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Dense alumina ceramics doped with 5 wt% 4CuO-TiO2-2Nb2O5 composite sintering aids were obtained at low sintering temperatures of 950∼975 °C. The ceramic sintered at optimal condition shows good microwave dielectric properties (er = 12.7, Q × f = 7400 GHz), high thermal conductivity (18.4 W/m K) and high bending strength (320 MPa). TEM and EDS analysis revealed that amorphous Cu-Ti-Nb-O interfacial films with nanometer thickness formed at the grain boundaries, which could provide paths of mass transportation for densification. Al3+ ions may be involved in mass transportation through substitution by Ti3+ and Ti4+ ions near the grain boundary during the sintering process. The accumulation of copper ions at the trigeminal grain boundary was observed. The migration and reaction of copper ions in grain boundaries may also play an important role in promoting mass transportation and low-temperature densification of alumina ceramics.

The terahertz (THz) dielectric constant ( e r ' ) and dielectric loss tangent ( tan δ ) of the commercial LTCC materials (Ferro A6M and DuPont 951), Al2O3 (ceramic and single crystal), AlN and β-Si3N4 ceramics were measured using a vector network analyzer (VNA) over the frequency range of 140–220 GHz and a time-domain spectrometer (TDS) from 0.2 to 1.0 THz. The results from the two instruments are compared with the literature and show good agreement and consistency. For Ferro A6M, e r ' = 6.06, tan δ = 0.012 at 1.0 THz. For DuPont 951, e r ' = 7.67, tan δ = 0.097 at 1.0 THz. For Al2O3 ceramic and single crystal, the measured THz dielectric properties are consistent with the reported works. The dielectric constant of AlN ( e r ' = 8.85) and β-Si3N4 ( e r ' = 8.41) ceramics in the THz region is a little lower than those reported for the MHz to GHz region. These results provide valuable and much needed reference information for device designers and material scientists.

A parallel preparation method was developed using dry powders as starting materials to synthesize multi-compositional microwave dielectric ceramics. The Li 2 O-Nb 2 O 5 -TiO 2 ternary system was investigated as a model material. The validity of the parallel ceramic preparation process was confirmed by synthesizing a group of LiNb 0.6 Ti 0.5 O 3 ceramics in parallel, which showed the same crystalline structure and close dielectric properties. The ceramic libraries with M-phase-rich samples and Li 2 TiO 3 -rich samples were prepared using the parallel process, and the microwave dielectric properties and crystal phases were investigated systematically. An excellent microwave ceramic with a composition of 0.55Li 2 O-0.05Nb 2 O 5 -0.40TiO 2 was obtained, which has a dielectric constant of 18.4 and a high quality value ( Q × f ) of 79000 GHz. This parallel process can be applied extensively to explore a variety of bulk ceramic libraries for discovering new functional materials with high performances.

The effects of β-Si 3 N 4 whiskers on the thermal conductivity of low-temperature sintered borosilicate glass–AlN composites were systematically investigated. The thermal conductivity of borosilicate glass–AlN ceramic composite was increased from 11.9 to 18.8 W/m K by incorporating 14 vol% β-Si 3 N 4 whiskers, and high flexural strength up to 226 MPa were achieved along with low relative dielectric constant of 6.5 and dielectric loss of 0.16% at 1 MHz. Microstructure characterization and percolation model analysis indicated that thermal percolation network formation in the ceramic composites led to the high thermal conductivity. The crystallization of the borosilicate microcrystal glass also contributed to the enhancement of thermal conductivity. Such ceramic composites with low sintering temperature and high thermal conductivity might be a promising material for electronic packaging applications.