RESUMEN
Titanium disulfide (TiS2) has drawn considerable attention in materials, physics, and chemistry thanks to its potential applications in batteries, supercapatteries and thermoelectric devices. However, the simplified and controlled synthesis of high-quality TiS2 remains a great challenge. In this study, a straightforward widely accessible approach to the one-step chemical vapor transport (CVT) process is presented. Meanwhile, combining high-pressure (HP) Raman spectroscopy measurements and first-principles calculations, the pressure-induced phase transition of TiS2 from P3Ìm1 phase (phase I) to C2/m phase (phase II) at 16.0 GPa and then to P6Ì2m phase (phase III) at 32.4 GPa was disclosed. The discovery of HP being within the Weyl semi-metallic phase represents a significant advancement towards understanding the electronic topological states, discovering new physical phenomena, developing new electronic devices, and gaining insight into the properties of elementary particles.
RESUMEN
Polycrystalline TiTa2O7 was synthesized directly by solid-state reaction methods. The structures were determined by using X-ray diffraction (XRD). The high-pressure Raman and UV-vis absorption spectra of TiTa2O7 were obtained up to 25 GPa in a diamond anvil cell (DAC) at room temperature. The Raman scattering results reveal that a pressure-induced amorphization occurs above 10.5 GPa. An inflection point was also observed at 11 GPa in the pressure-dependent bandgap energy spectra, which agrees well with the amorphization point found in Raman spectra. The temperature-dependent Raman and photoluminescence (PL) spectra of TiTa2O7 were also measured. The PL mechanism for TiTa2O7 was studied. It is worth noting that the Raman vibrations attributing to the bending vibration of the Ta (Ti)-O octahedron exhibit anomalous frequency shifts in both the high-pressure and temperature-dependent Raman spectra.
RESUMEN
The introduction of a piezoelectric field has been considered as a promising strategy to enhance photocatalytic activity by inhibiting the recombination of photogenerated electron-hole pairs in semiconductor photocatalysts. In this work, a novel heterostructured photocatalyst that combines piezoelectric KNbO3 nanowires and few-layer MoS2 nanosheets was designed and synthesized via a simple two-step hydrothermal method. Under simulated solar light illumination, the KNbO3/MoS2 heterostructures showed significantly enhanced photocatalytic H2 production and organic pollutant (e.g. rhodamine B) degradation efficiency, compared to pristine KNbO3 nanowires and MoS2 nanosheets. The photocatalytic activity can be further improved greatly by co-utilizing the solar and mechanical energy provided by ultrasonic vibration. The enhancement of photocatalytic activity can be attributed to the promotion of charge separation caused by the synergetic effect of the formation of a heterojunction and the internal piezoelectric field induced by mechanical vibration. Our findings may provide insight into strategies for designing highly efficient piezoelectric material-based nanocomposites for various photocatalytic applications such as environmental remediation and renewable energy production.