Electronic and structural origin of ultraincompressibility of 5d transition-metal diborides MB(2) (M=W, Re, Os).
First-principles theory was used to investigate the roles of bond topology and covalency in the phase stability and elastic strength of 5d transition-metal diborides, focusing on elements (M=W, Re, Os) that have among the lowest compressibilities of all metals. Among the phases studied, the ReB(2)-type structure exhibits the largest incompressibility (c axis), comparable to that of diamond. This ReB(2) structure is predicted to be the ground-state phase for WB(2) and a pressure-induced phase (above 2.5 GPa) for OsB(2). Both strong covalency and a zigzag topology of interconnected bonds underlie these ultraincompressibilities. Interestingly, the Vickers hardness of WB(2) is estimated to be similar to that of superhard ReB(2).
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6114, USA.
Xing-Qiu
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Chen
C L
CL
Fu
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Krcmar
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Painter