High decrease in CaZrO3 sintering temperature using complex fluoride fluxes

The effects of complex fluoride flux on the sintering and the electric/dielectric properties of CaZrO3 ceramics are investigated. Four fluoride mixtures are tested: LiF–CaF2–SrF2, LiF–CaF2–BaF2, LiF–SrF2–BaF2 and LiF–BaF2–B2O3. They are used because each of their associated phase diagrams shows the existence of an eutectic composition having a low melting temperature. This liquid phase is used to promote the densification at low temperature. The effect of various additions (nature and quantity) are also investigated to optimise the resulting thermal and physical properties. In terms of sintering behaviour, the results are unambiguous, leading to a drastic decrease of the densification temperature with all the non-boric additions (≤1000 °C). The dc/ac measurements carried out on the materials sintered at low temperature (900 and 1000 °C) and either in air or in reductive atmosphere follow the same trend when using non-boric additions, with high permittivities (≥25), low dielectric losses (<10 × 10−4), low temperature coefficients of the permittivity (<100 ppm/K) and high insulating resistivities (up to 1015 Ω cm); the high frequency measurements lead to similar conclusions revealing high QF products (up to 40 THz) using non-boric additions. The effect of the sintering temperature, the sintering atmosphere, the flux composition and its amount on these properties are also discussed.