Analysis of coloured Grooved Ware sherds from the Ness of Brodgar, Orkney

To the accumulation of evidence of painted decoration applied to Neolithic and Early Bronze Age pottery in Britain and elsewhere in Europe we report here the presence of decoration in red, black and white on some third millennium BC Grooved ware pottery at the Ness of Brodgar on Orkney. As expected, the red was identified as an iron-rich material and black was carbon black. The white was prepared from calcined (cow) bone; however, its identification encountered some issues arising principally from the effects of the prevailing burial conditions on the bone. Furthermore, whereas the chemical and FTIR data were consistent with the presence of apatite, XRD indicated that the white had a significant content of silicate minerals. This finding has suggested that the white required a preparatory step which might have included the calcined bone bring ground to powder in a stone mortar before application to the vessel surface. The results obtained at Ness of Brodgar are reviewed in the light of archaeometric data on similarly decorated prehistoric pottery reported from sites in Europe

An unexpected cubic symmetry in group IV alloys prepared using pressure and temperature

The cubic diamond (Fd-3m) group IVA element Si has been the material driver of the electronics industry since its inception. We report synthesis of a new cubic (Im-3m) group IVA material, a GeSn solid solution, upon heating Ge and Sn at pressures from 13 to 28 GPa using double-sided diamond anvil laser-heating and large volume press methods. Both methods were coupled with in-situ angle dispersive X-ray diffraction characterization. The new material substantially enriches the seminal group IVA alloy materials landscape by introducing an eightfold coordinated cubic symmetry, which markedly expands on the conventional tetrahedrally coordinated cubic one. This cubic solid solution is formed, despite Ge never adopting the Im-3m symmetry, melting inhibiting subsequent Im-3m formation and reactant Ge and Sn having unlike crystal structures and atomic radii at all these pressures. This is hence achieved without adherence to conventional formation criteria and routes to synthesis. This advance creates fertile avenues for new materials development

Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania

Mafic–ultramafic cumulates enclosed in gabbroic-dioritic rocks form part of the Mesozoic Ditrău Alkaline Massif in the Eastern Carpathians, Romania. The poikilitic olivine- and pyroxene-rich and nearly mono mineralic hornblendite rocks display typical cumulate textures with early crystallised olivine (Fo75–73), diopside and augite. In the early stages of their genesis the amphibole was intercumulus whilst in later stages it acquired cumulus status as the fractionating magma evolved. Using major and trace element compositions of minerals and whole-rock samples the origin of these cumulates is determined and the parental magma composition and depth of emplacement are calculated. Cumulus clinopyroxene has more primitive composition than intercumulus amphibole suggesting closed system fractionation for the evolution of poikilitic olivine- and pyroxene-rich cumulates. The evolution of the amphibole-rich mesocumulates is more clearly the result of closed system crystallisation dominated by the precipitation of clinopyroxene and amphibole cumulus crystals. Lamprophyre dykes of the Ditrău Alkaline Massif are proposed to reflect multiple basanitic parental magma batches from which the cumulus olivine and clinopyroxene crystallised. Relative to these dykes the calculated equilibrium melts for intercumulus amphibole in the cumulates was more primitive whilst that for the cumulus amphibole was more evolved. The calculated crystallisation temperature and pressure of ~1000–1050 °C and ~0.7 GPa, based on the composition of the amphiboles, indicate crystallisation at lower crustal depths. Rare earth element compositions are consistent with an intra-plate tectonic setting

Unconventional Route to High-Pressure and -Temperature Synthesis of GeSn Solid Solutions

Ge and Sn are unreactive at ambient conditions. Their significant promise for optoelectronic applications is thus largely confined to thin film investigations. We sought to remove barriers to reactivity here by accessing a unique pressure, 10 GPa, where the two elements can adopt the same crystal structure (tetragonal, $I4_1$/$amd$) and exhibit compatible atomic radii. The route to GeSn solid solution, however, even under these directed conditions, is different. Reaction upon heating at 10 GPa occurs between unlike crystal structures (Ge, $Fd3m$ and Sn, $I$4/$mmm$), which also have highly incompatible atomic radii. They should not react, but they do. A reconstructive transformation of $I$4/$mmm$ into the $I$4$_1$/$amd$ solid solution then follows. The new tetragonal GeSn solid solution ($I$4$_1$/$amda$ = 5.280(1) Å, c = 2.915(1) Å, Z = 4 at 9.9 GPa and 298 K) also constitutes the structural and electronic bridge between 4-fold and newly prepared 8-fold coordinated alloy cubic symmetries. Furthermore, using this high-pressure route, bulk cubic diamond-structured GeSn alloys can now be obtained at ambient pressure. The findings here remove confining conventional criteria on routes to synthesis. This opens innovative avenues to advanced materials development

Hexagonal Si-Ge Class of Semiconducting Alloys Prepared Using Pressure and Temperature

Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500–1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery atambient pressure of hexagonal Ge-Si solid solutions (P6$_3$/mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be preparedfor all Ge-Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge-Sisolid solution family, and is of interest for optoelectronic applications