Discovery of a conical feature in Halmahera waters, Indonesia: traces of a late-stage hydrothermal activity

An expedition to confirm the presence of underwater hazards was carried out in Halmahera waters, Indonesia, to the west of Halmahera Island from August to September 2021. The expedition carried out a multibeam survey, surface-towed magnetic survey, and seafloor sampling. A ~ 615-m-tall conical feature with traces of hydrothermal activity was discovered. The feature is bounded on the southeastern (SE) side by a series of normal faults at the peak, with possible dextral strike-slip faults traced west of the feature. The feature displays the potential presence of volcanic rocks based on the observed contrasting magnetic anomaly signature of down to − 100 nT, which at the magnetic equator corresponds to the presence of highly magnetised material. Four 2.5-D magnetic models were built to test various scenarios on the subsurface structure of the feature, mainly focusing on the presence of volcanic rocks at different epochs and a possible presence of serpentinisation. X-ray diffraction (XRD) of the silt and clay sediments sampled confirms traces of late-stage hydrothermal activity, indicated by a high percentage of quartz (53.87%), followed by calcite (34.56%), kaolinite (6.54%), and illite minerals (5.04%). Non-carbonate materials are yet to be found in the sampled sand and gravel sediments, which mainly consist of shell and coral fragments. The discovery of the conical feature, now termed the Yudo Sagoro Hill, provides new information on the structure and activities on the seafloor of Halmahera waters

Spectroscopic study of hydration and carbonation effects of La2O3-based materials

Póster presentado al LII Congreso Anual de la Sociedad Española de Cerámica y Vidrio celebrado en Burgos del 3 al 6 de octubre de 2012.One of the main applications of Lanthanum oxide is as support of catalysts for methane oxidation. In this field, a great effort has been made in establishing the thermal evolution of La2O3 and La2O3-related phases, such as La(OH)3 and La carbonates, in varying atmospheric conditions. The goal of these studies is twofold: to predict, on the one hand, the aging behavior of the catalysts, and to test the conditions yielding the best performance. In this work we have focused in the identification of phase content and thermal mechanisms involving hydration and carbonation effects of La2O3-based materials by means of Raman spectroscopy. It is known that, in air, La2O3 hydrates easily to form La(OH)3 together with small amounts of Lanthanum carbonates. The thermal evolution of La(OH)3, however, is highly dependent upon environmental conditions, such as presence of humidity and CO2 partial pressure, as well as on the heating rates and retention times at each temperature. In vacuum La(OH)3 evolves to LaOOH and this phase dehydrates first to a mixture of C- and ALa2O3 until, upon further heating, only A-La2O3 phase remains. Experiments suggest that A phase forms directly from La(OH)3 whereas C phase forms preferably from LaOOH. In air, the path of La(OH)3 dehydration to A-La2O3 is a function of heating rates: the first dehydration step yields LaOOH, as in vacuum, but under slow heating this oxyhydroxide is not allowed to decompose to La2O3. Instead, carbonation occurs, resulting in a full conversion of LaOOH to several types of oxycarbonates, usually denoted as I, Ia and II-La2O2CO3. Thermal stability of these phases increases in the sequence I-Ia-II, so that at 670 ºC only II-La2O2CO3 remains. In our in-situ experiments II-La2O2CO3 converts to La2O3 at 700 ºC.This work has been supported by Spanish Government MAT2010-19837-C06-06. G. Larraz acknowledges the financial support provided by Gobierno de Aragón through a PhD grant. A. Orera acknowledges the financial support provided by Consejo Superior de Investigaciones Científicas through a JAE-Doc contract.Peer reviewe

Cubic phases of garnet-type Li7La3Zr2O12: the role of hydration

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.We address the controversial issue of the structural stability of Li 7La3Zr2O12 garnets, focusing on the mechanisms that result in the transformation from tetragonal to cubic symmetry. We show that undoped tetragonal Li7La3Zr2O 12 not exposed to humidity at any moment undergoes a reversible phase transition to cubic symmetry at Tc ≃ 645 °C that we ascribe to lithium dynamic effects. On the other hand, a close correlation has been found between the appearance of a cubic phase between 100 and 200 °C in X-ray diffractograms and the presence of water, either in the atmosphere in which experiments are performed or already in the starting material. The natures of the high and low-temperature cubic garnets are totally different: the one found above the phase transition does not involve any change in the stoichiometry, whereas the cubic phase formed at low temperature is a hydrated, lithium defective phase, due to the combined effect of water insertion into the garnet structure and the H+/Li+ exchange mechanism. Differences in the actual compositions of the samples depending on their thermal history are corroborated by TG-MS experiments. Chemical reactions and phases formed along the thermal evolution are elucidated with the help of Raman spectroscopy. © 2013 The Royal Society of Chemistry.This work has been supported by the Spanish Ministerio de Economía and Feder funds through grant MAT2010-19837-C06-06. A. Orera acknowledges the financial support provided by CSIC and ESF through a JAE-Doc contract. G. Larraz acknowledges the financial support provided by Gobierno de Aragón through a PhD grant (B108/11).The authors also thank the Unit of Information Resources for Research (URICI-CSIC) for the co-financing of this publication in Open Access.Peer Reviewe

SWE_of_Bathymetry.m: A geomorphometric tool to automate discrimination between detachment and magmatic seafloor at slow-spreading ridges from shipboard multibeam bathymetry

The shapes and directionality of the oceanic crust at slow-spreading ridges are key to understanding its magmatic or tectonic emplacement. At slow-spreading ridges, magmatic terrain is marked by linearly fault-bounded abyssal hills, while a more tectonic emplacement termed detachment terrain is marked by long-lived detachment faults forming Oceanic Core Complexes (OCCs). However, the quantitative description of the magmatic and detachment regimes is still limited. We develop a novel geomorphometric technique to automate terrain classification based on the parameterisation of the shape, directionality, and curvature of the seafloor. The algorithm consists of two steps: (1) characterising the pattern observed in the horizontal axes by computing the horizontal eigenvalues of the slope vectors at each multibeam cells and (2) building a weight matrix derived from the computed slopes. The eccentricity of the horizontal eigenvalues defines the dipping pattern in the horizontal axes, hence the term slope-weighted eccentricity (SWE). The technique is applied through a moving window and is tested at 12.5°–15.5° N on the Mid-Atlantic Ridge (MAR), where the two distinct modes of spreading occur. The application of this novel geomorphometric technique yields results consistent with published qualitative interpretation and the distribution of seismicity observed from the peak amplitudes of the tertiary waves (T-waves) in the study area. Using the established algorithm, we found that 41% of the seafloor in our study area experienced detachment faulting (up to 28% are identified as OCCs), 25% experienced typical magmatic accretion, and a buffer zone termed extended terrain affects 34% of the seafloor, where the morphology shows a transition from detachment to magmatic spreading or vice versa. These findings provide new insights into seafloor classification based on the observed morphology and the potential to automate such mapping at other slow-spreading ridge regions

Influence of Li+ and H+ distribution on the crystal structure of Li7-xHxLa3Zr2O12 (0 = ≤ x ≤ = 5) garnets

With appropriate doping or processing, LiLaZrO (LLZO) is an excellent candidate to be used in Li batteries either as a solid electrolyte or as a separator between the Li anode and a liquid electrolyte. For both uses, the reactivity with water either from the air or in aqueous media is a matter of interest. We address here the structural changes undergone by LLZO as a result of H/Li exchange and relate them with the amount of H content and atomic distribution. Neutron diffraction is performed to elucidate Li and H location. Two different cubic phases derive from LLZO through H/Li exchange: Deep hydration up to 150°C yields a noncentrosymmetric I43d phase in which octahedral Li ions are exchanged by H ions, tetrahedral Li ions split into two sites with very different occupancies, and H ions form OH entities around the less occupied tetrahedral site. Annealing above 300°C results in a centrosymmetric Ia3d phase with lower H content in which Li ions occupy the usual sites of the cubic garnets and H ions occupy a split pseudooctahedral site. The centrosymmetric or noncentrosymmetric character is determined by the temperature at which exchange is performed and the H content. Both factors are not independent: at low temperature, the high H content favors H ordering around the vacant tetrahedra, while low H content and higher mobility at 350°C lead to a disordered configuration of Li and H ions. The deeply hydrated garnets are stable up to at least 300°C and also upon aging at room temperature.This work has been supported by the Spanish Ministerio de Economia and Feder funds through Grant MAT2010-19837-C06-06. A.O. and G.L. acknowledge financial support provided by the Spanish Ministerio de Ciencia e Innovacion through a Juan de la Cierva contract and by Gobierno de Aragon through a Ph.D. grant (B108/11), respectively.Peer Reviewe

Spectroscopic study of the competition between dehydration and carbonation effects in La2O3-based materials

La2O3 takes part in a variety of technologically interesting solids, but it has a known tendency to react with water and CO2, which may result in nonstoichiometry of the final product and the appearance of impurities. We apply Raman spectroscopy to study hydration and carbonation effects of La2O3-based materials, using La(OH)3 as starting material. The thermal evolution of La(OH)3 reflects the competition between dehydration and carbonation kinetics, and thus is highly dependent upon environment and experimental conditions. In vacuum, La(OH)3 evolves first to LaOOH and then to a mixture of C- and A-La2O3 until, upon further heating, only A-La2O3 phase remains. In air, La(OH)3 yields first LaOOH, but under slow heating LaOOH converts to I, Ia and II-type oxycarbonates, in increasing order of thermal stability. II-La2O2CO3, in turn, decomposes to La2O3 at 700°C. Structural relations governing phase conversion within hexagonal or orthogonal-like compounds are discussed. © 2013 Elsevier Ltd.This work has been supported by Spanish Government and Feder funds through grant MAT2010-19837-C06-06. A. Orera acknowledges the financial support provided by CSIC through a JAE-Doc contract. G. Larraz acknowledges the financial support provided by Gobierno de Aragón through a Ph.D. grant (B108/11).Peer Reviewe

Investigation of the stability of Co-doped apatite ionic conductors in NH3

Hydrogen powered solid oxide fuel cells (SOFCs) are of enormous interest as devices for the efficient and clean production of electrical energy. However, a number of problems linked to hydrogen production, storage and transportation are slowing down the larger scale use of SOFCs. Identifying alternative fuel sources to act as intermediate during the transition to the full use of hydrogen is, therefore, of importance. One excellent alternative is ammonia, which is produced on a large scale, is relatively cheap and has the infrastructure for storage and transportation already in place. However, considering that SOFCs operate at temperatures higher than 500 °C, a potential problem is the interaction of gaseous ammonia with the materials in the cathode, anode and solid electrolyte. In this paper, we extend earlier work on high temperature reactions of apatite electrolytes with NH3 to the transition metal (Co) doped systems, La9.67Si5CoO26 and La10(Si/Ge)5CoO26.5. A combination of PXRD, TGA and XAFS spectroscopy data showed a better structural stability for the silicate systems. Apatite silicates and germanates not containing transition metals tend to substitute nitride anions for their interstitial oxide anions, when reacted with NH3 at high temperature and, consequentially, lower the interstitial oxide content. In La9.67Si5CoO26 and La10(Si/Ge)5CoO26.5 reduction of Co occurs as a competing process, favouring lower levels of nitride¿oxide substitution.A. Orera and P.R. Slater would like to thank EPSRC for funding (Grant EP/F015178/1). Part funded by the European Regional Development Fund (ERDF). D.A. Headspith and M.G. Francesconi would like to thank the Leverhulme Trust for funding (Grant F/00 181/L).Peer Reviewe

A Raman spectroscopy study of tetragonal and cubic lithium garnets

Resumen del póster presentado al "31st RSC Solid State Group Christmas Meeting" celebrado en Liverpool (UK) del 19 al 20 de diciembre de 2011.Lithium garnets have been proposed as good candidates for their use as electrolytes in lithium batteries but, however, there is still controversy about the sites occupied by lithium ions in the structure and the mechanisms involved in the conduction process. One of the reasons for these discrepancies is the fact that materials with different properties are obtained depending on the synthesis method, thermal history and storage conditions of the samples. In this context, we use Raman scattering with the hope that a spectroscopic technique might provide a new perspective on the local environment of lithium ions and their diffusion mechanism. Specifically, we have focused on the role of temperature and lithium stoichiometry on the tetragonal to cubic transition in Li7La3Zr2O12 observed at about 150ºC. We have found that this transition is accompanied by the formation of lithium carbonate, indicating a loss of lithium in the garnet phase and leading to some differences between this low temperature cubic phase and that obtained at high temperature. The reversibility of this low temperature phase transformation has also been studied.Peer Reviewe

NMR study of Li distribution in Li7−xHxLa3Zr2O12 garnets

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Despite the large number of NMR studies performed on lithium conductors with a garnet-type structure, the distribution of the lithium ions in Li7La3Zr2O12 (LLZO), and their contribution to ionic conductivity are still a matter of controversy. In this work we present a magic-angle spinning (MAS) NMR study of enriched 6Li7−xHxLa3Zr2O12 (0 ≤ x ≤ 5) garnets with the aim of identifying the bands arising from the different lithium sites occupied in the garnet lattice. Taking advantage of the known sensitivity of this material to moisture and facile proton-for-lithium exchange, we have been able to alter the relative population of tetrahedral and octahedral sites (the exchange is favoured in the latter) by submitting the samples to different post-treatments to obtain samples with varying lithium content. This has allowed the identification of three different bands that we ascribe to Li in different environments within the garnet structure. In addition, variable temperature measurements have indicated the presence of dynamic exchange processes between the octahedral and tetrahedral Li sites. Protons inserted in the garnet structure were analyzed using 1H-MAS-NMR and Raman spectroscopies. 6Li-1H-CP-MAS experiments have allowed the investigation of the relative distribution of protons and lithium ions in partially exchanged samples.This work has been supported by the Spanish Ministerio de Economía and Feder funds through grant MAT2010-19837-C06-06 and MAT2010-19837-C06-03. A. Orera and G. Larraz acknowledge the financial support provided by the Spanish Ministerio de Ciencia e Innovación through a Juan de la Cierva contract and by Gobierno de Aragón through a PhD grant (B108/11) respectively.We acknowledge the support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

Snapshots of a solid-state transformation: coexistence of three phases trapped in one crystal

Crystal-to-crystal transformations have been crucial in the understanding of solid-state processes, since these may be studied in detail by means of single crystal X-ray diffraction (SCXRD) techniques. The description of the mechanisms and potential intermediates of those processes remains very challenging. In fact, solid-state transient states have rarely been observed, at least to a sufficient level of detail. We have investigated the process of guest extrusion from the non-porous molecular material [Fe(bpp)(H2L)](ClO4)2$1.5C3H6O (bpp ¼ 2,6-bis(pyrazol-3-yl)pyridine; H2L ¼ 2,6-bis(5-(2- methoxyphenyl)-pyrazol-3-yl)pyridine; C3H6O ¼ acetone), which occurs through ordered diffusion of acetone in a crystal-to-crystal manner, leading to dramatic structural changes. The slow kinetics of the transition allows thermal trapping of the system at various intermediate stages. The transiting single crystal can be then examined at these points through synchrotron SCXRD, offering a window upon the mechanism of the transformation at the molecular scale. These experiments have unveiled the development of an ordered intermediate phase, distinct from the initial and the final states, coexisting as the process advances with either of these two phases or, at a certain moment with both of them. The new intermediate phase has been structurally characterized in full detail by SCXRD, providing insights into the mechanism of this diffusion triggered solid-state phenomenon. The process has been also followed by calorimetry, optical microscopy, local Raman spectroscopy and powder X-ray diffraction. The discovery and description of an intermediate ordered state in a molecular solid-state transformation is of great interest and will help to understand the mechanistic details and reaction pathways underlying these transformations