Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction

A Practical Review of the Laser-Heated Diamond Anvil Cell for University Laboratories and Synchrotron Applications

In the past couple of decades, the laser-heated diamond anvil cell (combined with in situ techniques) has become an extensively used tool for studying pressure-temperature-induced evolution of various physical (and chemical) properties of materials. In this review, the general challenges associated with the use of the laser-heated diamond anvil cells are discussed together with the recent progress in the use of this tool combined with synchrotron X-ray diffraction and absorption spectroscopy.

Anomalous Conductivity in the Rutile Structure Driven by Local Disorder

Many rutile-type materials are characterized by a softness in shear with pressure which is coupled to a Raman-active librational motion. Combining direct studies of anion positions in SnO₂ with measurements of its electronic properties, we find a correlation between O sublattice disorder between 5 and 10 GPa and an anomalous decrease up to 4 orders of magnitude in electrical resistance. Hypotheses into the atomistic nature of the phenomenon are evaluated via ab initio calculations guided by extended X-ray absorption fine structure spectroscopy analysis, and the most likely mechanism is found to be the displacement of single anions resulting from the pressure-induced softening of the librational mode. On the basis of this mechanism, we propose that the same behavior should feature across all materials exhibiting a rutile → CaCl₂ phase transition and that conductivity in other rutile-type materials could be facilitated at ambient pressure by appropriate design of devices to enhance defects of this nature.

Probing disorder in high-pressure cubic tin (IV) oxide: a combined X-ray diffraction and absorption study

The transparent conducting oxide, SnO₂, is a promising optoelectronic material with predicted tailorable properties via pressure-mediated band gap opening. While such electronic properties are typically modeled assuming perfect crystallinity, disordering of the O sublattice under pressure is qualitatively known. Here a quantitative approach is thus employed, combining extended X-ray absorption fine-structure (EXAFS) spectroscopy with X-ray diffraction, to probe the extent of Sn-O bond anharmonicities in the high-pressure cubic (Pa\bar{3}) SnO₂ - formed as a single phase and annealed by CO₂ laser heating to 2648 ± 41 K at 44.5 GPa. This combinational study reveals and quantifies a large degree of disordering in the O sublattice, while the Sn lattice remains ordered. Moreover, this study describes implementation of direct laser heating of non-metallic samples by CO₂ laser alongside EXAFS, and the high quality of data which may be achieved at high pressures in a diamond anvil cell when appropriate thermal annealing is applied.