Phase Evolution, Densification and Dielectric Properties of [KNbO3]1-x[BaNi½Nb½O3-δ]x[x=0.1,0.2] Ferroelectric Ceramics Prepared by Conventional Sintering and Spark Plasma Sintering

Abstract

Ferroelectric semiconducting ceramics with band gap (Eg)< 2 eV will be very useful for photovoltaic and photocatalytic application. Unfortunately all the current ferroelectric oxides have wide band gaps (Eg>2.7 eV for BiFeO3, Eg>3.5 eV for PZT) and can utilize only about 8%–20% of the solar spectrum and efficiency is very small. Recently, Grinberg et al. [US patent 2013/0104969, Nature 503 (2013) 509] invented a complex ceramic solid solution of KNbO3-BaNiNbO3 (KN-BNNO) which is ferroelectric and band gap < 2 eV. However, the problems associated with the development of the KNbO3-based materials lies on its complex densification behavior and alkali evaporation leading to poor density. There is no literature available for the preparation of highly dense KN-BNNO ceramics by SPS sintering and study of it's dielectric property. Present thesis reports the preparation of (1-x)KNbO3-xBaNiNbO3 powder by solid state synthesis route. Phase evolution with composition modification and calcination temperature was discussed. Dense (1-x)KNbO3-xBaNiNbO3 (x=0.1, 0.2) ceramics were prepared by a novel spark plasma sintering (SPS) technique. The sintering was conducted at temperatures ranging from 800 to 1075oC under 35 MPa pressure. A bulk density value up to 97% of true density was achieved in the process. This contrast to around 83% of the true density achieved by conventional sintering at around 1120oC. The dielectric properties also improved (with respect to conventionally sintered sample) for spark plasma sintered samples