Phase evolution, morphology and photodegradation kinetics of hydrothermally synthesized tetragonal sodium niobate

Abstract

The optimum synthesis conditions of tetragonal sodium niobate (NaNbO3) have been successfully determined to be a hydrothermal treatment of 15 M precursor solution at a treatment temperature of 180 °C for a time period of 6 h. This phase is formed through transition of an intermediate orthorhombic phase of NaNbO3, and feasibility of such a transformation has been considered from a thermodynamic perspective. Moreover, FESEM results have revealed that initially formed rod-like structures reach a final spherical form through an intermediate step of cubical morphology. Each of these morphological transformations has been found to be associated with corresponding transformations in phase of NaNbO3. Photodegradation properties of the samples have been found to improve progressively in the order of orthorhombic NaNbO3, tetragonal NaNbO3 and annealed orthorhombic NaNbO3. The kinetics study of the first two samples exhibited mixed mechanism consisting of pseudo-first order and Jander model, while the last one showed a single mechanism (pseudo-first order model) throughout.