Density of valence states of the superionic conductor AgI

Temperature dependent photoelectron spectra of AgI are measured between room temperature and 251 0C for photon energies h/2πω = 21.2 and 40.8 eV. The spectra are decomposed into approximate partial p and d densities of valence states by using atomic cross sections for the corresponding partial photoexcitation probabilities. Significant abrupt reversible changes are observed in the partial p density of states at Tsub(c) = 147 0C, where the crystal structure changes from the wurtzite (β) phase to the superionic 'disordered' α-phase. In contrast, the partial d density of states, except for a slow continuous broadening with temperature, shows no sudden change at Tsub(c). The results strongly support the model, that in the α-phase the Ag+ ions occupy lattice sites with tetrahedral symmetry for a large fraction of the time. (author)