Oxygen-vacancy and charge hopping related dielectric relaxation of CuMoO4 ceramic

Highlights: • The transition process from γ phase to α phase for CuMoO₄ is observed by dielectric means for the first time. • The dielectric relaxation mechanisms of CuMoO₄ related to oxygen vacancies and polarons are first proposed. • All research results open a new path for research methods and defect transmission mechanisms of related materials. -- Abstract: Single-phase CuMoO₄ samples were prepared by a modified sol-gel method, and the functional relationship between dielectric properties of the samples and temperature (−130 °C–150 °C) or frequency (1 Hz–10 MHz) was investigated by measuring the dielectric spectrum. The temperature dependence of ε ́ and tan δ can determine the first-order phase transition (γ→α) in the CuMoO₄ material. Three thermally activated relaxations were observed in the frequency dependence of tan δ and M ́ ́. The results show that relaxation 1 is related to the hopping motion of partial charge carriers between Cu²⁺ and Cu⁺, so this relaxation of the low-temperature segments is attributed to polarization relaxation. Relaxation 2 and relaxation 3 are dominated by the oxygen vacancy motion, where relaxation 2 is due to a movement of singly ionized oxygen vacancies and relaxation 3 is the result of an ordered movement of doubly ionized oxygen vacancies.