Modulated calcination temperatures of EDTA/Citrate-Synthesized NaNbO3 for optimized structural and optical properties

Abstract

This study investigates the precise tailoring of perovskite-type sodium niobate (NaNbO3) powders, synthesized via a combined EDTA/citrate complexation route. The study evaluated the impacts of varying citric acid concentrations (1:1:1.5 and 1:1:3 molar ratios) and calcination temperatures (600, 700, and 800 °C) on structural and optical properties. Rietveld refinement and Raman spectroscopy confirmed the stabilization of a non-centrosymmetric orthorhombic phase (P21ma space group). While the citric acid ratio altered the precursors thermal decomposition, calcination temperature drove phase maturation systematically increasing crystallinity, growing crystallite size, and inducing key distortions in the NbO6 polyhedra. Optically, the synthesized NaNbO3 exhibited a narrowed optical bandgap (2.40 to 3.17 eV), marking a significant redshift from the conventional 3.4 eV literature value and extending its photoresponse into the visible light spectrum. Photoluminescence and time resolved photoluminescence spectroscopies showed that higher calcination temperatures suppressed radiative defect centers. This structural ordering achieved a two to three-fold increase in photogenerated charge carrier lifetimes, up to 10 ns, indicating efficient electron/hole separation. A calcination temperature of 700 °C achieved an optimal balance between of phase crystallinity, morphology, and minimization of defect trapping. Finnally, this EDTA/citrate route allows the introduction of intermediate states and beneficial structural modifications, overcoming traditional broad bandgap limitations. The resulting prolonged carrier lifetimes and visible light absorption position this tailored NaNbO3 as a highly promising candidate for advanced solar driven photocatalysis and next generation optoelectronic devices.