Defect pressure, formation volume, and temperature dependence of formation properties of point defects in ionic solids

Abstract. — The concept of local defect pressure is developed and is applied to determine the elastic relaxation about point defects in ionic solids. The method is superior to that of Kanzaki forces for treatment of Coulomb and many-atom interactions. The lattice sums for the Coulomb interaction and the relaxation volume of Schottky defects in NaCl and KC1 in the static limit are given; the use of neutral Evjen cubes rather than charged Mott-Littleton regions is found unavoidable for a complete and satisfactory atomistic treatment of charged defects in ionic solids. In both alkali and silver halides, the temperature dependence of the volume and the enthalpy of formation of equilibrium defects is understood in terms of the temperature dependence of the shear moduli. The high-temperature anomalies of defect formation volume, tracer diffusion, and ionic conductivity of the silver halides is traced to an intrinsic property of the Frenkel defect caused by an exceptional temperature dependence of elastic properties of the perfect erwal 1. Introduction