Compositional dependence of intensity tensor and electric field gradient tensor for Fe²⁺ at M2 sites of enstatites by single crystal Mössbauer spectroscopy

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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 En_65.5Fs_31.7Wo_2.7-enstatite and En_90.7Fs_8.7Wo_0.6-enstatite are I_XX = 0.577(6), I_YY = 0.454(6), and I_ZZ = 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, I_XY, I_YZ, and I_XZ, of the intensity tensor due to Mössbauer nuclei that occupy general positions in the space group Pbca pyroxene structure are derived as I_XY = I_YZ = I_XZ = 0 by the symmetric summation of equivalent Mössbauer nuclei in the structural site. Three components, I_XX, I_YY, and I_ZZ, were determined by applying constraint of I_XY = I_YZ = I_XZ = 0. The intensity tensors by Mössbauer nuclei at general positions obtained without any constraints (I_XY ≠ I_YZ ≠ I_XZ ≠ 0) are consistent with those derived by applying the symmetrical constraint (I_XY = I_YZ = I_XZ = 0). This indicates that the intensity tensor due to Mössbauer nuclei that occupy general positions can be simplified by the symmetrical constraint.