| Summary: | Abstract A novel transition metal oxide CeMn3Rh4O12 has been synthesized using high‐pressure and high‐temperature conditions of 12 GPa and 1573 K. CeMn3Rh4O12 crystallizes in the AA'3B4O12‐type quadruple perovskite structure with A‐site ordering in a cubic space group of Im3¯$ar 3$ in the high‐temperature phase at above 310 K, whereas CeMn3Rh4O12 undergoes a structural phase transition with symmetry lowering down to probable triclinic symmetry on cooling below this temperature. X‐ray absorption spectroscopy reveals that all the constituent ions are trivalent at room temperature, suggesting the valence state of Ce3+Mn3+3Rh3+4O12. Magnetization study demonstrates an antiferromagnetic transition attributed to A'‐site Mn3+ ions at TN = 35 K, whereas a Curie–Weiss analysis finds an additional paramagnetic component attributed to the Ce3+ 4f1 ions. We discuss the differences in structural and magnetic properties between CeMn3Rh4O12 and LaMn3Rh4O12, eventually proposing a possible stereochemical effect of Ce3+ on crystal structure in the quadruple perovskite.
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