LaMn₃Rh₄O₁₂: An Antiferromagnetic Quadruple Perovskite Synthesized at High Pressure

A quadruple perovskite LaMn₃Rh₄O₁₂ with A' = Mn and B = 4d transition metal was synthesized at high pressure (8 GPa) and temperature (1423 K) for the first time. Room temperature powder X-ray diffraction indicates that LaMn₃Rh₄O₁₂ forms in cubic symmetry (Im3̅, a = 7.4997(1) Å). X-ray absorption near-edge spectroscopy shows predominantly Mn³⁺ and Rh³⁺ oxidation states. An antiferromagnetic transition at T_N ∼ 41 K is corroborated by specific heat measurements. The resistivity measurements indicate a three-dimensional Mott variable-range hopping conduction mechanism between 300 and 160 K.