Departamento de Química Inorgánica y Nuclear, Facultad de Química, ‡Instituto de Investigaciones en Materiales, and §Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria , Coyoacán CP 04510, Mexico City, Mexico.
Inorg Chem. 2013 Sep 16;52(18):10306-17. doi: 10.1021/ic400627c. Epub 2013 Aug 22.
Synthesis of high-purity BiFeO3 is very important for practical applications. This task has been very challenging for the scientific community because nonstoichiometric Bi(x)Fe(y)O(z) species typically appear as byproducts in most of the synthesis routes. In the present work, we outline the synthesis of BiFeO3 nanostructures by a combustion reaction, employing tartaric acid or glycine as promoter. When glycine is used, a porous BiFeO3 network composed of tightly assembled and sintered nanocrystallites is obtained. The origin of high purity BiFeO3 nanomaterial as well as the formation of other byproducts is explained on the basis of metal-ligand interactions. Structural, morphological, and optical analysis of the intermediate that preceded the formation of porous BiFeO3 structures was accomplished. The thorough characterization of BiFeO3 nanoparticles (NPs) included powder X-ray diffraction (XRD); scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM); thermogravimetric analysis (TGA); UV-vis electronic absorption (diffuse reflectance mode), Raman scattering, Mössbauer, and electron paramagnetic resonance (EPR) spectroscopies; and vibrating sample magnetometry (VSM). The byproducts like β-Bi2O3 and 5 nm Bi2Fe4O9 NPs were obtained when tartaric acid was the promoter. However, no such byproducts were formed using glycine in the synthesis process. The average sizes of the crystallites for BiFeO3 were 26 and 23 nm, for tartaric acid and glycine promoters, respectively. Two band gap energies, 2.27 and 1.66 eV, were found for BiFeO3 synthesized with tartaric acid, obtained from Tauc's plots. A remarkable selective enhancement in the intensity of the BiFeO3 A1 mode, as a consequence of the resonance Raman effect, was observed and discussed for the first time in this work. For glycine-promoted BiFeO3 nanostructures, the measured magnetization (M) value at 20,000 Oe (0.64 emu g(-1)) was ∼5 times lower than that obtained using tartaric acid. The difference between the M values has been associated with the different morphologies of the BiFeO3 nanostructures.
高纯度 BiFeO3 的合成对于实际应用非常重要。由于大多数合成路线中通常会出现非化学计量比的 Bi(x)Fe(y)O(z)物种作为副产物，因此这项任务对科学界来说极具挑战性。在本工作中，我们概述了通过燃烧反应合成 BiFeO3 纳米结构的方法，使用酒石酸或甘氨酸作为促进剂。当使用甘氨酸时，得到了由紧密组装和烧结的纳米晶组成的多孔 BiFeO3 网络。基于金属-配体相互作用，解释了高纯度 BiFeO3 纳米材料以及其他副产物形成的原因。完成了形成多孔 BiFeO3 结构之前的中间产物的结构、形态和光学分析。通过粉末 X 射线衍射 (XRD)、扫描电子显微镜 (SEM) 和高分辨率透射电子显微镜 (HRTEM)、热重分析 (TGA)、紫外-可见电子吸收 (漫反射模式)、拉曼散射、穆斯堡尔和电子顺磁共振 (EPR) 光谱以及振动样品磁强计 (VSM) 对 BiFeO3 纳米粒子 (NPs) 进行了彻底的表征。当使用酒石酸作为促进剂时，得到了 β-Bi2O3 和 5nm 的 Bi2Fe4O9 NPs 等副产物。然而，在使用甘氨酸进行合成过程中，没有形成这样的副产物。BiFeO3 的晶粒平均尺寸分别为 26nm 和 23nm，对应的促进剂分别为酒石酸和甘氨酸。从 Tauc 图中得到 BiFeO3 用酒石酸合成时的两个带隙能量分别为 2.27eV 和 1.66eV。首次观察到并讨论了 BiFeO3 的 A1 模式强度的显著选择性增强，这是共振拉曼效应的结果。对于甘氨酸促进的 BiFeO3 纳米结构，在 20000Oe（0.64emu g-1）下测量的磁化（M）值约为使用酒石酸时的 5 倍。M 值的差异与 BiFeO3 纳米结构的不同形态有关。
