POLYAMORPHIC SYSTEMS · High-pressure phase transitions in poly-amorphic systems of semi-conducting elements
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2009-04-01 → 2010-03-31
- EU contribution
- €56,134
- Participants
- 1
- Scheme
- IIF
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Results in brief
Final Activity and Management Report Summary - POLYAMORPHIC SYSTEMS (High-pressure phase transitions inpolyamorphic systems of semiconducting elements)
The effect of pressure on amorphous Ge was probed by Raman spectroscopy combined with molecular dynamics simulations. A large jump occurs in Raman peak position at 11-12 GPa and 7-5.5 GPa respectively during increasing/decreasing pressure runs. This effect is due to a transition between the Low density amorphous semiconductor (LDA) and a metallic high density (HDA) modifications of amorphous germanium. We measured the superconducting transition temperature (Tc) using magnetic susceptibility measurements in the diamond anvil cell. The Tc for the HDA modification was found substantially higher than that for the beta-Sn structured Ge-II crystalline phase. Our results demonstrate that HDA form of Ge contains atoms in higher average coordination than the tetrahedrally-bonded LDA polyamorph. During compression the LDA-to-HDA transformation occurs at P app. 8-12 GPa, while a reverse transformation occurs between P app. 5.5-6.5 GPa indicating hysteresis characteristic for the first order-like transition as observed previously for a-Si at slightly higher pressure. We expect that the LDA-HDA transformation in amorphous Ge is linked to a density-driven liquid-to-liquid phase transition that is predicted theoretically to occur in the supercooled liquid state of Ge.
Data: CORDIS, © European Union
Project objective
The project is aimed to acquisition the experimental information about the transformations occurred in amorphous silicon and germanium within wide pressure and temperature intervals, characterization of the different amorphous phases formed under high pressure. This will be done by in situ high-pressure experiments using Raman, infrared spectroscopy and X-ray diffraction. The incoming phase period is based in the University College of London (UCL) using the range of diamond anvils cells installed there for optical measurements. The structural experiments are planned on the X-ray synchrotron sources in SRS (Daresbury, UK) and ESRF (Grenoble, France). The return phase in the Institute of Solid State Physics (Russian Academy of Sciences), is planned to obtain bulk samples of the quenched high-pressure amorphous Si and Ge samples by means of quenching under pressure" method employing large-volume high pressure cells and for measuring the pressure dependence of the super-conducting transition temperature of Si and Ge samples up to 60GPa.The project is a stage of the general research program planned UCL and is directed to complex investigations of the "polyamorphism" phenomenon in the systems demonstrated the first-order phase transitions within liquid (amorphous) state. The experience, experimental skills and technical approaches obtained during the accomplishment of the project will be used for studding ionic-covalent framework liquids such as SiO2 and GeO2 important from the geological point of view. The project can be accomplished completely in the experimental centres of Europe serving for promotion of the intra-European scientific relations. The engaging of the Russian scientists for realization of the research projects in Europe will also work for these very objectives as far as Russia still possesses a high knowledge-based potential"
Original text from CORDIS.
Participants
- INSTITUTE OF SOLID STATE PHYSICS, RUSSIAN ACADEMY OF SCIENCES · CHERNOGOLOVKACoordinatorCity levelRussia
Links
Data: CORDIS, © European Union