Ceramics of (Ba _{1− x} Sr _x ) ₂ SmTi ₂ Nb ₃ O ₁₅ , denoted as BS _x STN ( x = 0, 0.25 and 0.5), were synthesized by the conventional solid-state reactions route.

The effects of Na⁺ substitution by Y³⁺ on the structural, microstructural, dielectric and electrical properties of Ba₂Na_(1-3x)Y_xNb₅O₁₅ compositions with (x = 0, 0.02 and 0.04) have been studied in detail. The solid solutions of different compositions were prepared by the solid state reaction route method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Complex Impedance Spectroscopy (CIS) techniques. The XRD study confirmed that all prepared compositions have a single-phase orthorhombic tungsten bronze structure with space group Cmm2 at room temperature. The microstructural studies revealed a grain shape and size change in response to increasing Y³⁺ concentration. The dielectric properties of the obtained compositions are evaluated over a temperature range of 40–600 °C. The dielectric properties were improved for the Y₂O₃-substituted Ba₂NaNb₅O₁₅ compound compared to the undoped Ba₂NaNb₅O₁₅ compound. The non-Debye type relaxation mechanism is confirmed by the -Z″ versus Z′ traces. The grain contribution was studied using an equivalent electrical circuit with a Resistor R, a Capacitor C, and a Constant-Phase Element CPE in parallel, in the absence of the grain boundary response and the electrode effect in the frequency range 10 Hz-1MHz. The experimental AC conductivity data were evaluated by using Jonscher's power law. The activation energies obtained from the relaxation and conduction processes, present two different regions as a function of temperature related to the two electrical processes for the prepared ceramics.