Relaxor behavior in the Perovskitex-type Bi0.5(Na1-xLix)0.5TiO3 (0≤x≥0.2) solid solution

In the search of lead – free ferroelectric ceramics with improved properties, bismuth sodium titanate Na0.5Bi0.5TiO3 (NBT) was thoroughly investigated in our group. Solid solutions of the perovskite-type compounds, with Bi0.5(Na1-xLix)0.5TiO3, formula, were prepared by solid state reaction. The results of X-ray diffraction (XRD) data evidenced for a single perovskite phase, with a solubility limit of (Na,Li) estimated to x ≈ 0.2. The dielectric properties of sintered ceramics were investigated in wide temperature (25–800°C) and frequency (1kHz-1MHz) ranges. For low substitution rate, (0 ≤ x ≤ 0.2) the compounds exhibit diffuse phase transition and are characterised by high Curie temperature and a relaxor – like behavior. In the high temperature range, the thermal variation of permittivity is well described by a law $$ \frac{1}{\varepsilon }-\frac{1}{\varepsilon_m}=C{\left(T-{T}_m\right)}^\gamma $$ , where γ is close to 1.5. Such a relaxor behavior is interpreted in terms of cation disorder, due to the statistical repartition of Na and Li, or correlated to the relaxation of polar clusters induced by the Na substitution by Li in the A site of the perovskite unit cell.