Investigation of diffuse phase transition in ferroelectric Pb2−x K1+x Li x Nb5O15 (0 ≤ x ≤ 1.5) ceramics

Substitution of Pb with Li and K in the Pb2KNb5O15 phases leads to a new composition with chemical composition Pb2−x K1+x Li x Nb5O15 which crystallizes with tetragonal tungsten bronze-type structure. Ferroelectric ceramics with different compositions were synthesized using solid-state reaction and complex dielectric permittivity measurements in these compounds were performed in a frequency and temperature range of 20 Hz–1 MHz and from 25 to 550 °C, respectively. Special attention was paid to the diffuse phase transition (DPT) that occurs close to the Curie temperature. The empirical equation proposed by Santos–Eiras for a phenomenological description of the temperature dependence of the dielectric permittivity ( $$\varepsilon_{\text{r}}^{{\prime }}$$ ) peak is used to calculate some characteristic parameters of DPT. From the results, it must be assumed that these compounds show a diffuse phase transition with non-relaxor behavior. A basic phase diagram showing the evolution of T m function of composition x is deduced from this study.