Dielectric measurements on a novel Ba1 - xCaxTiO3 (BCT) bulk ceramic combinatorial library

Pullar, Robert C., Zhang, Yong, Chen, Lifeng, Yang, Shoufeng, Evans, Julian R.G., Salak, Andrei N., Kiselev, Dmitry A., Kholkin, Andrei L., Ferreira, Victor M. and Alford, Neil McN. (2009) Dielectric measurements on a novel Ba1 - xCaxTiO3 (BCT) bulk ceramic combinatorial library. [in special issue: International Conference on Electroceramics] Journal of Electroceramics, 22 (1-3), 245-251. (doi:10.1007/s10832-008-9430-5).

Abstract

High-throughput combinatorial methods have the potential to discover new materials. They can investigate the effects of a wide range of dopants on the dielectric properties to optimize existing systems, encouraging the short innovation cycles that industry requires. We are currently part of a consortium of London Universities exploring methods of producing and measuring combinatorial libraries of microwave dielectric ceramics. The London University Search Instrument (LUSI) is a fully automated, high-throughput combinatorial robot that has the potential capability to produce combinatorial libraries consisting of large numbers of sintered bulk ceramic samples with varying composition, on alumna substrates. We have reported the manufacture and characterisation of Ba x Sr1???x TiO3 libraries (x in steps of 0.1) as a proof of concept to demonstrate that the robot works and to confirm a compositional and functional change throughout the libraries, as well as proving that reliable measurements can be made on such small samples. Libraries of Ba1???x Ca x TiO3 samples were made with varying compositions of x?=?0–1 in steps of 0.1, and fired to 1400 °C for 1 h, by LUSI. X-ray diffraction (XRD) data agreed with the few previous reports on this little-studied system, namely that after initially forming a solid solution with Ca addition, above x?=?0.2 a two phase system forms with values of 0.2?<?x?<?0.9, after which a single phase system again appears with values of x?=?0.9 and higher. Dielectric measurements (100 Hz–1 MHz) showed a previously reported unusual initial increase in the Curie point with substitution up to x?=?0.2, followed by a rapid decrease to below 125 K when x?>?0.4. This initial increase has been attributed to the Ca substituting in both the Ba2+ A sites and the Ti4+ B sites of the perovskite up to x?=?0.2, after which T c decreases greatly as the two phase system forms. Scanning probe microscopy and piezo response force microscopy (PFM) experiments also showed evidence of an increase in piezoelectricity with small amounts of x (0.1–0.2), followed by a decrease with increasing x.

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Contributors

Author: Shoufeng Yang

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