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The need for ferroelectric materials with both narrow bandgaps (Eg) and large remanent polarization (Pr) remains a key challenge to the development of high-efficiency ferroelectric photovoltaic (FPV) devices. In this work, [(K0.43Na0.57)0.94Li0.06][(Nb0.94Sb0.06)0.95Ta0.05]O3 (KNLNST)-based lead-free ceramics with narrow Eg and large Pr are obtained via Fe2O3 doping. By optimizing the level of Fe2O3 doping, a KNLNST+1.3% Fe2O3 ceramic is fabricated that simultaneously possesses a narrow Eg of 1.74 eV and a large Pr of 27.05 μC/cm2. These values are much superior to those of undoped KNLNST ceramics (Eg = 3.1 eV and Pr = 17.73 μC/cm2). While the large Pr stems from the increment of the volume ratio between the orthorhombic and tetragonal phases (VO/VT) in KNLNST ceramics by proper amount of Fe3+ doping, the narrow Eg is attributed to the coupling interaction between the Fe3+ dopants and the B-site Sb3+ host ions. Moreover, a switchable photovoltaic effect caused by the ferroelectric depolarization electric field (Edp) is observed in the KNLNST+1.3% Fe2O3 ceramic-based device. Thanks to the narrower Eg and larger Pr of the doped ceramic, the photovoltaic performance of the corresponding device (open-circuit voltage (Voc) = −5.28 V and short-circuit current density (Jsc) = 0.051 μA/cm2) under a downward poling state is significantly superior to that of an undoped KNLNST-based device (Voc = −0.46 V and Jsc = 0.039 μA/cm2). This work offers a feasible approach to developing ferroelectric materials with narrow bandgaps and large Pr for photovoltaic applications.

Abstract Dynamic manipulation of electromagnetic (EM) waves with multiple degrees of freedom plays an essential role in enhancing information processing. Currently, an enormous challenge is to realize directional terahertz (THz) holography. Recently, it was demonstrated that Janus metasurfaces could produce distinct responses to EM waves from two opposite incident directions, making multiplexed dynamic manipulation of THz waves possible. Herein, we show that thermally activated THz Janus metasurfaces integrating with phase change materials on the meta-atoms can produce asymmetric transmission with the designed phase delays. Such reconfigurable Janus metasurfaces can achieve asymmetric focusing of THz wave and directional THz holography with free-space image projections, and particularly the information can be manipulated via temperature and incident THz wave direction. This work not only offers a common strategy for realizing the reconfigurability of Janus metasurfaces, but also shows possible applications in THz optical information encryption, data storage, and smart windows.

AgNbO3 based antiferroelectric (AFE) ceramics have large maximum polarization and low remanent polarization, and thus are important candidates for fabricating dielectric capacitors. However, their energy storage performances have been still large difference with those of lead-based AFEs because of their room-temperature ferrielectric (FIE) behavior. In this study, novel La3+ and Ta5+ co-substituted AgNbO3 ceramics are designed and developed. The introduction of La3+ and Ta5+ decreases the tolerance factor, reduces the polarizability of B-site cations and increases local structure heterogeneity of AgNbO3, which enhance AFE phase stability and refine polarization-electric field (P–E) loops. Besides, adding La3+ and Ta5+ into AgNbO3 ceramics causes the decrease of the grain sizes and the increase of the band gap, which contribute to increased Eb. As a consequence, a high recoverable energy density of 6.79 J/cm3 and large efficiency of 82.1%, which exceed those of many recently reported AgNbO3 based ceramics in terms of overall energy storage properties, are obtained in (Ag0.88La0.04)(Nb0.96Ta0.04)O3 ceramics. Furthermore, the discharge properties of the ceramic with discharge time of 16 ns and power density of 145.03 MW/cm3 outperform those of many lead-free dielectric ceramics.

Self-driven solar-blind ultraviolet photodetectors (SBUVPDs) have attracted considerable interest for their superior sensitivity and operation flexibility. Herein, we demonstrate realization of a simple vertical-structured self-driven SBUVPD by pulsed laser deposition of β-Ga2O3 thin film on commercially available fluorine doped tin oxide (FTO) substrate, adopting multi-layer graphene (MLG) as the top electrode. On the one hand, the introduction of MLG with both high electrical conductance and UV transmittance greatly enhances photocurrent and responsivity of the photodetector. On the other hand, the dominating Schottky contact between Ga2O3 and MLG creates a net built-in electric field, leading to self-driven photoresponse of the device with improved response speed. With optimized thickness (8 ± 2 single layers of graphene) of the top electrode, the device exhibits the best detection performance that is superior to most of previous reports towards UV illumination at 0 V bias. It delivers a photocurrent as high as 31 nA towards 250 nm-light with ultra-fast response speed (τr = 2 ms, τd = 8.8 ms), and exhibits a maximum responsivity of 9.2 mA/W and detectivity of 5.27 × 1011 Jones under 230 nm-light illumination, while the response cuts off at light wavelength of 261 nm, falling completely within the solar blind band. In addition, the device has good multi-cycle repeatability and stability, showing great application potential in solar-blind UV detection.

Polymer-based dielectric capacitors with excellent elevated-temperature capacitive performances are highly demanded in next-generation electronic power systems. Here, we design an effective and low-cost way to fabricate high-temperature polymer capacitors via adding Al2O3 nanoparticles (NPs) into polyetherimide (PEI) nanocomposites. Benefited from good thermal stability, high thermal conductivity of Al2O3 NPs and high glass transition temperature of PEI, the Joule heat caused by high temperature and large electric field, dissipate quickly. Therefore, the nanocomposites present low dielectric loss and superior high-temperature capacitive properties. Consequently, even at 150 °C, the Al2O3 NPs/PEI nanocomposite delivers still slim electric displacement-electric field (D-E) loops, small remnant electric displacement (Dr), and large maximum electric displacement (Dmax). Thus, it results in an ultra-high discharged energy density (Ue) of 6.68 J cm−3, which far exceeds the state-of-the-art polymer and polymer composites, and high efficiency (η) of 84.77% at 150 °C. This work addresses the paradox that large Ue and high η cannot be simultaneously achieved in high-temperature polymer composites.

Two-dimensional (2D) lead halide perovskites have garnered increasing interest due to their high photoluminescence quantum yields and tunable luminescence characters, making them excellent materials in light-emitting, especially for white-light emission. In contrast to their 3D analogues, they are formed by inserting large organic cations between the anionic layers of lead halide octahedra. Herein, we designed and prepared AVA2PbClxBr4-x (x = 0, 1, 2, 3, 4) alloy perovskites, in which AVA (5-aminovaleric acid) was used as an organic cation to separate the layers of chlorine-substituted lead bromide 2D perovskite, in order to identify the role of Cl substitution in tuning the bandgap and luminescence characters of the 2D AVA2PbBr4 perovskite. X-ray diffraction measurements revealed achievement of single-phase thin films of AVA2PbClxBr4-x perovskites with a (001) orientation. With increasing Cl/Br ratio from 0 to 1, the lattice constant c was found to decrease from 1.672 nm to 1.597 nm following c(x) = 1.674 – 0.076x, while the bandgap increased from 3.11 eV to 3.76 eV as approximated with Eg(x) = 3.08 + 0.62x. Correspondingly, the alloy luminescence character evolved from narrow-band blue-violet to broadband white-light emission, which was attributed to transformation from free-exciton to self-trapped-exciton emission with increasing octahedral distortion caused by Cl substitution. Based on an alloy system with continuously varying content designed for the first time, the work highlighted the role of Cl incorporation in changing the crystal lattice structure, and tuning bandgap as well as the light emission characters in 2D lead halide perovskites.

With the rapid development of shale gas exploration and development in China, casing deformation in shale gas horizontal wells happens frequently, which directly impacts the development efficiency and benefits of shale gas. In order to explore casing deformation prediction, prevention and treatment methods, this paper analyzes the geological and engineering causes of casing deformation in shale-gas horizontal wells through laboratory work, such as the casing resistance to internal pressure alternating test, the ground simulation test and systematical casing deformation characteristic analysis of MIT24 caliper logging, and the large-scale physical simulation test and numerical simulation of casing deformation. Then, combined with the generalized shear activity criterion, a new method for evaluating casing deformation risk points and some technical measures for preventing casing deformation were formulated. And the following research results were obtained. First, the deformation characteristics of 119 casing deformation points in 23 wells interpreted by MIT24 caliper logging are consistent with the mechanical behaviors of shear compression deformation test. Second, the large-scale physical simulation test shows that natural fault-fractures slip obviously under the state of strike-slip stress. Third, numerical simulation shows that the compression stress on casing increases with the increase of fault-fracture slip. When the fault-fracture slip is between 7.5 mm and 9.0 mm, the casing reaches the critical yield strength and begins to undergo plastic deformation. The “temporary fracture plugging + long segment and multi-cluster” and other technologies are field tested in 28 wells in Weiyuan area of southern Sichuan Basin. The casing deformation rate decreases from 54% (before this research) to 14.3%, and the segment loss rate decreases from 7.8% to 0, which reveals remarkable achievements in casing deformation treatment. In conclusion, the shear slip of fault and macro fractures (referred to as fault-fracture) is the main cause of casing deformation in shale gas horizontal wells, and some measures (e.g. “temporary fracture plugging + long segment and multi-cluster”, reducing fracturing scale and releasing wellbore pressure properly) shall be taken in advance to reduce the fault-fracture activity before the risk point of casing deformation is fractured, so as to reach the goal of casing deformation prevention.

(200) facets preferential oriented Ag nanowires were controllably prepared by a simple modified one-step polyol method, in which Cl ions and polyvinyl pyrrolidone (PVP) were employed as nucleating agent and crystal plane inducer, respectively. The evolution in morphology and structure of Ag nanowires were systematically studied by field emission scanning electron microcopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), from which the optimum synthesis conditions for (200) preferentially oriented Ag nanowires were obtained. Based on further electrochemical studies including cyclic voltammetry (CVs) and amperometry analyses, it is interesting found that the enrichment of (200) facets in the Ag nanowires display higher electrocatalytic activity than those of (111) facets towards glucose oxidation. This is attributed that dominant activity (200) facets of Ag nanowires have relatively higher surface energy and stronger adsorption capacity for glucose molecules, which can provide better electrocatalytic performance. The non-enzymatic glucose sensor based (200) facets preferential oriented Ag nanowires exhibits wide linear range of 0.5–3442 ​μM, low detection limit of 0.5 ​μM, and sensitivity is estimated to be 3246.74 ​μA ​cm−2 ​mM−1. Furthermore, the Ag nanowires based non-enzymatic sensor was successfully used for non-invasive detection of glucose in sweat with high accuracy.

Lead-free (Na0.5358K0.4042Li0.06)(Nb0.893Sb0.057Ta0.05)O3 (NKLNST) nanotubes were successfully grown on Pt(111)/Ti/SiO2/Si(001) substrates by using pulsed laser deposition (PLD) with home-made ceramic target under relatively high O2 partial pressures. The as-grown NKLNST nanotubes exhibited a perovskite phase and grew along (001) direction. The nanotubes’ outer diameters are ranging between 100 and 200 nm, their typical length is around 1 µm with a wall thickness of 10−20 nm. The films composed of NKLNST nanotubes show well-defined P–E hysteresis loops, with Pr of 3.77 μC/cm2 and Ec of 37.6 kV/cm. While under low electric field, the charge transport is dominated by ohmic conduction, at high electric fields, space charge-limited current turns out to be the governing leakage mechanism in these films. The work shows the potential of PLD in the synthesis of nanostructures of complex oxides under proper conditions.

Ceramics show brittle nature because of ionic and covalent bondings. However, the need for reliable high-power applications with vibrational displacements under high electric fields and stress loadings demands robust piezoelectric ceramics. In this work, three series of Lead Zirconium Titanate-based piezoelectric ceramics for high-power applications are synthesized via solid solution reaction technique. The microstructures and phases are manipulated by doping different rare-earth oxides Nd2O3, Dy2O3 and Yb2O3. Although all as-sintered piezoelectric ceramics show a perovskite structure with a coexistence of rhombohedral and tetragonal phases, phase fraction, grain size distribution and attendant electrical and mechanical properties vary depending on the doping species and contents. The comprehensive properties of optimized piezoelectric ceramics for high-power applications are: d33 = 292–308 pC/N, kp = 54.2–57.0%, Qm = 320–400, ε33T/ε0 = 1140–1210 and KIC = 1.55–1.60 MPa m1/2. These properties are improved by 19.0%–27.0% compared to the original composition without doping. The toughening mechanism by doping rare-earth oxides is discussed. Nd3+, Dy3+ and Yb3+ substitution and compensation at A-sites of perovskite unit cells generate extrinsic vacancies besides the intrinsic vacancies caused due to PbO evaporation during sintering, which make the domain wall highly mobile and result in softened ferroelectrics. Our results show an efficient route to toughen the PZT-based piezoelectric ceramics and enhance electrical properties synergistically via doping appropriate amounts of rare-earth oxides.

Inorganic ferroelectric filler/polymer nanocomposites combining large maximum electric displacement (Dmax) of ferroelectric materials with good flexibility and high electric breakdown strength (Eb) of the polymers are regarded as the most promising materials for preparing flexible dielectric capacitors with superior energy storage properties. Besides dielectric capacitors are always faced with high temperature environment in many application cases, and thus the applicability of high temperature is also highly desired. To develop nanocomposite-based dielectric capacitors with superior energy storage properties in a wide temperature range, in this study, we synthesize Pb0.97La0.02(Zr0.5Sn0.38Ti0.12)O3 (PLZST) antiferroelectric nanoparticles (NPs) with larger Dmax and smaller remnant electric displacement (Dr) in comparison with ferroelectric nanoparticles and disperse them into polyimide (PI) polymer matrix with good temperature stability. The results indicate that by adjusting reasonably the PLZST filler content, in a wide temperature range of 20–120 °C, 7 wt.% PLZST/PI nanocomposite exhibits slim electric displacement-electric field hysteresis loops and low Dr, and thus the discharge energy density and energy efficiency are always higher than 4 J/cm3 and 90%, respectively. These indicate this nanocomposite is a good candidate material for developing flexible dielectric capacitors applicable in high temperature environment.

To develop antiferroelectric based dielectric capacitors with superior energy storage capacity, antiferroelectric materials must possess simultaneously large recoverable energy density and high energy efficiency. With this motivation, in this work, we design and prepare Pb0.97La0.02(Zr0.50Sn0.43Ti0.07)O3 antiferroelectric ceramics with high Sn content considering that Sn element can narrow the electric hysteresis loops and thus improve the energy density and efficiency. The experiment results indicate that a large room-temperature recoverable energy density of 3.47 J/cm3 and a high energy efficiency of 78% are realized simultaneously in this kind of ceramic. Besides, in the wide temperature range of 20–120 °C, the recoverable energy density and the energy efficiency both show superior temperature stability. The large recoverable energy density and high energy efficiency in a wide temperature range demonstrate that the Pb0.97La0.02(Zr0.50Sn0.43Ti0.07)O3 antiferroelectric ceramic is a good candidate for preparing pulse power capacitors usable in various conditions. Keywords: Antiferroelectric, High Sn content, Energy storage, Recoverable energy density, Energy efficiency

Defects significantly affect the mechanical properties of materials. However, quantitatively correlating the point defects with mechanical property could be a challenge. In this study, we explore the point defect effects on the structure and property of magnetron sputtered TiN nanocrystalline films (synthesized using different negative bias potential) via a combination of analytical techniques and density functional theory (DFT) calculations. We gain insights into the structural evolution and properties of nanocrystalline films at different length scales. It is found that nanocrystal microstructure and local electronic structure triggered by various point defects remarkably change. Along with the structural evolution and point defect changes, the electrical conductivity and the fracture toughness of TiN are improved. Furthermore, the fracture toughness, Young’s modulus, and cleavage energy and stresses for TiN films with different point defect structures are calculated. The experimental data is in excellent agreement with first-principle calculations. Our results suggest a direct correlation of the point defect structure with TiN films' mechanical properties.

A silver-deposited nickel (Ag/Ni) wire electrode was prepared via a galvanic replacement reaction between Ag+ and Ni wire in aqueous solution. It was then found that the Ag/Ni wire electrode could be modified with Pt simply by treating it in an aqueous solution of K2PtCl4. Although the deposition of Ag on Ni wire was limited in amount, forming Ag deposits less than 100 nm in size, a considerable increase in the electrocatalytic currents for the oxidation of alcohols could be observed after further modification of the Ag/Ni wire electrodes with Pt. This is in contrast to the fact that it was difficult to produce sufficient electrocatalytic response by modifying Ni wire with Pt directly via a simple galvanic replacement between PtCl42− and Ni wire. Thus, the prior deposition of Ag was found to strongly promote modification with Pt via a simple stepwise treatment using AgNO3 and K2PtCl4. This approach should be effective in modifying various Ni materials with Pt, including Ni microparticles.

The monitoring results of production logging show that almost one third of perforation clusters produce no or less gas after volumetric fracturing is initially applied in shale gas reservoirs. Besides, the production decline after the commissioning is commonly faster. In this paper, a fracture network prediction model and a fracturing well productivity prediction model were established based on microseismic interpretation data and hydraulic fracture network propagation results. After petrophysics, microseism, production performance were taken into consideration comprehensively, shale re-fracturing development potential evaluation index (RDPEI) was proposed. Then, a re-fracturing design and evaluation method was developed and targeted interval selection and evaluation was realized and applied on site. And the following research results were obtained. First, due to the heterogeneity of natural fractures, hydraulic fracture networks are more different, so an obvious “dead gas zone” can be easily formed and its re-fracturing potential is high. Second, the initial hydraulic fracture network is more affected by natural fractures. The main part of a fracture network propagates along the direction of maximum horizontal major stress, the fractures in regional stimulated intervals propagate in the form of double wing, and the length of a liquid swept fracture network is 52–70% of seismic interpretation result. Third, the RDPEI model avoids the limitations of single factor analysis and realizes the quantitative prediction on three types of indexes of recoverability, compressibility and re-fracturing. Fourth, re-fracturing of the case well is remarkable in stimulation effect. Its shale gas productivity is increased by 38.9%, and its cumulative gas production in one year is increased by 62.5%. In conclusion, re-fracturing is an effective and feasible method for improving the single well ultimate recovery reserves of shale gas. This method provides a theoretical and technical support for the selection and effect evaluation of re-fracturing intervals in shale-gas horizontal wells. Keywords: Shale gas, Re-fracturing, Productivity, Prediction, Fracture network propagation, Microseismic, Production decline, Single-well ultimate recoverable reserves

Oxygen contamination during the mixing of precursor powders for nanocrystalline materials affects alloy microstructure, but exactly how remains unclear. Here, the authors show that stable nano-oxides can form easily inside severely deformed Cu-Fe grains during heating.

Heterostructures such as heterojunctions, quantum wells, and superlattices are core components of advanced optoelectronic devices. Herein, we attempted the first investigations on the band alignment of nonpolar m-plane oriented ZnO1−xSx/Mg0.4Zn0.6O heterojunctions by X-ray photoelectron spectroscopy. All the heterojunctions were revealed to show a type-I band alignment, and the valence band offset (VBO; ΔEV) increased significantly, while the conduction band offset (ΔEC) decreased insignificantly with increasing S content in the ZnO1−xSx layer. Specifically, for the ZnO1−xSx/Mg0.4Zn0.6O heterojunctions with x = 0, 0.13, and 0.22, ΔEV (ΔEC) was determined to be 0.24 (0.22), 0.61 (0.17), and 0.79 (0.11) eV, respectively. The VBOs of ZnOS/MgZnO heterojunctions are significantly larger than those of heterojunctions involving only cation-substituted alloys (ZnO/MgZnO or ZnO/CdZnO) due to the opposite shift in the VB maximum of ZnOS and MgZnO with respect to ZnO. Knowing band alignment parameters of the ZnOS/MgZnO interface can provide a better understanding of the carrier transport mechanism and rational design of ZnO-based optoelectronic devices.