Anion-Substituted Garnets Ca3Mn2 – x(Ni, Co)xVyGe3 – yO12 (x = 0, 1; y = 0, 1, 2): Preparation and Characterization

Resumo

Garnets with the structure similar to that of Ca₃Mn₂Ge₃O₁₂ have been prepared with simultaneous substitutions of Ge⁴⁺ by V⁵⁺ in tetrahedra and of Mn³⁺ by Ni²⁺ or Co²⁺ in octahedra. X-ray photoelectron spectroscopy (XPS) proved the absence of V⁴⁺ in tetrahedra of the lattice of the compounds prepared and determined the valences of elements in octahedral sites. The increasing d-cation size in octahedra is accompanied by an increase in unit cell volume regardless of the composition of tetrahedra (V_yGe_{3 – y})O₁₂. The electrical conductivity of Ca₃Mn_{2 – x}(Ni, Co)_xV_yGe_3–yO₁₂ (x = 0, 1; y = 0, 1, 2) garnet ceramic samples and the calculated bandgap widths make it possible to classify them with medium-gap semiconductors.