Investigations of BaFe0.5Nb0.5O3 nano powders prepared by a low temperature aqueous synthesis and resulting ceramics (original) (raw)
Related papers
J Mater Sci (2018) 53:1024–1034, 2018
Full-text available at: http://rdcu.be/v7Fn Abstract: 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 d 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. Fulltext: http://rdcu.be/v7Fn
In the paper the influence of mechanical activation of the powder on the final dielectric properties lead-free Ba(Fe1/2Nb1/2)O3 (BFN) ceramic was examined. The BFN ceramics were obtained by 3-steps route. Firstly, the substrates were pre-homogenized in a planetary ball mill. Than, the powder was activated in vibratory mill (the shaker type SPEX 8000 Mixer Mill) for different duration between 25 h and 100 h. The influence of the milling time on the BFN powder was monitored by X-ray diffraction. The diffraction data confirmed that the milling process of the starting components is accompanied by partial synthesis of the BFN materials. The longer of the high-energy milling duration the powders results in increasing the amount of amorphous/nanocrystalline content. The mechanically activated materials were sintered in order to obtain the ceramic samples. During this temperature treatment the final crystallisation of the powder appeared what was confirmed by XRD studies. The performed dielectric measurements have revealed the reduction of the dielectric loss of the BFN ceramics compared to materials obtained by classic methods.
Processing and Application of Ceramics
In this work, the effects of Ba(Fe0.5Nb0.5)O3 (BFN) addition on the structure and dielectric behaviour of Ba0.06(Na0.5Bi0.5)0.94TiO3 (BNBT) ceramics have been reported. The lead-free (1-x)BNBT-xBFN (where 0 ? x ? 1.0) solid-solutions were synthesized by traditional ceramics fabrication technique and sintered at temperatures up to 1325?C. The X-ray diffraction peaks of the compounds of the entire series were indexed. It is found that the crystal structure of the obtained solid solutions changed from rhombohedral (R3c) to cubic (Pm3m) with an increase in BFN content. The Fourier transformed infrared and Raman spectra also confirmed the formation of solid-solutions. SEMstudies were carried out to evaluate the purity and microstructure of the fabricated ceramics. The dependence of phase transition broadening, phase transition temperature and dielectric parameters with compositional changes were also studied.