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

摘要

A new low-temperature-cofired ceramics (LTCC) material that consists of ZnAl2O4 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 ZnAl2O4 ceramics from more than 1400 degrees C-930 degrees C. The influences of the LMZBS glass content on the phase composition, crystallization activation energy and microwave dielectric properties of ZnAl2O4 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 ZnAl2O4 ceramics were analyzed. X-ray diffractometer results showed that the LMZBS glass crystallized forming Mg2B2O5 and Li2ZnSiO4, and did not react with ZnAl2O4 ceramics. As LMZBS glass was increased, Mg2B2O5 and Li2ZnSiO4 gradually dominated the composite and ZnAl2O4 phase decreased. Meanwhile, the flexural strength (sigma), dielectric constant (epsilon(r)) and temperature coefficient of resonant frequency (tau(f)) demonstrated gradually increase, whereas the quality factor (Qxf) presented a trend of rise first and then fall. The composite which the mass ratio of ZnAl2O4 ceramics to LMZBS glass is 1:2 can be sintered at 930 degrees C for 3h exhibited optimal microwave dielectric properties: epsilon(r) = 7.4, Qxf = 34,100 GHz, tau(f) = -43.99 ppm/degrees C and flexural strength (sigma = 141 MPa). In addition, the new LTCC material can be co-fired with Ag electrode that have high electrical conductivity. (C) 2019 Elsevier B.V. All rights reserved.