Twin formation in hematite during dehydration of goethite

Springer 2016-11

Twin formation in hematite during dehydration was investigated using X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy (TEM). When synthetic goethite was heated at different temperatures between 100 and 800 degrees C, a phase transformation occurred at temperatures above 250 degrees C. The electron diffraction patterns showed that the single-crystalline goethite with a growth direction of [001](G) was transformed into hematite with a growth direction of [100](H). Two non-equivalent structures emerged in hematite after dehydration, with twin boundaries at the interface between the two variants. As the temperature was increased, crystal growth occurred. At 800 degrees C, the majority of the twin boundaries disappeared; however, some hematite particles remained in the twinned variant. The electron diffraction patterns and high-resolution TEM observations indicated that the twin boundaries consisted of crystallographically equivalent prismatic (100) (010), and (10) planes. According to the total energy calculations based on spin-polarized density functional theory, the twin boundary of prismatic (100) screw had small interfacial energy (0.24 J/m(2)). Owing to this low interfacial energy, the prismatic (100) screw interface remained after higher-temperature treatment at 800 degrees C.

Dehydration; Twinning; Transformation; Goethite; Hematite; Thermal decomposition; Twin boundary; 549; article (author version)

Open access content. Open access content
The final publication is available at link.springer.com

English

YX@ oai:eprints.lib.hokudai.ac.jp:2115/67493
Physics and chemistry of minerals, 43(10): 749-757
1201266758

HOKKAIDO UNIV
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