Jason Knight

In Situ Single-Crystal Diffraction Studies of the Structural Transition of Metal-Organic Framework Copper 5-Sulfoisophthalate, Cu-SIP-3

The flexibility of the metal-organic framework Cu(2)(OH)(C(8)H(3)O(7)S)(H(2)O) x 2 H(2)O (Cu-SIP-3) toward reversible single-crystal to single-crystal transformations is demonstrated using in situ diffraction methods at variable temperature. At temperatures below a dehydration-induced phase transition (T < 370 K) the structure is confirmed as being hydrated. In the temperature range where the transition takes place (370 K < T < 405 K) no discrete, sharp Bragg peaks can be seen in the single-crystal X-ray diffraction pattern, indicating significant loss of long-range order. At temperatures higher than 405 K, the Bragg peaks return and the structure can be refined as dehydrated Cu-SIP-3. The loss of guest water molecules can be followed at temperatures below the phase transition giving insight into the mechanism of the dehydration. Addition of nitric oxide gas to the material above the gating opening pressure of 275 mbar also leads to loss of Bragg scattering in the diffraction pattern.

In situ phase transformation and deformation of iron at high pressure and temperature

With a membrane based mechanism to allow for pressure change in a sample in a radial diffraction diamond anvil cell and simultaneous infrared laser heating, it is now possible to investigate texture changes during deformation and phase transformations over a wide range of temperature-pressure conditions. The device is used to study bcc (α), fcc (γ), and hcp (e) iron. In bcc iron, room temperature compression generates a texture characterized by (100) and (111) poles parallel to the compression direction. During the deformation induced phase transformation to hcp iron, a subset of orientations is favored to transform to the hcp structure first and generate a texture of (011¯0) at high angles to the compression direction. Upon further deformation, the remaining grains transform, resulting in a texture that obeys the Burgers relationship of (110)bcc//(0001)hcp. Contrary to these results for low temperature, at high temperature texture is developed through dominant pyramidal ⟨a+c⟩ {21¯1¯2} ⟨21¯1¯3⟩ and basal ...

Photocrystallography ? design and methodology for the use of a light-emitting diode device

With the increase in interest in photocrystallographic experiments, the use of light-emitting diodes (LEDs) provides an alternative, low-budget light source (by comparison to lasers) and allows photocrystallographic experiments to be carried out readily. Here the design of an LED array device suitable for use in single-crystal X-ray diffraction experiments is reported, and the experimental methodology used for determining the structures of metastable species is described.

Determination of the variation of the fluorescence line positions of ruby, strontium tetraborate, alexandrite, and samarium-doped yttrium aluminum garnet with pressure and temperature

The pressure and temperature dependent fluorescence line-shift of strontium tetraborate has been measured concurrently with x-ray diffraction from the pressure standards sodium chloride or gold. Temperature was found to have a small effect on the fluorescence line-shift under pressure. We found a maximum pressure uncertainty of ±1.8 GPa at 25 GPa (7.2%) and 857 K when making no temperature correction. The fluorescence line-shifts for ruby, Alexandrite, and samarium-doped yttrium aluminum garnet were also determined, using our strontium tetraborate calibration to determine pressure and a thermocouple to measure temperature. Fluorescence measurements were extended up to 800 K for ruby and Alexandrite. Temperature was found to have a small effect on the fluorescence line-shift of samarium-doped yittrium aluminum garnet. We found a maximum uncertainty of ±2.7 GPa at 25 GPa (11.1%) and 857 K when no temperature correction was applied. We determined equations relating to the fluorescence line position from thes...

Combined resistive and laser heating technique for in situ radial X-ray diffraction in the diamond anvil cell at high pressure and temperature

To extend the range of high-temperature, high-pressure studies within the diamond anvil cell, a Liermann-type diamond anvil cell with radial diffraction geometry (rDAC) was redesigned and developed for synchrotron X-ray diffraction experiments at beamline 12.2.2 of the Advanced Light Source. The rDAC, equipped with graphite heating arrays, allows simultaneous resistive and laser heating while the material is subjected to high pressure. The goals are both to extend the temperature range of external (resistive) heating and to produce environments with lower temperature gradients in a simultaneously resistive- and laser-heated rDAC. Three different geomaterials were used as pilot samples to calibrate and optimize conditions for combined resistive and laser heating. For example, in Run#1, FeO was loaded in a boron-mica gasket and compressed to 11 GPa then gradually resistively heated to 1007 K (1073 K at the diamond side). The laser heating was further applied to FeO to raise temperature to 2273 K. In Run#2, Fe-Ni alloy was compressed to 18 GPa and resistively heated to 1785 K (1973 K at the diamond side). The combined resistive and laser heating was successfully performed again on (Mg0.9Fe0.1)O in Run#3. In this instance, the sample was loaded in a boron-kapton gasket, compressed to 29 GPa, resistive-heated up to 1007 K (1073 K at the diamond side), and further simultaneously laser-heated to achieve a temperature in excess of 2273 K at the sample position. Diffraction patterns obtained from the experiments were deconvoluted using the Rietveld method and quantified for lattice preferred orientation of each material under extreme conditions and during phase transformation.

Shock synthesis of lanthanum-III-pernitride †

Lanthanum-III-pernitride is unique amongst pernitrides because of the seemingly misfit charge balance and stoichiometry. La+3N2 has been predicted to be stabilized by resonance between two mesomeric states of bonding in the pernitride group, which include a remarkable N‒N single bond limiting state. However, successful synthesis of this compound remained extant. Here, we report synthesis of LaN2 through shock-driven decomposition of lanthanum nitrate. The result is noteworthy as a first quantitative measure of the stability of N‒N single bonds in solids formed at GPa-level pressure and with respect to a possible cross-over of redox potentials in the nitrogen- and oxygen-systems at high pressure and temperature.

Elastic moduli and hardness of highly incompressible platinum perpnictide PtAs2

PtAs2 appears to be the least compressible known arsenide with a bulk modulus of 220(5) GPa and a shear modulus of between 64 and 77 GPa. PtAs2 has a hardness of 11(1) GPa, which is remarkably high for an arsenide. These elastic and mechanical properties in combination with the known chemical inertness and the small indirect band gap add interest to the use and occurrence of PtAs2 at Pt-GaAs contacts in transistors. We note the modest fracture toughness of 1.1–1.6 MPa m1/2 of PtAs2.

Beamline 12.2.2: An Extreme Conditions Beamline at the Advanced Light Source

The Advanced Light Source (ALS) is a 1.9-GeV, third-generation synchrotron optimized for the production of VUV and soft X-rays from undulators. There is also a hard X-ray program at the ALS, which is based around three 6-T superconducting bending magnets [1] that shift the critical energy from 3 keV to 12 keV. The extreme conditions beamline at the ALS is situated on Beamline 12.2.2, which benefits from radiation produced by one of these superbend sources. The beamline is designed for X-ray diffraction, X-ray spectroscopy, and X-ray imaging of samples held in diamond-anvil high-pressure cells (DACs). In a DAC, samples are on the order of 10 to 50 μm in diameter and 10 to 30 μm thick and are contained in a metal gasket of typical inner diameters of 100 to 150 μm. For high-quality diffraction patterns with little or no contamination from diffraction from the gasket, the X-ray beam size needs to be on the order of 10 μm × 10 μm.

Investigation of phase transition of mercury decomposed from mercury oxide up to 20 GPa

The high pressure behavior of mercury decomposed from mercury oxide up to 20.4 GPa was investigated using angular-dispersive X-ray diffraction. The results showed that liquid mercury solidified at 2.0 GPa and was resolved as α hexagonal, R-3m, a=3.3743±0.0007 Å and c=6.8199±0.0013 Å. When compressed up to 5.7 GPa, α mercury transformed into orthorhombic γ phase directly, which is not the case of transforming from an α structure to a body-centered tetragonal structure (β). The space group of orthorhombic γ phase was interpreted successfully as Pmmn, with a=2.7722±0.0010 Å, b=4.0792±0.0028 Å and c=6.8285±0.0029 Å at 8.9 GPa.

High-pressure compressibility and phase stability of Mn-dolomite (kutnohorite)

Abstract We measured the bulk modulus and phase stability of a natural Mn-dolomite, kutnohorite, to 19 GPa. At room temperature, kutnohorite is stable in the rhombohedral dolomite phase up to 19 GPa, with an isothermal bulk modulus of 85(6) GPa (Kʹ = 4). The compressibility of kutnohorite is found to match well with both single and double carbonate trends with respect to bulk modulus and unit-cell volume. The thermoelastic properties measured in this study show that the Mn dolomite end-member fits well with the systematic of all the rhombohedral carbonates, both calcite (single carbonate) and dolomite (double carbonate) type.