Magnetic, Optical, Dielectric, and Sintering Properties of Nano-crystalline BaFe0.5Nb0.5O3 Synthesized by a Polymerization Method. (#50847)

Abstract.

J. Mater. Sci. 53 (2018) 1024–1034. (DOI: 10.1007/s10853-017-1609-1).

A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative density 90 %) can be obtained either after conventional sintering above 1250 °C for 1 h or after two-step sintering at 1200 °C. Depending on the sintering regime the ceramics have average grain sizes between 0.3 μm and 52 μm. The optical band gap of the nano-sized powder is 2.75(4) eV and decreases to 2.59(2) eV after sintering. Magnetic measurements of ceramics reveal a Néel temperature of about 23 K. A weak spontaneous magnetization might be due to the presence of a secondary phase not detectable by XRD. Dielectric measurements show that the permittivity values increase with decreasing frequency and rising temperature. The highest permittivity values of 10.6x10^4 (RT, 1 kHz) were reached after sintering at 1350 °C for 1 h. Tan values of all samples show a maximum at 1-2 MHz at RT. The frequency dependence of the impedance can be well described using a single RC-circuit.