Thermal Expansion of Molybdenum Phosphides

Transition metal phosphides, nitrides and carbides are well known for their useful material proper-ties, such as hardness, strength, and high melting points. In addition, they show interesting physical properties, such as comparatively high transition temperatures for the on-set of superconductivity (e.g. TaC) with corresponding anomalies in their phonon dispersion relations, while the phosphides may be potentially useful in hydro-processing reactions (e.g. [1]). Only little is known about phase diagrams and thermodynamic properties. Here, high-resolution temperature-dependent synchrotron diffraction experiments performed at the beamline B2 are re-ported. MoP and MoP2 were studied at atmospheric conditions up to temperatures of approx. 1300 K applying a mirror furnace. Samples were prepared in corundum capillaries and tempera-tures were determined by following the thermal expansion of corundum. The diffraction patterns were analysed by the pattern matching procedure, implemented in the Rietveld program Fullprof [2]. MoP crystallises in the WC-type structure [3]. Within the experimental uncertainties there is no deviation from a linear thermal expansion behaviour in MoP (Fig. 1). The thermal expansion coefficients were determined by linear fits. For T0 = 300 K they are α||a = 6.7(1) · 10−6 K−1 an