BaCu(B 2 O 5 ) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B 2 O 5 ) phase was formed at 7001C and melted above 8501C. The BaCu(B 2 O 5 ) ceramic sintered at 8101C had a dielectric constant (e r ) of 7.4, a quality factor (Q Â f) of 50 000 GHz and a temperature coefficient of resonance frequency (s f ) of À32 ppm/1C. As the BaCu(B 2 O 5 ) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B 2 O 5 ) was added to the Ba(Zn 1/3 Nb 2/3 )O 3 (BZN) ceramic, BZN ceramics were well sintered even at 8501C. BaCu(B 2 O 5 ) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q Â f 5 16 000 GHz, e r 5 35, and s f 5 22.1 ppm/1C were obtained for the BZN16.0 mol% BaCu(B 2 O 5 ) ceramic sintered at 8751C for 2 h. J ournal

Re 3 Ga 5 O 12 (Re: Nd, Sm, Eu, Dy, Yb, and Y) garnet ceramics were synthesized and their microwave dielectric properties were investigated for advanced substrate materials in microwave integrated circuits. The Re 3 Ga 5 O 12 ceramics sintered at 13501-15001C had a high-quality factor (Q Â f) ranging from 40 000 to 192 173 GHz and a low-dielectric constant (e r ) of between 11.5 and 12.5. They also exhibited a relatively stable temperature coefficient of resonant frequency (s f ) in the range of À33.7 to À12.4 ppm/1C. In particular, the Sm 3 Ga 5 O 12 ceramics sintered at 14501C exhibited good microwave dielectric properties of e r 5 12.4, Q Â f 5 192 173 GHz, and s f 5 À19.2 ppm/1C.

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The effects of Al2O3 additive on the microstructure and microwave dielectric properties of Ba(Zn1/3Ta2/3)O3 (BZT) ceramics were investigated. The BZT ceramics has a 1:2 ordered hexagonal structure. The degree of the 1:2 ordering did not decrease with the addition of Al2O3. Grain growth occurred and the liquid phase formed for the Al2O3-added BZT ceramics sintered above 1580°C. The liquid phase contains high concentrations of Ba and Al ions, which could be responsible for the grain growth. When a small amount of Al2O3 was added, the relative density slightly decreased but the Q value was markedly enhanced. The increase in the Q value was not related to the relative density or the 1:2 ordering. In contrast, the improvement in the Q value occurred in specimens in which grain growth occurred. Therefore, the increase in the grain size is considered to be responsible for the improvement in the Q value of Al2O3-added BZT.