Thermal expansion and elasticity of PdFe 3N within the quasiharmonic approximation

We have explored the bulk modulus and the thermal expansion of PdFe 3N (space group $Pm\overline 3 m$ ) using ab initio phonon dynamics within the quasiharmonic approximation in the temperature range from 50 to 1000 K. PdFe 3N possesses a linear thermal expansion coefficient common for typical ceramics. The calculated average linear thermal expansion coefficient of 6.4 × 10 -6 K -1 is consistent with the average measured coefficient of 6.7 × 10 -6 K -1 . We have shown here that the thermal behavior of this compound can be understood based on the electronic structure and the lattice dynamics thereof. PdFe 3N exhibits both metallic as well as covalent-ionic bonding. The Fe–N covalent-ionic bonding suppresses the lattice vibrations of the PdFe 3 matrix. The bulk modulus of 188 GPa for PdFe 3N decreases by 15% in the temperature range studied, which is expected due to presence of stiff Fe–N bonds. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010