High-frequency dielectric characterization of novel lead-free ferroelectrics

Novel lead-free BFO–STO, BFO–CTO, and BFO–BZO ceramics were fabricated by the conventional method and their structural, microstructural, and dielectric properties were characterized. Dielectric measurements were carried out at room temperature in a large frequency range, from 20 Hz to 1.8 GHz. XRD analysis has demonstrated differences in the crystalline structure of the samples. BFO–STO exhibits a very different behavior compared to BFO–CTO and BFO–BZO ceramics because its XRD pattern contains peaks from diffracting planes of BFO and STO simultaneously. In comparison, the diffraction patterns of BFO–BZO and BFO–CTO are dominated by the peaks from diffracting planes of BZO and CTO, respectively. SEM observation has also revealed important differences in their microstructure. BFO–BZO and BFO–CTO have presented similar values of dielectric constant at low and high frequencies, ε′ ~ 85 from 1 to 100 MHz. The lowest value of the loss tangent was measured on BFO–CTO with tan δ = 5 × 10–3 at f = 50 MHz. The BFO–STO ceramic has given higher values of the dielectric constant, closer to those reported for the bulk STO. Nearly frequency-independent high dielectric constant with very low loss over a broad frequency range (20 Hz to 1.8 GHz) of BFO–STO ceramic makes this material a potential candidate for high-temperature and high-frequency application with superior energy performance.