Abstract The properties of Mn-doped hematites and their Mn-doped precursors were investigated using the 57Fe Mossbauer spectroscopy, XRD, FT-IR, UV/Vis/NIR and FE SEM. Mn-doped goethite precursors were synthesized in a high alkaline pH medium starting with iron choline citrate. The XRD analysis of all Mn-doped goethites and Mn-doped hematites showed only the presence of a goethite or hematite crystal structure. The RT Mossbauer spectrum of reference goethite showed typical features of precipitated goethite. With increased Mn-doping the spectral lines of the goethite precursor were broadening, the hyperfine magnetic field decreased and the relative intensity of central quadrupole doublets increased. The RT Mossbauer spectra of Mn-doped hematite showed features of the hematite phase and increased relative intensity of a central quadrupole doublet which disappeared in the spectra recorded at liquid N2 temperature. The presence of this superparamagnetic component in the RT Mossbauer spectra is a direct consequence of Mn-doping. In the FT-IR spectra the characteristic IR bands sensitive to Mn-doping were identified. The UV/Vis/NIR spectra showed shifts of optical absorption bands and a strong absorption increase in the visible part of the spectrum. FE SEM images of Mn-doped goethite precursor showed a change in shape from rod to star-like particles. Upon heating at 300 °C for 4 h in air, the obtained Mn-doped hematite particles preserved the original morphologies of Mn-doped goethite precursors. Taking into account the superparamagnetic spectra (RT and liquid N2 temperature), XRD and the corresponding FE SEM images of Mn-doped hematite particles it can be concluded that these particles contained substructure. In this substructure of Mn-doped hematites the fraction of superparamagnetic crystallites (domains) is given by calculated value for the superparamagnetic doublet present.

中文翻译：

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一维锰掺杂赤铁矿颗粒的合成与性能

摘要 使用 57Fe 穆斯堡尔光谱、XRD、FT-IR、UV/Vis/NIR 和 FE SEM 研究了 Mn 掺杂的赤铁矿及其 Mn 掺杂的前驱体的性质。Mn 掺杂的针铁矿前体是在高碱性 pH 介质中合成的，起始材料为柠檬酸胆碱。所有 Mn 掺杂的针铁矿和 Mn 掺杂的赤铁矿的 XRD 分析表明仅存在针铁矿或赤铁矿晶体结构。参考针铁矿的 RT Mossbauer 光谱显示出沉淀针铁矿的典型特征。随着Mn掺杂的增加，针铁矿前驱体的谱线变宽，超细磁场降低，中心四极双峰的相对强度增加。Mn 掺杂赤铁矿的 RT Mossbauer 光谱显示出赤铁矿相的特征和中心四极双峰的相对强度增加，这在液氮温度记录的光谱中消失。RT Mossbauer 光谱中这种超顺磁性成分的存在是 Mn 掺杂的直接结果。在 FT-IR 光谱中，确定了对 Mn 掺杂敏感的特征 IR 带。UV/Vis/NIR 光谱显示光吸收带的移动和光谱可见部分的强烈吸收增加。Mn 掺杂的针铁矿前驱体的 FE SEM 图像显示形状从棒状变为星状颗粒。在空气中在 300°C 下加热 4 小时后，获得的掺锰赤铁矿颗粒保留了掺锰针铁矿前驱体的原始形态。考虑到锰掺杂的赤铁矿颗粒的超顺磁性光谱（RT 和液氮温度）、XRD 和相应的 FE SEM 图像，可以得出结论，这些颗粒包含亚结构。在掺锰赤铁矿的这种亚结构中，超顺磁性微晶（域）的分数由超顺磁性双峰的计算值给出。