Piezoelectric Property of a Tetragonal (Ba,Ca)(Zr,Ti)O₃ Single Crystal and Its Fine-Domain Structure

A tetragonal (Ba,Ca)­(Zr,Ti)­O₃ (BCZT) single crystal was grown by a flux method, and the piezoelectric coefficient (<i>d</i>₃₃) was characterized. The piezoelectric response was proved to be associated with polarization extension, which was successfully used to explain the variation in <i>d</i>₃₃^*. From the intrinsic aspect, the compositional effect on Landau free-energy profiles was discussed, showing an “extender” nature of the as-grown crystal and the increasing tendency of structural instability toward the morphotropic phase boundary. From the extrinsic aspect, the evolution of domain structure under various external fields (electric and temperature) was studied, revealing that the fine-domain structure of the as-grown BCZT single crystal was stable to E-field and temperature. The results manifest possibilities of further improving the piezoelectric property of the BCZT single crystal, which requires optimization of the crystal growth technique in future work

Hexagonal Crown-Capped Zinc Oxide Micro Rods: Hydrothermal Growth and Formation Mechanism

Hexagonal crown-capped ZnO micro rods were successfully prepared by a facile low-temperature hydrothermal method. The as-prepared ZnO micro rods are 4.4–5.2 μm in length and 2.4–3.6 μm in diameter, possessing a single-crystal hexagonal structure. The morphology evolution and structure changes were tracked during hydrothermal growth by field-emission scanning electron microscopy and X-ray diffraction, respectively. A three-stage growth mechanism of the hexagonal crown-capped ZnO micro rods was proposed and further verified by a growth solution renewal experiment. The room-temperature photoluminescence (PL) spectrum of the hexagonal crowns exhibits a strong UV emission at about 382 nm. The temperature dependent PL results indicate that the UV emission originates from the radiative free-exciton recombination

Nanosecond-Response Speed Sensor Based on Perovskite Single Crystal Photodetector Array

A nanosecond-response speed sensor is demonstrated based on a CH₃NH₃PbI₃ perovskite single crystal photodetector array. The responsivity of the CH₃NH₃PbI₃ photodetector unit is as high as 1.55 × 10² A/W under 1.93 × 10^–2 mW/cm² illumination with a 532 nm laser. The ultrafast response time of less than 12.5 ns makes it possible for ultra-high-speed detection. Owing to the uniformity of as-prepared CH₃NH₃PbI₃ single crystals, each array element shows a consistent performance. When a shelter moves across the photodetector array, the time delay of the photoresponses between two neighboring array elements can be recorded promptly. Therefore, the speed of the moving shelter can be calculated easily. Besides speed sensing, the ability to capture the trajectory of a moving object is also demonstrated. The nanosecond-response speed sensor presented here demonstrates great potential for applying in high-speed detection

An Origami Perovskite Photodetector with Spatial Recognition Ability

Flexible photodetectors are attracting substantial attention because of their promising applications in bendable display and smart clothes which cannot be fulfilled by the existing rigid counterparts. In this work, we demonstrate a newly designed photodetector constructed on the common printing paper. Pencil trace was applied as the graphite electrode. With such a simple and convenient method, the as-prepared photodetector exhibited a satisfactory responsivity of 4.4 mA/W, on/off current ratio of 32, coupled with a high response speed of <10 ms. It also demonstrated excellent mechanical flexibility and durability. Most inspiringly, by an ingenious origami, we created the first perovskite photodetector with a 3D configuration. The cubic photodetector array displayed an excellent spatial recognition ability which could not be achieved in all the previously reported 2D photodetectors. Such a fusion of materials science and the art of origami provides a robust strategy for the design of low-cost flexible electronics, especially for the applications in 3D configurations

Self-Powered Ultrabroadband Photodetector Monolithically Integrated on a PMN–PT Ferroelectric Single Crystal

Photodetectors capable of detecting two or more bands simultaneously with a single system have attracted extensive attentions because of their critical applications in image sensing, communication, and so on. Here, we demonstrate a self-powered ultrabroadband photodetector monolithically integrated on a 0.72Pb­(Mg_1/3Nb_2/3)­O₃–0.28PbTiO₃ (PMN–28PT) single crystal. By combining the optothermal and pyroelectric effect, the multifunctional PMN–28PT single crystal can response to a wide wavelength range from UV to terahertz (THz). At room temperature, the photodetector could generate a pyroelectric current under the intermittent illumination of incident light in absence of external bias. A systematic study of the photoresponse was investigated. The pyroelectric current shows an almost linear relationship to illumination intensity. Benefiting from the excellent pyroelectric property of PMN–28PT single crystal and the optimized device architecture, the device exhibited a dramatic improvement in operation frequency up to 3 kHz without any obvious degradation in sensitivity. Such a self-powered photodetector with ultrabroadband response may open a window for the novel application of ferroelectric materials in optoelectronics

CsCu₅Se₃: A Copper-Rich Ternary Chalcogenide Semiconductor with Nearly Direct Band Gap for Photovoltaic Application

Discovery of new semiconductor candidates with suitable band gaps is a challenge for optoelectronic application. A facile solvothermal synthesis of a new ternary chalcogenide semiconductor CsCu₅Se₃ is reported. The telluride CsCu₅Te₃ is also predicted to be stable. CsCu₅Se₃ is isostructural with CsCu₅S₃ (space group <i>Pmma</i>). The band gap calculations of these chalcogenide semiconductors using hybrid density functional theory indicate nearly direct band gaps, and their values (about 1.4 eV) were confirmed by the optical absorption spectroscopy. These alkali metal copper chalcogenides are interesting examples of copper-rich structures which are commonly associated with favorable photovoltaic application