Phase transition, Raman spectra. Infrared spectra, band gap and microwave dielectric properties of low temperature firing (Na_(0.5x)Bi_(1-0.5x))(Mo_xV_(1-x))O4 solid solution ceramics with scheelite structures

摘要

A scheelite based structure that could host the solid solution (Na_(0.5x)Bi_(1-0.5x))(Mo_xV_(1-x))O4 (0.0 ≤ x ≤ 1.0) was prepared via the solid state reaction method. All the compositions can be sintered well below a temperature of 800 °C. A structural phase transition occurs from the monoclinic scheelite structure to a tetragonal scheelite structure at x = 0.10 at room temperature. This structural transition is related to a displacive ferroelastic-paraelastic phase transition. This phase transition was also confirmed by in situ high temperature XRD and Raman studies, and a room temperature infrared spectra study. The compositions near the phase boundary possessed high dielectric permittivities (>70), and large Qf values (>80 000 GHz) with variable temperature coefficients of frequency and capacitance. For example, a temperature stable dielectric made as a composite with compositions of x = 0.05 and x = 0.10 was designed and co-sintered at 720 °C for 2 h to produce a dielectric with a permittivity of ~77.3, a Qf value between 8 000 GHz-10 000 GHz, and a temperature coefficient of <±20 ppm/°C at 3.8 GHz over a temperature range of 25-110 °C. This material is a candidate for dielectric resonators and low temperature co-fired ceramics technologies. Near the phase boundary at x = 0.10 in the monoclinic phase region, the samples show strong absorption in the visible light region and we determine a band gap energy of about 2.1 eV, which means that it might also be useful as a visible light irradiation photocatalyst.