Phase refinement through density modification

Biophysical Structural Chemistr

Grazing incidence synchrotron X-ray diffraction of marbles consolidated with diammonium hydrogen phosphate treatments : non-destructive probing of buried minerals

Diammonium hydrogen phosphate (DAP)-based consolidating treatments react with carbonatic stones and form calcium phosphates phases, whose composition depends on the availability of free calcium ions. In this work, an innovative non-destructive approach based on grazing incidence X-ray diffraction (GIXRD) with synchrotron radiation (SR) is used to investigate DAP-treated Carrara marble specimens and to study the influence of the substrate composition on the crystallization of calcium phosphate phases. The outcomes indicate that the presence of compositional micro-heterogeneity of Carrara marble favours the formation of specific phases. Dicalcium phosphate dihydrate, a calcium phosphate with a low Ca/P molar ratio, is formed on carbonatic phases with a low Ca amount, such as dolomite grains and Mg-containing veins. Furthermore, this study highlights the potentialities of SR-GIXRD as a powerful non-destructive tool for the diagnostic of Cultural Heritage objects since it allows investigating the conservation history of stone materials and their interaction with the environment

Crystal structure of an empty capsid of turnip yellow mosaic virus

Biophysical Structural Chemistr

What’s underneath? : A non-destructive depth profile of painted stratigraphies by synchrotron grazing incidence X-ray diffraction

Many works of art are complex systems consisting of a core finished by the overlapping of several painted layers. In this work, we apply an innovative method based on grazing incidence X-ray diffraction (GIXRD) with synchrotron radiation (SR) to investigate polychrome stratigraphies with a completely non-destructive approach. The SR-GIXRD measurements provided direct and unambiguous compositional and stratigraphic information of the crystalline species lying in different layers. The investigations performed on a small fragment sampled from a painted terracotta statue allowed identifying pigments, fillers, aggregates of the matrix and newly formed decay salts in micrometric-thin paint layers. Furthermore, the great potentiality of this study is the feasibility of depth profile investigations on multi-layered painted samples from Cultural Heritage objects without resorting to cross sectional analyses. Currently, the method is non-destructive but it can be potentially non-invasive in situations where small moveable artworks can be placed into the measurement chamber of the SR-XRD beamlines. The overall study paves the way to a new scenario of artwork investigations, shading light on new unexplored approaches for non-destructive studies of Cultural Heritage objects, their conservation history and their interaction with the environment

Crystal structure, electronic, and magnetic properties of the bilayered rhodium oxide Sr3Rh2O7

The bilayered rhodium oxide Sr3Rh2O7 was synthesized by high-pressure and high-temperature heating techniques. The single-phase polycrystalline sample of Sr3Rh2O7 was characterized by measurements of magnetic susceptibility, electrical resistivity, specific heat, and thermopower. The structural characteristics were investigated by powder neutron diffraction study. The rhodium oxide Sr3Rh2O7 [Bbcb, a = 5.4744(8) A, b = 5.4716(9) A, c = 20.875(2) A] is isostructural to the metamagnetic metal Sr3Ru2O7, with five 4d electrons per Rh, which is electronically equivalent to the hypothetic bilayered ruthenium oxide, where one electron per Ru is doped into the Ru-327 unit. The present data show the rhodium oxide Sr3Rh2O7 to be metallic with enhanced paramagnetism, similar to Sr3Ru2O7. However, neither manifest contributions from spin fluctuations nor any traces of a metamagnetic transition were found within the studied range from 2 K to 390 K below 70 kOe.Comment: To be published in PR

Candidate carbonate phases in the Earth

With the current state of art of experimental facilities, we conducted studies on carbonates at the variable pressures and temperatures existing from the Earth\u2019s crust to the mantle/core region conditions. The quality of the diffraction data (single crystal and powder) allow full structural analysis for all the phases encountered. We present an updated overview of all the possible candidate carbonate phases in the inner Earth, based on model carbonate system and on most-likely composition in the ternary diagram CaCO3-MgCO3-FeCO3. The model BaCO3 studied at high temperatures and high pressures present the sequence of transition from aragonite-type phase to disorder-calcite phase and finally NaCl structure. At high pressure, the aragonitetype transform into the post-aragonite above 8 GPa. A similar scenario is observed in CaCO3, but new highpressure polymorphs denser than aragonite are present above 15 GPa. Dolomite, previously considered unstable at mantle conditions, is demonstrated to be stable above 30 GPa at the high pressures and temperatures existing in the Earth\u2019s interior up to the mantle/core boundary. It transforms to dense polymorphs based on distorted calcite-type structure at intermediate pressures, and, above the Mbar, transforms into new polymorphs featuring ring-carbonate C3O9 groups. This structure is likely the candidate phase for carbon storage in a carbonate in the Earth\u2019s mantle, and may form complete solid solution with CaCO3 and MgCO3. Fe-magnesite, stabilized at high pressures and temperatures, undergoes complex redox reactions, with the formation of Fe3+ bearing carbonates with stoichiometry different from ABO3

Beyond the oxygen redox strategy in designing cathode material for batteries: Dynamics of a prussian blue-like cathode revealed by operando X-ray diffraction and X-ray absorption fine structure and by a theoretical approach

The dynamics of the lithiation/delithiation process and the nitrosyl electroactivity in copper nitroprusside were studied by operando X-ray diffraction and operando X-ray absorption fine structure (XAFS). Data were interpreted based on a joint study performed by means of density functional theory calculations. This approach allows the relevant structural and electronic information to be retrieved from the measured scattering and absorption data and therefore the lithiation mechanism in copper nitroprusside to be untangled, which occurs with the reduction of both metals generating a lattice basal plane contraction and an axial elongation. An increase in the Debye-Waller factors for Cu-N bonds and a decreasing trend for the Cu-NC-Fe linear chains along with lithium insertion reveal a general increase in the Cu local disorder, which is thought to be the main cause of the rapid capacity fading observed during cycling. The ligand electroactivity of the nitrogen atom, detected by following vibrational frequencies, delivers an extra capacity and represents an alternative path to cationic and oxygen redox