Sarah J. Day

New synchrotron powder diffraction facility for long-duration experiments

The world’s first dedicated synchrotron instrument for long-duration experiments has been built and commissioned at Diamond Light Source. The new beamline I11 user facility is designed for the study of slow kinetics in polycrystalline materials.

Room Temperature Magnetically Ordered Polar Corundum GaFeO3 Displaying Magnetoelectric Coupling

The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d5 cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO3-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO3-type GaFeO3 under the synthesis conditions. The A3+/Fe3+ cations are shown to be more ordered in polar corundum GaFeO3 than in isostructural ScFeO3. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO3 exhibits weak ferromagnetism at room temperature that arises from its Fe2O3-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.

Photoluminescence in amorphous MgSiO

Samples of amorphous MgSiO_3 annealed at temperature steps leading up to their crystallisation temperature show a rise in photoluminescence activity, peaking at ~450C. The photoluminescence band has a main peak at 595nm and a weaker peak at 624nm. We present laboratory data to show that the maximum in photoluminescence activity is related to substantial structural reordering that occurs within a relatively narrow temperature range. We attribute the origin of the photoluminescence to non-bridging oxygen hole centre defects, which form around ordered nano-sized domain structures as a result of the breakup of tetrahedral connectivity in the disordered inter-domain network, aided by the loss of bonded OH. These defects are removed as crystallisation progresses, resulting in the decrease and eventual loss of photoluminescence. Thermally processed hydrogenated amorphous silicate grains could therefore represent a potential carrier of extended red emission.

\boldsymbol {_{3}}

There is evidence to suggest that clathrate hydrates have a significant effect on the surface geology of icy bodies in the Solar System. However the aqueous environments believed to be present on these bodies are likely to be saline rather than pure water. Laboratory work to underpin the properties of clathrates in such environments is lacking. We fill this gap by carrying out a laboratory investigation of the physical properties of CO

silicate

_2

Properties of CO2 clathrate hydrates formed in the presence of MgSO4 solutions with implications for icy moons

clathrates produced in weak aqueous solutions of MgSO

In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy

_4

Non-aqueous formation of the calcium carbonate polymorph vaterite: astrophysical implications

. We use synchrotron X-ray powder diffraction to investigate clathrates formed at high CO

CARBONATE FORMATION IN NON-AQUEOUS ENVIRONMENTS BY SOLID-GAS CARBONATION OF SILICATES

_2

Fine-grained amorphous calcium silicate CaSiO3 from vacuum dried sol–gel – Production, characterisation and thermal behaviour

pressure in ice that has formed from aqueous solutions of MgSO