Morphology-Tuned Phase Transitions of Horseshoe Shaped BaTiO₃ Nanomaterials under High Pressure

Exploring new physical properties of nanomaterials with special morphology have been important topics in nanoscience and nanotechnology. Here we report a morphology-tuned structural phase transition under high pressure in the horseshoe shaped BaTiO₃ nanomaterials with an average diameter of 26 ± 4 nm. A direct structural phase transition from the tetragonal to the cubic phase without local rhombohedral distortion was observed at about 7.7 GPa by in situ high-pressure X-ray diffraction and Raman spectroscopy, which is clearly different from the phase transition processes of the BaTiO₃ bulks and nanoparticles. Additionally, bulk modulus of the tetragonal and cubic phases were determined to be 125.0 and 211.7 GPa, respectively, obviously smaller than the estimated values for BaTiO₃ nanoparticles with the same grain size. Further analysis shows that the unique phase transition process and the enhanced structural stability of the tetragonal horseshoe shaped BaTiO₃ nanomaterials, may be attributed to the similar axes compressibility. Comparing with the high-pressure study on BaTiO₃ nanoparticles, this study suggests that the morphology plays an important role in the pressure-induced phase transition of BaTiO₃ nanomaterials

High-Performance Sn-Based Quasi-Two-Dimensional Perovskite Photodetectors by Altering Dark Current Shunt Pathways

Self-powered perovskite photodetectors (PDs) have been widely used in the fields of communications and imaging, but their performance is still restricted by the high dark current of devices. This study has shown that the dark current of PDs can be significantly reduced by adjusting the composition of the dark current shunting paths. We have fabricated a less toxic high-performance PDs based on two-dimensional tin-based perovskite BA2FASn2I7. By controlling the grain size of the perovskite film with potassium salt of hydroquinone sulfonic acid (KHQSA), we increased the number of horizontal shunting paths and the dark current was reduced to 1/50th of its original value. The device shows a high responsivity of 1.4 A W–1, a high detectivity of 8.2 × 1013 Jones, a maximum on/off current ratio of 6.74 × 105, and a rapid rise/decay time of 12.2/14 ms. In addition, as a light signal receiver in an imaging system, the device can accurately and sensitively identify light signals under weak light conditions. This study provides a new way for further improving the performance of self-powered perovskite PDs by adjusting the composition of horizontal and vertical dark current shunting paths

Linear Tunability of the Band Gap and Two-Dimensional (2D) to Three-Dimensional (3D) Isostructural Transition in WSe₂ under High Pressure

Transition metal dichalcogenides (TMDs) have recently gained tremendous interest for use in electronic and optoelectronic applications. Unfortunately, the electronic structure or band gap of most TMDs shows noncontinuously tunable characteristics, which limits their application to energy-variable optoelectronics. Thus, layered materials with better tunability in their electronic structures and band gaps are desired. Herein, we experimentally demonstrated that layered WSe₂ possessed highly tunable transport properties under various pressures, with a linearly decreasing band gap that culminates in metallization. Pressure tuned the band gap of WSe₂ linearly, at a rate of 25 meV/GPa. The high tunability of WSe₂ was attributed to the larger electron orbitals of W²⁺ and Se^2– in WSe₂ compared to the Mo²⁺ and S^2– in MoS₂. WSe₂ underwent an isostructural phase transition from a 2D layered structure to a 3D structure at approximately 51.7 GPa, where a conversion from van der Waals (vdW) to covalent-like bonding was observed in the valence electron localization function (ELF). Our results present an important advance toward controlling the band structure of layered materials and suggest significant implications for energy-variable optoelectronic devices via pressure engineering