The equation of state of the Pmmn phase of NiSi

The equation of state of the orthorhombic phase of NiSi with Pmmn symmetry has been determined at room temperature from synchrotron-based X-ray diffraction measurements of its lattice parameters, made in a diamond anvil cell. Measurements were performed up to 44 GPa, using Ne as the pressure medium and Au as the pressure standard. The resulting pressure-volume (P-V) data have been fitted with a Birch-Murnaghan equation of state of third order to yield V0 = 11.650 (7) Å3 atom-1, K0 = 162 (3) GPa and K0' = 4.6 (2). In addition, P-V data have been collected on Ni53Si47 in the B20 structure using both Ne and He as the pressure media and Cu and Au as the pressure standards, also to 44 GPa. A fit using the same Birch-Murnaghan equation of state of third order yields V0 = 11.364 (6) Å3 atom-1, K0 = 171 (4) GPa and K0' = 5.5 (3).