Effect of nonstoichiometry on the microstructure and microwave dielectric properties of Ba(Mg1/2W1/2)O-3 ceramics

Effects of nonstoichiometry on crystal structure and the microstructure of double perovskite Ba(Mg1/2W1/2)O-3 ceramics have been investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Raman spectrometry in this paper. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8-11 GHz. The results show that small deviation from stoichiometric composition has little influence on the crystal structure such as B-site 1:1 ordering degree. Evaporation of BaO was confirmed during the sintering of BMW ceramics, which in turn produce more BaWO4 phase. Ba-deficiency or W-excess in BMW could improve the sinterability and Q x f value, while Ba-excess or W-deficiency could suppress the formation of BaWO4 at the expense of increase in sintering temperature and decrease in Q x f value. Mg nonstoichiometry has little effect on the variation of BaWO4 content and Q x f value. Maximum Q x f value of about 140,000 GHz could be obtained for the Ba-deficient or W-excessive samples after sintering at 1500 degrees C/2 h or 1550 degrees C/2 h, respectively. All Mg-nonstoichiometric compositions exhibit high Q x f value of about 120,000 GHz after sintering at 1550 degrees C/2 h. All well-densified samples have dielectric permittivity of about 19-20 and tau(f) value varied within the range of -21 similar to -28 ppm/degrees C. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.