Compositional dependence of intensity tensor and electric field gradient tensor for Fe²⁺ at <i>M</i>2 sites of enstatites by single crystal Mössbauer spectroscopy

The intensity tensor for Fe2+ doublets at the M2 sites and electric field gradient tensor for Fe2+ at the M2 sites in two enstatites (En) with the orthorhombic system were determined by single crystal Mössbauer spectroscopy to examine the ferrosilite (Fs) component dependence of the intensity tensor of enstatite. The components of the intensity tensor for Fe2+ doublets at the M2 sites in the En65.5Fs31.7Wo2.7-enstatite and En90.7Fs8.7Wo0.6-enstatite are IXX = 0.577(6), IYY = 0.454(6), and IZZ = 0.470(12), and 0.616(2), 0.458(4), and 0.426(6), respectively. Thus, those three components have a weak dependence on the contents of Fs component. The components, IXY, IYZ, and IXZ, of the intensity tensor due to Mössbauer nuclei that occupy general positions in the space group Pbca pyroxene structure are derived as IXY = IYZ = IXZ = 0 by the symmetric summation of equivalent Mössbauer nuclei in the structural site. Three components, IXX, IYY, and IZZ, were determined by applying constraint of IXY = IYZ = IXZ = 0. The intensity tensors by Mössbauer nuclei at general positions obtained without any constraints (IXY ≠ IYZ ≠ IXZ ≠ 0) are consistent with those derived by applying the symmetrical constraint (IXY = IYZ = IXZ = 0). This indicates that the intensity tensor due to Mössbauer nuclei that occupy general positions can be simplified by the symmetrical constraint.