Low sintering temperature effect on crystal structure and ferroelectric properties lead-free piezoelectric BNT-FNT

Bi0.5Na0.5TiO3 (BNT) emerges as a promising ferroelectric and piezoelectric lead-free candidate to substitute the contaminant Pb[TixZr1-x]O3 (PZT). However, to obtain optimal ferroelectric and pi-ezoelectric properties, BNT must be sintered at high temperatures. In this work, the reduction of sintering temperature by using Fe added to BNT is demonstrated, without significative detriment in the electric properties. BNT-xFe with Fe in the range from x= 0 to 0.1 mol (x=0.025) were synthe-sized by high-energy ball milling followed by sintering at 900 °C. XRD analysis confirmed the presence of rhombohedral BNT together with a new phase of NaFeTiO4 (NFT), also corroborated by means of optical and electronic microscopy. The relative permittivity, in the range of 400 to 500 across all the frequencies demonstrated the stabilization effect of the iron in BNT. Additionally, the presence of iron elevates the Curie temperature, increasing it from 330°C in the Fe free sample to 370 °C in the sample with the maximum Fe concentration (0.1 mol). The dielectric losses maintain a constant values lower than 0.1. In this case, low dielectric loss values are ideal for ferroelectric and piezoelectric materials, as they ensure minimal energy dissipation. Likewise, the electrical conduc-tivity maintains a semiconductor behavior across range of 50 Hz to 1x106 Hz, indicate the potential of these materials for applications at different frequencies. Additionally, it was observed that the introduction of iron in BNT in low concentration promotes a flattening of the hysteresis loops by improving the alignment of electric dipoles, displaying values of 6 and 12 µC/cm2. Similarly, the piezoelectric constant (d33) values undergo a slight decrease when low concentrations of iron are added, maintaining values between 30 and 48 pC/N for BNT-0.025Fe and BNT-0.05Fe respectively.

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