Theoretical study of metal borides stability

We have recently identified metal-sandwich (MS) crystal structures and shown with ab initio calculations that the MS lithium monoboride phases are favored over the known stoichiometric ones under hydrostatic pressure. According to previous studies synthesized lithium monoboride (Li By) tends to be boron deficient (y=0.8-1.0), however, the mechanism leading to this phenomenon is not fully understood. We use a simple model to simulate this compound with ab initio methods and discover that the boron-deficient lithium monoboride is a remarkable adaptive binary alloy: it has virtually no energy barriers to change its composition post synthesis within a small but finite range of y at zero temperature. Having demonstrated that the model well explains the experimentally observed off-stoichiometry, we next compare the Li By and MS-LiB phases and find that the latter have lower formation enthalpy under high pressures. We also systematically investigate the stability of MS phases for a large class of metal borides. Our results suggest that MS noble-metal borides are less unstable than the corresponding Al B2 -type phases but not stable enough to form under equilibrium conditions. © 2006 The American Physical Society.

Duke Scholars

Author Stefano Curtarolo Thomas Lord Department of Mechanical Engineering and Materia ...