Interaction of crystal water with the building block in Y2Mo3O12 and the effect of Ce3+ doping

Abstract

Ce³⁺ ions are introduced into the lattice of Y₂Mo₃O₁₂ with a sol–gel method with the aim to reduce its hygroscopicity and pursue the interaction of crystal water molecules with the building block. It is found that Ce³⁺ ions occupy the positions of Y³⁺ in the lattice and have the function of expelling crystal water molecules in the microchannels so that the number of crystal water molecules decreases significantly as the Ce³⁺ content increases and a complete depletion of the crystal water is achieved when the content of Ce³⁺ is higher than 8 mol%. Based on the binding energy changes of Mo 3d and Y 3d with and without Ce³⁺ in the lattice, the configuration of the crystal water in the building block is deduced, namely, a crystal water serves as a spring with its O²⁻ pointing to the Y³⁺ in an octahedron and with its H⁺ approaching the next nearest O²⁻ in the Y–O–Mo bridge. With such a configuration, the effects of the crystal water on the thermal expansion properties of Y₂Mo₃O₁₂ and the like are explained. It is also shown that the number of crystal water molecules per molecular formula can be quantified by the full width at half maximum of the Raman bands or relative intensity with linear relationships, suggesting that Raman spectroscopy can be a potential tool in quantifying crystal water molecules at room temperature in this or related materials.