Composition dependent 3C and 6H perovskites, A3MTiSbO9 (A = Sr, Ba; M = Mn, Co): Structural, magnetic and dielectric properties

The compounds of the title series, A(3)MTiSbO(9) (A = Sr, Ba; M = Mn, Co), are prepared by conventional solid-state reactions. Rietveld structure refinements establish stabilization of complete B-site disordered 3C perovskite structures (space group Pm-3m, No.221) for the Sr containing compounds with all corner connected M-III/Ti-IV/(SbO6)-O-V octahedra, while for Ba analogs a 6H perovskite structure (space group P6(3)/mmc, No. 194) is adopted with corner and edge shared octahedral connectivity. While the HR-TEM and SAED reaffirmed the above structure types, XPS supported +3 oxidation states for the transition metals, Mn and Co. Magnetic data revealed paramagnetic behavior down to 5 K for the hexagonal perovskites, Ba3MnTiSbO9 and Ba3CoTiSbO9, while the cubic perovskites, Sr3MnTiSbO9 and Sr3CoTiSbO9, showed antiferromagnetic-type transitions at similar to 10 and 20 K, respectively. The low temperature (at 5 K) hysteretic behavior seen in the M - H data for Sr3CoTiSbO9 is indicative of very weak ferromagnetic interactions, which may originate from a cluster-glass type behavior due to cation-disorder at the B-sites of the 3C perovskite. The higher dielectric constant for the Co member perovskites than the Mn members is attributable to higher carrier mobility, while relatively high dielectric constant for the 3C perovskites is perhaps due to their increased space charge polarization as compared to that of the 6H members.