Synthesis of the perovskite-like layered 12R phase of BaCe_0.25Mn_0.75O₃ (12R-BCM) at higher yields (> 97 wt%) than previously reported. The influence of sintering temperature and redox cycling on the composition and weight fraction of secondary phases is investigated. The anisotropy between thermal expansion along the c-axis and within the ab plane is examined with synchrotron-based diffraction measurements.

Nearly complete conversion to a Ba₃Nb_0.75Mn_2.25O₉-6H structure was observed following thermochemical reduction of the parent Ba₄NbMn₃O₁₂-12R material. The Ba₃Nb_0.75Mn_2.25O₉-6H structure represents a hexa­gonal perovskite that displays substitution of Mn onto Nb sites in order to satisfy the 3:1 Mn:Nb ratio within the 6H structural motif.