resumo
Potassium tantalate (KTaO(3) - KT) ceramics with controlled initial K/Ta ratio=1, 1.02 and 1.05 were synthesised by solid-state reaction. Crystal structure and microstructure of the sintered ceramics were examined by XRD and SEM/EDS, respectively. Their dielectric properties were then studied as a function of the temperature over the radio frequency range. Ceramics with K/Ta ratio=1 exhibits potassium-poor secondary phases, in contrast to ceramics with initial K/Ta ratio = 1.05, where no secondary phases are detected. Moreover, the grain size increases dramatically with K/Ta ratio >1. The quantum paraelectric behaviour of KT ceramics is weakly affected by the variation of K/Ta ratio and their dielectric response is well described by Barrett's equation. Though, no anomaly is induced in the dielectric permittivity by potassium excess, it yields an increase of its lowest temperature magnitude up to similar to 4000, which is to the best of our knowledge, the highest value ever reported for KT ceramics. (C) 2011 Elsevier Ltd. All rights reserved.
palavras-chave
MICROWAVE DIELECTRIC-PROPERTIES; KTAO3; TEMPERATURE
categoria
Materials Science
autores
Tkach, A; Vilarinho, PM; Almeida, A
nossos autores
Oleksandr Tkach
Investigador Auxiliar
Paula Maria Lousada Silveirinha Vilarinho
Vice-Diretoragradecimentos
This work was supported by Fundacao para a Ciencia e Tecnologia, through the Project PTDC/CTM/64805/2006. Alexander Tkach acknowledges the FCT (Portuguese Foundation for Science and Technology) for financial support (Ref. SFRHJBPD/34607/2007). SEM/EDS characterisation was supported by project REDE/1509/RME/2005.