Synthesis and crystallographic studies of garnet-type AgCa2Mn2V3O12 and NaPb2Mn2V3O12

High-purity powder specimens of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 have been successfully synthesized by solid-state chemical reaction. The Rietveld refinements from X-ray powder diffraction data verified that these compounds have the garnet-type structure (space group Ia3¯d, No. 230) with the lattice constant of a=12.596(2) Å for AgCa2Mn2V3O12 and a=12.876(2) Å for NaPb2Mn2V3O12. Calculation of the bond valence sum supported that Mn is divalent and V is pentavalent in these garnets. Estimation of the quadratic elongation and the bond angle variance showed that the distortions of the MnO6 octahedra and the VO4 tetrahedra are significantly suppressed. Our new results of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 are compared to those of AgCa2M2V3O12 and NaPb2M2V3O12 (M=Mg, Co, Ni, Zn).