Solid state studies on K2Ti6−xNbxFe2O16 (x = 0 and 1) and lithium insertion into K2Ti6M2O16 (M = Cr, Fe and Ga) and K2Ti5NbFe2O16 hollandite type phases

A new niobium-substituted hollandite K2Ti5NbFe2O16 has been synthesised for the first time. The compound is crystallised in tetragonal structure. A two to three orders change in electrical resistivity is observed with temperature as compared to the parent phase K2Ti6Fe2O16. The niobium-substituted phase shows antiferromagnetic ordering with TN=37 K at a field of 0.1 T and the antiferromagnetic ordering disappears at higher field (0.2 T) indicating field induced magnetic behaviour. The Mössbauer spectrum of K2Ti5NbFe2O16 shows majority of the Fe ions are 3+ oxidation state (96%). For the first time, we have intercalated lithium into K2Ti6M2O16 (M=Cr, Fe and Ga) and K2Ti5NbFe2O16 hollandite type phases using n-butyllithium in hexane. The estimated lithium content for all the phases are in the range 1.7–2.7 mol per formula unit.