Effect of Zn and Ca modifications on crystallization and microwave dielectric properties of lanthanum borates

Low loss dielectrics based on two borate glasses, (13-19)CaO center dot(13-19)La2O3 center dot 68B(2)O(3) and (13-19)ZnO center dot(13-19)La2O3 center dot 68B(2)O(3), have been investigated with a focus on effects of the CaO/La2O3 and ZnO/La2O3 ratios on physical and dielectric properties. All samples were prepared by mixing glass with 40 wt% Al2O3 filler and by firing at 850 degrees C for 30 min. The effects of increasing relative contents of Ca and Zn were found to be opposite specifically in microstructure evolution and crystallization behavior, and thus, dielectric properties. For example, the 13CaO center dot 19La(2)O(3)center dot B2O3 sample having the lowest Ca content showed the highest Q x f of similar to 8100, while the 19ZnO center dot 13La(2)O(3)center dot B2O3 sample having the highest Zn content showed the highest Q x f of similar to 18,100. The extensive crystallization of low loss phases, i.e.. LaBO3 and LaAl2.03(B4O10)O-0.54, as well as the improved level of densification are assumed to be responsible for better dielectric performance. (C) 2010 Elsevier B.V. All rights reserved.