Structure and stability trends in the platinum metal-silicon systems

Abstract: The stability of group 8-10 silicides has been studied by LMTO-ASA band structurecalculations. In the Rh-Si and Ir-Si systems the lowest calculated heat of formation isfound in compounds near the equiatomic composition. Model calculations forsuperstructures in bcc and fcc solid solutions show that in group 8 and 9 silicides thebcc based structures have a maximum in stability near 50% Si. In group 10 systemsthe energy minimum is shifted to lower Si contents and the minimum is less clearlydeveloped.The heats of formation in monosilicides are predicted to have a minimum for metalatoms from group 9.Calculated one electron densities of states are in good agreement with spectroscopicmeasurements and confirm the generally accepted picture of silicide stability. Themain stabilising factor is metal d - silicon p bonding. With increasing Si contents or group number of the metal atoms dp antibonding states become increasingly filled. A stabilising effect in the highest occupied states is metal-silicon pp interactions and insilicon rich compounds also silicon-silicon pp interactions.

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