Phase transitions of YbX (X = P, As and Sb) with a NaCl-type structure at high pressures

Abstract

The powder X-ray diffraction of YbX (X = P, As and Sb) with a NaCl-type structure has been studied with synchrotron radiation up to 63 GPa at room temperature. YbSb undergoes the first-order structural phase transition from the NaCl-type (B1) to the CsCl-type (B2) structure at around 13 GPa. The structural change to the B2 structure occurs with the volume collapse of about 1% at 13 GPa. The transition pressure of YbSb is surprisingly lower than that of any other heavier LnSb (Ln = Dy, Ho, Er, Tm and Lu). The pressure-induced phase transitions in YbP and YbAs are observed at around 51 GPa and 52 GPa respectively. The transition pressure of both compounds is much higher than that of YbSb. The high-pressure structural behaviour of YbX (X = P, As and Sb) is discussed. The volume versus pressure curve for YbX with the NaCl-type structure is fitted by a Birch equation of state. The bulk moduli of these compounds with the NaCl-type structure are 104 GPa for YbP, 85 GPa for YbAs and 52 GPa for YbSb.