Thermal expansion and elasticity of PdFe<Subscript>3</Subscript>N within the quasiharmonic approximation

We have explored the bulk modulus and the thermal expansion of PdFe<Subscript>3</Subscript>N (space group <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$Pm\overline 3 m$</EquationSource> </InlineEquation>) using ab initio phonon dynamics within the quasiharmonic approximation in the temperature range from 50 to 1000 K. PdFe<Subscript>3</Subscript>N possesses a linear thermal expansion coefficient common for typical ceramics. The calculated average linear thermal expansion coefficient of 6.4 × 10<Superscript>-6</Superscript> K<Superscript>-1</Superscript> is consistent with the average measured coefficient of 6.7 × 10<Superscript>-6</Superscript> K<Superscript>-1</Superscript>. 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<Subscript>3</Subscript>N exhibits both metallic as well as covalent-ionic bonding. The Fe–N covalent-ionic bonding suppresses the lattice vibrations of the PdFe<Subscript>3</Subscript> matrix. The bulk modulus of 188 GPa for PdFe<Subscript>3</Subscript>N 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