngony, space group C2/m (a = 12.726(1) Å, b = 4.2605(4) Å, c = 5.5668(5) Å, β = 102.51(1)°, V = 299.95(5) Å3, Z = 2). A high-temperature modification of β-PdBi2, which is registered at a temperature of 673K (400°C), has tetragonal syngony and space group I4/mmm (a = 3.3876(3) Å, c = 13.092(2) Å, V = 150.24(4) Å3, Z = 1) and is a structural analog of urvantsevite. The phase transition is referred to as type I and is a reconstructive polymorphic transformation with the rearrangement of the first coordination sphere.