Sintered compacts of nano and micron-sized BaTiO 3 : Dramatic influence on the microstructure and dielectric properties
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Henry Ip Department of Chemistry and Biochemistry, Center for Materials Research and Education, Rowan University, Glassboro, New Jersey 08028
Ashok K. Gangulia) Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India (Received 16 April 2005; accepted 3 October 2005)
Sintered compacts of nano-sized and micron-sized BaTiO3 show sharp ferroelectric transition and high dielectric constant at specific compositions. The sintered compacts with 1 wt% nano-BaTiO3 show a maximum dielectric constant of 1680. At the transition temperature (Tc) there are two maxima at 0.5 and 2 wt%. The variation in the dielectric constant at Tc is also reflected in the behavior of the ferroelectric transition as studied by differential scanning calorimetry. This interesting oscillatory variation of the dielectric constant and dielectric loss with increase in the amount of nanoparticles in the sintered compacts is observed for the first time. The variation of the dielectric properties and the ferroelectric transition of the sintered compacts could be related to subtle changes in the microstructure.
I. INTRODUCTION
BaTiO3 has been the cornerstone of research in electronic materials due to its stability (chemical and mechanical) and wide ranging applications as a ferroelectric material.1–4 Added to the unique properties is its simple structure (perovskite), which allows new theoretical models to be developed and the results to be compared with experimental data. The dielectric properties of BaTiO3 depends on several factors, like the structure, grain size, temperature, etc.5–7 At room temperature, BaTiO3 has a tetragonal structure that changes to cubic at the ferroelectric transition temperature. However the structure also changes with grain size and smaller grains lead to a cubic structure. The properties of BaTiO3 (micron-sized grains) have been discussed in detail in many reports.1,2,8–10 More recently the synthesis and properties of nanocrystalline barium titanate has been of interest. Fine particles of barium titanate have been synthesized by the sol-gel11,12 and polymeric precursor routes.13–16 Uniform and mono-
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0102 816
J. Mater. Res., Vol. 21, No. 4, Apr 2006 http://journals.cambridge.org Downloaded: 25 Mar 2015
disperse nanoparticles of BaTiO3 could be obtained using microemulsions at low temperature of 800 °C.17 Evidence for tetragonal distortion has been found in these nano-sized (20–25 nm) particles of barium titanate from careful x-ray diffraction studies as well as from Raman spectroscopy. The grain size shows an increase on sintering being 35 nm at 900 °C to 120 nm at 1100 °C, which is much lower than the grain size (0.5–1 m) obtained at this temperature by the normal solid-state route. The dielectric constant depends on sintering temperature and is found to increase from 210 (900 °C sintering) to 520 (1100 °C sintering) at 100 kHz. It is known that well-sintered barium titanate is n
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