Oxygen Vacancy Engineering toward Enhanced Dielectric and Ionic Conductivity Properties in Single Crystal LiNbMoO₆

The quantity and distribution of oxygen vacancies within the unit cell directly determine the electrical properties of the crystals. It is critical to design and grow crystals with high concentrations of oxygen vacancies and excellent electrical properties. Here, single crystals of LiNbMoO₆ were successfully grown by a flux method for the first time. The crystal crystallizes in the tetragonal space group P4̅2₁m with lattice parameters a = 4.728 Å, c = 9.287 Å, and Z = 2. Comprehensive characterization of the LiNbMoO₆ crystal was performed, revealing a significant quantification of oxygen vacancies. Notably, the relative dielectric constant ε₃₃ of LiNbMoO₆ exhibited a substantial increase from 157 to 10,000 at 1 kHz, with the temperature ranging from 25 to 500 °C. Moreover, the oxide ion conductivity reached 1.01 × 10^-3 S·cm^-1 at a temperature of 460 °C. Analysis of the temperature dependence of the crystal structure indicated that the oxygen vacancies were located at specific sites (Mo-O1). The dielectric and conductivity properties of the sample were studied by using AC impedance spectroscopy. The XPS testing data verified the existence of oxygen vacancies, as made evident by changes in the valence states of molybdenum and oxygen ions. Our findings highlight the significant contribution of oxygen vacancies to the dielectric properties and electrical conductivity of LiNbMoO₆.