Pressure-induced Isostructural Transition Research Articles

Pressure-induced iso-structural phase transition and metallization in WSe2

We present in situ high-pressure synchrotron X-ray diffraction (XRD) and Raman spectroscopy study, and electrical transport measurement of single crystal WSe2 in diamond anvil cells with pressures up to 54.0–62.8 GPa. The XRD and Raman results show that the phase undergoes a pressure-induced iso-structural transition via layer sliding, beginning at 28.5 GPa and not being completed up to around 60 GPa. The Raman data also reveals a dominant role of the in-plane strain over the out-of plane compression in helping achieve the transition. Consistently, the electrical transport experiments down to 1.8 K reveals a pressure-induced metallization for WSe2 through a broad pressure range of 28.2–61.7 GPa, where a mixed semiconducting and metallic feature is observed due to the coexisting low- and high-pressure structures.

Pressure-induced isostructural transition in a distorted perovskite via octahedron reconfiguration

Perovskite material studies encompass many fields such as energy harvesting, superconductivity, magnetism, and beyond. Thus, it is very important to investigate their structural varieties in external environments. Here, the pressure-induced structure change of a distorted perovskite, Y0.7Lu0.3AlO3, was examined by synchrotron x-ray diffraction. Upon compression, it underwent an isostructural transition near 22 GPa. The quenchable high-pressure phase had a much higher bulk modulus than the low-pressure phase. This work shows the flexibility of perovskite distortion and will help to understand the property anomalies in prevailing perovskite ABO3 systems and design more functional materials.

Phonon instability and pressure-induced isostructural semiconductor-semimetal transition of monoclinic VO2

Recent experiments have revealed an intriguing pressure-induced isostructural transition of the low temperature monoclinic $\mathrm{V}{\mathrm{O}}_{2}$ and hinted to the existence of a new metallization mechanism in this system. The physics behind this isostructural phase transition and the metallization remains unresolved. In this work, we show that the isostructural transition is a result of pressure-induced instability of a phonon mode that relates to a $\mathrm{CaC}{\mathrm{l}}_{2}$-type of rotation of the oxygen octahedra, which alleviates, but does not completely remove, the dimerization and zigzagging arrangement of V atoms in the M1 phase. This phonon mode shows an increasing softening with pressure, ultimately leading to an isostructural phase transition characterized by the degree of the rotation of the oxygen octahedra. We also find that this phase transition is accompanied by an anisotropic compression, in excellent agreement with experiments. More interestingly, in addition to the experimentally identified M1\ensuremath{'} phase, we find a closely related ${\mathrm{M}1}^{\ensuremath{'}\ensuremath{'}}$ phase, which is nearly degenerate with the ${\mathrm{M}1}^{\ensuremath{'}}$ phase. Unlike the ${\mathrm{M}1}^{\ensuremath{'}}$ phase, which has a nearly pressure-independent electronic band gap, the gap of the ${\mathrm{M}1}^{\ensuremath{'}\ensuremath{'}}$ drops quickly at high pressures and vanishes at a theoretical pressure of about 40 GPa.

Charge and magnetic ordering in mixed valence system Sm 4(Bi 1− xSb x) 3

The mixed valence compound Sm 4Bi 3 shows the charge ordered state of Sm 2+ and Sm 3+ with a ratio of 3 : 1 and its behavior is similar to that of well-known compound Yb 4As 3. The main interest in Sm 4Bi 3 is a pressure-induced iso-structural transition from a mixed valence state to a trivalent state, in which physical properties are very similar to that of Sm 4Sb 3. To reproduce the high-pressure phase, we synthesized and investigated Sm 4(Bi 1− x Sb x ) 3 system. With increasing Sb content, the carrier concentration decreases and the charge ordering temperature slightly increases, while by applying pressure the ordering temperature decreases. These relationships between the substitution and pressure effect in Sm 4Bi 3 is very similar to that in Yb 4As 3. So, it may be suggested that Sm 4Bi 3 is a semimetal in the same way as the case of Yb 4As 3. The substitution effect may be different from the pressure effect though both effects finally lead to a trivalent state.

A Pressure-Induced Isostructural Transition in Black Phosphorus

The crystal structure of orthorhombic black phosphorus under pressure is calculated as a function of volume using the pseudopotential total-energy method. As a result, it is shown that the anomaly of the lattice constants observed experimentally at the density of 17.5Å3/atom is due to an unusual isostructural second order phase transition and its physical origin is attributed the repulsive force effect due to overlap between valence electron charge clouds of neighboring puckered layers.