Bruce J. Baer

The phase diagram of rdx (hexahydro-1,3,5-trinitro-s-triazine) under hydrostatic pressure

Abstract Raman spectroscopy has been used to determine the phase diagram and phase behavior of RDX (hexahydro-1,3,5-trinitro-s-triazhe) up to 16 GPa at temperatures ranging from 150 K to over 450 K. Two new stable solid polymorphs have been identified: a high pressure/low temperature form that converts reversibly to α-RDX (the form stable at ambient conditions) at 3.8 GPa, independent of temperature from 150 to 375 K. We also find a high pressure/high temperature form of RDX that is highly metastable, shows a very large hysteresis, and is probably the polymorph known as β-RDX.

Tuning the electronic and the crystalline structure of LaBi by pressure: From extreme magnetoresistance to superconductivity

Extreme magnetoresistance (XMR) in topological semimetals is a recent discovery which attracts attention due to its robust appearance in a growing number of materials. To search for a relation between XMR and superconductivity, we study the effect of pressure on LaBi. By increasing pressure, we observe the disappearance of XMR followed by the appearance of superconductivity at

Phase diagram of RDX (hexahydro-1,3,5-trinitro-s-triazine) at high pressures and temperatures

Pensuremath{approx}3.5

Raman spectra of the lattice vibrations of solid nitrogen near room temperture

GPa. We find a region of coexistence between superconductivity and XMR in LaBi in contrast to other superconducting XMR materials. The suppression of XMR is correlated with increasing zero-field resistance instead of decreasing in-field resistance. At higher pressures,

High-pressure Raman study of one-dimensional crystals of the very polar molecule hydrogen cyanide

Pensuremath{approx}11

High-pressure binary phase diagram of N2-O2 at 295 K determined by Raman spectroscopy.

GPa, we find a structural transition from the face-centered cubic lattice to a primitive tetragonal lattice, in agreement with theoretical predictions. The relationship between extreme magnetoresistance, superconductivity, and structural transition in LaBi is discussed.

Coherent anti-stokes Raman spectroscopy of highly compressed solid deuterium at 300 K: evidence for a new phase and implications for the band gap.

Abstract The phase diagram of RDX-h6 (hexahydro-1,3,5-trinito-s-triazine) and RDX-d6 has been studied by Raman spectroscopy to more than 13 GPa at 295 K and 7.5 GPa between 150 and 450 K. Two stable high pressure phases have been found. γ-RDX or RDX-III forms from α-RDX above 3.8 GPa below 380 K. β-RDX forms when α- or γ-RDX are heated, can be retained metastably at low temperatues, and may be related to a very unstable form occasionally recovered at ambient pressure. Deuterium isotopic substitution and shear increase the temperature where β-RDX begins to form on heating.

Temperature and pressure dependent optical dephasing of pentacene in triclinic and monoclinic p-terphenyl

Abstract Low-frequency peaks begin to appear in Raman spectra of solid N2 when δ-N2 transforms to either the ϵ- or η-N2 phase and orientational order develops in δ-N2. These same peaks are known at 15 K but are very much broader at the higher temperatures. Near the phase boundaries, these peaks are extremely weak and remain weak even under the best of conditions. We have used Raman spectra of these modes to map the δ-ϵ and δ-ϵ phase boundaries.