Phase transitions of LnSb (Ln=lanthanide) with NaCl-type structure at high pressures

Using synchrotron radiation, X-ray diffraction patterns of LnSb (Ln=Pr, Nd, Sm, Gd and Tb) with a NaCl-type structure have been measured up to 30 GPa at room temperature. First-order phase transitions with a crystallographic change occur at around 13 GPa for PrSb and 15 GPa for NdSb. The structure of the high-pressure phases of both antimonides is tetragonal (Ln: 0,0,0; Sb: 1/2, 1/2, 1/2; space group P4/mmm), and can be viewed as a distorted CsCl structure. The structure of the high-pressure phase of LnSb (Ln=La, Ce, Pr and Nd) is more anisotropic compared with that of corresponding LnP. Pressure-induced phase transitions of SmSb, GdSb and TbSb are observed at around 19, 22 and 21 GPa, respectively.