Low-temperature sintering mechanism and microwave dielectric properties of ZnAl2O4-LMZBS composites

Abstract A new low-temperature-cofired ceramics (LTCC) material that consists of ZnAl 2 O 4 ceramics and highly crystallized Li–Mg–Zn–B–Si (LMZBS) glass has been synthesized by solid state reaction. The LMZBS glass acts as a sintering aid to reduce sintering temperature of ZnAl 2 O 4 ceramics from more than 1400 °C–930 °C. The influences of the LMZBS glass content on the phase composition, crystallization activation energy and microwave dielectric properties of ZnAl 2 O 4 ceramics were investigated. Based on the Rietveld refinement and complex chemical bond theory, the influence of LMZBS glass on the structure and bond length of ZnAl 2 O 4 ceramics were analyzed. X-ray diffractometer results showed that the LMZBS glass crystallized forming Mg 2 B 2 O 5 and Li 2 ZnSiO 4 , and did not react with ZnAl 2 O 4 ceramics. As LMZBS glass was increased, Mg 2 B 2 O 5 and Li 2 ZnSiO 4 gradually dominated the composite and ZnAl 2 O 4 phase decreased. Meanwhile, the flexural strength (σ), dielectric constant ( e r ) and temperature coefficient of resonant frequency ( τ f ) demonstrated gradually increase, whereas the quality factor ( Q×f ) presented a trend of rise first and then fall. The composite which the mass ratio of ZnAl 2 O 4 ceramics to LMZBS glass is 1:2 can be sintered at 930 °C for 3h exhibited optimal microwave dielectric properties: e r  = 7.4, Q×f  = 34,100 GHz, τ f  = −43.99 ppm/°C and flexural strength (σ = 141 MPa). In addition, the new LTCC material can be co-fired with Ag electrode that have high electrical conductivity.