Effect of W doping on phase transition behavior and dielectric relaxation of CuMoO4 obtained by a modified sol-gel method

Abstract

Tungsten (W)-doped copper molybdate (CuMo1−xWxO4, x = 0∼0.12) compounds were prepared by the sol-gel method. The effects of doping content on the phase transition behavior and dielectric properties of CuMo1−xWxO4 (x = 0∼0.12) were investigated. X-ray diffraction and UV–vis diffuse reflectance spectroscopy clarified that W doping facilitated the transition of green α-phase to brown γ-phase. The chemical composition and structure of the CuMo1−xWxO4 (x = 0∼0.12) were investigated by Fourier transform infrared (FT-IR) spectroscopy and Raman spectra. The dielectric spectra of CuMo1−xWxO4 at −130 °C∼150 °C and the color-change of CuMo0.94W0.06O4 at 20 °C∼50 °C illustrated that the phase-transition temperature moves toward high temperature with increasing W. The functional relationship between the electrical modulus M’ and the frequency (1 Hz∼10 MHz) indicated that there are two dielectric relaxation mechanisms for CuMo1−xWxO4, which correspond to the polarization relaxation caused by hopping motion of polaron at low-temperature region (R1) and the relaxation dominated by oxygen vacancies at high temperatures (R2). It has also been confirmed that the phase transition of relaxation type exists in CuMo1−xWxO4, and that R1 occurs in γ-phase and R2 occurs in α-phase. It is of great significance to establish the dielectric relationship between phase transition and relaxation. With the content of W, the intensity of relaxation peak and activation energy of R1 did not change too much, but the relaxation behavior of R2 was inhibited and the activation energy increased gradually. The above results show that dielectric spectra are an important discovery as a new method to study the phase transition of materials, and is conducive to exploring the motion state of micro-particles. The control of phase-transition temperature is of great significance for this thermochromic material as a temperature sensor.