STRUCTURAL PHASE-STABILITY OF THSB AND THAS UNDER PRESSURE

The high-pressure behaviour of thorium monopnictides is of considerabl e interest as these systems exhibit structural phase transitions under pressure, At ambient conditions these compounds crystallize in the Na Cl-type(B1) structure. Experiments show that with the application of p ressure these compounds transform to the CsCl-type (B2) structure. ThS b and ThAs are found to exhibit B1-B2 transition in the pressure range between 9-12 GPa and 1826 GPa respectively. In this work, we present the electronic and high-pressure behaviour of ThAs and ThSb performed using the tight-binding linear muffin-tin orbital method. The total en ergies within the atomic sphere approximation were calculated as a fun ction of volume for both the B1 and B2 structures. The total energy ca lculations reveal that both ThSb and ThAs are stable in the B1 structu re at ambient conditions and undergo structural transition to the B2 s tructure at pressures 78 and 240 kbar respectively, which are in good agreement with the experimental values. The calculated values of equil ibrium lattice parameter and the transition pressure are found to be i n good agreement with the experimental results.