Precise Structure Analysis Consistent with Mössbauer Quadrupole Effect: A Case of the Ordered Double Perovskites Sr₂FeMO₆ (M = Mo and Re)

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We propose the use of Mössbauer quadrupole effect as a sensitive probe to determine structural feature precisely. This method has been applied, together with the high-resolution neutron powder diffraction measurements, to the structure analysis of the ordered double perovskites Sr₂FeMoO₆ and Sr₂FeReO₆ at room temperature. Results of Rietveld refinement were verified by the Mössbauer quadrupole effect. We have concluded that the space groups of Sr₂FeMO₆ (M = Mo and Re) are I4⁄m, but not I4⁄mmm as has been frequently pronounced. The spins of M = Re specimen are aligned in ab-plane, while those of M = Mo specimen are aligned in ab-plane or along c-axis.