TY - JOUR
T1 - Synchrotron X-ray diffraction study of the structure and dehydration behavior of todorokite
AU - Post, Jeffrey E.
AU - Heaney, Peter J.
AU - Hanson, Jonathan
PY - 2003/1
Y1 - 2003/1
N2 - Real-time, temperature-resolved synchrotron powder X-ray diffraction data and Rietveld refinements were used to investigate the behavior of the todorokite structure from 100 to 820 K. At 298 K. the lower valence cations, such as Mn3+, occupy large octahedral sites at the edges of the triple chains, and four water/cation sites are in the tunnels. In our heating experiments in vacuum, todorokite began to break down at ∼450 K and fully decomposed by 620 K, at which point hausmannite started to form. Our results suggest that the loss of O2 accompanied the reduction of Mn4+ to Mn3+ and Mn2+, and these reactions impelled a breakdown of the octahedral framework and the subsequent release of the tunnel water molecules. Rietveld refinements revealed a gradual thermal expansion of the todorokite structure to ∼450 K. At higher temperatures, the unit-cell volume gradually decreased, primarily as a result of a decrease in c, and the decline in β with increasing temperature was accelerated. A mechanism for forming the inverse spinel hausmannite structure from todorokite is presented.
AB - Real-time, temperature-resolved synchrotron powder X-ray diffraction data and Rietveld refinements were used to investigate the behavior of the todorokite structure from 100 to 820 K. At 298 K. the lower valence cations, such as Mn3+, occupy large octahedral sites at the edges of the triple chains, and four water/cation sites are in the tunnels. In our heating experiments in vacuum, todorokite began to break down at ∼450 K and fully decomposed by 620 K, at which point hausmannite started to form. Our results suggest that the loss of O2 accompanied the reduction of Mn4+ to Mn3+ and Mn2+, and these reactions impelled a breakdown of the octahedral framework and the subsequent release of the tunnel water molecules. Rietveld refinements revealed a gradual thermal expansion of the todorokite structure to ∼450 K. At higher temperatures, the unit-cell volume gradually decreased, primarily as a result of a decrease in c, and the decline in β with increasing temperature was accelerated. A mechanism for forming the inverse spinel hausmannite structure from todorokite is presented.
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U2 - 10.2138/am-2003-0117
DO - 10.2138/am-2003-0117
M3 - Article
AN - SCOPUS:0037217312
SN - 0003-004X
VL - 88
SP - 142
EP - 150
JO - American Mineralogist
JF - American Mineralogist
IS - 1
ER -