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High pressure studies in solid state chemistry and biology

Hazael, R.T.; (2012) High pressure studies in solid state chemistry and biology. Doctoral thesis, UCL (University College London).

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Abstract

The new family of multiferroic perovskites SeMO3 (M= Ni, Mn, Cu) are obtained under high-P,T synthesis conditions from mixtures of the oxides (NiO, MnO, SeO2 etc.) or the corresponding metal hydroxides at pressures between 2-7 GPa and at temperatures up to 1000°C. However, those syntheses can result in retention of the starting oxides in the reaction products, leading to difficulties in analysis of the magnetic properties. We have developed a precursor route based on the reaction of Na2SeO3 with anhydrous MCl2 compounds, leading to the formation of the crystalline perovskite material with formation of only diamagnetic NaCl as a reaction product. This reaction procedure also allows us to lower the reaction temperature. We studied the synthesis both in the laboratory using multi-anvil and piston cylinder techniques, and also using in situ synchrotron X-ray diffraction using the Paris-Edinburgh press at ESRF ID27, to follow the synthesis reactions and optimise the reaction conditions. Our results indicate initial formation of Se-bearing perovskites such as SeCuO3, in a low-P, T range kinetically stabilised during the early stages of the reaction, followed by further reactions to yield well-crystallised materials at higher-P, T conditions. We also used similar techniques to study possible formation of SeMS3 perovskites indicated to be stable from DFT calculations. Here we could not find any evidence for formation of the perovskite structures, but instead we observed synthesis of pyrite-type materials Bacteria show the greatest adaptability, which enables them to occupy extreme habitats on the planet. It is important to complete a proper evaluation of the biosphere of our planet and to achieve this we must understand the mechanisms and limits for bacterial survival. This work will help us constrain models for the origin of life and is readily transferable to many astrobiological studies. It is now extremely relevant to study the effect of high P on the development and evolution of organisms to understand their survivability mechanisms. We are experimenting with the adaptability of E.coli to pressures greater than 1 GPa. Until recently it was thought that no organisms could survive at P> 120 MPa (Zeng et al 2009). However, a recent study indicated that E.coli and S. onodeinsis remained viable to 1.4-1.7 GPa (Sharma et al 2002), but the results have been questioned (Yayanos 2002). However, our collaborative directed evolution study of E. coli has now confirmed that microbes can adapt and survive at least up to 2 GPa (Vanlint et al 2011).

Type:Thesis (Doctoral)
Title:High pressure studies in solid state chemistry and biology
Language:English
Additional information:Permission for digitisation not received
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry

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