Phase transitions of LnAs (Ln = Pr, Nd, Sm, Gd, Dy and Ho) with NaCl-type structure at high pressures

Abstract

By use of synchrotron radiation the powder x-ray diffraction of lanthanide monoarsenides LnAs (Ln = Pr, Nd, Sm, Gd, Dy and Ho) with a NaCl-type structure has been studied up to 60 GPa at room temperature. First-order phase transitions with crystallographic change were found at around 27.1 GPa for PrAs, 24.2 GPa for NdAs and 32.1 GPa for SmAs. The high-pressure form of the lighter LnAs (Ln = Pr, Nd and Sm) is a tetragonal structure and can be viewed as a distorted CsCl-type structure. The atoms in the tetragonal structure are located at Ln: 0,0,0; As: 1/2,1/2,1/2. The space group is P4/mmm. Pressure-induced phase transitions of the heavier LnAs (Ln = Gd, Dy and Ho) with many f electrons occur at around 36 GPa for GdAs, 44 GPa for DyAs and 46 GPa for HoAs. The structure of these high-pressure phases is unknown. The high-pressure structural behaviour of LnAs (Ln = Pr, Nd, Sm, Gd, Dy and Ho) with the NaCl-type structure is discussed.