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

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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.