Dielectric ceramics in the BaO-Sm 2 O 3 -TiO 2 -Ta 2 O 5 quaternary system

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Dielectric ceramics in the BaO–Sm2O3–TiO2–Ta2O5 quaternary system X.M. Chen, Z.Y. Xu, and J. Li Laboratory of Materials for Electronics and Communication, Department of Materials Science & Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China (Received 15 March 1999; accepted 19 October 1999)

Dielectric ceramics in the BaO–Sm2O3–TiO2–Ta2O5 quaternary system were prepared and characterized for five typical compositions: BaSm5Ti7Ta3O30, Ba2Sm4Ti6Ta4O30, Ba3Sm3Ti5Ta5O30, Ba4Sm2Ti4Ta6O30, and Ba5SmTi3Ta7O30. The latter three compositions tended to form the tungsten–bronze phase, and the ceramics based on these compositions had a high dielectric constant (134–175) and a low dielectric loss (on the order of 10−3) but a larger temperature coefficient of the dielectric constant. Meanwhile, the former two compositions generally had a more complex phase constitution, containing the tungsten–bronze phase combined with some unknown phase, and a relatively small temperature coefficient of the dielectric constant in the temperature range of 20 to 85 °C could be achieved in these two compositions.

I. INTRODUCTION

Recent development of microelectronic technologies and microwave communication technologies has been strongly driving the investigation of new dielectric materials with temperature-stable high ⑀ and low dielectric loss.1–7 So far, the most important high-⑀ dielectric ceramics, which are used both as temperature-compensated capacitors and microwave resonators, have been investigated and developed in the BaO–Ln2O3–TiO2 system (Ln ⳱ Nd, Sm). A dielectric constant of 80–94, a Qf [the product of quality factor (Q) and frequency (f)] value greater than 5,000 GHz, and a ␶f value between −10 and 15 ppm/°C can be achieved for the modified ceramics in this system.3–7 For searching new materials with dielectric constants greater than 100, some work has been carried out in lead-containing perovskite systems,8,9 and the authors have proposed an alternative new material system of BaO–Nd2O3–TiO2–Ta2O5, where the ceramics with A6B10O30 tungsten–bronze structures have a dielectric constant of 70–160 and a very low dielectric loss even less than 0.0001 at 1 MHz.10,11 In the present work, dielectric ceramics in the BaO– Sm2O3–TiO2–Ta2O5 quaternary system are prepared and characterized, for five typical compositions BaSm5Ti7Ta 3 O 3 0 , Ba 2 Sm 4 Ti 6 Ta 4 O 3 0 , Ba 3 Sm 3 Ti 5 Ta 5 O 3 0 , Ba4Sm2Ti4Ta6O30, and Ba5SmTi3Ta7O30, and the interesting variation of dielectric properties with sintering temperature is discussed. II. EXPERIMENTS

High-purity powders of BaCO3 (>99.95%), Sm2O3 (>99.5%), TiO2 (>99.7%), and Ta2O5 (>99.99%) were adopted as the starting materials, and the objective ceJ. Mater. Res., Vol. 15, No. 1, Jan 2000

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ramic powders with the compositions BaSm5Ti7Ta3O30, Ba 2 Sm 4 Ti 6 Ta 4 O 30 , Ba 3 Sm 3 Ti 5 Ta 5 O 30 , Ba 4 Sm 2 Ti 4 Ta6O30, and Ba5SmTi3Ta7O30 were synthesized by calcination of the mix