Multi-functional perovskites – an investigation of compositional and processing influence on microstructure, dielectric and ferroelectric properties

Ba(Ni_0.5Nb_0.5)O_2.75 (BNNO) doped KNbO₃ (KN) and (K_0.5Na_0.5)NbO₃ (KNN), abbreviated as KBNNO and KNBNNO, respectively, have been recently reported to co-exhibit narrow band gaps (visible range) and strong piezoelectric/pyroelectric effects simultaneously within the same material. This had never been achieved in a single ceramic material. Such a breakthrough may allure the development of fundamentally novel multi-source energy harvesters based on only one piece of material as well as advanced optoelectronic devices with multiple functions. It has been found that the window of getting the unique combination of these properties is very narrow. Even a slight shifting away from the stoichiometry of the compositions may induce a significant loss of the properties. The reasons are expected to be in the compositions and microstructure of these materials. However, detailed information — e.g. the correlation of the compositions, processing conditions, microstructure and properties — remains to be investigated for such novel materials. In this paper, the inter-influence of different doping amounts of BNNO, calcination and sintering temperatures, phase structures and defects (potassium loss and oxygen vacancy) on the dielectric and ferroelectric properties are studied. The paper reveals the principles and provides guidance to achieving good ferroelectric properties in these emerging perovskite structured materials.