Investigations of nano-crystalline Sr0.5Ba0.5Nb2O6 and Bulk Ceramics Synthesized by a Polymerization Method Using PEG400
33 Pages Posted: 28 Jun 2019
Date Written: 2018
Nano-crystalline Sr0.5Ba0.5Nb2O6 was synthesized by a one-pot method using PEG400 and citric acid. Calcination of the (Sr,Ba,Nb)-gel at 600 °C leads to Sr0.5Ba0.5Nb2O6 with a crystallite size of 24(2) nm and a specific surface area of 38.5(10) m2 g-1. Sintering up to 1325 °C leads to ceramics with globular or irregular-shaped grains and average grain sizes between 1.3 and 2.4 μm, whereas higher temperatures lead to a rod-like microstructure. The indirect allowed optical band gap varies between 3.70(5) and 3.29(5) eV. Dielectric measurements show a diffuse phase transition and weak relaxor properties. The maximum of the permittivity occurs between 116 and 147 °C. The frequency dependence of the impedance can be well described by one or two RC-circuits depending on sintering temperature. The melting temperature is determined as 1506(7) °C with dHf = 140(20) kJ mol-1. The average linear thermal expansion coefficient is found to be 10.5(5)*10-6 K-1.
Keywords: niobate, permittivity, nano-particle, band gap, relaxor, PEG, thermal expansion, Sr0.5Ba0.5Nb2O6, SrBaNb4O12
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