Correlation between infrared, THz and microwave dielectric properties of vanadium doped antiferroelectric BiNbO₄

Terahertz (THz) transmissivity and infrared (IR) reflectivity spectra of orthorhombic microwave (MW) ceramics Bi(Nb_1-xV_x)O₄ (0.002 < x < 0.032) were measured between 4 and 3000 cm^-1 (0.09-90 THz) at room temperature. A well underdamped mode, presumably the ferroelectric soft mode, was observed at 25 cm^-1. Complex permittivity spectra obtained from the fits to our data were extrapolated down to the MW range and compared with the dielectric data near 5 GHz. The linear extrapolation of dielectric losses from THz down to the MW range is in agreement with the experimental MW losses. Addition of 3.2% of vanadium reduces the sintering temperature to 850 °C and the dielectric properties (ε′ = 42.2, Q·f = 14,000 GHz, τ_f = +10 ppm/°C) remain at a level satisfactory for MW applications. Somewhat lower MW losses were observed in a sample sintered in the N₂ atmosphere.