In Situ Observation of Dehydration-Induced Phase Transformation from Na2Nb2O6–H2O to NaNbO3

• Published in: Journal of physical chemistry. C Vol. 116; no. 42; pp. 22261 - 22265
• Main Authors: Jung, Jong Hoon, Chen, Chih-Yen, Wu, Wen-Wei, Hong, Jung-Il, Yun, Byung Kil, Zhou, Yusheng, Lee, Nuri, Jo, William, Chen, Lih-Juann, Chou, Li-Jen, Wang, Zhong Lin
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 25.10.2012
• Subjects: Chemistry; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General and physical chemistry; Ion-exchange; Materials science; Methods of nanofabrication; Physics; Specific phase transitions; Structural transitions in nanoscale materials; Surface physical chemistry; Gibbs free energy; Phase transformations; Crystallization; Niobates; XRD; High temperature; Nanostructures; Dehydration; Molecular sieves; Real time; Transmission electron microscopy; Hydrothermal synthesis; Piezoelectric materials; Arrhenius equation; Lead free ceramics; Kinetics; Nanowires; Activation energy; Nanostructured materials
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp308289r

We have monitored the phase transformation from a Sandia octahedral molecular sieve Na2Nb2O6–H2O to a piezoelectric NaNbO3 nanowire through in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements at high temperatures. After dehydration at 288 °C, the Na2Nb2O6–H2O becomes significantly destabilized and transforms into NaNbO3 with the increase of time. The phase transformation time is exponentially proportional to the inverse of temperature, for example, ∼105 s at 300 °C and ∼101 s at 500 °C, and follows an Arrhenius equation with the activation energy of 2.0 eV. Real time TEM investigation directly reveals that the phase transformation occurs through a thermally excited atomic rearrangement due to the small difference of Gibbs free energy between two phases. This work may provide a clue of kinetic control for the development of high piezoelectric lead-free alkaline niobates and a deep insight for the crystallization of oxide nanostructures during a hydrothermal process.