Study on cation distributions and structural changes in Fe³⁺-Ga-bearing melilite using neutron and X-ray diffraction and Mössbauer spectral analyses

Abstract

To reveal the distribution of Fe³⁺ between two tetrahedral site in melilite and the relationship between ionic substitution and incommensurate structure, two Fe-Ga-melilite samples were synthesized. The result of Rietveld refinement using X-ray and neutron diffraction data and Mössbauer spectroscopy revealed that Fe³⁺ distribution between T1 and T2 sites but Fe³⁺ prefers T1 sites. Mössbauer spectroscopic method, has a sensitive reaction for behavior of Fe, also indicates Fe³⁺ prefers larger T1 site. Doublets, given by Mössbauer spectroscopy indicate the existence of multiple T1 and T2 sites. This result indicates the incommensurate structure in melilite. Therefore, ionic substitution between T1 and T2 sites give rise to incommensurate structure.