Low Temperature Sintering of ZnAl2O4 Ceramics with CuO-TiO2-Nb2O5 Composite Oxide Sintering Aid

ZnAl 2 O 4 and ZnAl 2 O 4 -based ceramics have attracted much attention from researchers due to their good microwave dielectric, thermal and mechanical properties.In this work, the influence of 5% (in mass) CuO-TiO 2 -Nb 2 O 5 (CTN) ternary composite oxide additives with different composition ratios on sintering behavior and properties of ZnAl 2 O 4 microwave dielectric ceramics was investigated.When the molar fraction ranges of Cu, Ti and Nb elements in 5% CTN additives are 0.625-0.875,0-0.250 and 0.125-0.625,respectively, sintering temperature of ZnAl 2 O 4 ceramics can be reduced from above 1400 to below 1000 .The sintering additives CN (Cu : Nb=1 : 1, molar ratio) and CTN (Cu : Ti : Nb=4 : 1 : 3, molar ratio) can reduce sintering temperature of ZnAl 2 O 4 ceramics to 975 and 1000 , respectively, while maintaining good dielectric properties (dielectric constant r =11.36, quality factor Q=8245 GHz and r =9.52, Q=22249 GHz) and flexural strengths (200 and 161 MPa), which are expected to be applied in preparation of low temperature co-fired ceramic (LTCC) materials with copper electrodes.Low-temperature sintering of the ZnAl 2 O 4 +CTN system is characterized as activated sintering.Nanometer-level amorphous interfacial films containing Cu, Ti, and Nb elements are observed at the grain boundaries, which may provide fast diffusion pathways for mass transportation during the sintering process.Valence changes of Ti and Cu ions, along with changes of oxygen vacancies, are confirmed, which provides a potential mechanism for reduced sintering temperature of ZnAl 2 O 4 ceramics.In addition, a series of reactions occurring at the grain boundaries can activate these boundaries and further promote the sintering densification process.These results suggest a promising way to design a novel LTCC material with excellent properties based on the low temperature sintering of ceramics with the sintering aid of CuO-TiO 2 -Nb 2 O 5 composite oxide.Key words: ZnAl 2 O 4 ; CuO-TiO 2 -Nb 2 O 5 ; low-temperature sintering; microwave dielectric ceramic; low temperature co-fired ceramicMultilayer co-fired ceramic substrates have extensive application in various electronic devices for miniaturization, high density, multi-function and high reliability.Based on the sintering temperature, these substrates can be divided into high temperature co-fired ceramic (HTCC) substrate and LTCC substrate.Alumina dielectrics combined with Mo and W conductors are typically selected for the HTCC material system, which are co-fired at temperatures exceeding 1500 .HTCC substrate materials exhibit superior mechanical strength, high thermal conductivity and stable chemical