Stabilization of Ca1-δFe2-xMnxO4(0.44 ≤ x ≤ 2) with CaFe2O4-Type Structure and Ca2+ Defects in One-Dimensional (1D) Channels

Solid solutions of Ca1-delta Fe2-xMnxO4(0.44 <= x <= 2) were synthesized from CaCl2 as flux at 850 degrees C in air. The entire series, even with x = 2, crystallizes in the CaFe2O4-type structure (Puma), rather than in the CaMn2O4-type structure (Pbcm). Rietveld refinements confirmed mixed-valency Mn3+/Mn4+ and a substantial level of Ca2+ deficiency (delta approximate to 0.25) at high x. With increasing x, the unit-cell dimensions a and h decrease, while that of c increases. Detailed structural analyses, together with Mn K-edge X-ray absorption and Fe-57 Mossbauer spectroscopy studies, revealed that the stabilization of CaFe2O4-type structure, even at high values of x, is due to the existence of non-Jahn-Teller active Mn4+ (and Fe3+), which is compensated by the formation of the Ca2+ deficiencies in the one-dimensional (ID) channels of Ca1-delta Fe2-xMnxO4 during the flux synthesis. Antiferromagnetic (AFM) long-range ordering is achieved for all compounds at low temperature, because of strong A FM interactions between Mn3+/Mn4+ and Fe3+. In addition, a spin (or cluster) glass component was also observed, as expected, because of the extensive Mn/Fe structural and Mn3+/Mn4+ charge disordering.