Magnus Lipp

Dynamic diamond anvil cell (dDAC): A novel device for studying the dynamic-pressure properties of materials

We have developed a unique device, a dynamic diamond anvil cell (dDAC), which repetitively applies a time-dependent load/pressure profile to a sample. This capability allows studies of the kinetics of phase transitions and metastable phases at compression (strain) rates of up to 500 GPa/s (approximately 0.16 s(-1) for a metal). Our approach adapts electromechanical piezoelectric actuators to a conventional diamond anvil cell design, which enables precise specification and control of a time-dependent applied load/pressure. Existing DAC instrumentation and experimental techniques are easily adapted to the dDAC to measure the properties of a sample under the varying load/pressure conditions. This capability addresses the sparsely studied regime of dynamic phenomena between static research (diamond anvil cells and large volume presses) and dynamic shock-driven experiments (gas guns, explosive, and laser shock). We present an overview of a variety of experimental measurements that can be made with this device.

Pseudotachylites generated in shock experiments : implications for impact cratering products and processes

Laboratory hypervelocity impact experiments in which quartz was shock-loaded from 42 to 56 gigapascals imply that type A pseudotachylites form by strain heating and contribute to the loss of strength of rocks in the central uplift of large impact structures. Shock impedance-matched aluminum sample containers, in contrast to steel containers, produced nearly single-wave pressure loading, and enhanced deformation, of silicate samples. Strain heating may act with shock heating to devolatilize planetary materials and destroy extraterrestrial organic material in an impact.

CARBON MONOXIDE : SPECTROSCOPIC CHARACTERIZATION OF THE HIGH-PRESSURE POLYMERIZED PHASE

AbstractSolid carbon monoxide transforms to the δ–phase at about 48 kbar at room temperature. In this pressure regime (50 kbar and greater), carbon monoxide undergoes a transformation at room temperature to a light–pink solid, which has not been studied in detail and may be different from the δ–phase. Exposure to moderate light intensities at these P–T conditions converts the system to a dark red material. We report visible and infrared absorption as well as Raman investigations of this dark red substance, which likely contains a polymeric product of the photochemical reaction. This material is stable upon pressure release down to ambient conditions. Previous studies speculated that the dark red product was a mixture of poly–carbonsuboxide (C3O2) and oxalic anhydride (C2O3). In contrast, we present evidence that this material is composed of graphitic–like carbon, carbon dioxide, and possibly a polymerized network containing

High pressure crystal structure of PrN

- \left( {{\text{C = O}}} \right) - {\text{O}} - \left( {{\text{C}} - } \right) = {\text{C}} <

Cryogenic loading of large volume presses for high-pressure experimentation and synthesis of novel materials

as a repeating unit.

Vibrational Spectroscopy at High Pressures in CF4: Implications to the Phase Diagram

Core-shell X-ray emission spectroscopy (XES) is a valuable complement to X-ray absorption spectroscopy (XAS) techniques. However, XES in the hard X-ray regime is much less frequently employed than XAS, often as a consequence of the relative scarcity of XES instrumentation having energy resolutions comparable with the relevant core-hole lifetimes. To address this, a family of inexpensive and easily operated short-working-distance X-ray emission spectrometers has been developed. The use of computer-aided design and rapid prototype machining of plastics allows customization for various emission lines having energies from ∼3 keV to ∼10 keV. The specific instrument described here, based on a coarsely diced approximant of the Johansson optic, is intended to study volume collapse in Pr metal and compounds by observing the pressure dependence of the Pr Lα emission spectrum. The collection solid angle is ∼50 msr, roughly equivalent to that of six traditional spherically bent crystal analyzers. The miniature X-ray emission spectrometer (miniXES) methodology will help encourage the adoption and broad application of high-resolution XES capabilities at hard X-ray synchrotron facilities.

Persistent Fe moments in the normal-state collapsed-tetragonal phase of the pressure-induced superconductor Ca 0.67 Sr 0.33 Fe 2 As 2

Compression of PrN yields a phase transformation to a tetragonal structure with ~8.8 % volume collapse at ~40 GPa at ambient temperature. A refinement reveals a distorted CsCl-like structure for the high pressure phase PrN(II), which is different from the high pressure phases seen among other lanthanide monopnictides. The space group of the new structure is P4/nmm (#129) with Pr in the 2c(0,1/2,0.3546) and N in the 2a(0,0,0) positions. PrN(II) persists to 85 GPa.

Equation of state measurements by radiography provide evidence for a liquid-liquid phase transition in cerium

We present design and performance details for a polycapillary-coupled x-ray spectrometer that provides very high collection efficiency at a moderate energy resolution suitable for many studies of nonresonant x-ray emission spectroscopy, especially for samples of heavy elements under high pressures. Using a single Bragg analyzer operating close to backscattering geometry so as to minimize the effect of the weak divergence of the quasicollimated exit beam from the polycapillary optic, this instrument can maintain a typical energy resolution of 5 eV over photon energies from 5 keV to 10 keV. We find dramatically improved count rates as compared to a traditional higher-resolution instrument based on a single spherically bent crystal analyzer.