Abstract
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.
Highlights
Lead zirconate titanate (PZT) ceramics have been extensively used in electronic applications such as transducers, capacitors and piezoelectric motors, due to their excellent ferroelectric and piezoelectric properties [1,2,3,4,5]
Chou et al [17] reduced the sintering temperature from 1100 °C for pure bismuth sodium titanate (BNT) ceramics to 950 °C by adding 4 wt% CuO which enhanced the relative density to 95%
The single-phase region has been demonstrated at higher Fe contents of doped BNT ceramics
Summary
Lead zirconate titanate (PZT) ceramics have been extensively used in electronic applications such as transducers, capacitors and piezoelectric motors, due to their excellent ferroelectric and piezoelectric properties (coercive field of 1 kV/mm and remnant polarization of 35 μC/cm2) [1,2,3,4,5]. The use of PZT is under review in Europe, due to the high toxicity and evaporation of lead oxide (PbO) at higher sintering temperatures, which cause health and environmental hazards [3, 6,7,8]. Watcharapasorn et al [19] lowered the sintering temperature of BNT to 850 °C with a high densification of 95% relative density by adding 0.15 mol% Fe2O3. Chou et al [17] reduced the sintering temperature from 1100 °C for pure BNT ceramics to 950 °C by adding 4 wt% CuO which enhanced the relative density to 95%. Reducing energy consumption in BNT sintering through lower sintering temperatures was the primary aim of the present work. Process as follows: (i) Heat from room temperature at 3 °C/min to 300 °C and hold at this temperature for 1 h; (ii) heat at 3 °C/min from 300 °C to 700 °C and hold at this temperature for 1 h; (iii) and heat at 5 °C/min from 700 °C to 900 °C (samples BFe0.00 to BFe10.00) or 1075 °C (sample SB0) and hold at this temperature for 2 h; allow samples to cool slowly inside the furnace to room temperature
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