Bi1-xSbx under high pressure:: Effect of alloying on the incommensurate Bi-III type composite structure -: art. no. 134203

The high-pressure structural behavior of alloys Bi1-xSbx was investigated experimentally and by means of first-principles calculations in order to study the effect of alloying on the incommensurate Bi-III type composite structure, which is adopted by the high-pressure phases Bi-III and Sb-II of the pure elements. High-pressure experiments of Bi0.75Sb0.25 and Bi0.50Sb0.50 resulted in a decomposition into Sb-rich phases with the ambient A7 structure and Bi-rich phases with the Bi-III structure. For Bi0.50Sb0.50 two composite phases were observed with different compositions. Bi0.25Sb0.75 transformed from A7 to Bi-III, such as elemental Sb, and did not show a phase separation under pressure. For the pure elements, the structural parameters of the high-pressure composite phase are similar and vary only very slightly with pressure. The parameters of the alloy composite phases distribute rather smoothly in between those for the elements. The incommensurate composite phases in alloys Bi1-xSbx appear to be site disordered. Importantly, the incommensuration of the Bi-III structure is virtually not influenced by either composition or pressure. Total energy calculations as a function of pressure yielded endothermic enthalpies of formation for alloys Bi1-xSbx in both the ground-state A7 structure and the high-pressure Bi-III structure. The formation enthalpy takes a maximum value at a pressure corresponding to the alloy A7-->Bi-III transition, which explains the experimentally observed phase separations.