Ab initio simulations on AgCl(1 1 1) surface and AgCl(1 1 1)/α-Al₂O₃(0 0 0 1) interface

The defect chemistry and ionic transport properties of the AgCl(1 1 1)/α-Al₂O₃(0 0 0 1) interface were considered by using ab initio slab calculations. These calculations were performed in the framework of plane-wave basis set combined with the density functional theory (DFT), as implemented into the VASP computer code, and Gaussian basis set combined with the Hartree-Fock method (CRYSTAL-98 code). We analyze the electron density distribution on the interface and the electrostatic potential distribution near the AgCl surface. The size of the silver ion is too great to enter the corundum surface layer and to create excess silver ions in this way. This is in agreement with the experiments on heterogeneous doping of AgCl revealing α-alumina to be inactive compared with γ-alumina. The energy to thermally create a vacancy in the first layer at the expense of an interstitial ion is large compared with the bulk Frenkel energy. Despite the calculated low activation energy for vacancy transport in the first layer (ΔHs#=0.23 eV), the vacancy concentration will be too small to generate perceptible surface conductivity. The striking similarity of ΔHs# with the bulk value is due to the quite symmetrical arrangement of the considered interface.