Simon MacLeod

Thallium under extreme compression

We present a combined theoretical and experimental study of the high-pressure behavior of thallium. X-ray diffraction experiments have been carried out at room temperature (RT) up to 125 GPa using diamond-anvil cells (DACs), nearly doubling the pressure range of previous experiments. We have confirmed the hcp-fcc transition at 3.5 GPa and determined that the fcc structure remains stable up to the highest pressure attained in the experiments. In addition, HP-HT experiments have been performed up to 8 GPa and 700 K by using a combination of XRD and a resistively heated DAC. Information on the phase boundaries is obtained, as well as crystallographic information on the HT bcc phase. The equation of state (EOS) for different phases is reported. Ab initio calculations have also been carried out considering several potential high-pressure structures. They are consistent with the experimental results and predict that, among the structures considered in the calculations, the fcc structure of thallium is stable up to 4.3 TPa. Calculations also predict the post-fcc phase to have a close-packed orthorhombic structure above 4.3 TPa.

Titanium Alloys at Extreme Pressure Conditions

The electronic structures of the early transition metals are characterised by the relationship that exists between the occupied narrow d bands and the broad sp bands. Under pressure, the sp bands rise faster in energy, causing electrons to be transferred to the d bands (Gupta et al., 2008). This process is known as the s-d transition and it governs the structural properties of the transition metals. At ambient conditions, pure Ti crystallizes in the 2-atom hcp, or  phase crystal structure (space group P63/mmc) and has an axial ratio (c/a) ~ 1.58. Under pressure, the  phase undergoes a martensitic transformation at room temperature (RT) into the 3-atom hexagonal, or  phase structure (space group P6/mmm). The appearance of the ω phase at high pressure raises a number of scientific and engineering issues mainly because the  phase appears to be fairly brittle compared with the  phase, and this may significantly limit the use of Ti in high pressure applications. Furthermore, after pressure treatment the ω phase appears to be fully, or at least, partially recoverable at ambient conditions, thus raising questions as to which is the lowest thermodynamically stable crystallographic phase of Ti at RT and pressure.

Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6

The ferroelectric to paraelectric phase transition of multiferroic

High-pressure/high-temperature phase diagram of zinc

{\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}

An Ultrahigh CO2-Loaded Silicalite-1 Zeolite: Structural Stability and Physical Properties at High Pressures and Temperatures

has been investigated at high pressures and ambient temperature by second-harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray diffraction. We have found that

Equation of state and high-pressure/high-temperature phase diagram of magnesium

{\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}

Ultrafast X-Ray Diffraction Studies of the Phase Transitions and Equation of State of Scandium Shock Compressed to 82?GPa

undergoes a pressure-induced structural phase transition (

Experimental and theoretical study of Ti-6Al-4V to 220 GPa

P{4}_{2}mc\ensuremath{\rightarrow}P{4}_{2}/nmc

Structural Evolution of CO2-Filled Pure Silica LTA Zeolite under High-Pressure High-Temperature Conditions

) at

Structural Behavior of Natural Silicate–Carbonate Spurrite Mineral, Ca5(SiO4)2(CO3), under High-Pressure, High-Temperature Conditions

\ensuremath{\sim}7\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}