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Nanoscale potassium niobate crystal structure and phase transition

Haiyan Chen1*, Yixuan Zhang2 and Yanling Lu3

Author Affiliations

1 Institute of Marine Materials Science and Engineering, Shanghai Maritime University, 1550 Harbor Avenue, Lingang New City, Shanghai 201306, China

2 State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, 800 Dongchuan Road, Shanghai 200240, China

3 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 239 Zhangheng Road, Shanghai 201204, China

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Nanoscale Research Letters 2011, 6:530  doi:10.1186/1556-276X-6-530

Published: 23 September 2011

Abstract

Nanoscale potassium niobate (KNbO3) powders of orthorhombic structure were synthesized using the sol-gel method. The heat-treatment temperature of the gels had a pronounced effect on KNbO3 particle size and morphology. Field emission scanning electron microscopy and transmission electron microscopy were used to determine particle size and morphology. The average KNbO3 grain size was estimated to be less than 100 nm, and transmission electron microscopy images indicated that KNbO3 particles had a brick-like morphology. Synchrotron X-ray diffraction was used to identify the room-temperature structures using Rietveld refinement. The ferroelectric orthorhombic phase was retained even for particles smaller than 50 nm. The orthorhombic to tetragonal and tetragonal to cubic phase transitions of nanocrystalline KNbO3 were investigated using temperature-dependent powder X-ray diffraction. Differential scanning calorimetry was used to examine the temperature dependence of KNbO3 phase transition. The Curie temperature and phase transition were independent of particle size, and Rietveld analyses showed increasing distortions with decreasing particle size.

Keywords:
potassium niobate; crystal structure; phase transition; nanoscale powder.