Low-temperature sintering of V₂O₅-added and -substituted ZnNb₂O₆ microwave ceramics

The sintering behaviors and microwave dielectric properties of V ₂O₅-added and -substituted ZnNb₂O₆, ceramics with columbite structure (abbreviated as ZNV and ZVN, respectively) have been investigated. It was found that the addition or substitution of V ₂O₅ to ZnNb₂O₆ ceramics lowers the sintering temperature from 1150°C to ∼900°C, but the sintering mechanisms are different. The formation of a ternary liquid phase is attributed to enhanced sintering in ZNV samples. Interaction between ZnNb₂O ₆ and V₂O₅ also led to the formation of a second phase, V₃Nb₁₇O₅₀. In contrast, it has been observed that with up to 8 mol% substitution of V₂O₅ in ZnNb₂O₆, a complete solid solution is formed. The sintering temperature for the ZVN sample becomes lower due to the decreased temperature of liquidus according to the substitution of V for Nb ions. The microwave dielectric properties of ZNV samples are seriously degraded due to the presence of a V₃Nb₁₇O₅₀ second phase. This was confirmed by measuring the dielectric properties of V₃Nb ₁₇O₅₀ second phase. However, V-substituted Zn(Nb _0.94V_0.06)₂O₆ samples sintered at 875°C for 2 h exhibit excellent microwave dielectric properties: Q × f of 65,000 GHz, ε_r of 24, and τ_f of -72 ppm/°C.