A portable high-pressure stress cell based on the V7 Paris-Edinburgh apparatus

International audienceWe describe a newdevice, based on aV7 Paris–Edinburgh press, for torsional testing of material at pressures up to 7GPa (extendable to 15 GPa). Samples are deformed using a simple shear geometry between opposed anvils by rotating the lower anvil, via a rotational actuator, with respect to an upper, stationary, anvil. Use of conical anvil profiles greatly increases sample dimensions more than other high-pressure torsional apparatus did. Samples of polycrystalline Zr (2mm thick, 3.5mm diameter) have been sheared at strains exceeding γ∼1.5 at constant strain rate and at pressures from 1.8 to 5GPa, and textural development has been studied by electron microscopy. Use of amorphous-boron-epoxy gaskets means that nearly simple shear of samples can be routinely achieved. This apparatus allows study of the plastic and anelastic behaviour of materials under high pressure, and is particularly suited for performing in situ investigations using synchrotron or neutron radiatio

The thermodynamics of displacive phase transitions in framework silicates

SIGLEAvailable from British Library Document Supply Centre- DSC:D60922 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

β phase and γ-β metal-insulator transition in multiferroic BiFeO3

We report on extensive experimental studies on thin film, single crystal, and ceramics of multiferroic bismuth ferrite BiFeO3 using differential thermal analysis, high-temperature polarized light microscopy, high-temperature and polarized Raman spectroscopy, high-temperature x-ray diffraction, dc conductivity, optical absorption and reflectivity, and domain imaging, and show that epitaxial (001) thin films of BiFeO3 are clearly monoclinic at room temperature, in agreement with recent synchrotron studies but in disagreement with all other earlier reported results. We report an orthorhombic order-disorder β phase between 820 and 925 (±5) °C, and establish the existence range of the cubic γ phase between 925 (±5) and 933 (±5) °C, contrary to all recent reports. We also report the refined Bi2O3-Fe2O3 phase diagram. The phase transition sequence rhombohedral-orthorhombic-cubic in bulk [monoclinic-orthorhombic-cubic in (001)BiFeO3 thin film] differs distinctly from that of BaTiO3. The transition to the cubic γ phase causes an abrupt collapse of the band gap toward zero (insulator-metal transition) at the orthorhombic-cubic β-γ transition around 930 °C. Our band structure models, high-temperature dc resistivity, and light absorption and reflectivity measurements are consistent with this metal-insulator transition

Improved Conductivity in Dye-sensitised Solar Cells Through Block-copolymer Confined TiO2 Crystallization

Anatase TiO2 is typically a central component in high performance dye-sensitised solar cells (DSCs). This study demonstrates the benefits of high temperature synthesised mesoporous titania for the performance of solid-state DSCs. In contrast to earlier methods, the high temperature stability of mesoporous titania is enabled by the self-assembly of the amphiphilic block copolymer polyisoprene-block-polyethylene oxide (PI-b -PEO) which compartmentalises TiO2 crystallisation, preventing the collapse of porosity at temperatures up to 700 °C. The systematic study of the temperature dependence on DSC performance reveals a parameter trade-off: high temperature annealed anatase consisted of larger crystallites and had a higher conductivity, but this came at the expense of a reduced specific surface area. While the reduction in specific surface areas was found to be detrimental for liquid-electrolyte DSC performance, solid-state DSCs benefitted from the increased anatase conductivity and exhibited a performance increase by a factor of three.This work was funded in part by the EPSRC Nanotechnology Grand Challenges Energy grant (EP/F056702/1), and EP/F065884/1, the Department of Energy (DE-FG02 87ER45298)through the Cornell Fuel Cell Institute (CFCI), the National Science Foundation (DMR-0605856), and the Cornell Universiy KAUST Center for Research and Education. SG acknowledges support by the Studienstiftung des deutschen Volkes and CD thanks the Royal Society for funding. We thank T. Abraham for help with the XRD measurements, P. Laity for help with SAXS measurements, and P.M€uller-Buschbaum for useful discussions

Acoustic properties of multiferroic BiFeO 3 over the temperature range 4.2–830 K

The longitudinal acoustic wave velocity and attenuation in BiFeO3 ceramics have been measured by ultrasonic pulse-echo technique at a frequency of 10 MHz in the temperature range from 4.2 K to 830 K. The anomalies observed in the sound velocity and attenuation behavior versus temperature are attributed to the assumed relaxation in the temperature range 200–500 K and antiferromagnetic phase transition at higher temperatures. Order parameter fluctuations along with magnetostriction are discussed as the factors determining the acoustic wave velocity anomaly in the vicinity of the antiferromagnetic phase transition point