title: Mechanisms on the morphology variation of hematite crystals by Al substitution: The modification of Fe and O reticular densities.
abstract: Al substitution in hematite is ubiquitous in soils. With the increase of Al amount, the hematite morphology changes from rhombohedral crystals to disk-shaped ones, but the underlying mechanism is poorly understood. Herein, a series of Al-substituted hematite were synthesized and characterized by synchrotron X-ray diffraction (SXRD), field emission scanning electron microscopy (FESEM), high resolution electron transmission microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy, to investigate the effects of Al3+substitution on the hematite structure and morphology. EXAFS and Rietveld structural refinement analyses find an increase in face-sharing (along c axis) Fe-Me (Me = Al, Fe) distances, edge-sharing (in a-b plane) Fe-Me (Me = Al, Fe) distances, and O-O average distances. Moreover, the face-sharing Fe-Me distances and O-O distances along c axis increase more significantly. This indicates a more apparent decrease in the reticular densities of Fe and O along the direction of c axis, which facilitates faster crystal growth along c axis and results in the evolution of morphology of Al-substituted hematite to disk-shaped crystals. The above results provide new insights into the morphology changes and environmental geochemistry behaviors of Al-contained hematite in soils, and are benefit for the control of crystal morphologies during its application as environmentally-friendly materials.
authors: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
authors: Wei
authors: W
authors: Li
authors: CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China.
authors: Xiaoliang
authors: X
authors: Liang
authors: Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
authors: Pengfei
authors: P
authors: An
authors: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
authors: Xionghan
authors: X
authors: Feng
authors: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
authors: Wenfeng
authors: W
authors: Tan
authors: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
authors: Guohong
authors: G
authors: Qiu
authors: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.|CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China.
authors: Hui
authors: H
authors: Yin
authors: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
authors: Fan
authors: F
authors: Liu