Mollusc shells are composite structures made of calcite and/or aragonite crystals and biopolymers, arranged in a great variety of microstructures. The formation of shell microstructures is affected by environmental and physiological factors and differences among microstructural types are believed to be of phylogenetic and adaptive biomechanical significance. Here, we characterise and illustrate for the first time, through SEM and XRD analyses, the shell microstructure and mineralogy of specimens of the bivalves Anadara uropigimelana (Bory de Saint-Vincent, 1827) and Tivela stefaninii (Nardini, 1933), and of the gastropod Oliva bulbosa (Röding, 1798), collected in the Upper Holocene HAS1 settlement and in a shell midden in the Khor Rori Archaeological Park (Oman). Anadara uropigimelana shows an aragonitic shell with an outer crossed lamellar layer, an inner complex crossed lamellar layer and an irregular simple prismatic pallial myostracum; periodic bands of dendritic nondenticular composite prisms occur in the outer part of the outer layer, reflecting seasonal changes in water temperatures and growth rates. Shells of Tivela stefaninii are aragonitic with an outer composite prismatic layer, a middle crossed lamellar layer and an inner complex crossed lamellar layer, whereas those of Oliva bulbosa are characterised by an irregular alternation of aragonitic crossed lamellar layers; a transitional layer defined by the occurrence of tidally controlled growth lines, a crossed lamellar callus and a myostracal layer are also described are also described in Oliva bulbosa. With this investigation, we provide novel microstructural and mineralogical data on these poorly known mollusc species, providing useful characters for phylogenetic, evolutionary, crystallographic, and palaeoenvironmental studies.

AbstractMollusk shells from archeological deposits are often exposed to high temperatures through human-caused or natural heating events. While heat exposure affects reliability of mollusk shells for environmental reconstructions based on geochemistry, it can provide a valuable source of information on past human behaviors and human–environment interactions. We analyzed burned and not-burned bivalve and gastropod specimens collected within two megalithic circular structures in the HAS1 settlement in Oman (Late Iron Age and Classical Period). Through a multi-methodological approach, we investigated shell microstructure using scanning electron microscopy (SEM), shell mineralogy using X-ray diffraction (XRD), and shell stable-isotopic composition (δ18O, δ13C) using isotope-ratio mass spectrometry (IRMS) to infer the temperatures these specimens were exposed to and to reconstruct the processes responsible for heating the shells. Thermal response of aragonite and calcite shells having different microstructures were also determined. We found that mollusk shells at this site were exposed to three temperature ranges: a) no exposure or <300°C, b) between 250°C and 500°C, and c) ≥500°C. The heat source was likely a fire which engulfed the entire settlement, which is also supported by evidence of carbonized wooden poles found in situ inside the circular structures.

Abstract The coccolithophore algae (Calcihaptophycidae) produce an extracellular covering of calcium carbonate plates (coccoliths) and are responsible for up to 10% of global carbon fixation through photosynthesis and biomineralization. Therefore, any alteration in cell functioning and calcification may strongly affect the ocean-atmosphere system. In this regard, the identification of any variation of the element pathways to the cell and their incorporation in the coccolith is important to understand the response of these organisms to changes in (past) environmental conditions and to identify (paleo)ecological proxies. Here, we focus on manganese which is an essential element for coccolithophore functioning: understanding whether manganese is also incorporated in coccolith calcite and if its distribution is species-specific is of seminal importance. In order to obtain ultra-high resolution (50 x 50 nm) spatial elemental distribution maps of Early to mid-Cretaceous (ca. 122 to 110 Ma) coccoliths we used synchrotron-based XRF analyses at the nano scale. The studied nannofossils belong to different taxa preferring low to higher surface-water fertility and were extracted from samples of different ages (from early Aptian to early Albian) collected in distant oceanic settings including the western Tethys, the Pacific and proto-North Atlantic Ocean. The analyses showed a high correlation in the spatial distribution of calcium and manganese in the coccoliths, suggesting that manganese is present in the coccolith calcite, and it was likely incorporated during coccolith formation. Moreover, the studied species show different Mn/Ca ratios suggesting that there is a species-specific control on the manganese uptake. Secondary calcite was also identified but it displays higher Mn/Ca ratios compared to biogenic calcite. Only the specimens collected from a black shale displayed secondary calcite crusts probably formed at the sediment-water interface after coccolith precipitation to the seafloor. Suboxic/anoxic conditions promoted manganese remobilization from Mn-oxides and Mn-oxyhydroxides which was incorporated in the secondary calcite. The Mn/Ca ratio in coccolith calcite crusts may therefore be indicator of (past) oxygen variations in bottom waters.

At the microscale, C-S-H gels from alite, or neat Portland cements, has a Ca/Si ratio close to 1.80. At the nanoscale, C-S-H is described by a defective tobermorite structure which allows a maximum Ca/Si ratio close to 1.40. There is no agreement in the location of the extra 0.40 mol of Ca(OH)(2) at the nanoscale. Atomistic modelling studies reported Ca(OH)(2) species within the tobermorite interlayer space. Other works point toward a fine intermixing of defective tobermorite and nanoportlandite. Here, we have prepared a series of alite blended with silica fume and studied the pastes by several techniques including synchrotron pair distribution function (PDF). In the employed conditions, the C-S-H gel formed by the pozzolanic reaction has nearly the same local structure than the primary C-S-H gel. Furthermore, differential PDF points toward Ca(OH)(2) excess having a local structure compatible with few-layer thick nanoparticles stretched along the c-axis.

The paper presents a quick method for the quantification of nickel species in spent FFC catalysts; the quantification of known quantities NiO and $$\hbox{NiAl}_2\hbox{O}_{4}$$ is first done in a matrix of fresh zeolite Y, and then in a complex matrix, similar to the one of a real spent catalyst. The method is carefully checked and the errors in the quantification are critically evaluated. After the validation of the method with known quantities of NiO, well below the law limit for direct re-use, a set of real spent catalysts (representative of a period of 12 months) is analysed.

Extended x-ray absorption fine structure (EXAFS) has been measured at the K edge of Sn in SnTe in the temperature range from 5 to 480 K. EXAFS results are consistent with the presence of a local rhombohedral distortion in the full temperature range from 5 to 300 K, even well above the ferroelectric transition temperature, suggesting a partial order-disorder character of the transition. At and above 300 K, the anomalous behaviour of the third and fourth EXAFS cumulants reveals a modification of the anharmonicity of the effective pair potential, possibly connected with the softening of high frequency modes or to the presence of multiple phases.

Scheelite-type materials such as LaNbO4 are increasingly attracting attention as a possible alternative to the most common fluorite and perovskite structure as ion conductors. However, they are much less used and investigated. The introduction of tungsten in lanthanum orthoniobate leads to conduction properties that are compatible with oxygen ion conductivity. In this paper, we studied the effect of the introduction of tungsten in the LaNbO4 structure. High resolution X-ray diffraction showed that in LaNb1-xWxO4+x/2 with x = 0.16 the monoclinic distortion is largely suppressed and the tetragonal phase is predominant at room temperature. By XANES/EXAFS we proved that tungsten is in its 6+ valence state and no W5+ was detected. With X-ray microspectroscopy, we studied in detail with a submicrometre-probe the interdiffusion and degradation processes taking place between the material and LSM, a common electrode material, during their long-term contact at high temperatures. (C) 2020 Elsevier B.V. All rights reserved.

Aluminosilicate-based oxide-glasses are natural materials forming volcanic magmas [1] and frequently the main constituent of manufactured products like ceramic glazes, fiber optic materials and, more recently, biocompounds [2].To characterise the atomic structure of these materials requires techniques sensitive to the very local structural environment, like spectroscopies (i.e.Nuclear Magnetic Resonance -NMR, Extended X-ray Absorption Fine Structure -EXAFS) and scattering methods (i.e.Total Scattering), due to their lack in periodic order that prevents the application of conventional crystallography.The oxide-glass structure is shaped by silicon centered corner-sharing tetrahedra, which can be combined, depending on composition, with aluminium centered motifs, while large cations like sodium, potassium and calcium tend to depolymerize the network, affecting, in this way, some of the glass properties, such as thermal expansion and glass transition temperature, as demonstrated in a previous study [3].The glass structural complexity increases when their composition involves some intermediate element, like zinc and beryllium, whose role in the network can vary as a function of the bulk composition, see [4] for some examples.This is the case of the present study that is based on a structural modeling of 2 series of different aluminosilicate-based oxide-glasses with different zinc amounts (3 samples each series).These samples have been prepared by melt-quenching route at 1350°C and then measured by combining EXAFS spectroscopy (BM23 beamline, ESRF, France) with both neutron (SANDALS instrument, ISIS, UK) and synchrotron (ID11 beamline, ESRF, France) Total Scattering data.Zn K-edge EXAFS has been applied at the beginning, in order to evaluate some of the bond distances and the Zn geometrical environment, and this information is used later as constraints for total scattering data modelling, performed by the Empirical Potential Structure Refinement (EPSR) method [5].The refinements show good residuals, as displayed in Figure 1 (on the left-hand side) and the results indicate that zinc is mostly 4-fold coordinated, but with some 3-fold, 5-fold and 6-fold species.In such complex glasses, therefore, the parameters describing the polymerization degree, like NBO (Non-Bonding-Oxygens), BO (Bonding Oxygens) and triclusters are not predictable by theoretical models, based on prior assumptions of the structural role of zinc. Figure 1 (on the right-hand side) shows the variations of NBO with ZnO mole fraction, comparing the results of this work and of theoretical calculations.Furthermore, the data modelling gave access to a wide number of structural parameters like bond angles, cluster size and cation charge compensating characteristics, that are valuable for further structure-properties studies.Figure 1.On the left, example of EPSR fit (for x-ray data) of one glass samples.On the right, non-bridging oxygen (NBO) polymerization parameter obtained by EPSR (black and white squares represent neutron and x-ray results, respectively) and by theoretical calculation (blue and red square are assuming zinc as network modifier and network former, respectively).

The atomic structure of a soda-lime-aluminosilicate network glass that underwent two different thermal treatments has been investigated by in-situ Synchrotron Powder Diffraction experiments in the 30-1000 circle C temperature range. First Sharp Diffraction Peak analysis has been initially performed to investigate intermediate range order characteristics: it provided information on volume variations upon heating and cooling, and final relaxation level as a function of the different thermal treatment. Pair Distribution Function analysis has been performed by Empirical Potential Structure Refinement modeling: it pointed out the short range order peculiarities of the samples. In particular, the thermal expansion behaviour of different atomic pairs has been revealed, together with a wide range of structural features like coordination numbers and polymerization degree. The present work well describes the multiple over temperature phenomenology of the investigated composition and discloses how the local range behaves independently from the thermal history of the sample.

The genus Xenophora comprises species of marine gastropods (Cretaceous-Recent) able to add fragments of various origins to their shell surface. Agglutination potentials vary, from species lacking attachments to species completely covered by agglutinated materials, as in the Mediterranean species Xenophora crispa. Here, we analyse Recent and fossil specimens of Xenophora crispa from the Mediterranean area using SEM and XRD, to better understand their biomineralization patterns and the mechanisms leading to the agglutination of shells, bioclasts and lithoclasts, and their evolution in time. We also provide new data on poorly studied gastropod shell microstructures. We conclude that: (1) most of the Xenophora crispa shell consists of an aragonitic crossed lamellar fabric, but fibrous to spherulitic prismatic fabrics, seemingly of calcite, have been found in the columella and peripheral edge (the thickest parts of the shell); (2) attachment of objects is mediated by a prismatic microstructure, indicating that this may be the most functional fabric in attachment areas in molluscs; and (3) the functional purpose of the agglutination in Xenophora crispa may be related to a snowshoe strategy to successfully colonize muddy substrates, coupled with tactile and olfactory camouflage. Indeed, this species secretes in the columella and peripheral edge a less dense and a more organic rich calcitic fabric, possibly to lighten the shell thickest parts in order not to sink in soft sediments and to facilitate the shell raising from the substrate to create a protected feeding area. This behaviour seems to have been maintained by X. crispa over 2 My time span.

Influences of Vacancies on the Electrical Resistivity Size effect of Nanocrystalline MetalTo maxim rehenihil inciur ma quo optatec toriat acera coratem nosam sequam resti bea conse nostior res il ipsaepuda debis seque dolor sitem velis am sit exerfer feribus sim facipie nisquia voluptium, ium et la voluptate sus alicipi tamus, sum a quae dita que et lias nonsendio occature venis des ex eum qui omnimpo ribere, sum facime maion rest et dion et re, occatur ibusam iur recum qui quatia nobitianis eium quos aborum conecti nvereic aestibus repudipsam fugia sunda dolorep ernatquam consendi sandae nullabo rectempore prat. Bea dit quis alignis este consero eium laut estrum adi ipsusdae nonestium num res velita dolum eum dus nempore cusci blab imporrumet ut et et reperuntis essitatenim sumquatet aut re dis maxime nimi, audae. 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Umquodi orestib usaperovid ullupta ecatur as es ad que perspel ibeaturianis dolum nos re, tectassus et laborunt eum nem ipiciat iistotat. Erovitiur, omnit, sumquia sitiorendis doluptas quaestiis con con peristi orataquati cum acerore mporum qui ipienime natquoditia doluptatenit exerehent fugiatem. Et inist dolorectecto eaquo eliquib erferi sam ditibus endant volo ipsunditiam quatempor as ut list latur sunt, coritio. Ehent estrumquid modis rescide rchillanda sit quam aut aditatistios et iderum et voluptatis si si conseruntet, ipsandi gnature net quia velignihil mo im fugit lam, cusanihilit volorestio volupta sum, solorerum fugiti ullorer itatem qui soluptaquo to te si a simaximpor ad quatius. Cum quiam, voluptas erumque nis dolore molum et aut remodior sequidunt. Unt facerspe atque cus ani nem il eosae de vit eum receseque denihitium est volore aut ationsequae velibus am dit maximpere, ipienimi, officta sperum nos qui non comni re isciae ex eaquiassunt, cullabo rrorum, nectorrum lab iminus ium quatur, que laut quatem volorio. Iquia es aut lam rescit omnieni dis ad mincius cipsand ucillant ullibus, iuntio blat enisquidi ut volupti re et adis quatem ex eaquam doloria speriae ligendant quo volor sita volorrovid qui sequod qui consed erferum que ipsam hilignimodit vent quam quaerum rehent ut aliqui sit magnissin cus dis eturionse doloritione quistio. Rume nonsed eaqui te occum, veribust, ut undenti untotae sit faccupta et et quatist iations equiae ommoluptius. Hicimos erum nus ad utatios pres molor magnimus inimil ipid ut maios quas ma nulliquodis se dolupta estias sollaborum vellamCorepelicium ex et aut magnatur ad que pariatur? Influences of Vacancies on the Electrical Resistivity Size effect of Nanocrystalline MetalTo maxim rehenihil inciur ma quo optatec toriat acera coratem nosam sequam resti bea conse nostior res il ipsaepuda debis seque dolor sitem velis am sit exerfer feribus sim facipie nisquia voluptium, ium et la voluptate sus alicipi tamus, sum a quae dita que et lias nonsendio occature venis des ex eum qui omnimpo ribere, sum facime maion rest et dion et re, occatur ibusam iur recum qui quatia nobitianis eium quos aborum conecti nvereic aestibus repudipsam fugia sunda dolorep ernatquam consendi sandae nullabo rectempore prat. Bea dit quis alignis este consero eium laut estrum adi ipsusdae nonestium num res velita dolum eum dus nempore cusci blab imporrumet ut et et reperuntis essitatenim sumquatet aut re dis maxime nimi, audae. Luptios ad eossit CMT Ceramics in Modern Technologies, Vol. 1, No 1, april 2019

Spinel gahnite (ZnAl2O4) has been obtained through a hydrothermal synthesis method with a grain size of about 2 nm. The sample was calcined for a few hours at two different temperatures (800 and 900 °C) in order to obtain larger grain sizes to be analyzed by means of powder diffraction with the Rietveld method, and by means of total scattering with the Pair Distribution Function (PDF) method. The idea is to compare the average to the local structure, as a function of increasing grain size. The total scattering data were collected at the European Synchrotron Radiation Facility (ESRF), Grenoble. The samples have been also characterised by means of high resolution Transmission Electron Microscopy (TEM), showing an increasing grain size up to about 9 nm. The average structure presented variations in the inversion degree and an increase in grain size. TEM observations demonstrated that the small crystals are well crystallised: the high resolution images neatly showed the atomic planes, even in the smallest particles. However, the average structure did not properly fit the PDF data in the local region, owing to a slightly different coordination among the octahedra. A new structural model is proposed for the local region of the PDF, that helped our understanding of the differences between a real nanostructured sample and that of a microcrystalline one. The oxygen disorder, due to the inversion grade of the spinel, is demonstrates to be at the basis of the local deviation. No signals of interstitial Zn atoms were detected.

Coccolithophores are phytoplanktonic algae which produce an exoskeleton made of single platelets of calcite named coccoliths. They are widespread in all oceans and directly impact the short- and long-term C cycle. The study of coccolith size, morphology and elemental composition reveals important information regarding the ability of the cell to calcify and on the factors that influence this process. In this regard, very little is known about coccolith composition and its changes under altered environmental conditions. Here, we present high resolution (50 × 50 nm) elemental spatial distribution in pristine coccoliths of Coccolithus pelagicus and Gephyrocapsa oceanica reconstructed via X-ray fluorescence analyses at synchrotron. The studied specimens are from control culture and metal-enriched (V, Ni, Zn and Pb) experiments. The analysed specimens produced under stress conditions, display an irregular shape and are thinner, especially in the external rim, with ca. 1/3 lower Ca concentrations compared to specimens from the control. The same specimens also have higher Sr/Ca ratio with highest values in the coccolith external rim, suggesting that difficulty in calcification is additionally reflected in increased Sr/Ca ratios. Selenium is found in the coccolith as possible substitute of carbonate in the calcite. V and Pb apparently did not interact with the coccoliths while Zn and Ni were deposited on the coccolith surface.

The amazing properties of ferroelectric perovskite BaTiO3 (BT) and its solid solutions make them indispensable for many technological applications (e.g. multilayer capacitors). Unfortunately, the so-called `size effect' limits their use. Indeed, under a certain critical particle size, these materials show a suppression of the spontaneous polarization and thus of the ferroelectric properties. In pure nanometric BaTiO3, this is related to a certain local structural disorder. However, only a few studies have explored BT solid solutions, where the doping effect, coupled to the reduced particle size, can play an important role. Therefore, in this work, the structure of BaCexTi1-xO3 (x = 0.02-0.20) was explored by traditional Rietveld method and Pair Distribution Function. Samples present a particle size from 80-160 nm to 400-1000 nm depending on increasing x. The carbox approach was applied, investigating the evolution of the local structure, its modifications and the structural coherent correlation length, as a function of cerium amount. Results demonstrate a cooperative effect of composition and reduced size in the ferroelectricity loss. The two, in fact, contribute to intensify the local structural disorder, decreasing the structural coherent correlation length. The local structural disorder is thus confirmed to be a relevant factor in the ferroelectric properties degradation.

Macroscopic properties measurements, such as dielectric permittivity and ferroelectric hysteresis, differential scanning calorimetry, and average structure information are combined with complementary techniques sensitive to the local structure, i.e. Pair Distribution Function (PDF) and Raman spectroscopy, to gain comprehensive insight into the structure-property relationships and origin of relaxor behaviour in BaCexTi1-xO3 ceramics over a broad composition (x = 0.02-030) and temperature (100-450 K) range. The resulting phase diagram displays sequential phase transitions with a tricritical point (TCP) at x approximate to 0,09 and a ferroelectric to relaxor crossover (FRC) at x >= 0.20. In contrast, the local structure is rhombohedral irrespective of x and the PDF reveals the existence of a high level of disorder and significant local strains determined by the ionic size mismatch (Ce4+: 0.87 angstrom, Ti4+: 0.605 angstrom). The diffuse character of the phase transitions observed when x >= 0.05 is most likely originated by these deformations. Parallel of BaCexTi1-xO3 phase diagrams (M = Sn, Hf, Zr, Ce) shows that the compositions corresponding to TCP and FRC are nearly independent of M. This suggests that, irrespective of the ionic radius of M4+, in homovalentsubstituted BaTiO3 a critical number of Ti-O-Ti bonds has to be broken before a new "state" is established, whereas local electric and strain fields seem to have a marginal effect. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ceramics with perovskite structure and composition BaCe x Ti1−x O3 (x = 0.02–0.30) show a progressive evolution with increasing x, from the long-range polar order of ferroelectric BaTiO3 to the short-range polar order typical of relaxors. The ionic size mismatch between Ti4+ and Ce4+ determines strong local strains which have a significant impact on dielectric properties and phase transitions. The pair distribution function, coupled with transmission electron microscopy analysis, was applied to study the local structure. Because of the inner B-cation sizes, the superposition of rigid B—O octahedra with different volumes is not compatible with the construction of an ideal perovskite structure. In this light, local structure can be described by an original model which allows (i) different Ti—O and Ce—O distances and (ii) the typical distortions of the two end members: off-center displacement of Ti occurring in BaTiO3 and octahedral tilt in BaCeO3. The results show a clear difference, in terms of volumes, between oxygen octahedra with titanium and those related to cerium. In addition, the inclusion of cerium causes a tilt of its oxygen cage, as occurs in pure BaCeO3, creating contra-rotations and distortions of the octahedra containing titanium. This complex arrangement entails a substantial distortion, increasing as a function of cerium amount, which strongly influences the directions of titanium displacements, their local correlation and consequently their long-range cooperative effects.

Tricalcium silicate, the main constituent of Portland cement, hydrates to produce crystalline calcium hydroxide and calcium-silicate-hydrates (C-S-H) nanocrystalline gel. This hydration reaction is poorly understood at the nanoscale. The understanding of atomic arrangement in nanocrystalline phases is intrinsically complicated and this challenge is exacerbated by the presence of additional crystalline phase(s). Here, we use calorimetry and synchrotron X-ray powder diffraction to quantitatively follow tricalcium silicate hydration process: i) its dissolution, ii) portlandite crystallization and iii) C-S-H gel precipitation. Chiefly, synchrotron pair distribution function (PDF) allows to identify a defective clinotobermorite, Ca11Si9O28(OH)2.8.5H2O, as the nanocrystalline component of C-S-H. Furthermore, PDF analysis also indicates that C-S-H gel contains monolayer calcium hydroxide which is stretched as recently predicted by first principles calculations. These outcomes, plus additional laboratory characterization, yielded a multiscale picture for C-S-H nanocomposite gel which explains the observed densities and Ca/Si atomic ratios at the nano- and meso- scales.

The temperature dependent behaviour of a complex aluminosilicate glass (SiO2-Al2O3-ZnO-Na2O system), which is a reference for ceramic glaze technology, has been determined, by combining techniques that cover a scale ranging from atomistic to macroscopic. The system shows a linear thermal expansion up to about 600 °C. The glass transition temperature is at 620 °C, as observed from Differential Scanning Calorimetry. Ex situ synchrotron diffraction experiments found a further transformation consisting of albite crystallization above 810 °C. This reaction is very slow and induces permanent structural modifications in the material at both intermediate and short ranges, as shown by in situ synchrotron diffraction experiments. These observations explain why ceramic glaze technology still faces challenges for large scale manufacturing and show the critical thermal range where interventions should be focussed. Eventually, melting takes place at 1190 °C, from hot stage microscopy.

The role of KOH and NaOH as mineralisers in kaolinite-quartz (KQ) and kaolinite-quartz-feldspar (KQF) systems has been investigated, in order to determine how they affect the phase composition of ceramic bodies, and if they can replace traditional flux to boost formation of amorphous phases. Attention was paid to the effects induced by mineralisers on (i) the fundamental ceramic equilibrium reaction between crystal phases and amorphous phase, and (ii) on the morphology of the final ceramic product in terms of secondary mullite habit. NaOH and KOH turn out to be amorphous content boosters, but their efficiency to promote amorphous phases is related to quartz particle size, too. The amorphous component appears at the expenses of mullite and quartz, and an analysis of the formation Gibbs energy demonstrates that an increase in mineraliser content shifts the fundamental ceramic equilibrium reaction towards amorphous formation, though Na differs from K in affecting such transformation.