The crystal structure of MnAs above 40°C

Abstract

The crystal structure of MnAs between 40 and 125 °C has been found to be of the MnP (Bal) type, with a=5.72, b =3-676 and c =6.379 A, space group Prima (D~Sh). The orthorhombic cell is very close in dimensions to the orthohexagonal cell of a hexagonal structure and twinning invariably occurs to give pseudo-hexagonal symmetry. The atomic parameters have been deduced from intensity data for twinned crystals obtained at 55 °C with a precession camera. The distortions from a NiAs type structure are like those in MnP but less in magnitude. The extent of the distortion was found to be temperature dependent and to disappear at 125 °C with a reversion to a 1NiAs type structure, which occurs also below 40 °C.