Structural phase transitions and conducting properties in Bimetallic sulfates

Bimetallic sulfate minerals, hydrated as well as anhydrous are important multifunctional materials which exhibit interesting properties like fast-ion conduction, ferroelectricity and magnetism with variation in temperature [1,2,3]. These properties are generally entwined with structural phase transitions and show structural frameworks made of interconnection of octahedra and tetrahedra [1]. Bimetallic sulfates, indeed are intercalation compounds of alkali ions generated by these frameworks and they possess high ionic conductivity [1]. In the present study, anhydrous and hydrous compounds of Na6M(SO4)4, (M=Mn, Ni, Co) were synthesized to understand the structural phase transitions and its relation to fast-ion conducting properties. Na6Mn(SO4)4, is monoclinic, space group P21/c with Z=2 and is isostructural to its Co and Ni analogues and shows high ionic conductivity and structural phase transition > 450 ⁰C. Na6Co(SO4).2H2O, Na6Ni(SO4).2H2O are isostructural with triclinic system having space group P-1 with Z =1. In addition, structural features and correlation with ionic conductivity in Na6Co(SO4).2H2O, Na6Ni(SO4).2H2O and Na6Mn(SO4) will be outlined. These studies open up the utility of hydrated bimetallic sulfates as possible precursor for the design of functional materials.