•Pure BNT prepared at sintering temperatures (Tsint = 850 to 1150 °C) by solid state route exhibits single phase R3c symmetry.•Change in direct bandgap by 7% originates from thermal modulation in size confinement of crystallites.•A stark spectral extension in low loss frequency stable εr zone occurs with increase in Tsint.•Correlation between Tsint dependent structural features and functional responses has been established.•BNT conductivity exhibits a sequential shift in charge-translation mechanism with increasing frequency. A facile way to control the functional properties of pure Bi0.5Na0.5TiO3 (BNT) could be of great significance when it comes to manufacturing and application of Pb free dielectrics. Herein, a stark modulation in optical, dielectric and conductivity responses of pure BNT with morphological and crystallographic modifications brought about simply by changing the processing temperature (850 ≤ Tsint≤ 1150 °C) along with a detailed correlation between the functional and structural properties has been reported, which are yet to be addressed in detail for BNT in particular. Industrially, the solid state reaction (SSR) route being the most viable mass production technique was adopted in this study. A conspicuous change in crystallographic distortion along with microstructural development was rendered by increasing Tsint without generating any 2nd phase. A noticeable modulation in direct-mode optical transition energy enabled by morphology dependent size confinement effect with increase in Tsint makes BNT based compositions a potential candidate for photochemical application. An optimum Tsint corresponding to peak εr' for pure BNT was established and a technologically desired frequency-stable εr' plateau with low loss was observed to extend remarkably from over 1 MHz to below 0.1 kHz as Tsint reaches 1150 °C, in which both temperature dependent structure and morphology played a decisive role. Distinct frequency dependent conductivity zones were also identified for pure BNT under different measurement and processing temperatures, which were also in direct congruence with the dielectric responses.