POLYAMORPHIC SYSTEMS · High-pressure phase transitions inpolyamorphic systems of semiconducting elements
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2005-10-01 → 2007-03-31
- EU contribution
- €173,130
- Participants
- 1
- Scheme
- IIF
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Results in brief
Final Activity Report Summary - POLYAMORPHIC SYSTEMS (High-pressure phase transitions in polyamorphic systems of semiconducting elements)
The initial goal of our project was to prepare bulk samples of amorphous Ge and GexSi1-x alloys and study their polyamorphic transformation as a function of pressure. This would result in new metallic amorphous materials that might be recoverable to ambient conditions. Firstly, we had to synthesise the amorphous Ge and GexSi1-x alloy samples. A procedure for preparing amorphous Si and Ge was recently described using a metathesis reaction between Zintl phases, like NaSi or NaGe, and an ammonium halogenide, such as NH4Cl or NH4Br. We developed and optimised the procedure in order to increase the yield of amorphous product and eliminate traces of crystalline material formed. Using this new method we could prepare hundred milligram quantities of amorphous Ge powder. The disordered (amorphous) structure of the final product was confirmed by X-ray diffraction and Raman spectroscopy. The effect of pressure on the amorphous Ge was probed by in situ Raman spectroscopy. Upon increasing pressure the main Raman peak weakened and shifted abruptly to lower wavenumber above 11 to 12 GPa pressure (P) confirming the presence of a polyamorphic transition to a high-density form of a-Ge with a higher coordination number. During decompression the reverse transition took place at lower pressure, ranging between 6 and 7 GPa. The large hysteresis indicated that the polyamorphism resembled a first order phase transition. Moreover, we attempted to use the synthesis method to prepare samples of amorphous GexSi1-x alloys to carry out similar pressurisation studies; however the syntheses were not successful and another method had to be devised. During our study we investigated the high pressure phase transformation behaviour of the Zintl phase NaSi, which appeared to undergo an amorphisation and polymerisation reaction at pressure greater than 12 GPa.
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 pres sure.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 superconducting transition temperature of Si and Ge samples up to 60 GPa.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
- UNIVERSITY COLLEGE LONDON · LONDONCoordinatorUnited Kingdom
Links
Data: CORDIS, © European Union