Pressure-induced phase transition and fracture in α-MoO3 nanoribbons

Manifestation of anharmonicities in terms of Fano scattering and phonon lifetime of scissors modes in α-MoO3

α-MoO3 exhibits promising potential in the field of infrared detection and thermoelectricity owing to its exceptional characteristics of ultra-low-loss phonon polaritons (PhPs). It is of utmost importance to comprehend the phonon interaction exhibited by α-MoO3 in order to facilitate the advancement of phonon-centric devices. The intriguing applications of α-MoO3 for phonon-centric technology are found to be strongly dependent on scissors Raman modes. In this study, we have investigated the temperature-dependent asymmetric Raman line-shape characteristics of two scissors modes, Ag(1) and B1g(1), in the orthorhombic phase of bulk α-MoO3 within a temperature range spanning from 138 K to 498 K at 633 nm excitation wavelength. The Fano-Raman line-shape function was employed to analyze the asymmetry in terms of electron-phonon coupling strength, which varies from 0.050 to 0.313 and -0.017 to -0.192 for Ag(1) and B1g(1) modes, respectively, with temperature. This asymmetric behavior of Ag(1) and B1g(1) scissors modes are attributed to interference between the electronic energy continuum and discrete TO and LO phonon states, respectively. Therefore, the line-shape asymmetry in two scissors modes with increasing temperature stemming from the Fano resonance is also consistent with a 488 nm excitation wavelength. Additionally, anharmonicity caused by temperature results in redshift, and linewidth broadening of these two scissors modes through cubic-phonon decay has been observed. Moreover, the ultrashort lifetime of these optical phonons diminishes from ∼1.37 ps to ∼0.53 ps with increasing temperature due to the dominance of cubic-phonon decay over quartic-phonon decay. Our findings strongly emphasize the significance of investigating anharmonic interactions with Fano resonance to acquire an extensive comprehension of the vibrational characteristics of α-MoO3 for novel functionalities.

Ag2Mo3O10·2H2O nanorods under high pressure: In situ Raman spectroscopy

This work presents a pressure-dependent behavior of silver trimolybdate dihydrate (Ag₂Mo₃O₁₀·2H₂O) nanorods using in situ Raman scattering. The Ag₂Mo₃O₁₀·2H₂O nanorods were obtained by the hydrothermal method at 140 °C for 6 h. The structural and morphological characterization of the sample was performed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pressure-dependent Raman scattering studies were performed on Ag₂Mo₃O₁₀·2H₂O nanorods up to 5.0 GPa using a membrane diamond-anvil cell (MDAC). The vibrational spectra under high pressure showed splitting and emergence of new bands above 0.5 GPa and 2.9 GPa. Reversible phase transformations under pressure were observed in silver trimolybdate dihydrate nanorods: Phase I - ambient phase (1 atm - 0.5 GPa) → Phase II (0.8 GPa - 2.9 GPa) → Phase III (above 3.4 GPa).

Structural and electronic properties of tungsten oxides under high pressures

Tungsten (W) oxides have shown broad applications such as photocatalyst and cathode of lithium ion batteries. It is well-known that pressure can induce structural phase transition, producing novel properties. On the other hand, the study of W oxides under high pressures is beneficial for the control of the oxygen fugacity. In this work, we built the high-pressure phase diagram of W-O binary compounds through first-principles swarm-intelligence structural search calculations. WO₂ and WO₃ are stable in the whole considered pressure range from 0 to 300 GPa. Besides reproducing the known structures, we identify two new phases of WO₂ (e.g. C2/m and Cmca) and three ones for WO₃ (e.g. Pnma, Cmcm, and Pm-3n), associating with the evolution of polyhedron (i.e. octahedron  →  distorted octahedron for WO₂, and octahedron  →  hendecahedron  →  tetradecahedron  →  icosahedron for WO₃). More interestingly, the Pm-3n-structured WO₃ shows the highest coordination number of 12. Electron structure calculations indicate that pressure-induced nonmetal  →  metal transition occurs for WO₂ and WO₃. Our study provides an opportunity to understand the structures and electronic properties of W-O system under high pressure.

Template conversion of MoO3 to MoS2 nanoribbons: synthesis and electrochemical properties

Electrochromic α-MoO₃ nanoribbons were prepared by a hydrothermal method and converted to MoS₂ with the same morphology.