Phase evolution and near-zero shrinkage in BaAl2Si2O8 low-permittivity microwave dielectric ceramics

The mechanism of near-zero shrinkage, phase evolution induced by calcining temperature and dispersant, and their effects on the microwave dielectric properties of BaAl2Si2O8 ceramics prepared by the solid-state reaction were investigated. Research showed that deionized water was beneficial to preparing BaAl2Si2O8 ceramics with high density of about 95%, and can induce the phase evolution from hexagonal to monoclinic when the calcining temperature was over 1175 degrees C. With ethanol, however, the single hexagonal phase always existed in the porous ceramics with near-zero shrinkage, and a porous microstructure originated from the decomposition of residual BaCO3 during sintering. The best microwave dielectric properties can both be obtained in the BaAl(2)Sl(2)O(8) ceramics calcined at 1150 degrees C and sintered 1475 degrees C for 3 h using dispersants such as deionized water (epsilon(r) = 6.36, Q x f= 44,800 GHz and tau(f) = -46.9 ppm/degrees C) and ethanol (epsilon(r) = 4.64, Q x f = 35,580 GHz and tau(f) = -43.5 ppm/degrees C). (C) 2013 Elsevier Ltd. All rights reserved.