Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H 2O]

Joanne E. Stubbs, Jeffrey E. Post, David C. Elbert, Peter J. Heaney, David R. Veblen

Research output: Contribution to journalArticle

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Abstract

The metatorbernite [Cu(UO2)2(PO4) 2·8H2O] structure comprises autunite-type sheets of corner-sharing uranyl square bipyramids and phosphate tetrahedra, with the interlayer region occupied by Cu2+ ions and molecular water. Previous studies have shown that heating induces stepwise dehydration and reduction in basal spacing. Structures ofthe lower hydrates have not been determined previously because suitable single crystals of these phases have yet to be prepared. We have used synchrotron X-ray diffraction data collected during in situ, continuous heating of powdered metatorbernite to elucidate structures of its lower hydrates. Using Rietveld analysis, we have determined that autunite-type sheets remain intact through the first dehydration event above room temperature (onset 102 °C). We have discovered that the second dehydration event (onset 138 °C) triggers a major reconstruction to uranophane-type sheets, composed of chains of edge-sharing uranyl pentagonal bipyramids linked to one another by sharing edges and vertices with phosphate tetrahedra. This reconstruction enables the structure to overcome steric constraints on the minimum possible basal spacing, while maintaining Cu within the interlayer. Four distinct phases have been identified with increasing temperature: Cu(UO2)2(PO4)2· 8H2O, space group P4/n, a = 6.96519(23), c = 17.3102(8) Å; Cu(UO2)2(PO4)2·6.1H 2O, space group P4/n, a = 6.95510(29), c = 16.6604(9) Å; Cu(UO2)2(PO4)2·3H 2O, space group P21, a = 14.4979(23), b = 7.0159(9), c = 6.6312(10) Å, β = 107.585(14)°; and a lower hydrate with monoclinic or triclinic symmetry, a ≈ 6.7, b ≈ 7, c ≈ 11 Å, β ≈ 100°. As shown here, in situ heating experiments and the Rietveld method provide fundamental insights into the crystal chemistry and structural behaviors of the important meta-autunite mineral group.

Original languageEnglish (US)
Pages (from-to)1132-1140
Number of pages9
JournalAmerican Mineralogist
Volume95
Issue number8-9
DOIs
StatePublished - Aug 1 2010

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autunite
Hydrates
Dehydration
dehydration
phosphates
phosphate
hydrates
heating
Heating
spacing
Rietveld analysis
Phosphates
tetrahedrons
Crystal chemistry
Rietveld method
interlayers
crystal chemistry
Synchrotrons
Minerals
symmetry

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

Stubbs, Joanne E. ; Post, Jeffrey E. ; Elbert, David C. ; Heaney, Peter J. ; Veblen, David R. / Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H 2O]. In: American Mineralogist. 2010 ; Vol. 95, No. 8-9. pp. 1132-1140.
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title = "Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H 2O]",
abstract = "The metatorbernite [Cu(UO2)2(PO4) 2·8H2O] structure comprises autunite-type sheets of corner-sharing uranyl square bipyramids and phosphate tetrahedra, with the interlayer region occupied by Cu2+ ions and molecular water. Previous studies have shown that heating induces stepwise dehydration and reduction in basal spacing. Structures ofthe lower hydrates have not been determined previously because suitable single crystals of these phases have yet to be prepared. We have used synchrotron X-ray diffraction data collected during in situ, continuous heating of powdered metatorbernite to elucidate structures of its lower hydrates. Using Rietveld analysis, we have determined that autunite-type sheets remain intact through the first dehydration event above room temperature (onset 102 °C). We have discovered that the second dehydration event (onset 138 °C) triggers a major reconstruction to uranophane-type sheets, composed of chains of edge-sharing uranyl pentagonal bipyramids linked to one another by sharing edges and vertices with phosphate tetrahedra. This reconstruction enables the structure to overcome steric constraints on the minimum possible basal spacing, while maintaining Cu within the interlayer. Four distinct phases have been identified with increasing temperature: Cu(UO2)2(PO4)2· 8H2O, space group P4/n, a = 6.96519(23), c = 17.3102(8) {\AA}; Cu(UO2)2(PO4)2·6.1H 2O, space group P4/n, a = 6.95510(29), c = 16.6604(9) {\AA}; Cu(UO2)2(PO4)2·3H 2O, space group P21, a = 14.4979(23), b = 7.0159(9), c = 6.6312(10) {\AA}, β = 107.585(14)°; and a lower hydrate with monoclinic or triclinic symmetry, a ≈ 6.7, b ≈ 7, c ≈ 11 {\AA}, β ≈ 100°. As shown here, in situ heating experiments and the Rietveld method provide fundamental insights into the crystal chemistry and structural behaviors of the important meta-autunite mineral group.",
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Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H 2O]. / Stubbs, Joanne E.; Post, Jeffrey E.; Elbert, David C.; Heaney, Peter J.; Veblen, David R.

In: American Mineralogist, Vol. 95, No. 8-9, 01.08.2010, p. 1132-1140.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H 2O]

AU - Stubbs, Joanne E.

AU - Post, Jeffrey E.

AU - Elbert, David C.

AU - Heaney, Peter J.

AU - Veblen, David R.

PY - 2010/8/1

Y1 - 2010/8/1

N2 - The metatorbernite [Cu(UO2)2(PO4) 2·8H2O] structure comprises autunite-type sheets of corner-sharing uranyl square bipyramids and phosphate tetrahedra, with the interlayer region occupied by Cu2+ ions and molecular water. Previous studies have shown that heating induces stepwise dehydration and reduction in basal spacing. Structures ofthe lower hydrates have not been determined previously because suitable single crystals of these phases have yet to be prepared. We have used synchrotron X-ray diffraction data collected during in situ, continuous heating of powdered metatorbernite to elucidate structures of its lower hydrates. Using Rietveld analysis, we have determined that autunite-type sheets remain intact through the first dehydration event above room temperature (onset 102 °C). We have discovered that the second dehydration event (onset 138 °C) triggers a major reconstruction to uranophane-type sheets, composed of chains of edge-sharing uranyl pentagonal bipyramids linked to one another by sharing edges and vertices with phosphate tetrahedra. This reconstruction enables the structure to overcome steric constraints on the minimum possible basal spacing, while maintaining Cu within the interlayer. Four distinct phases have been identified with increasing temperature: Cu(UO2)2(PO4)2· 8H2O, space group P4/n, a = 6.96519(23), c = 17.3102(8) Å; Cu(UO2)2(PO4)2·6.1H 2O, space group P4/n, a = 6.95510(29), c = 16.6604(9) Å; Cu(UO2)2(PO4)2·3H 2O, space group P21, a = 14.4979(23), b = 7.0159(9), c = 6.6312(10) Å, β = 107.585(14)°; and a lower hydrate with monoclinic or triclinic symmetry, a ≈ 6.7, b ≈ 7, c ≈ 11 Å, β ≈ 100°. As shown here, in situ heating experiments and the Rietveld method provide fundamental insights into the crystal chemistry and structural behaviors of the important meta-autunite mineral group.

AB - The metatorbernite [Cu(UO2)2(PO4) 2·8H2O] structure comprises autunite-type sheets of corner-sharing uranyl square bipyramids and phosphate tetrahedra, with the interlayer region occupied by Cu2+ ions and molecular water. Previous studies have shown that heating induces stepwise dehydration and reduction in basal spacing. Structures ofthe lower hydrates have not been determined previously because suitable single crystals of these phases have yet to be prepared. We have used synchrotron X-ray diffraction data collected during in situ, continuous heating of powdered metatorbernite to elucidate structures of its lower hydrates. Using Rietveld analysis, we have determined that autunite-type sheets remain intact through the first dehydration event above room temperature (onset 102 °C). We have discovered that the second dehydration event (onset 138 °C) triggers a major reconstruction to uranophane-type sheets, composed of chains of edge-sharing uranyl pentagonal bipyramids linked to one another by sharing edges and vertices with phosphate tetrahedra. This reconstruction enables the structure to overcome steric constraints on the minimum possible basal spacing, while maintaining Cu within the interlayer. Four distinct phases have been identified with increasing temperature: Cu(UO2)2(PO4)2· 8H2O, space group P4/n, a = 6.96519(23), c = 17.3102(8) Å; Cu(UO2)2(PO4)2·6.1H 2O, space group P4/n, a = 6.95510(29), c = 16.6604(9) Å; Cu(UO2)2(PO4)2·3H 2O, space group P21, a = 14.4979(23), b = 7.0159(9), c = 6.6312(10) Å, β = 107.585(14)°; and a lower hydrate with monoclinic or triclinic symmetry, a ≈ 6.7, b ≈ 7, c ≈ 11 Å, β ≈ 100°. As shown here, in situ heating experiments and the Rietveld method provide fundamental insights into the crystal chemistry and structural behaviors of the important meta-autunite mineral group.

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