Sintering and dielectric properties of perovskite SrTaO2N ceramics

Single-phase perovskite oxynitride SrTaO2N ceramics were prepared by pressureless sintering at 1400 °C under a nitrogen atmosphere, using 5 wt% of SrCO3 or La2O3 as a sintering additive. In contrast, SrTaO2N bulks without additives contained TaC and Ta3N5 impurities. Sintering in nitrogen led to oxygen/nitrogen deficiencies in the oxynitride, while post annealing in flowing ammonia was effective to eliminate the anion vacancies. The introduction of additives significantly improved the sinterability of SrTaO2N ceramics. A relative density of >90% in the bulk was achieved with a highly dense microstructure with smaller grain sizes. The SrTaO2N bulk with SrCO3 additive exhibited superior dielectric performance with a high relative permittivity (ɛr = 1.0 × 104) and dissipation factor (tan δ = 0.039) at a frequency of 1 MHz.