Lattice Parameters of Nine Oxides and Sulfides as a Function of Pressure

Abstract

The lattice parameters of seven oxides and two sulfides have been measured as a function of pressure to several hundred kilobars. FeO, CoO, NiO, MnO, and MnS have the NaCl structure or slight distortions thereof. The data can be fit by a Born—Mayer equation. For FeO, CoO, and NiO the crystal‐field stabilization term contributes 5% to 15% of the total attractive pressure. FeS₂ (pyrites) has a cubic structure which can be related to the fcc lattice. Its compressibility is much less than MnS and more comparable to the oxides. The binding is appraently covalent. SnO₂, MnO₂, and TiO₂ all have the same tetragonal structure. For SnO₂ and MnO₂ the c axis actually expands with increasing pressure at low pressure, then passes through a maximum and ultimately contracts. The compressibilities of these two compounds are low at low pressure and increase at pressures beyond the maximum in c. TiO₂ behaves more normally. It is apparent that central forces, and therefore ionic binding, contribute little to the cohesion of these crystals.