SiC-AlN multiphase ceramics with 10 wt. %Y₂O₃-BaO-SiO₂ additives were fabricated by pressureless sintering in a nitrogen atmosphere. The effects of SiC contents and sintering temperatures on the sinterability, microstructure, thermal conductivity and high-frequency dielectric properties were characterized. In addition to 6H-SiC and AlN, the samples also contained Y₃Al₅O₁₂ and Y₄Al₂O₉. SiC-AlN ceramics sintered with 50 wt. % SiC at 2173 K exhibited the best thermal diffusivity and thermal conductivity (26.21 mm²·s⁻¹ and 61.02 W·m⁻¹·K⁻¹, respectively). The dielectric constant and dielectric loss of the sample sintered with 50 wt. % SiC and 2123 K were 33–37 and 0.4–0.5 at 12.4–18 GHz. The dielectric constant and dielectric loss of the samples decreased as the frequency of electromagnetic waves increased from 12.4–18 GHz. The dielectric thermal conductivity properties of the SiC-AlN samples are discussed.

6BaO·xCaO·2Al₂O₃ (x = 0.8, 1.2, 1.6, 2, and 2.2) aluminates were synthesized via a liquid phase co-precipitation method. Effects of the molar amount of CaO on the phase of aluminates before and after melting and their hygroscopic phase, melting properties, environmental stability, evaporation, and emission properties were systematically studied. The results show that with the increase of the molar amount of CaO, the aluminates change from a mixture phase to a single phase of Ba₃CaAl₂O₇, and the diffraction peak shifts to a higher angle. The melted phase of the aluminates changed from a single phase to a mixed phase of Ba₅CaAl₄O₁₂ and Ba₃CaAl₂O₇. Meanwhile, the comprehensive properties of the aluminates are improved. The weight gain of 6BaO·2CaO·2Al₂O₃ aluminates is only 10.88% after exposure to air for 48 h; the pulse emission current density of barium tungsten cathodes impregnated with 6BaO·2CaO·2Al₂O₃ aluminates in the porous tungsten matrix can reach 28.60 A/cm² at 1050 °C, and the evaporation rate is 2.52 × 10⁻¹⁰ g/(cm²·s).