Structure of synthetic 2-line ferrihydrite by electron nanodiffraction

被引:120
作者
Janney, DE
Cowley, JM
Buseck, PR
机构
[1] Arizona State Univ, Dept Geol, Tempe, AZ 85287 USA
[2] Arizona State Univ, Dept Chem Biochem, Tempe, AZ 85287 USA
[3] Arizona State Univ, Dept Phys & Astron, Tempe, AZ 85287 USA
关键词
D O I
10.2138/am-2000-8-910
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Comparison of experimental single-crystal electron diffraction patterns of synthetic two-line ferrihydrite (2LFh) with simulated single-crystal electron-diffraction patterns indicates that a synthetic 21,Fh sample contains highly disordered material and nanocrystals with structures based on hexagonal (ABAB) and cubic (ABC) stacking of close-packed layers of O2- and OH- ions. An apparently continuous variation in ordering exists between the highly disordered material and each of the crystalline structures, suggesting that both nanocrystalline structures represent local extremes of three-dimensional ordering. Experimental diffraction patterns were obtained using electron nanodiffraction, a technique in which the finely focused beam from a field-emission gun in an electron microscope can be used to produce diffraction patterns from areas <1 nm across. Nanodiffraction patterns from the highly disordered material have diffuse streaks rather than distinct reflections, and are consistent with a two-dimensional structure that consists of close-packed anionic layers with essentially complete stacking disorder and nearly random distribution of Fe atoms. The structure with cubic stacking is similar to maghemite and has similar to 25% of the Fe in tetrahedral sites. The structure with hexagonal stacking consists of double chains of face-sharing Fe octahedra; each octahedron shares one face, two edges, and three corners with adjacent octahedra. Previous results from transmission electron microscopy, powder X-ray and electron diffraction, and synchrotron-based techniques reflect the overall high degree of structural disorder rather than the characteristics of the maghemite-like and double-chain structures.
引用
收藏
页码:1180 / 1187
页数:8
相关论文
共 34 条
[21]   Surface structural model for ferrihydrite [J].
Manceau, A ;
Gates, WP .
CLAYS AND CLAY MINERALS, 1997, 45 (03) :448-460
[22]   LOCAL-STRUCTURE OF FERRIHYDRITE AND FEROXYHITE BY EXAFS SPECTROSCOPY [J].
MANCEAU, A ;
DRITS, VA .
CLAY MINERALS, 1993, 28 (02) :165-184
[23]  
POST JE, 1991, AM MINERAL, V76, P272
[24]   From Fe(III) ions to ferrihydrite and then to hematite [J].
Schwertmann, U ;
Friedl, J ;
Stanjek, H .
JOURNAL OF COLLOID AND INTERFACE SCIENCE, 1999, 209 (01) :215-223
[25]  
Schwertmann U., 1989, Minerals in Soil Environments, SSSA Book Series, no. 1., P379
[26]  
Schwertmann U., 1991, Iron oxides in the laboratory. preparation and characterization
[27]   LOCAL-STRUCTURE OF FERRIC HYDROXIDE FE(OH)3 IN AQUEOUS-SOLUTION BY THE ANOMALOUS X-RAY-SCATTERING AND EXAFS METHODS [J].
SHINODA, K ;
MATSUBARA, E ;
MURAMATSU, A ;
WASEDA, Y .
MATERIALS TRANSACTIONS JIM, 1994, 35 (06) :394-398
[28]   MINERALOGICAL CONSTITUTION OF COLLOIDAL HYDROUS FERRIC OXIDES [J].
TOWE, KM ;
BRADLEY, WF .
JOURNAL OF COLLOID AND INTERFACE SCIENCE, 1967, 24 (03) :384-&
[29]  
Warren B.E., 1990, X-ray Diffraction
[30]  
WAYCHUNAS GA, 1991, REV MINERAL, V25, P11