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Several compounds of the NaMn(Fe_1–xIn_x)₂(PO₄)₃ solid solution were synthesized by solid state reaction in air; pure alluaudite-like compounds were obtained for x = 0.00 to 1.00. X-ray Rietveld refinements indicate the presence of Na⁺ at the A1 and A2′ sites, Mn²⁺ at the M1 site, and Fe²⁺, Fe³⁺, and In³⁺ at the M2 site. The presence of small amounts of In³⁺ at the M1 site, and Mn²⁺ at the M2 site, indicates a partially disordered distribution between these cations. A good correlation was also established between the M1–M2 bond distance and the β angle of the alluaudite-like compounds. The disordered distribution of Fe²⁺, Fe³⁺, and In³⁺ at the M2 site is confirmed by the broadness of the infrared absorption bands. The Mössbauer spectra, measured between 90 and 295 K, were analyzed in terms of a model that takes into account the next-nearest neighbor interactions around the M2 crystallographic …