Journal of Materials Chemistry C最新文献

Lithium niobate (LN) is a multifunctional crystal with excellent piezoelectric properties, making it a potential candidate for piezoelectric sensing applications. In this study, the mechanism of the discrepancies of piezoelectric properties between near stoichiometric lithium niobate (NSLN) and congruent lithium niobate (CLN) were probed using Raman spectrum, first principles calculations and single crystal X-ray diffraction (XRD), where the V⁻_Li defect demonstrated a significant impact on the distortion of the NbO₆ octahedron, which in turn affected the piezoelectric properties of the LN crystal. The NSLN crystal exhibited a strong performance, with high piezoelectric coefficients d₁₅ and d₂₂ on the orders of 77.6 pC N⁻¹ and 22.8 pC N⁻¹, respectively, showing increases of 17.4% and 18.1% over the CLN crystal, and highlighting its enhanced piezoelectric characteristics. Finally, temperature-dependent behaviours of the electro-elastic constants for the NSLN and CLN crystals were discussed. The high-temperature piezoelectric performance of NSLN crystal was evaluated utilizing a prototype of shear-mode acceleration sensor, demonstrating remarkable sensing performance up to 650 °C with good temperature stability (sensitivity variation <5%).

We present a novel ZnO/Au/Ti/p-GaN self-powered ultraviolet photodetector (UVPD) featuring a sandwich structure of asymmetric interdigitated electrodes. This unique design skillfully integrates the conventional vertically-structured ZnO/p-GaN UVPD, asymmetric Au/ZnO/Au UVPD, and asymmetric Ti/p-GaN/Ti UVPD into a single device, which effectively enhances the separation and collection efficiency of photogenerated carriers while reducing their composite depletion through the coupling of the built-in electric fields of the Schottky junctions (ZnO/Au, p-GaN/Ti) and the heterojunction (ZnO/p-GaN), creating a synergistic enhancement in performance. At 0 bias, while achieving a fast response speed (0.98/0.63 ms), the ZnO/Au/Ti/p-GaN UVPD also shows improvements in light-to-dark ratios by 7.78, 15.79, and 20.0 times, and in responsivity peaks by 2.7, 4.12, and 152.84 times, compared to the ZnO/p-GaN UVPD, the MSM ZnO UVPD, and the MSM GaN UVPD, respectively. Our proposed sandwich structure of asymmetric interdigitated electrodes offers significant performance enhancement and a simple preparation process, and it can also be applied to other semiconductor heterojunctions, demonstrating wide practical application potential. This work provides a valuable strategy for the development of high-performance and low-cost self-powered UV photodetectors.

Novel glass-ceramics (GCs) containing polymorphic CaTa₂O₆:Er³⁺/Yb³⁺ nanocrystals were prepared in this study using an aerodynamic levitation method followed by heat treatment of the precursor glasses (PGs). The phase transition from cubic to orthorhombic crystal forms depending on the heat-treatment temperature was observed. The appearance of the corresponding GCs changed gradually from transparent to translucent and opaque with increasing temperatures. The evolution of phase composition and microstructure was investigated through X-ray diffraction (XRD), Rietveld refinement and transmission electron microscopy (TEM). Both XRD refinement results and spectroscopic properties, including the decrease in unit cell parameters, significant enhancement in upconversion (UC) luminescence, obvious Stark splitting of the UC and near-infrared (NIR) emission bands and the extension of lifetimes, confirmed the incorporation of the rare-earth (RE) ions into the crystalline phases. Furthermore, the temperature-dependent UC and NIR luminescence variations of the GCs containing polymorphic CaTa₂O₆:Er³⁺/Yb³⁺ nanocrystals were investigated. Based on the fluorescence intensity ratio (FIR) technique, the thermally coupled levels (TCLs) (²H_11/2/⁴S_3/2), non-thermally coupled levels (NTCLs) (⁴S_3/2/⁴F_9/2) and Stark sublevels (⁴I_13/2) of Er³⁺ ions were used for three-mode thermometry. The maximum absolute sensitivities of FIR(H/S) and FIR(S/F) were 3.8 × 10⁻³ and 3.7 × 10⁻² K⁻¹, respectively, which are much higher than those reported in previous reports. Furthermore, FIR(1500/1532) based on the Stark sublevels of orthorhombic phase GC offers a complementary way of temperature sensing. These results suggest the potential application of the GCs in self-referenced optical thermometry.

Far-red (FR) emission (>700 nm) with high efficiency and excellent thermal stability is in great demand for solid-state lighting applications in health illumination. However, currently used FR materials often face challenges such as complex synthesis, low efficiency, and thermal instability. In this study, we present a highly efficient and thermally stable far-red phosphor, Mn⁴⁺-activated La_1−xCa_xAlO_3−yF_y, with a dominant emission wavelength of 731 nm. Based on this, an ultrathin phosphor–glass composite (PGC), with a FR luminescence quantum yield of 68.2%, is prepared using a tape-casting process combined with a low-temperature cofiring technique. The impact of ionic substitution on the crystal structure and luminescence properties is examined to establish the optimal doping conditions. Interestingly, we observed that the prepared PGC exhibits temperature-dependent luminescence distinct from that of FR phosphor. The luminescence lifetime for the PGC is measured to be nearly 3.576 ms, representing a 28.4% decrease compared to that of the pure phosphor. Ultimately, light-emitting diodes (LEDs) are fabricated by combining the PGC with a violet chip, and their electroluminescence (EL) properties are strongly dependent on the configuration of the PGC composite. This research offers a straightforward and versatile method for producing ultrathin far-red PGCs that hold promise for diverse photonic applications.

A 2D-MoS₂/2D-SnS₂ photocatalyst with a van der Waals (vdW) heterojunction has been prepared in this work by the self-assembly of MoS₂ nanosheets on the SnS₂ microflake surface. The multi-scale micro-nano hierarchical structure of MoS₂ with a narrow bandgap (1.27 eV) exhibits an obvious photothermal effect and significantly enhanced light absorption ability in the wide wavelength range of 200–2000 nm. Both experimental investigation and corresponding simulations based on the density functional theory demonstrate that the vdW interaction and internal electric field between MoS₂ and SnS₂ favor direct Z-scheme charge separation and transportation effectively. As a result, the optimized MoS₂/SnS₂ Z-scheme heterojunction photocatalyst with full-spectrum response displays excellent photocatalytic CO₂ reduction performance. In particular, the MoS₂/SnS₂ photocatalyst was able to maintain excellent photocatalytic CO₂ reduction performance under NIR light irradiation at 880 nm and achieved a maximum CO yield of 0.033 mmol cm⁻² h⁻¹ when the laser output power reached 20 W. This work may provide valuable guidance for the construction of vdW Z-scheme heterojunction photocatalysts for high-efficiency photocatalytic CO₂ reduction and effective solar light utilization.

Ce-containing Nd–Fe–B magnets have been widely used because of their low cost, but the effects of Ce content in the magnets on the grain boundary diffusion (GBD) behavior are still unclear. In this work, Pr–Nd–Ce–Fe–B sintered magnets with various Ce contents were treated by using a Tb–Cu GBD process. The effects of Ce content on the diffusion behavior of Tb and the microstructure evolution of the magnets were systematically investigated. The results indicate that the coercivity of magnets with Ce/TRE (TRE: total rare earth) ratios of 0, 4, 10, 25, and 35 wt% was increased by 68%, 81%, 79%, 42% and 21%, respectively, after Tb–Cu diffusion. The coercivity enhancement increases firstly with the increasing Ce/TRE ratio from 0 to 10 wt% then decreases with the further increase of Ce content in the magnet. For the magnets with low Ce content, an increase of Ce content lowers the melting point of the RE-rich GB phase, which is beneficial to the diffusion of Tb. In the magnets with high Ce contents, a large amount of REFe₂ phase formed in GBs, which acts as an obstacle to Tb diffusion. The formation of the REFe₂ phase not only blocks the liquid diffusion channel but also consumes Tb. Meanwhile, Tb, Nd, and Pr elements can enter into the REFe₂ phase during the GBD treatment, leading to the transition of the REFe₂ phase from paramagnetic to ferromagnetic, which is not beneficial to magnetic isolation and coercivity enhancement. This study thus provides a deep understanding of the role of Ce in the diffusion of HRE, which could provide a reference for the industrial development of the GBD process.

Here we report a novel conjugated polymer with deep red-light absorption, consisting of indacenothiophene (IDTT) and dinitrobenzothiadiazole (DNBT) units, which can be used as a gate-sensing layer (GSL) in organic phototransistors (OPTRs). The PIDTT–DNBT polymer was synthesized by the Stille coupling reaction between the IDTT monomer with tin end groups and the DNBT monomer with bromine end groups. The PIDTT–DNBT films showed two pronounced optical absorptions in the wavelength (λ) ranges of 350–470 nm and 470–800 nm and the highest occupied molecular orbital (HOMO) energy of −5.9 eV. The OPTRs with the PIDTT–DNBT GSLs operated in p-channel modes and exhibited noticeable photo-sensing performances under the illumination of three monochromatic lights (λ = 550, 670, and 700 nm). When visible light-cutting layers (VLCLs) were applied, the OPTRs with the PIDTT–DNBT GSLs could only sense deep-red light with a narrow spectral range of λ = 650–800 nm in the absence of other visible light interferences.

Over the past few decades, organic thin-film transistors (OTFTs) have shown remarkable progress in both device performance and functional applications, owing to the development of organic synthesis and fabrication methods. Electrohydrodynamic (EHD) deposition techniques, including electrospraying, electrospinning, and EHD printing, have emerged as powerful and effective material deposition technologies for electronic device fabrication. These techniques, driven by electric fields, represent a methodological innovation in OTFT fabrication and are currently competitive with other well-established approaches. This study presents a comprehensive overview of EHD deposition for OTFT fabrication, focusing on the high performance and practical applications of these devices, including artificial synapses, memories, and sensors. Our aim is not only to shed light on the existing excellent capabilities but also to stimulate the interest of more researchers and promote further constructive work in this burgeoning research domain.

Conjugated donor–acceptor polymers have been regarded as attractive organic semiconductors for perovskite solar cells (PSCs) as hole-transport materials (HTMs). Herein, we report the design of four novel (X-DAD)_n conjugated polymers based on alternating benzodithiophene unit (X) and thiophene-spaced benzene derivatives or pyridine (A). The variation of A building blocks has been shown to control the backbone geometry, which is crucial for achieving high charge-transport characteristics of HTMs. Particularly, introducing fluorine and methoxy-substituted blocks enabled rigid and planar backbone structure of PBPh-ff and PBPh-mm HTMs due to non-covalent intramolecular interactions. Benefiting from this merit, PBPh-ff and PBPh-mm exhibited improved hole mobilities and better hole extraction ability from MAPbI₃. As a result, employing PBPh-ff as the HTM in n–i–p PSCs provided power conversion efficiency of 19.1% with an outstanding fill factor of ca. 80%. These findings highlight the importance of molecular design and geometry control of hole-transporting polymers for efficient perovskite photovoltaic devices.

The search for high-performance intrinsic quantum anomalous Hall (QAH) insulators is crucial for the development of topological electronics. Here, based on density–functional theory calculations, TaPdSTe and TaPdSeTe monolayers are demonstrated to be intrinsic QAH insulators with topological band gaps of 88 and 79 meV, respectively. Both TaPdSTe and TaPdSeTe monolayers show an out-of-plane magnetic anisotropy with the Curie temperatures of 260 and 262 K by Monte Carlo simulations, respectively. The calculated Chern number C for both materials is −1. The analysis of the electronic structures reveals that the ferromagnetic topological property is caused by the energy band inversions of d_xz and d_yz orbitals of Ta atoms. Additionally, the effects of biaxial strain on the magnetic and topological properties are discussed for the current TaPdSTe and TaPdSeTe monolayers. During −3 to 3% biaxial strains, TaPdSTe and TaPdSeTe monolayers maintain the QAH effect, but their topological band gaps increase gradually from compressive to tensile strains. This study presents two intrinsic topological insulators that can help develop low-power electronic devices.