High-Pressure Bulk Synthesis of InN by Solid-State Reaction of Binary Oxide in a Multi-Anvil Apparatus.

We present a new method to synthesize bulk indium nitride by means of a simple solid-state chemical reaction carried out under hydrostatic high-pressure/high-temperature conditions in a multi-anvil apparatus, not involving gases or solvents during the process. The reaction occurs between the binary oxide InO and the highly reactive LiN as the nitrogen source, in the powder form. The formation of the hexagonal phase of InN, occurring at 350 °C and ≥ 3 GPa, was successfully confirmed by powder X-ray diffraction, with the presence of LiO as a unique byproduct.

γ-BaFeO: a fresh playground for room temperature multiferroicity.

Multiferroics, showing the coexistence of two or more ferroic orderings at room temperature, could harness a revolution in multifunctional devices. However, most of the multiferroic compounds known to date are not magnetically and electrically ordered at ambient conditions, so the discovery of new materials is pivotal to allow the development of the field. In this work, we show that BaFeO is a previously unrecognized room temperature multiferroic.

Exploring Cu-Doping for Performance Improvement in SbSe Photovoltaic Solar Cells.

Copper-doped antimony selenide (Cu-doped SbSe) thin films were deposited as absorber layers in photovoltaic solar cells using the low-temperature pulsed electron deposition (LT-PED) technique, starting from SbSe targets where part of the Sb was replaced with Cu. From a crystalline point of view, the best results were achieved for thin films with about SbCuSe composition. In order to compare the results with those previously obtained on undoped thin films, Cu-doped SbSe films were deposited both on Mo- and Fluorine-doped Tin Oxide (FTO) substrates, which have different influences on the film crystallization and grain orientation.

Nonadiabatic coupling of the dynamical structure to the superconductivity in YSrCuMoO and SrCuO.

A crucial issue in cuprates is the extent and mechanism of the coupling of the lattice to the electrons and the superconductivity. Here we report Cu K edge extended X-ray absorption fine structure measurements elucidating the internal quantum tunneling polaron (iqtp) component of the dynamical structure in two heavily overdoped superconducting cuprate compounds, tetragonal YSrCuMoO with superconducting critical temperature, T = 84 K and hole density = 0.3 to 0.

Metastable (CuAu-type) CuInS Phase: High-Pressure Synthesis and Structure Determination.

We report on the high-pressure solid-state synthesis and the detailed structural characterization of the metastable, CuAu-type CuInS (CA-CIS) phase. Although often present in CIS thin films as unwanted phase, it has been never synthesized in pure form, and its effect on the performance of CIS-based solar cells has been long debated. In this work, pure CA-CIS phase is synthesized in bulk polycrystalline form through a high-pressure-high-temperature solid-state reaction.

Phase Transitions in the Metastable Perovskite Multiferroics BiCrO and BiCrScO: A Comparative Study.

The temperature behavior of the crystal structure as well as dielectric and magnetic properties of the perovskite bismuth chromate ceramics with the 10 mol % Cr-to-Sc substitution were studied and compared with those of the unmodified compound. Using a high-pressure synthesis, BiCrO and BiCrScO were obtained as metastable perovskite phases which are monoclinic 2/ with the √6 × √2 × √6 superstructure (where is the primitive perovskite unit-cell parameter) under ambient conditions. At room temperature, the unit cell volume of BiCrScO is ∼1.

Local lattice distortions and dynamics in extremely overdoped superconducting YSrCuMoO.

A common characteristic of many "overdoped" cuprates prepared with high-pressure oxygen is values ≥ 50 K that often exceed that of optimally doped parent compounds, despite O stoichiometries that place the materials at the edge or outside of the conventional boundary between superconducting and normal Fermi liquid states. X-ray absorption fine-structure (XAFS) measurements at 52 K on samples of high-pressure oxygen (HPO) YSrCuMoO, = 84 K show that the Mo is in the (VI) valence in an unusually undistorted octahedral geometry with predominantly Mo neighbors that is consistent with its assigned substitution for Cu in the chain sites of the structure. Perturbations of the Cu environments are minimal, although the Cu X-ray absorption near-edge structure (XANES) differs from that in other cuprates.

Centrosymmetry Breaking and Ferroelectricity Driven by Short-Range Magnetic Order in the Quadruple Perovskite (YMn)MnO.

By means of single-crystal X-ray diffraction, we give direct crystallographic evidence of a centrosymmetry breaking below = 200 K, concomitant with the onset of a commensurate structural modulation in the quadruple perovskite YMnMnO. This result, which explains the anomalously large thermal coefficient of the Y ion in previously reported structural models, is attributed to the small size of the Y ion, which causes its underbonding within the dodecahedral coordination polyhedron. The present data are consistent with a commensurate superstructure described by an I-centered pseudo-orthorhombic cell with polar symmetry and ≈ √2 = 10.

A comprehensive study of the magnetic properties of the pyroxenes series CaMgSiO-CoSiO as a function of Co content.

We report a detailed study on the magnetic properties of the pyroxene series M2M1SiO, with M2  =  Ca and M1  =  Mg, where magnesium and then calcium are progressively substituted by cobalt. For cobalt site occupancy larger than 0.7 at the M1 site, a collinear antiferromagnetic phase is detected for T  <  T   =  12 K with a monodimensional character (i.

Poling-Written Ferroelectricity in Bulk Multiferroic Double-Perovskite BiFe0.5Mn0.5O3.

We present a comprehensive study of the electrical properties of bulk polycrystalline BiFe0.5Mn0.5O3, a double perovskite synthesized in high-pressure and high-temperature conditions.

Field effects on spontaneous magnetization reversal of bulk BiFe0.5Mn0.5O3, an effective strategy for the study of magnetic disordered systems.

We report a comprehensive study of the spontaneous magnetization reversal (MRV) performed on the disordered polycrystalline perovskite BiFe(0.5)Mn(0.5)O(3), an intriguing compound synthesized in high pressure-high temperature conditions.

High pressure and multiferroics materials: a happy marriage.

The community of material scientists is strongly committed to the research area of multiferroic materials, both for the understanding of the complex mechanisms supporting the multiferroism and for the fabrication of new compounds, potentially suitable for technological applications. The use of high pressure is a powerful tool in synthesizing new multiferroic, in particular magneto-electric phases, where the pressure stabilization of otherwise unstable perovskite-based structural distortions may lead to promising novel metastable compounds. The in situ investigation of the high-pressure behavior of multiferroic materials has provided insight into the complex interplay between magnetic and electronic properties and the coupling to structural instabilities.

Structural evolution under pressure of BiMnO3.

The structural behavior of BiMnO3 under pressure was studied in a quantitative way by single-crystal synchrotron X-ray diffraction up to 36 GPa. Two phase transitions were observed at moderate pressures (1 and 6 GPa, respectively), leading the system at first to the P21/c and then to the Pnma symmetry. The breaking of C-centering in the first transition does not affect significantly Jahn-Teller (JT) distortion and orbital order (OO) but determines a significant change in the cooperative tilting of the MnO6 octahedra.

Influence of packing on low energy vibrations of densified glasses.

A comparative study of Raman scattering and low temperature specific heat capacity has been performed on samples of B2O3, which have been high-pressure quenched to go through different glassy phases having growing density to the crystalline state. It has revealed that the excess volume characterizing the glassy networks favors the formation of specific glassy structural units, the boroxol rings, which produce the boson peak, a broad band of low energy vibrational states. The decrease of boroxol rings with increasing pressure of synthesis is associated with the progressive depression of the excess low energy vibrations until their full disappearance in the crystalline phase, where the rings are missing.

Using high pressure to prepare polymorphs of the Ba2Co(1-x)Zn(x)S3 (0 ≤ x ≤ 1.0) compounds.

In this work, high pressure was used as a tool to induce structural transition and prepare metastable polymorphs of ternary sulfides. Structural transformations under high pressure of compounds belonging to the Ba(2)Co(1-x)Zn(x)S(3) (0 ≤ x ≤ 1.0) series were studied using X-ray diffraction and electron microscopy.