Madelung potentials and the sizes of ions in oxides and nitrides

Abstract

It is shown that to a good approximation, the Madelung potential at anion sites in simple structures depends on the size of the cation but not on the cation charge or crystal structure. The effect of Madelung potential on ionic radii is illustrated by comparing the apparent radii of the oxygen and nitrogen ions.

Bond length variation in hydronitride molecules and nitride crystals

“…Variable radii for oxide and sulfide ions runs contrary to the assumption of a constant anion radius made in the derivation of ionic radii (Pauling 1927(Pauling , 1929Shannon and Prewitt 1969;Shannon 1976Shannon , 1981, but it is consistent with the work of Fajans (1941), Paschalis and Weiss (1969), Johnson (1973Johnson ( , 1975, O'Keeffe (1979) and Gibbs etal. (1992).…”

“…In a study of the Madelung potential at oxide ion sites in binary oxides, O'Keeffe (1979) showed that the potential increases as the radius of the cation decreases (Paschalis and Weiss 1969). This implies that the radius of the oxide anion should increase as bond length increases.…”

Bond-valence parameters for solids

“…Equations (4) and (5) are derived from raw data only. The fact that bond lengths in oxides, fluorides and nitrides could not be described using additive radii has been noted before (O'Keeffe, 1979). The strong linear correlation of bond-valence parameters for bonds to different anions suggests that bond-valence parameters that are not readily available could be obtained by linear interpolation.…”

Interatomic Distance Predictions for Computer Simulation of Crystal Structures

“…It has been found empirically that in structures with corner-connected polyhedra the minimum distances between the cations are remarkably con stant (O'Keeffe andHyde, 1976, 1979;Glidewell, 1977). In fact, it has been shown that they are more constant than the O-O distances in the edges of the polyhedra.…”