tailieunhanh - Báo cáo hóa học: " Nanoscale potassium niobate crystal structure and phase transition"

Tuyển tập các báo cáo nghiên cứu về hóa học được đăng trên tạp chí hóa hoc quốc tế đề tài : Nanoscale potassium niobate crystal structure and phase transition | Chen et al. Nanoscale Research Letters 2011 6 530 http content 6 1 530 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Nanoscale potassium and phase transition Haiyan Chen1 Yixuan Zhang2 and Yanling Lu3 niobate crystal structure 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. Background Lead oxide-based perovskites are a commonly used piezoelectric material and are now widely used in transducers and other electromechanical devices 1-4 . However the high toxicity and high processing vapor pressure of lead oxide cause serious environmental problems. A promising way to address this issue is to develop lead-free piezoelectric ceramics to minimize lead pollution. Recently as demand has increased many studies have focused on the development .