Spectral characterization of lanthanum heptamolybdate single crystals

Using sodium metasilicate gel, lanthanum heptamolybdate (La2Mo7O24·nH2O) single crystals are grown by the diffusion of lanthanum nitrate into the set gel embedded with a mixture of molybdenum trioxide, ammonium hydroxide and concentrated nitric acid. The infrared (IR) absorption spectrum of lanthanum heptamolybdate (LHM) single crystals identifies the presence of molybdate (MoO4)2− groups and water of crystallization, while energy dispersive X-ray analysis (EDAX) confirms the presence of heavy elements (La and Mo) in LHM. X-ray photoelectron spectroscopic (XPS) studies of LHM re-establish the presence of lanthanum and molybdenum besides their chemical states as their respective oxides. It is shown that the oxygens in the sample are present in three different environments as terminal oxygen (MoO), bridging oxygen (MoOLa) and oxygen of lattice water (HOH). The implications are discussed.