@article{KrstulovićRosaBiedermannetal.2021, author = {Krstulović, Marija and Rosa, Angelika D. and Biedermann, Nicole and Irifune, Tetsuo and Wilke, Max}, title = {Structural changes in aluminosilicate glasses up to 164 GPa and the role of alkali, alkaline earth cations and alumina in the densification mechanism}, series = {Chemical geology : official journal of the European Association for Geochemistry}, volume = {560}, journal = {Chemical geology : official journal of the European Association for Geochemistry}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2541}, doi = {10.1016/j.chemgeo.2020.119980}, pages = {14}, year = {2021}, abstract = {Pressure induced structural changes in silicate melts have a great impact on their physico-chemical properties and hence on their behaviour in the deep Earth's interior. In order to gain a deeper understanding we have studied the densification mechanism in multicomponent aluminosilicate glasses (albitic and albit-diopside composition) by means of extended X-ray absorption fine structure spectroscopy coupled to a diamond anvil cell up to 164 GPa. We have monitored the structural modifications from the network-former Ge as well as the network-modifier Sr. Notably, we tracked the evolution of Ge-O and Sr-O bond lengths (RGe-O, RSr-O) and their coordination number with pressure. We show that RGe-O increases strongly up to about 32 GPa, whereas RSr-O increases only slightly up to similar to 26 GPa. We assign these extensions to the increase of the coordination number from 4 to 6 (Ge) and from similar to 6 to at least 9 (Sr). Upon further compression RGe-O and RSr-O exhibit a continuous decrease to the highest probed pressure. These bond contractions, notably of RGe-O, that are continuous and exceed the one observed in pure SiO2 and GeO2, reflect a higher structural flexibility of multi-component glasses compared to those simple systems. Particularly, the high fraction of non-bridging oxygen atoms due to the presence of Na, Sr, Ca, Mg in the studied glasses, favours the simple compression of the highly-coordinated polyhedra of Si and Ge at pressure greater than 30 GPa. This is in strong contrast to pure oxides where cation polyhedral distortions govern the densification mechanism of the glass. The results of this study demonstrate that low field-strength alkali and alkaline earth cations, ubiquitous in deep Earth's melts, have a profound influence on the densification mechanism of glasses. Our results provide important constrains for interpreting the observed low velocity anomalies at the Earth's core-mantle boundary that have been, beyond others, referred to the presence of high-density melts. The hypothesis that non-buoyant melts at the Earth's core-mantle boundary can be formed by peculiar structural transformations in melts leading to higher coordination numbers compared to their crystalline equivalents is not supported from the present observations. The present results rather suggest that if velocity anomalies are to be explained by melts, these likely have considerable differences in chemical composition to the surrounding crystalline phase assemblage.}, language = {en} } @article{RosaDewaeleGarbarinoetal.2022, author = {Rosa, Angelika D. and Dewaele, Agn{\`e}s and Garbarino, Gaston and Svitlyk, Volodymyr and Morard, Guillaume and De Angelis, Filippo and Krstulovic, Marija and Briggs, Richard and Irifune, Tetsuo and Mathon, Olivier and Bouhifd, Mohamed Ali}, title = {Martensitic fcc-hcp transformation pathway in solid krypton and xenon and its effect on their equations of state}, series = {Physical review / publ. by The American Institute of Physics. B}, volume = {105}, journal = {Physical review / publ. by The American Institute of Physics. B}, number = {14}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.105.144103}, pages = {14}, year = {2022}, abstract = {The martensitic transformation is a fundamental physical phenomenon at the origin of important industrial applications. However, the underlying microscopic mechanism, which is of critical importance to explain the outstanding mechanical properties of martensitic materials, is still not fully understood. This is because for most martensitic materials the transformation is a fast process that makes in situ studies extremely challenging. Noble solids krypton and xenon undergo a progressive pressure-induced face-centered cubic (fcc) to hexagonal close-packed (hcp) martensitic transition with a very wide coexistence domain. Here, we took advantage of this unique feature to study the detailed transformation progress at the atomic level by employing in situ x-ray diffraction and absorption spectroscopy. We evidenced a four-stage pathway and suggest that the lattice mismatch between the fcc and hcp forms plays a key role in the generation of strain. We also determined precisely the effect of the transformation on the compression behavior of these materials.}, language = {en} } @article{KrstulovićRosaFerreiraSanchezetal.2022, author = {Krstulović, Marija and Rosa, Angelika D. and Ferreira Sanchez, Dario and Libon, L{\´e}lia and Albers, Christian and Merkulova, Margarita and Grolimund, Daniel and Irifune, Tetsuo and Wilke, Max}, title = {Effect of temperature on the densification of silicate melts to lower earth's mantle conditions}, series = {Physics of the earth and planetary interiors}, volume = {323}, journal = {Physics of the earth and planetary interiors}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-9201}, doi = {10.1016/j.pepi.2021.106823}, pages = {13}, year = {2022}, abstract = {Physical properties of silicate melts play a key role for global planetary dynamics, controlling for example volcanic eruption styles, mantle convection and elemental cycling in the deep Earth. They are significantly modified by structural changes at the atomic scale due to external parameters such as pressure and temperature or due to chemistry. Structural rearrangements such as 4- to 6-fold coordination change of Si with increasing depth may profoundly influence melt properties, but have so far mostly been studied at ambient temperature due to experimental difficulties. In order to investigate the structural properties of silicate melts and their densification mechanisms at conditions relevant to the deep Earth's interior, we studied haplo basaltic glasses and melts (albite-diopside composition) at high pressure and temperature conditions in resistively and laser-heated diamond anvil cells using X-ray absorption near edge structure spectroscopy. Samples were doped with 10 wt\% of Ge, which is accessible with this experimental technique and which commonly serves as a structural analogue for the network forming cation Si. We acquired spectra on the Ge K edge up to 48 GPa and 5000 K and derived the average Ge-O coordination number NGe-O, and bond distance RGe-O as functions of pressure. Our results demonstrate a continuous transformation from tetrahedral to octahedral coordination between ca. 5 and 30 GPa at ambient temperature. Above 1600 K the data reveal a reduction of the pressure needed to complete conversion to octahedral coordination by ca. 30 \%. The results allow us to determine the influence of temperature on the Si coordination number changes in natural melts in the Earth's interior. We propose that the complete transition to octahedral coordination in basaltic melts is reached at about 40 GPa, corresponding to a depth of ca. 1200 km in the uppermost lower mantle. At the core-mantle boundary (2900 km, 130 GPa, 3000 K) the existence of non-buoyant melts has been proposed to explain observed low seismic wave velocity features. Our results highlight that the melt composition can affect the melt density at such extreme conditions and may strongly influence the structural response.}, language = {en} } @article{PohlenzRosaMathonetal.2018, author = {Pohlenz, Julia and Rosa, Angelika D. and Mathon, O. and Pascarelli, S. and Belin, S. and Landrot, G. and Murzin, V. and Veligzhanin, A. and Shiryaev, A. and Irifune, Tetsuo and Wilke, Max}, title = {Structural controls of CO2 on Y, La and Sr incorporation in sodium-rich silicate - carbonate melts by in-situ high P-T EXAFS}, series = {Chemical geology : official journal of the European Association for Geochemistry}, volume = {486}, journal = {Chemical geology : official journal of the European Association for Geochemistry}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2541}, doi = {10.1016/j.chemgeo.2017.12.023}, pages = {1 -- 15}, year = {2018}, abstract = {Carbonate-rich silicate and carbonate melts play a crucial role in deep Earth magmatic processes and their melt structure is a key parameter, as it controls physical and transport properties. Carbon-rich melts can be strongly enriched in trace elements, but the structural incorporation mechanisms of these elements are difficult to study because such melts generally cannot be quenched to glasses. In this contribution we investigate the influence of CO2 on the local environments of trace elements contained in silicate glasses with variable CO2 concentrations and in silicate and carbonate melts. The melts were studied in-situ at high pressure and temperature conditions using the Paris-Edinburgh press (2.2 to 2.6 GPa and 1200 to 1500 degrees C). The compositions studied include sodium-rich peralkaline silicate melts and glasses and carbonate melts similar to those occurring naturally at Oldoinyo Lengai volcano. The local environments of yttrium (Y), lanthanum (La) and strontium (Sr) were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. Main findings of the study suggest: (1) In peralkaline silicate glasses the local structure of Y is unaffected by the CO2 content. Contrary, a slight increase of oxygen bond lengths of Sr and La is inferred with increasing CO2 content in peralkaline glasses, while they remain constant in glasses of even higher peralkalinity independent of the CO2 content. (2) In silicate melts of different CO2 contents Y-O bond lengths are constant, while a slight increase within carbonate melt compositions is deduced. On the other hand, a steady bond lengths increase over the whole compositional range is inferred for La-O and Sr-O. This may well be explained by distinct preferences of these elements for specific local environments. Based on these new data, we suggest potential mechanisms for the structural incorporation of these elements, a key step towards understanding their partitioning behavior in natural magmatic systems.}, language = {en} } @article{RosaPohlenzdeGrouchyetal.2016, author = {Rosa, Angelika D. and Pohlenz, Julia and de Grouchy, C. and Cochain, B. and Kono, Y. and Pasternak, S. and Mathon, O. and Irifune, Tetsuo and Wilke, Max}, title = {In situ characterization of liquid network structures at high pressure and temperature using X-ray absorption spectroscopy coupled with the Paris-Edinburgh press}, series = {High pressure research}, volume = {36}, journal = {High pressure research}, publisher = {American Geophysical Union}, address = {Abingdon}, issn = {0895-7959}, doi = {10.1080/08957959.2016.1199693}, pages = {332 -- 347}, year = {2016}, abstract = {We review recent progress in studying structural properties of liquids using X-ray absorption spectroscopy coupled with the Paris-Edinburgh press at third-generation synchrotron facilities. This experimental method allows for detecting subtle changes in atomic arrangements of melts over a wide pressure-temperature range. It has been also employed to monitor variations of the local coordination environment of diluted species contained in glasses, liquids and crystalline phases as a function of the pressure and temperature. Such information is of great importance for gaining deeper insights into the physico-chemical properties of liquids at extreme condition, including the understanding of such phenomena as liquid-liquid phase transitions, viscosity drops and various transport properties of geological melts. Here, we describe the experimental approach and discuss its potential in structural characterization on selected scientific highlights. Finally, the current ongoing instrumental developments and future scientific opportunities are discussed.}, language = {en} }