Thermal expansion of deuterated hopeite, Zn3(PO4)2{middle dot}4D2O

Schofield, P. F.; Knight, Kevin S.; Hodson, Mark E.; Lanfranco, A. M.

doi:10.2138/am.2007.2099

Cited by 7 publications

(2 citation statements)

References 17 publications

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“…The hydrogen-bonding scheme in arsenohopeite clearly shows its equivalence with a-hopeite. Deuterated hopeite and its thermal expansion were characterized by Schofield et al (2007). A synthetic Co-analogue of hopeite and its crystal structure have been reported recently (Lee et al, 2008).…”

Section: Relationship To Other Speciesmentioning

confidence: 99%

Arsenohopeite, a new zinc arsenate mineral from the Tsumeb mine, Namibia

Neuhold¹,

Kolitsch²,

Bernhardt³

et al. 2012

Mineral. mag.

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Arsenohopeite, ideally Zn3(AsO4)2·4H2O, is the arsenate analogue of hopeite, Zn3(PO4)2·4H2O (it is isostructural with α-hopeite). It was found as a single colourless to blue crystalline grain from the Tsumeb mine, Namibia. The holotype specimen is ∼1 × 1 × 1 mm in size. Arsenohopeite is associated with tiny white fibres of an unidentified Zn- and As-bearing phase. It is orthorhombic, space group Pnma, with a = 10.804(2), b = 19.003(4), c = 5.112(1) Å, V = 1049.5(4) Å3 and Z = 4. Electron microprobe analysis yielded: ZnO 44.92, Fe2O3 0.92, MnO 0.51, MgO 0.20, CuO 0.02, As2O5 45.84 (wt.%). The empirical formula is (Zn2.80Fe0.06Mn0.04Mg0.03)Σ2.93(As1.01O4)2·4H2O, based on 12 oxygen atoms. Optically, the mineral is biaxial negative, with α = 1.598(2), β = 1.606(2), γ = 1.613(2) (white light) and 2Vcalc = 86°. It is not pleochroic or fluorescent. Arsenohopeite is translucent with a vitreous lustre. It is brittle, has an uneven fracture and (by analogy with hopeite) a cleavage that is perfect on {010}, good on {100} and poor on {001}. The calculated density is 3.420 g cm–3. The five strongest calculated powder diffraction lines are [d in Å (I)(hkl)]: 9.502 (100)(020), 2.926 (95)(241), 4.937 (50)(011), 4.110 (48)(230) and 3.567 (31)(240). The crystal structure of arsenohopeite has been solved by direct methods and refined in space group Pnma to R1 = 0.0353. Raman spectroscopy confirms the crystal-structure data and indicates the presence of weak hydrogen bonds.

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Section: Relationship To Other Speciesmentioning

confidence: 99%

Arsenohopeite, a new zinc arsenate mineral from the Tsumeb mine, Namibia

Neuhold¹,

Kolitsch²,

Bernhardt³

et al. 2012

Mineral. mag.

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“…The first crystal-structure study of hopeite was attempted by Mamedov et al in 1961 [17], but their structural model was incorrect, which was demonstrated several years later by Gamidov et al [18] and Liebau [19]. Since then, the crystal structure, chemical composition and properties of hopeite have been the subject of numerous studies [20][21][22][23][24][25][26][27][28]. In 1908, Spenser [29] found out that there are two varieties of hopeite, αand β-, which were slightly different in their solubilities, but it was not until 2004 that Herschke et al [30] demonstrated that the difference between the two forms lies in the different systems of hydrogen bonding in their crystal structures.…”

Section: Introductionmentioning

confidence: 99%

The Crystal Structure of Sergeysmirnovite, MgZn2(PO4)2·4H2O, and Complexity of the Hopeite Group and Related Structures

2022

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The crystal structure of sergeysmirnovite, MgZn2(PO4)2·4H2O (orthorhombic, Pnma, a = 10.6286(4), b = 18.3700(6), c = 5.02060(15) Å, V = 980.26(6) Å3, Z = 4), a new member of the hopeite group of minerals, was determined and refined to R1 = 0.030 using crystals from the Këster mineral deposit in Sakha-Yakutia, Russia. Similar to other members of the hopeite group, the crystal structure of sergeysmirnovite is based upon [Zn(PO4)]– layers interlinked via interstitial [MO2(H2O)4]2– octahedra, where M = Mg2+. The layers are parallel to the (010) plane. Within the layer, the ZnO4 tetrahedra share common corners to form chains running along [001]. Sergeysmirnovite is a dimorph of reaphookhillite, a mineral from the Reaphook Hill zinc deposit in South Australia. The relations between sergeysmirnovite and reaphookhillite are the same as those between hopeite and parahopeite. Topological and structural complexity analysis using information theory shows that the hopeite (sergeysmirnovite) structure type is more complex, both structurally and topologically, than the parahopeite (reaphookhillite) structure type. Such complexity relations contradict the general observation that more complex polymorphs possess higher physical density and higher stability, since parahopeite is denser than hopeite. It could be hypothesized that hopeite is metastable under ambient conditions and separated from parahopeite by a structural and topological reconstruction that requires an essential energy barrier that is difficult to overcome.

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The thermal expansion of Ti-substituted CaAl12O19

Schofield,

Berry,

Doyle

et al. 2024

Phys Chem Minerals

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CaAl12O19, which can incorporate Ti as both Ti3+ and Ti4+ (charge coupled substitution with Mg2+), is one of the first minerals to condense from a gas of solar composition and is used as a ceramic. It is variously known as hibonite, calcium hexaluminate (CaO.6Al2O3), and CA6. The lattice parameters and unit cell volumes of Ti-substituted hibonite (P63/mmc) with the formulae CaAl11.8Ti3+0.2O19 and CaAl9.8Ti3+0.54Mg0.83Ti4+0.83O19 were determined as a function of temperature from ~ 10 to 275 K by neutron powder diffraction. The thermal expansion is highly anisotropic with the expansion in c a factor of ~ 5 greater than that in a. The change in a is approximately equal for the two compounds whereas the change in c is almost 50% larger for CaAl11.8Ti3+0.2O19. CaAl11.8Ti3+0.2O19 also exhibits negative thermal expansion between 10 and 70 K. The change in unit cell volume with temperature of both compositions is well described by a two term Einstein expression. The large change in c is consistent with substitution of Ti onto the M2 and M4 sites of the R-block structural unit.

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Thermal expansion of deuterated hopeite, Zn3(PO4)2{middle dot}4D2O

Cited by 7 publications

References 17 publications

Arsenohopeite, a new zinc arsenate mineral from the Tsumeb mine, Namibia

Arsenohopeite, a new zinc arsenate mineral from the Tsumeb mine, Namibia

The Crystal Structure of Sergeysmirnovite, MgZn2(PO4)2·4H2O, and Complexity of the Hopeite Group and Related Structures

The thermal expansion of Ti-substituted CaAl12O19

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