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The LiMoO melt structure and its Raman spectral characteristics are the key for establishing the composition-structure relationship of lithium molybdate melts. In this work, Raman spectroscopy, factor group analysis, and density functional theory (DFT) were applied to investigate the structural and spectral details of the H-LiMoO crystal and a LiMoO melt. Factor group analysis shows that the crystal has 171 vibrational modes (84A + 87A), including three acoustic modes (3A), six librational modes (2A + 4A), 21 translational modes (7A + 14A), and 141 internal modes (75A + 66A). All of the A modes are Raman-active and were assigned by the DFT method. The LiMoO melt structure was deduced from the H-LiMoO crystal structure and demonstrated by the DFT method. The results show that the LiMoO melt is made up of Li ions and MoO groups, each of which is formed by four corner-sharing MoOØ/MoOØ tetrahedra (Ø = bridging oxygen). The melt has three acoustic modes (3A) and 54 optical modes (54A). All of the optical modes are Raman-active and were accurately assigned by the DFT method.

LiB3O5 is the most widely used nonlinear optical crystal. Li2Mo3O10 (a nominal composition) is a typical flux used to produce large-sized and high-quality LiB3O5 crystals. The structure of the LiB3O5–Li2Mo3O10 high-temperature solution is essential to understanding the flux behavior of Li2Mo3O10 but still remains unclear. In this work, high-temperature Raman spectroscopy combined with density functional theory (DFT) was applied to study the LiB3O5–Li2Mo3O10 solution structure. Raman spectra of a LiB3O5–Li4Mo5O17–Li2Mo4O13 polycrystalline mixture were recorded at different temperatures until the mixture melted completely. The solution structure was deduced from the spectral changes and verified by DFT calculations. When the mixture began to melt, its molybdate component first changed into the Li2Mo3O10 melt; meanwhile, the complicated molybdate groups existing in the crystalline state transformed into Mo3O10 2– groups, which are formed by three corner-sharing MoO3Ø–/MoO2Ø2 (Ø = bridging oxygen atom) tetrahedra. When LiB3O5 dissolved in the Li2Mo3O10 melt, the crystal structure collapsed into polymeric chains of [B3O4Ø2 –] n . Its basic structural unit, the B3O4Ø2 – ring, coordinated with the Mo3O10 2– group to form a MoO3·B3O4Ø2 – complex and a Mo2O7 2– group. On the basis of the LiB3O5–Li2Mo3O10 solution structure, we discuss the LiB3O5 crystal growth mechanism and the compositional dependence of the solution viscosity.