Further Investigations of Crystal Structure in Nb and Mo-based Double Perovskites

Double perovskite crystals exhibit a wide range of properties including superconductivity, magnetoresistance and geometric magnetic frustration, owing to close relationships between their structural, electrical and magnetic properties. The samples, of the chemical formula A2BB'X6, where A = Ba and B' = Mo and Nb, were synthesized using solid state methods with B elements including samarium, lanthanum and praseodymium, and compared to previously synthesized samples. The niobium samples were synthesized in air but the molybdenum samples required hydrogen reduction to achieve the desired 5+ oxidation state. The crystal structures were determined using x-ray diffraction followed by Rietveld refinement. The addition of Sm explored the transition between cubic and tetragonal crystal symmetries as progressively larger cations required octahedral distortion to incorporate them. The combinations of La and Pr investigated the tetragonal-monoclinic transition as further distortion occurred to incorporate even larger cations. Together, these samples paint a fuller picture of the nature of crystal structure, and its interplay with electronic and magnetic properties, in double perovskites.