Authors: Jia Huan Xu, Hua Ke, De Chang Jia, Wen Wang, Yu Zhou
Abstract: The present investigation reports on the preparation of BiFeO3 nanopowders by a sol-gel method using acetylacetone as a stabilizer. Single-phase BiFeO3 nanopowders without any impurity or amorphous phases were obtained when the precursor was thermal treated at temperatures as low as 400 oC for 2 h. Acetylacetone (acac) plays an important role on lowering the formation temperature of pure phase BiFeO3 nanopowders. It is found that Bi/acac molar ratio of 1/30 was favorable for a stable sol and for the lowest crystallization temperature of pure BiFeO3 nanopowders. X-ray diffraction and Fourier transform infrared spectroscopy revealed that thermally induced crystallization process of BiFeO3 nanopowders from Bi-Fe polymeric precursor. When the thermal treated temperature was below 200 oC, only amorphous phase existed. With the temperature increasing up to 300 oC, crystallized phase, carbonate, were detected. After annealed at 400 oC, Bi-Fe precursor totally changed to rhombohedral BiFeO3 nanopowders. Scanning electron microscopy characterized morphologies of BiFeO3 nanopowders calcined at 400 oC and 500 oC. The ferroelectric transition of BiFeO3 nanopowders at 827 oC has been detected by differential thermal analysis.
314
Authors: Chun Lin Fu, Meng Huo, Wei Cai, Xiao Ling Deng
Abstract: BiFeO3 powders were prepared by sol-gel process and calcined at different temperatures. The DTA curve shows an obvious exothermic peak near 480.5°C, the temperature close to BiFeO3 formation temperature, which is agreement with the XRD results (450°C). After calcining at 600°C for 1h, XRD spectra has the emergence of several sharp diffraction peaks, compared with the standard XRD spectrum of the crystal BiFeO3. As the calcining temperature increased, the diffraction peak intensity of the XRD spectra of BiFeO3 gradually increased and the diffraction peaks became sharply, indicating that the grain size gradually became larger. There is a clear endothermic peak near 825.1°C, which is the α phase to β phase transition from the knowledge of the phase diagram and in good agreement with the reported Curie temperature.
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Authors: Yi Hang Fang, Kai Miao, Si Qiao Feng, Jia Meng Cao, Huan Ping Wang, Shi Qing Xu
Abstract: The 0.95MgTiO3-0.05CaTiO3 (95MCT) powders and ceramics were prepared by a sol-gel method by using Mg(NO3)2•6H2O, Ca(NO3)2•4H2O and Ti(C4H9O)4 as the starting materials. The effects of calcination temperature on phase formation, morphology and particle size distribution of the proposed powders were examined, and the microwave dielectric properties of 95MCT ceramics made from different size particles were investigated. The dried gels were calcined at 600 °C, 700 °C, 800 °C and 900 °C, and the derived particle sizes of powders were 10-20 nm, 50-100 nm, 60-120 nm and 120-150 nm, respectively. The proper sizes, which range from 50-150 nm, lowered the sintering temperature of 95MCT ceramics effectively from 1400 °C to 1175 °C due to the high surface energy. Sintered at 1175 °C, the 95MCT ceramic prepared from 50-100 nm size particles had compact structure and exhibited good microwave dielectric properties: εr = 21.33 and Q×f = 36,315 GHz.
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Authors: Xiao Yan Zhang, Wen Shu Hu, Xi Wei Qi, Gui Fang Sun, Jian Quan Qi, Huan Huan Chen, Rui Xia Zhong
Abstract: Bi2Al4O9 powders were prepared by sol-gel process. The precursors were heated at 500-800°C for 2h to obtain Bi2Al4O9 powder and X-ray diffraction (XRD), Differential thermal analysis (DTA), thermogravimetric analysis (TG), field emission scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) techniques were used to characterize precursor and derived oxide powders. XRD analysis show that the powder is still amorphous after calcined at 500°C. The peaks of Bi2Al4O9 become sharp after calcined at 575°C though still existing some amorphous phase. After calcining at 675-800°C, the powder has fully turned into pure Bi2Al4O9 phase. The crystallization process can also be confirmed by DTA-TG and IR. Calcining the precursor at 575°C, the absorption bands at 527 cm-1, 738 cm-1, 777 cm-1, and 919 cm-1are observed, which are assigned to Bi2Al4O9 and becoming stronger and sharper with the increase of temperature.
34
Authors: Gunawan, I. Sopyan, A. Naqshbandi, S. Ramesh
Abstract: Biphasic calcium phosphate powders doped with zinc (Zn-doped BCP) were synthesized via sol-gel technique. Different concentrations of Zn have been successfully incorporated into biphasic calcium (BCP) phases namely: 1%, 2%, 3%, 5%, 7%, 10% and 15%. The synthesized powders were calcined at temperatures of 700-900°C. The calcined Zn-doped BCP powders were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential and thermogravimetric analysis (TG/DTA) and field-emission scanning electron microscopy (FESEM). X-ray diffraction analysis revealed that the phases present in Zn-doped are hydroxyapatite, β- TCP and parascholzite. Moreover, FTIR analysis of the synthesized powders depicted that the bands of HPO4 increased meanwhile O-H decreased with an increase in the calcination temperature. Field emission scanning electron microscopy (FESEM) results showed the agglomeration of particles into microscale aggregates with size of the agglomerates tending to increase with an increase in the dopant concentration.
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