Andrea Lausi

High temperature structural study of Gd-doped ceria by synchrotron X-ray diffraction (673 K ≤ T ≤ 1073 K).

The crystallographic features of Gd-doped ceria were investigated at the operating temperature of solid oxides fuel cells, where these materials are used as solid electrolytes. (Ce(1-x)Gd(x))O(2-x/2) samples (x = 0.1, 0.3, 0.5, 0.7) were prepared by coprecipitation of mixed oxalates, treated at 1473 K in air, and analyzed by synchrotron X-ray diffraction in the temperature range 673 K ≤ T ≤ 1073 K at the Elettra synchrotron radiation facility located in Trieste, Italy. In the whole temperature span a boundary was found at x ∼ 0.2 between a CeO2-based solid solution (for x ≤ 0.2) and a structure where Gd2O3 microdomains grow within the CeO2 matrix, taking advantage of the similarity between Gd(3+) and Ce(4+) sizes; the existence of the boundary at x ∼ 0.2 was confirmed also by measurements of ionic conductivity performed by impedance spectroscopy. Similar to what observed at room temperature, the trend of the cell parameter shows the presence of a maximum; with increasing temperature, the composition corresponding to the maximum moves toward lower Gd content. This evidence can be explained by analyzing the behavior of the coefficient of thermal expansion as a function of composition.

In situ reaction furnace for real-time XRD studies.

The new furnace at the Materials Characterization by X-ray Diffraction beamline at Elettra has been designed for powder diffraction measurements at high temperature (up to 1373 K at the present state). Around the measurement region the geometry of the radiative heating element assures a negligible temperature gradient along the capillary and can accommodate either powder samples in capillary or small flat samples. A double capillary holder allows flow-through of gas in the inner sample capillary while the outer one serves as the reaction chamber. The furnace is coupled to a translating curved imaging-plate detector, allowing the collection of diffraction patterns up to 2θ ≃ 130°.

High-pressure compressibility and thermal expansion of aragonite

Abstract The structure and isothermal equation of state of aragonite were determined to 40 GPa using synchrotron single-crystal X ray techniques. In addition, powder diffraction techniques were used to determine thermal expansion between 298–673 K. At room temperature, aragonite has orthorhombic Pnma structure to 40 GPa, with an isothermal bulk modulus of 66.5(7) GPa and K′ = 5.0(1). Between 25–30 GPa the aragonite unit cell begins to distort due to a stiffening of the c-axis compressibility, which is controlled by the orientation and distortion of the carbonate groups. The ambient pressure thermal expansion measurements yielded thermal expansion coefficients a0 = 4.9(2) × 10–5 and a1 = 3.7(5) × 10–8. The combined results allow the derivation of a thermal equation of state. The new data provide constraints on the behavior of carbonates and carbon cycling in the Earth’s crust and mantle.

High-temperature and high-pressure behavior of carbonates in the ternary diagram CaCO3-MgCO3-FeCO3

Abstract We report the thermal expansion and the compressibility of carbonates in the ternary compositional diagram CaCO3-MgCO3-FeCO3, determined by in situ X-ray powder and single-crystal diffraction. High-temperature experiments were performed by high-resolution X-ray synchrotron powder diffraction from ambient to decarbonation temperatures (25–850 °C). Single-crystal synchrotron X ray diffraction experiments were performed in a variable pressure range (0–100 GPa), depending on the stability field of the rhombohedral structure at ambient temperature, which is a function of the carbonate composition. The thermal expansion increases from calcite, CaCO3, α0 = 4.10(7) ×10–5 K–1, to magnesite, MgCO3, α0 = 7.04(2) ×10–5 K–1. In the magnesite-siderite (FeCO3) join, the thermal expansion decreases as iron content increases, with an experimental value of α0 = 6.44(4) ×10–5 K–1 for siderite. The compressibility in the ternary join is higher (i.e., lower bulk modulus) in calcite and Mg-calcite [K0 = 77(3) GPa for Ca0.91Mg0.06Fe0.03(CO3)] than in magnesite, K0 = 113(1) GPa, and siderite, K0 = 125(1) GPa. The analysis of thermal expansion and compressibility variation in calcite-magnesite and calcite-iron-magnesite joins clearly shows that the structural changes associated to the order-disorder transitions [i.e., R3c calcite-type structure vs. R3 CaMg(CO3)2 dolomite-type structure] do not affect significantly the thermal expansion and compressibility of carbonate. On the contrary, the chemical compositions of carbonates play a major role on their thermo-elastic properties. Finally, we use our P-V-T equation of state data to calculate the unit-cell volume of a natural ternary carbonate, and we compare the calculated volumes to experimental observations, measured in situ at elevated pressure and temperatures, using a multi-anvil device. The experimental and calculated data are in good agreement demonstrating that the equation of state here reported can describe the volume behavior with the accuracy needed, for example, for a direct chemical estimation of carbonates based on experimental unit-cell volume data of carbonates at high pressures and temperatures.

Crystal structure of Na3Fe(SO4)3: A high-temperature product (~400 °C) of sideronatrite [Na2Fe(SO4)2OH·3H2O]

Abstract The iron sulfate Na3Fe(SO4)3 studied here has been obtained as a high-temperature (HT) product (-400 °C) from the thermal decomposition of sideronatrite from Sierra Gorda (Chile) having composition Na2Fe(SO4)2(OH)⋅3H2O. The structure determination was carried out using synchrotron X‑ray powder diffraction. Structural data refined by the Rietveld method, up to Rp = 11.95%, are: space group R3̅, lattice parameters a = b = 13.6231(1) Å and c = 9.0698(1) Å, V = 1457.76(2) Å3, and Z = 6. The structure of Na3Fe(SO4)3 can be described in terms of FeO6 octahedra connected to sulfate tetrahedra by corner-sharing to form infinite chains [Fe(SO4)3]∞, running along c. These chains are joined together by Na atoms to build up a three-dimensional network of strong (Fe-O-S) and weak (Na-O) bonds. The topological relationships of Na3Fe(SO4)3 to the structure of some analog minerals are also discussed.

Thin Film Stress and Texture Analysis at the MCX Synchrotron Radiation Beamline at ELETTRA

The main instrumental characteristics of MCX, the new beamline at the Italian synchrotron Elettra in Trieste, are presented. Design and geometrical set-up are well suited to the X-ray diffraction stress and texture analysis of thin films and surfaces, and are such to guarantee a full control of the main instrumental errors. Besides exploiting the typical features of synchrotron radiation, like high brilliance, tuneable beam energy and optimal beam geometry, MCX can also host tools for in-situ studies, like X-ray diffraction during four point bending. A few examples of current applications are shown.

MCX@Elettra: powder diffraction in ambient and non-ambient conditions

The beamline Material Characterization by X-ray diffraction (MCX), is the general purpose powder diffraction beamline at the Elettra synchrotron in Trieste, one of currently four diffraction beamlines at Elettra . The beamline is designed to host a wide range of experiments, that cover many scientific fields with standard applications such as phase identification, structure determination, residual stress measurements and line profile analysis. The experimental station houses a four circle Huber diffractometer. The two-theta arm can be equipped with a scintillator detector either with slits or with a Si 111 analyzer crystal. A multichannel analyzer is also available, which can be used to eliminate the background signal resulting from the fluorescence of the sample in a diffraction experiment, or can be used to perform chemical analysis on samples. Alternatively, a ccd detector can be installed on the arm, which is especially useful in the case of in operando studies on for example batteries, where changes in the diffraction pattern in a range of 2-theta can be followed instantaneously while the battery is operating. A hot air blower and a cryo stream are available to measure powder samples in capillaries from 100 to 1273 K. As a second experimental setup a furnace has been installed, which has been designed for powder diffraction measurements at high temperature (up to 1373 K at the present state). Around the measurement region the geometry of the radiative heating element assures a negligible temperature gradient along the capillary and can accommodate either powder samples in capillary or small flat samples. A double capillary holder allows a flow of gas in the inner sample capillary while the outer one serves as the reaction chamber. The furnace is coupled to a translating curved imaging-plate detector, allowing the collection of diffraction patterns up to 130 degrees two-theta in order to follow chemical reactions and phase transformations. Here the current status of the beamline will be presented illustrated by recent experiments using the different setups available at MCX. A room temperature and high temperature structural studies have been performed through the whole compositional range of the (Ce1–xMx)O2–x/2 for M = Sm, Gd and Lu revealing a complicated hybrid structural behavior. The relation between microstructure and thermoluminiscence of LiF2 has been investigated using both the funcace and the hot air blower. Finally, the phase diagram at high temperature Cu-TiS2 has been studied using the furnace in an inert atmosphere.

The Indo–Italian cooperation at the Elettra synchrotron radiation facility

Indian research groups have been collaborating with researchers at the Italian Synchrotron radiation source Elettra since past two decades. The collaboration between Elettra and Indian research institutions is a part of a wider collaboration between the countries sponsored by the Department of Science and Technology, Government of India and the Italian Ministry for Foreign Affairs. The high standard of the collaboration in the field of synchrotron radiation was recognized in the joint statement by the prime ministers of both the countries, on the occasion of Italian prime ministers visit to India in February 2007. Statistics till 2015 indicate that the collaboration has led few hundred visits of Indian groups to Elettra (with an average of three scientists per visit) in the last 20 years and to the publication of more than 500 articles in peer-reviewed scientific journals. Till 2016, Elettra received around 959 experimental proposals from Indian research groups, corresponding to about 8% of the total: in third place, just after Italy and France (4873 and 1034 proposals respectively). This makes Elettra the most requested European national synchrotron radiation laboratory by Indian users.

The high pressure diffraction beamline "XPRESS" at Elettra

Andrea Lausi1, Boby Joseph1, Paolo Lotti2, Maurizio Polentarutti1, Giorgio Bais1, Surinder M Sharma3, Dipankar Das Sarma4 1Xpress Beamline, Elettra Sincrotrone Trieste, Trieste, Italy, 2Dept Earth Scieneces, Milano, Italy, 3Physics group, Bhabha Atomic Research Center, Trombay,400085, Mumbai, India, Mumbai, India, 4Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India, Bengaluru, India E-mail: andrea.lausi@elettra.euDifferent possibilities of transformation of light or thermal to mechanical motion are widely discussed in recent literature. Solid-state chemical reactions which are mostly accompanied by generation and relaxation of mechanical stresses and strains are strongly related to this topic. Homogeneous and heterogeneous single-crystal to single-crystal chemical reactions are of special interest since they make it possible to follow structural strain by single-crystal X-ray diffraction and optical microscopy. Some of these reactions are accompanied by various photoand thermomechanical effects, including bending, twisting, curling, jumping of crystals. The structural mechanisms of photoand thermally induced chemical reactions in crystals are closely related to the anisotropy of mechanical properties, which can be followed particularly well by studying the crystal structure under high pressure or low temperatire.

Multi-energy anomalous diffuse scattering

A new approach to local structure determination is presented. A three-dimensional region of the reciprocal space of a SrTiO(3) single crystal was mapped by measuring x-ray diffuse scattering patterns at different sample orientations in order to reconstruct the local atomic structure. The phase problem was solved by means of anomalous scattering from strontium atoms at photon energies near their K absorption edge. Real-space reconstruction provides the average short-range order atomic arrangement in the vicinity of anomalous scatterers up to a distance of several unit cells.