Probing the Long- and Short-Range Structural Chemistry in the C-Type Bixbyite Oxides ThNdCeO, ThNdCeO, and ThNdCeO via Synchrotron X-ray Diffraction and Absorption Spectroscopy.

The long- and short-range structural chemistry of the C-type bixbyite compounds ThNdCeO, ThNdCeO, and ThNdCeO is systematically examined using synchrotron X-ray powder diffraction (S-PXRD), high-energy resolution fluorescence detection X-ray absorption near edge (HERFD-XANES), and extended X-ray absorption fine structure spectroscopy (EXAFS) measurements supported by electronic structure calculations. S-PXRD measurements revealed that the title compounds all form classical C-type bixbyite structures in space group 3̅ that have disordered cationic crystallographic sites with further observation of characteristic superlattice reflections corresponding to oxygen vacancies. Despite the occurrence of oxygen vacancies, HERFD-XANES measurements on the Ce L-edge revealed that Ce incorporates as Ce into the structures but involves local distortion that resembles cluster behavior and loss of nearest-neighbors.

Grazing-incidence synchrotron radiation diffraction studies on irradiated Ce-doped and pristine Y-stabilized ZrO at the Rossendorf beamline.

In this work, Ce-doped yttria-stabilized zirconia (YSZ) and pure YSZ phases were subjected to irradiation with 14 MeV Au ions. Irradiation studies were performed to simulate long-term structural and microstructural damage due to self-irradiation in YSZ phases hosting alpha-active radioactive species. It was found that both the Ce-doped YSZ and the YSZ phases had a reasonable tolerance to irradiation at high ion fluences and the bulk crystallinity was well preserved.

Synthesis of Single Crystals of ε-Iron and Direct Measurements of Its Elastic Constants.

Seismology finds that Earth's solid inner core behaves anisotropically. Interpretation of this requires a knowledge of crystalline elastic anisotropy of its constituents-the major phase being most likely ε-Fe, stable only under high pressure. Here, single crystals of this phase are synthesized, and its full elasticity tensor is measured between 15 and 33 GPa at 300 K.

Deconvoluting Cr states in Cr-doped UO nuclear fuels via bulk and single crystal spectroscopic studies.

Cr-doped UO is a leading accident tolerant nuclear fuel where the complexity of Cr chemical states in the bulk material has prevented acquisition of an unequivocal understanding of the redox chemistry and mechanism for incorporation of Cr in the UO matrix. To resolve this, we have used electron paramagnetic resonance, high energy resolution fluorescence detection X-ray absorption near energy structure and extended X-ray absorption fine structure spectroscopic measurements to examine Cr-doped UO single crystal grains and bulk material. Ambient condition measurements of the single crystal grains, which have been mechanically extracted from bulk material, indicated Cr is incorporated substitutionally for U in the fluorite lattice as Cr with formation of additional oxygen vacancies.

High-Pressure and High-Temperature Chemistry of Phosphorus and Nitrogen: Synthesis and Characterization of α- and γ-PN.

The direct chemical reactivity between phosphorus and nitrogen was induced under high-pressure and high-temperature conditions (9.1 GPa and 2000-2500 K), generated by a laser-heated diamond anvil cell and studied by synchrotron X-ray diffraction, Raman spectroscopy, and DFT calculations. α-PN and γ-PN were identified as reaction products.

Single-Bonded Cubic AsN from High-Pressure and High-Temperature Chemical Reactivity of Arsenic and Nitrogen.

Chemical reactivity between As and N , leading to the synthesis of crystalline arsenic nitride, is here reported under high pressure and high temperature conditions generated by laser heating in a diamond anvil cell. Single-crystal synchrotron X-ray diffraction at different pressures between 30 and 40 GPa provides evidence for the synthesis of a covalent compound of AsN stoichiometry, crystallizing in a cubic P2 3 space group, in which each of the two elements is single-bonded to three atoms of the other and hosts an electron lone pair, in a tetrahedral anisotropic coordination. The identification of characteristic structural motifs highlights the key role played by the directional repulsive interactions between non-bonding electron lone pairs in the formation of the AsN structure.

Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO_{2}.

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe_{2}O_{3} and the appearance of FeO_{2}. Here, based on the results of in situ single-crystal x-ray diffraction, Mössbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory+dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO_{2} and isostructural FeO_{2}H_{0.5} is ferric (Fe^{3+}), and oxygen has a formal valence less than 2.

Pressure-induced symmetry lowering in NbSnsuperconductor.

Cubic-3NbSnsuperconductor (∼ 16 K) was found to exhibit tetragonal instabilities at the superconducting state (= 10 K). These instabilities are manifested through the appearance of reflections which are forbidden in the-3symmetry but are compatible with the4/structure which is observed in the NbSnsystem for higher Sn content at temperatures lower than ∼43 K. Nevertheless, the low-temperature structure of NbSnremains metrically fully cubic, as concluded from single crystal synchrotron radiation diffraction experiments.

Crystal Structure and Non-Hydrostatic Stress-Induced Phase Transition of Urotropine Under High Pressure.

High-pressure behavior of hexamethylenetetramine (urotropine) was studied in situ using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier-transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure-transmitting media to study the effect of deviatoric stress on phase transformations. Up to 4 GPa significant damping of molecular librations and atomic thermal motion was observed.

Incommensurate crystal structure of PbHfO.

Controversy in the description/identification of so-called intermediate phase(s) in PbHfO, stable in the range ∼420-480 K, has existed for a few decades. A synchrotron diffraction experiment on a partially detwinned crystal allowed the structure to be solved in the superspace group Imma(00γ)s00 (No. 74.

Anisotropic thermal expansion of black phosphorus from nanoscale dynamics of phosphorene layers.

Black phosphorus (bP) is a crystalline material which can be seen as an ordered stacking of two-dimensional layers, referred to as phosphorene. The knowledge of the linear thermal expansion coefficients (LTECs) of bP is of great interest in the field of 2D materials for a better understanding of the anisotropic thermal properties and exfoliation mechanism of this material. Despite several theoretical and experimental studies, important uncertainties remain in the determination of the LTECs of bP.

High Pressure Investigation of the S-N System up to the Megabar Range: Synthesis and Characterization of the SN Solid.

Sulfur and nitrogen represent one of the most studied inorganic binary systems at ambient pressure on account of their large wealth of metastable exotic ring-like compounds. Under high pressure conditions, however, their behavior is unknown. Here, sulfur and nitrogen were compressed in a diamond anvil cell up to about 120 GPa and laser-heated at regular pressure intervals in an attempt to stabilize novel sulfur-nitrogen compounds.

Pressure-induced transformation of CHNHPbI: the role of the noble-gas pressure transmitting media.

The photovoltaic perovskite, methylammonium lead triiodide [CHNHPbI (MAPbI)], is one of the most efficient materials for solar energy conversion. Various kinds of chemical and physical modifications have been applied to MAPbI towards better understanding of the relation between composition, structure, electronic properties and energy conversion efficiency of this material. Pressure is a particularly useful tool, as it can substantially reduce the interatomic spacing in this relatively soft material and cause significant modifications to the electronic structure.

High-pressure polymorphism of BaFeSe.

BaFeSe is a potential superconductor material exhibiting transition at 11 K and ambient pressure. Here we extended the structural and performed electrical resistivity measurements on this compound up to 51 GPa and 20 GPa, respectively, in order to distinguish if the superconductivity in this sample is intrinsic to the BaFeSe phase or if it is originating from minor FeSe impurities that show a similar superconductive transition temperature. The electrical resistance measurements as a function of pressure show that at 5 GPa the superconducting transition is observed at around 10 K, similar to the one previously observed for this sample at ambient pressure.

The High-Pressure Oxide Tb O and its Non-Centrosymmetric Low-Temperature Polymorph-A Comprehensive Study.

In this article, the first thoroughly characterized mixed-valent binary rare earth oxide synthesized under high-pressure/high-temperature conditions, and its low-temperature polymorph are reported. Crystalline HT-HP-Tb O has been prepared from an equimolar mixture of Tb O and Tb O under reaction conditions of 8 GPa and 1323 K. Single-crystal X-ray structure determination showed that HT-HP-Tb O crystallizes in the orthorhombic space group Pnma, isopointal to the β-Yb Sb -type structure.

The updated Zn-Sb phase diagram. How to make pure ZnSb ("ZnSb").

The Zn-Sb system contains two well-known thermoelectric materials, Zn1-δSb and Zn13-δSb10 ("Zn4Sb3"), and two other phases, Zn9-δSb7 and Zn3-δSb2, stable only at high temperatures. The current work presents the updated phases diagram constructed using the high-temperature diffraction studies and elemental analysis. All phases are slightly Zn deficient with respect to their stoichiometric compositions, which is consistent with their p-type charge transport properties.

Pressure-induced chemical reactions in the N(H) compound: from the N and H species to ammonia and back down into hydrazine.

Theory predicts a very rich high pressure chemistry of hydronitrogens with the existence of many NH compounds. The stability of these phases under pressure is being investigated by the compression of N-H mixtures of various compositions. A previous study had disclosed a eutectic-type N-H phase diagram with two stoichiometric van der Waals compounds: (N)(H) and N(H).

Structural stability and mechanism of compression of stoichiometric BC up to 68GPa.

Boron carbide is a ceramic material with unique properties widely used in numerous, including armor, applications. Its mechanical properties, mechanism of compression, and limits of stability are of both scientific and practical value. Here, we report the behavior of the stoichiometric boron carbide BC studied on single crystals up to 68 GPa.

Stability of iron-bearing carbonates in the deep Earth's interior.

The presence of carbonates in inclusions in diamonds coming from depths exceeding 670 km are obvious evidence that carbonates exist in the Earth's lower mantle. However, their range of stability, crystal structures and the thermodynamic conditions of the decarbonation processes remain poorly constrained. Here we investigate the behaviour of pure iron carbonate at pressures over 100 GPa and temperatures over 2,500 K using single-crystal X-ray diffraction and Mössbauer spectroscopy in laser-heated diamond anvil cells.

Synthetic Approach for (Mn,Fe)(Si,P) Magnetocaloric Materials: Purity, Structural, Magnetic, and Magnetocaloric Properties.

A conventional solid-state approach has been developed for the synthesis of phase-pure magnetocaloric MnFeSiP materials (x = 0.6, 0.7, 0.

Stability of Fe,Al-bearing bridgmanite in the lower mantle and synthesis of pure Fe-bridgmanite.

The physical and chemical properties of Earth's mantle, as well as its dynamics and evolution, heavily depend on the phase composition of the region. On the basis of experiments in laser-heated diamond anvil cells, we demonstrate that Fe,Al-bearing bridgmanite (magnesium silicate perovskite) is stable to pressures over 120 GPa and temperatures above 3000 K. Ferric iron stabilizes Fe-rich bridgmanite such that we were able to synthesize pure iron bridgmanite at pressures between ~45 and 110 GPa.

Superconductivity in alkali metal intercalated iron selenides.

Alkali metal intercalated iron selenide superconductors A x Fe2-y Se2 (where A  =  K, Rb, Cs, Tl/K, and Tl/Rb) are characterized by several unique properties, which were not revealed in other superconducting materials. The compounds crystallize in overall simple layered structure with FeSe layers intercalated with alkali metal. The structure turned out to be pretty complex as the existing Fe-vacancies order below ~550 K, which further leads to an antiferromagnetic ordering with Néel temperature fairly above room temperature.

Temperature- and Pressure-Induced Spin Crossover in Co1+xCr2-xSe4 (x = 0.24): A Diffraction Study.

The Co(2+) ions of the Co1+xCr2-xSe4 phase (Co1.24Cr1.76Se4 composition with x = 0.

Identification, structural characterization and transformations of the high-temperature Zn9-δSb7 phase in the Zn-Sb system.

The Zn9-δSb7 phase has been identified via high-temperature powder diffraction studies. Zn9-δSb7 adopts two modifications: an α form stable between 514 °C and 539 °C and a Zn-poorer β form stable from 539 °C till its melting temperature of 581 °C. The Zn9-δSb7 structure was solved from the powder data using the simulated annealing approach.