Dielectric properties of barium titanium niobates
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Dielectric properties of barium titanium niobates G. L. Roberts, R. J. Cava, W. F. Peck, Jr., and J. J. Krajewski AT&T Bell Laboratories, Murray Hill, New Jersey 07974 (Received 2 February 1996; accepted 1 October 1996)
The results of measurements of dielectric constants, in the vicinity of ambient temperature, are presented for eight barium titanium niobium oxides (BaTi1+2n Nb4 O13+4n for n 0, 1, 2, 3, 4; Ba3 Ti4 Nb4 O21 , Ba3 Ti5 Nb6 O28 , and Ba6 Ti2 Nb8 O30 ) in polycrystalline ceramic form. The dielectric constants are in the range of 30 to 70. The results of dielectric measurements on solid solutions obtained by partial substitution of Ta for Nb are also reported. These substitutions do not dramatically increase the dielectric constants. One material, Ta-substituted Ba3 Ti5 Nb6 O28 , has a very low temperature coefficient of dielectric constant at K ø 45.
I. INTRODUCTION
The growth of interest in bulk dielectrics for use in microwave frequency electronic components and the need for high dielectric constant materials in advanced microelectronic technologies such as DRAM’s (Dynamic Random Access Memories) suggests that renewed investigation of the dielectric properties of chemically simple ceramic materials might be fruitful. Barium Strontium Titanate (BST) and Ta2 O5 are presently under active investigation for use in microelectronic devices.1–5 Bulk ceramics such as Ba2 Ti9 O20 and Ba6–3x Ln8+2x Ti18 O54 , with dielectric constants (K) of 40 –90 and low dielectric constant temperature coefficients (TCK), are currently used as bulk coaxial resonators and inductors in microwave applications.6–8 Although the properties of many of the well-known dielectric materials are sufficient to satisfy present purposes, it is worthwhile to determine whether other families of materials might have equivalent or superior properties. In this study we present the results of dielectric measurements on a variety of compounds known to occur in the BaO–TiO2 –Nb2 O5 chemical system. The compounds are, in general, low loss dielectrics with K’s in the 30–70 range and moderate TCK’s. The study was extended to include solid solutions of Ta in many of the phases that affected K, TCK, and losses for all materials. The results of our survey suggest that some of the materials are worthy of further study. II. SYNTHESIS
The BaO–Nb2 O5 –TiO2 chemical system has been studied carefully and the crystallographic parameters reported based upon single crystal data.9,10 We synthesized eight phases in this system in order to study their dielectric properties, i.e., BaTiNb4 O13 , BaTi3 Nb4 O17 , BaTi5 Nb4 O21 , BaTi7 Nb4 O25 , BaTi9 Nb4 O29 , Ba3 Ti4 Nb4 O21 , Ba3 Ti5 Nb6 O28 , and Ba6 Ti2 Nb8 O20 . The first five are members of a BaTi1+2n Nb4 O13+4n homologous series. 526
http://journals.cambridge.org
J. Mater. Res., Vol. 12, No. 2, Feb 1997
Downloaded: 14 Mar 2015
Ceramic samples in the Ba –Ti–Nb–(Ta)–O system were made using conventional high-temperature synthesis. The starting materials were BaC
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