Synthesis and characterization of (Bi_1−xR_x)₂Mn₄O₁₀: structural, spectroscopic and thermogravimetric analyses for R = Nd, Sm and Eu

Mullite-type Bi₂Mn₄O₁₀ and R₂Mn₄O₁₀ (R = rare earth element) compounds are isostructural and are of ongoing research attentions because of their interesting crystal structures and the associated multiferroic properties. We report three series of mullite-type (Bi_1−xR_x)₂Mn₄O₁₀ compounds for R = Nd, Sm and Eu prepared by solid-state synthesis methods. Each phase of the solid solutions is characterized by X-ray powder diffraction followed by Rietveld refinement. Evolutions of the metric parameters, interatomic bond distances, average crystallite size and microstrain are carried out with respect to the compositional x-value. This study also emphasizes on how the crystal chemistry changes upon successive change of the stereochemical activity of the lone electron pair of the Bi³⁺ cation using the Wang–Liebau eccentricity parameter. Selective vibrational features have been discussed based on the Raman and Fourier transform infrared spectra. The thermal stability of the end-members is analyzed from the thermogravimetric data, demonstrating that the end-member Bi₂Mn₄O₁₀ differently decomposes than that of the other R₂Mn₄O₁₀ compounds.