Pressure-sensitive modeling of the reversible lithiation of vacant thiospinel (In-0.5 rectangle(0.5))[In1.5Sn0.5]S-4

A simple atomic model is described in which lithiation appears as a reversi ble pressure acting on confined atomic species which constitute the host ma terial. It is demonstrated, by ab initio calculations of the properties of a confined atom as a function of the cavity radius, that the ionization of Sn occurs in the manner which has been observed, i.e., it passes directly f rom Sn-IV to Sn-II without the appearance of Sn-III, This is shown not to b e the case for a confined atom with no d shell present, and therefore we co nclude that the observed property is of atomic origin and is directly relat ed to the high compressibility of d orbitals. Extensions of our model are s uggested to include relativistic effects, which would enable ab initio calc ulations of the Mossbauer signals to be attempted for the lithiated compoun ds. This would provide an independent test of our model. (C) 2000 Academic Press.