High-Pressure Synthesis of the β-ZnN Nitride and the α-ZnN and β-ZnN Polynitrogen Compounds.

High-pressure nitrogen chemistry has expanded at a formidable rate over the past decade, unveiling the chemical richness of nitrogen. Here, the Zn-N system is investigated in laser-heated diamond anvil cells by synchrotron powder and single-crystal X-ray diffraction, revealing three hitherto unobserved nitrogen compounds: β-ZnN, α-ZnN, and β-ZnN, formed at 35.0, 63.

Polymorphs of the Gadolinite-Type Borates ZrB O and HfB O Under Extreme Pressure.

Based on the results from previous high-pressure experiments on the gadolinite-type mineral datolite, CaBSiO (OH), the behavior of the isostructural borates β-HfB O and β-ZrB O have been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction experiments. On compression to 120 GPa, both borate layer-structures are preserved. Additionally, at ≈114 GPa, the formation of a second phase can be observed in both compounds.

Face-Centered Cubic Refractory Alloys Prepared from Single-Source Precursors.

Three binary -structured alloys (-IrPt, -RhPt and -RhPd) were prepared from [Ir(NH)Cl][PtCl], [Ir(NH)Cl][PtBr], [Rh(NH)Cl][PtCl]Cl and [Rh(NH)Cl][PdCl]·HO, respectively, as single-source precursors. All alloys were prepared by thermal decomposition in gaseous hydrogen flow below 800 °C. -IrPt and -RhPd correspond to miscibility gaps on binary metallic phase diagrams and can be considered as metastable alloys.

Raman Spectroscopy Study on Chemical Transformations of Propane at High Temperatures and High Pressures.

This study is devoted to the detailed in situ Raman spectroscopy investigation of propane CH in laser-heated diamond anvil cells in the range of pressures from 3 to 22 GPa and temperatures from 900 to 3000 K. We show that propane, while being exposed to particular thermobaric conditions, could react, leading to the formation of hydrocarbons, both saturated and unsaturated as well as soot. Our results suggest that propane could be a precursor of heavy hydrocarbons and will produce more than just sooty material when subjected to extreme conditions.

A Room-Temperature Verwey-type Transition in Iron Oxide, Fe O.

Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next-generation nanoelectronic devices. To date, vanadium dioxide (VO ) is the only known simple transition-metal oxide that demonstrates a near-room-temperature metal-insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed-valent iron oxide with an unconventional Fe O stoichiometry.

High pressure phase transitions of paracelsian BaAlSiO.

Three new polymorphs of aluminosilicate paracelsian, BaAlSiO, have been discovered using synchrotron-based in situ high-pressure single crystal X-ray diffraction. The first isosymmetric phase transition (from paracelsian-I to paracelsian-II) occurs between 3 and 6 GPa. The phase transition is associated with the formation of pentacoordinated Al and Si ions, which occurs in a stepwise fashion by sequential formation of Al-O and Si-O bonds additional to those in AlO and SiO tetrahedra, respectively.

Pressure tuning of charge ordering in iron oxide.

A Verwey-type charge-ordering transition in magnetite at 120 K leads to the formation of linear units of three iron ions with one shared electron, called trimerons. The recently-discovered iron pentoxide (FeO) comprising mixed-valent iron cations at octahedral chains, demonstrates another unusual charge-ordering transition at 150 K involving competing formation of iron trimerons and dimerons. Here, we experimentally show that applied pressure can tune the charge-ordering pattern in FeO and strongly affect the ordering temperature.

Charge-ordering transition in iron oxide Fe4O5 involving competing dimer and trimer formation.

Phase transitions that occur in materials, driven, for instance, by changes in temperature or pressure, can dramatically change the materials' properties. Discovering new types of transitions and understanding their mechanisms is important not only from a fundamental perspective, but also for practical applications. Here we investigate a recently discovered Fe4O5 that adopts an orthorhombic CaFe3O5-type crystal structure that features linear chains of Fe ions.

The Pressure-Induced Polymorphic Transformations in Fluconazole.

The structural properties and Raman spectra of fluconazole have been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 2.5 and 5.5 GPa, respectively.

The polymorphic phase transformations in the chlorpropamide under pressure.

The crystal structure and vibrational spectra of the chlorpropamide have been studied by means of the X-ray diffraction and Raman spectroscopy at pressures up to 24.6 and 4.4 GPa, respectively.

Experimental evidence of superionic conduction in H2O ice.

Ionic conductivity and molar volume measurements were performed on H(2)O ice at high pressure (P) and temperature (T) in a resistive-heated diamond anvil cell. The conductivity data obtained at P = 20-62 GPa, T = 304-930 K are well fitted with a single Arrhenius equation. Isothermal volume measurements at T = 873 K, P = 30-101 GPa indicate that H(2)O ice undergoes phase transitions at P = 50 GPa and 53 GPa due to hydrogen-bond symmetrization.

The S3- ion is stable in geological fluids at elevated temperatures and pressures.

The chemical speciation of sulfur in geological fluids is a controlling factor in a number of processes on Earth. The two major chemical forms of sulfur in crustal fluids over a wide range of temperature and pressure are believed to be sulfate and sulfide; however, we use in situ Raman spectroscopy to show that the dominant stable form of sulfur in aqueous solution above 250°C and 0.5 gigapascal is the trisulfur ion S(3)(-).

Unusual compression behavior of anatase TiO2 nanocrystals.

The size-dependent stiffness variations in nanocrystalline anatase, a leading material for applications in photovoltaics, photocatalysis, photoelectrochromics, sensors, and optical coatings, were determined using in situ synchrotron x-ray diffraction and Raman scattering. An unusual, abrupt change in the compression curve at approximately 10 GPa and subtle breaks in the pressure shifts of the intense E(g) Raman band at approximately 10 and approximately 15 GPa have been correlated with approximately 2 A-scale disordering of nanocrystalline anatase structure that fully amorphizes under high compression.

Optical absorption and radiative thermal conductivity of silicate perovskite to 125 gigapascals.

Mantle convection and plate tectonics are driven by the heat flow from Earth's core to the surface. The radiative contribution to heat transport is usually assumed to be negligible. Here, we report the near-infrared and optical absorption spectra of silicate perovskite, the main constituent of the lower mantle, to 125 gigapascals.

Size-dependent pressure-induced amorphization in nanoscale TiO2.

We investigated the size-dependent high-pressure phase transition behavior of nanocrystalline anatase TiO2 with synchrotron x-ray diffraction and Raman spectroscopy to 45 GPa at ambient temperature. Pressure-induced amorphization results in a high-density amorphous (HDA) form when the starting crystallite size is < 10 mm. The HDA-TiO2 transforms to a low-density amorphous form at lower pressures.

Pressure-induced magnetization in FeO: evidence from elasticity and Mössbauer spectroscopy.

The complete elastic tensor of Fe0.94O (wüstite) has been determined to 10 GPa using acoustic interferometry at GHz frequencies inside a diamond-anvil cell. The soft mode (C44) elastic constant of FeO is reduced by 20% over the experimental pressure range.