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Identification of unknown micro- and nano-sized mineral phases is commonly achieved by analysing chemical maps generated from hyperspectral datasets, particularly scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX). However, the accuracy and reliability are limited by subjective human interpretation and instrumental artefacts in the chemical maps. At the same time, machine learning has emerged as a powerful method to overcome the roadblocks. Here, we propose a self-supervised machine learning approach to not only identify unknown phases but also unmix the overlapped chemical signals of individual phases with no need for user expertise in mineralogy. This approach leverages the guidance of gaussian mixture modelling (GMM) clustering fitted on an informative latent space of pixel-wise elemental data points modelled using a neural network autoencoder, and deconvolutes the overlapped chemical signals of phases using non-negative matrix factorisation (NMF). We evaluate the reliability and the accuracy of the new approach using two hyperspectral EDX datasets. The first dataset was measured from an intentionally fabricated sample, where seven known mineral particles are physically overlapping with each other as well as the substrate. Without any prior knowledge, the proposed approach successfully identified all major phases and recovered the original chemical spectra of the individual phases with high accuracy. In the second case, the dataset was collected from a potential vehicular source of particulate matter air pollution, where identification of the individual pollution particles is complicated by the complex nature of the sample. The approach once again was able to identify the potential Fe-bearing ultrafine particles and isolate the background-subtracted elemental signal. We demonstrate a robust approach that potentially brings a significant improvement of mineralogical and chemical analysis in a fully automated manner. In addition, the proposed analysis process has been built into a user-friendly Python code with graphical user interface (GUI) for ease of use by general users.

We carried out a series of silicate fractional crystallization experiments at lower mantle pressures using the laser‐heated diamond anvil cell. Phase relations and the compositional evolution of the cotectic melt and equilibrium solids along the liquid line of descent were determined and used to assemble the melting phase diagram. In a pyrolitic magma ocean, the first mineral to crystallize in the deep mantle is iron‐depleted calcium‐bearing bridgmanite. From the phase diagram, we estimate that the initial 33%–36% of the magma ocean will crystallize to form such a buoyant bridgmanite. Substantial calcium solubility in bridgmanite is observed up to 129 GPa, and significantly delays the crystallization of the calcium silicate perovskite phase during magma ocean solidification. Residual melts are strongly iron‐enriched as crystallization proceeds, making them denser than any of the coexisting solids at deep mantle conditions, thus supporting the terrestrial basal magma ocean hypothesis (Labrosse et al., 2007)., Key Points Experimental determination of lower mantle melting reltaions and phase diagram by laser‐heated diamond anvil cellOne third of a pyrolitic magma ocean would first crystallize iron‐depleted bridgmanite, than contains a substantial amounts of calciumCalcium concentration in liquidus bridgmanite is constant from 52 to 129 GPa, and delays the crystallization of calcium‐silicate perovskite

Both seismic observations of dense low shear velocity regions and models of magma ocean crystallization and mantle dynamics support enrichment of iron in Earth’s lowermost mantle. Physical properties of iron-rich lower mantle heterogeneities in the modern Earth depend on distribution of iron between coexisting lower mantle phases (Mg,Fe)O magnesiowüstite, (Mg,Fe)SiO3 bridgmanite, and (Mg,Fe)SiO3 post-perovskite. The partitioning of iron between these phases was investigated in synthetic ferrous-iron-rich olivine compositions (Mg0.55Fe0.45)2SiO4 and (Mg0.28Fe0.72)2SiO4 at lower mantle conditions ranging from 33–128 GPa and 1900–3000 K in the laser-heated diamond anvil cell. The resulting phase assemblages were characterized by a combination of in situ X-ray diffraction and ex situ transmission electron microscopy. The exchange coefficient between bridgmanite and magnesiowüstite decreases with pressure and bulk Fe# and increases with temperature. Thermodynamic modeling determines that incorporation and partitioning of iron in bridgmanite are explained well by excess volume associated with Mg-Fe exchange. Partitioning results are used to model compositions and densities of mantle phase assemblages as a function of pressure, FeO-content and SiO2-content. Unlike average mantle compositions, iron-rich compositions in the mantle exhibit negative dependence of density on SiO2-content at all mantle depths, an important finding for interpretation of deep lower mantle structures.

International audience; Over the past several years, non-ablative femtosecond laser exposure with spatially overlapping (i.e. spatially cumulative) pulses has emerged as a key process in three-dimensional writing of patterns in bulk of dielectric substrates. When temporally non-cumulative and combined with post-processing steps, this process defines a novel manufacturing technique in fused silica, finding use in a broad number of applications, including-but not limited to-micromechanics, integrated optics, microelectronics, microfluidics, information storage, and combinations of these fields for novel integrated sensing applications. For fused silica, evidence has shown that there is a pulse-length duration threshold around 200 fs, marking the boundary between two radically different characteristic material modification regimes, each leading to a specific application. Pulse-widths below 200 fs lead to localized densification, enabling the direct-write of optical waveguides, while pulse-widths above this value produce self-organized nanostructures causing a localized volume expansion and enhanced etching susceptibility to various chemicals. Here, we focus our attention on the regime below 200 fs, using low repetition rate, temporally non-cumulative pulses. In particular, we use very short pulses, i.e. in the range of 30 fs-a regime as yet unexplored from the viewpoint of spatially cumulative modifications. Our goal is to understand how structural modifications obtained by overlapping pulses evolve with varying pulse overlap, and how shorter pulse duration may correlate with higher material densification. This knowledge is particularly important for the next generation of photonics devices, where increasing the level of laser-induced densification is a key factor for high-density photonic integration.

It is generally admitted that femtosecond laser pulses applied to fused silica in a non-ablative regime at repetition rates excluding cumulative effects leads to structural modifications of mainly two types: the formation of nanogratings and a reduction of volume leading to a localized densification. Here, we report recent observations that show that the taxonomy of material modifications induced by the laser is significantly richer than previously known. In particular, we observe evidences of complex polymorphic phases, including possible Si nano-cristallites, eventually embedded in an amorphous shell. In addition, exploring the cumulative regime further, we have observed that nanogratings can also be found in this regime characterized by a melting of the glass phase. This surprising results point out towards complex self-organization phenomena taking place also in the cumulative regime. Both observations, a richer taxonomy of phase transformations in the non-cumulative regime and the occurrence of nanogratings in the cumulative regime, beyond challenging our understanding of laser-induced phase transformation, have interesting applications potential that will be outlined in this presentation.

The heat flux across the core-mantle boundary (Q(CMB)) is the key parameter to understand the Earth's thermal history and evolution. Mineralogical constraints of the Q(CMB) require deciphering contributions of the lattice and radiative components to the thermal conductivity at high pressure and temperature in lower mantle phases with depth-dependent composition. Here we determine the radiative conductivity (k(rad)) of a realistic lower mantle (pyrolite) in situusing an ultra-bright light probe and fast time-resolved spectroscopic techniques in laser-heated diamond anvil cells. We find that the mantle opacity increases critically upon heating to similar to 3000 K at 40-135 GPa, resulting in an unexpectedly low radiative conductivity decreasing with depth from similar to 0.8 W/m/K at 1000 km to similar to 0.35 W/m/K at the CMB, the latter being similar to 30 times smaller than the estimated lattice thermal conductivity at such conditions. Thus, radiative heat transport is blocked due to an increased optical absorption in the hot lower mantle resulting in a moderate CMB heat flow of similar to 8.5 TW,on the lower end of previous Q(CMB) estimates based on the mantle and core dynamics. This moderate rate of core cooling implies an inner core age of about 1 Gy and is compatible with both thermally- and compositionally-driven ancient geodynamo. (C) 2020 Elsevier B.V. All rights reserved.

International audience; Carbonate minerals are important hosts of carbon in the crust and mantle with a key role in the transport and storage of carbon in Earth's deep interior over the history of the planet. Whether subducted carbonates efficiently melt and break down due to interactions with reduced phases or are preserved to great depths and ultimately reach the core-mantle boundary remains controversial. In this study, experiments in the laser-heated diamond anvil cell (LHDAC) on layered samples of dolomite (Mg,Ca)CO3 and iron at pressure and temperature conditions 23 reaching those of the deep lower mantle show that carbon-iron redox interactions destabilize the 24 MgCO3 component, producing a mixture of diamond, Fe7C3, and (Mg,Fe)O. However, CaCO3 is preserved, supporting its relative stability in carbonate-rich lithologies under reducing lower mantle conditions. These results constrain the thermodynamic stability of redox-driven breakdown of carbonates and demonstrate progress towards multiphase mantle petrology in the LHDAC at conditions of the lowermost mantle.

Transition element dopants (e.g., Y, La) are commonly used as sintering aids in polycrystalline alumina ceramics, which segregate to the grain boundaries and control the grain-boundary mobility. However, due to the extremely thin (

Small amounts of anion impurities (e.g. Cl), which are incorporated during the synthesis of ceramic powders, can affect the properties and microstructure of the final sintered ceramic. The effect of anion impurities is a little studied and poorly understood phenomenon. In this work a combination of STEM-EDX analysis and atomistic modeling approach was used to understand the segregation of Cl in transparent alumina ceramics. A high resolution analytical electron microscopy study showed the presence of Cl at the grain boundaries and especially at triple points. Atomistic simulations were carried out to understand the origins and consequences of such segregation. Segregation energy calculations predict a strong segregation of Cl at the different surfaces and grain boundaries of alumina. A higher coordination number of Cl at surfaces was observed, which indicates strong ionic bonds making it difficult to remove at low temperature, which explains the presence of Cl at triple points.

International audience; We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth's lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth's mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D" layer. The succession of layers could dynamically decouple the mantle above 2,000 km from the lowermost mantle, and provide a rheological basis for the stabilization and nonentrainment of large low-shear-velocity provinces below that depth.