Structural strain in pyrites evaluated by X-ray powder diffraction

Two parameters for measuring the structural strain, the effective Debye-Waller parameter, B_eff, and lattice strain, e{open}, were evaluated on a natural pyrite (FeS₂) after grinding. The effective Debye-Waller parameter, B_eff, which depends on the displacement of atoms in the crystal, was calculated for the overall crystal, B_eff(FeS₂), and for sulphur, B_eff(S), from the intensities of the X-ray diffraction lines. The B_eff(S) increased markedly with increasing grinding time, while B_eff(FeS₂) did not change significantly. The lattice strain, e{open}, was not recognized. These observations suggest that the displacement of sulphur atoms preferentially takes place by grinding. The relations between these B_eff values and crystallite size, L, were observed to be common for two different methods of grinding. This tendency was considered to be an inherent property of pyrite. The value of B_eff(S) is a useful index to estimate mechanically caused strain in pyrite.