Abstract
Ba(Ni0.5Nb0.5)O2.75 (BNNO) doped KNbO3 (KN) and (K0.5Na0.5)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.
Highlights
The European Physical Journal Special Topics provide a unique combination of semiconducting and ferroelectric properties
By careful selection of the calcination and sintering temperatures, the best possible level of densification can be achieved [29,30]. Similar to their pure KN and KNN counterparts, the KBNNO and KNBNNO ceramics require a careful determination of calcination and sintering temperatures, as well as the suppression of the volatilization of potassium
The further K loss for the 0.1 KBNNO slowed down when calcined at 900 ◦C (0.5% more compared to that at 850 ◦C), due to a relatively complete phase formation that occurred at 850 ◦C (Fig. 3) and resulting in much less standalone K-based compositions remaining
Summary
The European Physical Journal Special Topics provide a unique combination of semiconducting and ferroelectric properties. Such a significant improvement has given the KNBNNO the d33 of 100 pm/V and γ of 128 μC/m2K which are nearly the same with those of the parental KNN – a widely used lead-free piezoelectric material [27] This opens the door of development of a fundamentally novel multi-source energy harvester which is able to convert solar (narrow band gap photovoltaic), thermal (pyroelectric) and kinetic (piezoelectric) energy into electricity simultaneously on only a single piece of material [27]. A similar trend is found in the BNNO doped KNN (KNBNNO) [27] Such a phenomenon provides an opportunity to minimize the concentration of introduced oxygen vacancies, maximising the piezoelectric and pyroelectric properties while maintaining a narrow bandgap. Together with references [26,27], this paper serves as a comprehensive and detailed report of the KBNNO and KNBNNO multi-source energy harvesting/sensing materials, providing guidance for the working principles, fabrication, optimisation and characterisation of these materials
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