Specificity of Forming Structure, Microstructure and Developing Polarization Properties in [Ba1–xNax][Ti1–yZryNbx]O3 Solid Solutions in the Phase Instability Region

Abstract

The physicochemical properties of solid solutions [Ba_1–xNa_x][Ti_1–yZr_yNb_x]O₃ with varying concentrations of NaNbO₃ (x = 0.02, 0.04) and BaZrO₃ (y = 0.00, 0.05, 0.10) are investigated. The samples are synthesized using a two-stage solid-state reaction method with preliminary mechanoactivation. X-ray diffraction analysis reveals that all samples feature a perovskite-like structure with minor impurity phases. Increasing the Zr⁴⁺ concentration leads to broadening of diffraction peaks and the appearance of diffuse maxima; this may indicate modulation effects and inhomogeneous cation (Zr⁴⁺, Ti⁴⁺, Nb⁵⁺) distribution. The unit cell parameter gradually increases from 4.009 to 4.037 Å as Zr⁴⁺ content grows from 0 to 10 mol %. The relative density of the ceramics reaches a maximum of 88.50% at y = 0.10. SEM analysis reveals an underdeveloped fine-grained microstructure (average grain size ≈ 2 μm) with pronounced porosity, attributed to low-melting eutectics forming a liquid phase during sintering. Studies of dielectric hysteresis loops demonstrate an increase in total energy density from 0.998 to 1.551 J/cm³, accompanied by a sharp decrease in energy efficiency from 56.1 to 10.8% when Zr⁴⁺ increases. The highest energy storage density is expected in the concentration range 0 ≤ y < 0.05. The results obtained can be applied to the development of lead-free ceramics based on BaTi_(1–y)Zr_yO₃.