Pure (BNT) and iron-doped bismuth sodium titanate (Fe-BNT) ceramics were produced according to the formula Bi0.5Na0.5Ti1−xFexO3−0.5x, where x = 0 to 0.1. The addition of Fe2O3 enables decreasing the sintering temperature to 900 °C in comparison with 1075 °C for pure BNT, whilst also achieving lower porosities and greater densities. This is attributed to oxygen vacancy generation arising from substitution of Fe3+ onto the Ti4+ site of the BNT perovskite structure, and the resulting increase in mass transport that this enables during sintering. X-ray diffraction (XRD) analysis of Fe-BNT samples shows single-phase BNT with no secondary phases for all studied Fe contents, confirming complete solid solution of Fe. Rietveld refinement of XRD data revealed a pseudocubic perovskite symmetry (Pm-3m), and unit cell lengths increased with increasing Fe content. Scanning electron microscopy (SEM) showed that average grain size increases with increasing Fe content from an average grain size of ~ 0.5 μm in (x = 0) pure BNT to ~ 5 μm in (x = 0.1) Fe-doped BNT. Increasing Fe content also led to decreasing porosity, with relative density increasing to a maximum > 97% of its theoretical value at x = 0.07 to 0.1. The addition of Fe to BNT ceramics significantly affects electrical properties, reducing the remnant polarization, coercive field, strain and desirable ferroelectric properties compared with those of pure densified BNT. At room temperature, a high relative permittivity (ɛ′) of 1050 (x = 0.07) at an applied frequency of 1 kHz and a lower loss factor (tanδ) of 0.006 (x = 0.1) at an applied frequency of 300 kHz were observed by comparison with pure BNT ceramics.

The study in this project focuses on using three different processing routes, conventional solid-state sintering, microwave sintering and melt processing, to manufacture electrical ceramics and glass-ceramics in bismuth sodium titanate (BNT) and potassium sodium niobate (KNN) systems. Manufacturing electrical ceramics using a conventional solid-state processing route requires high sintering temperatures (more than 1100 o C) for long times (at least 10 hours including heating and cooling), with high energy consumption (20kWh) for electrical furnaces, leading to high cost. Moreover, laboratory-scale preparation of electrical ceramics in the author's home country, Iraq, is difficult because of equipment shortages and power watts. Therefore, in the present work, a microwave processing route using a standard kitchen microwave oven has been used to produce electrical ceramics, whilst dramatically reducing sintering times (heating between 20-25mins and cooling 2h) and thus energy consumption (0.4kWh). Also, a melt processing route has been used to manufacture electrical glass-ceramics as bulk and fibre samples, thus reducing processing steps and preparing KNN borosilicate glass-ceramic fibres for the first time.Microwave sintering/heating depends on the generation of heating throughout the sample simultaneously. This project has used a combination of direct microwave heating of the sample itself, combined with indirect heating by microwave susceptor disks placed close to the sample. In the present project, microwave susceptor disks composed of 50wt% graphite, 30wt% SiO2, 10wt% Mn2O3, 10wt% Fe3O4 have been used.Both conventional solid-state sintering and microwave processing have been used to prepare four different electrical ceramic compositions: pure bismuth sodium titanate (Bi0.5Na0.5TiO3), pure potassium sodium niobate (K0.5Na0.5NbO3), iron-doped bismuth sodium titanate (Bi0.5Na0.5Ti1-xFexO3-0.5x) and iron-doped potassium sodium niobate (K0.5Na0.5Nb1-xFexO3-x), with high sintering temperatures (900-1100 o C) for 2h inside an electrical furnace (conventional sintering) and short heating times (10-25 mins) inside a standard 900W kitchen microwave oven.A melt processing route has also been used, with the aim of preparing bismuth sodium titanate (Bi0.5Na0.5TiO3) and potassium sodium niobate (K0.5Na0.5NbO3) by heat treatment of bismuth sodium titanium silicate, bismuth sodium titanium borate, potassium sodium niobium silicate, potassium sodium niobium borate and potassium Pure KNN ceramics have been prepared by solid-state sintering and microwave sintering. In addition, KNN-silicate glasses, KNN-borate glasses, KNN-borosilicate glasses and KNN-borosilicate glass fibres have been prepared by melt processing, and subsequent heat treatment with the aim of forming KNN in the resulting glass-ceramics. A K0.5Na0.5NbO3 phase with orthorhombic structure has been successfully produced by solid-state sintering and microwave sintering processing. Also, a main K0.5Na0.5NbO3 phase with anorthic structure has been presented for KNN-...