Crystal synthesis and Debye temperature determination of PdSb₂: Usefulness of single crystal precise structure analysis

Single crystals of pyrite-type PdSb₂ were grown by sealing a stoichiometric proportion of the elements in an evacuated silica glass tube and heating the tube in a furnace at 930 K for 20 days. The crystal structure of PdSb₂ [space groupPa3¯, a = 6.4659(2) Å, u = 0.37331(3), Z = 4] was refined to R1 = 0.0171 for 374 unique reflections obtained by single-crystal X-ray diffraction experiments. The lattice constant, a, and anion-anion distance of 2.8677(3) Å are slightly different from the previously reported values. The single crystal diffraction method has excellent advantages such that the Debye temperature can be determined for each crystallographically independent site. The obtained Θ_D values for Pd and Sb in PdSb₂ are 258 K and 214 K, respectively. Characteristically, the Debye temperatures, Θ_D, of both atoms in PdSb₂ were found to be very low among the pyrite-type transition metal pnictides and chalcogenides. Certain regularities between the cation–anion bonding distances and Debye temperatures were found in pyrite-type compounds. The vibration of anion contributes to the highest energy part of the normal mode of thermal vibration, when the cation–anion bonding distances in pyrite-type compounds are shorter than 2.6 Å.