Microstructure and microwave dielectric properties of modified zinc titanates (I)

Abstract

Zinc metatitanate, ZnTiO3, decomposes into zinc orthotitanate and rutile on heating above 945 degrees C. It was found that this material could be a useful candidate for microwave resonator materials. The substitution of Zn by less than 10 mol% of Ba, Ca, or Sr achieves near zero tau(f) in spite of the fact that BaTiO3, CaTiO3, and SrTiO3 themselves have positive tau(f) The origin of the temperature-compensating characteristics of the modified system was found to be in the reduction or elimination of rutile by the formation of new phases such as Ba3Zn7Ti12O34, Ca2Zn4Ti15O36, and Sr2Zn4Ti15O36 polytitanates, which have much lower positive tau(f) than the rutile. It was revealed that zinc orthotitanate grains containing around 0.33 mol excess rutile have Zn2Ti3O8 nanosize precipitates in the grain. The precipitates had a structural coherency with the Zn2TiO4 cubic matrix phase. The modified system has microwave dielectric properties of epsilon(r) = 25-32, Q factor at 10 GHz = 2300-5400, and tau(f) = +56 to -22 ppm/degrees C. (C) 1998 Elsevier Science Ltd.