Magnetic, optical, dielectric, and sintering properties of nano-crystalline BaFe0.5Nb0.5O3 synthesized by a polymerization method

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 A degrees C. Calcination at 850 A degrees 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 A degrees C. Dense ceramic bodies (relative density aeA 90%) can be obtained either after conventional sintering above 1250 A degrees C for 1 h or after two-step sintering at 1200 A degrees C. Depending on the sintering regime, the ceramics have average grain sizes between 0.3 and 52 A mu m. 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 N,el 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 10.6 x 10(4) (RT, 1 kHz) were reached after sintering at 1350 A degrees C for 1 h. Tan delta 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.