Effect of the addition of Sr(Sn0.25Ti0.75)O3 on the dielectric properties in NaNbO3

Lead-free perovskite ceramics Sr_1-xNa_x(Sn_0.25Ti_0.75)_1-xNb_xO₃ (0.6 ≤ x ≤ 0.9), denoted SNSTNₓ, were synthesized by the conventional solid-state route and sintered at 1350 °C. X-ray diffraction analysis confirms the formation of a single-phase perovskite structure with tetragonal symmetry (space group P4mm) for all compositions. Dielectric measurements performed as a function of temperature and frequency reveal two distinct electrical behaviors depending on composition. Samples with x ≥ 0.8 exhibit classical ferroelectric characteristics with a well-defined, frequency-independent Curie temperature, whereas compositions with x < 0.8 show relaxor-like behavior characterized by diffuse phase transitions and strong frequency dispersion of the dielectric permittivity. The relaxor nature is further supported by deviation from the Curie–Weiss law and a diffuseness parameter γ ≈ 1.7. Ferroelectric hysteresis measurements performed for x = 0.9 confirm ferroelectricity, with a remanent polarization of 0.0125 µF mm⁻² and a coercive field of 5 V mm⁻¹. The observed evolution of dielectric behavior is attributed to structural disorder induced by simultaneous A-site (Sr²⁺/Na⁺) and B-site (Sn⁴⁺/Ti⁴⁺/Nb⁵⁺) substitutions, which modify lattice distortion and reduce the phase transition temperature. These results indicate that SNSTNₓ ceramics are promising lead-free materials for temperature-stable dielectric applications.