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The cascaded diode rectifier (DR)- MMC based HVDC system is recognized as a promising topology for integrating offshore wind farms. However, the capacity design of DR-MMC remains an unsolved challenge. This paper proposes a capacity design method based on operating region (OR) analysis. First, the analytical models of DR-MMC with V-F grid-forming (GFM) control are established, revealing its operating characteristics. Then, considering multiple constraints, the OR of DR-MMC is calculated. The impact of different MMC capacities on OR is analyzed, highlighting that a system with a low MMC capacity ratio may be incapable of covering its full active power range. Hence, a three-layer GFM control utilizing MMC DC voltage is proposed, enabling operation under a lower MMC capacity ratio. Then, an optimal MMC capacity ratio is determined by balancing the system stability margin and economic considerations. Finally, the effectiveness of the designed MMC capacity with the proposed three-layer GFM control is validated by stability analysis and simulations in PSCAD/EMTDC.

Lead-free molecular ferroelectrics have garnered considerable attention for their promising potential, but such species with narrow band gap and sensitive photoelectric response are yet inadequate. Herein, we demonstrated the bulk ferroelectric photovoltaic effect in a novel lead-free molecular ferroelectric [C4N2H14][BiI5] with a Curie temperature (Tc) of 366 K and a narrow band gap (Eg) of 1.92 eV. The transformation of the crystal structure from the polar space group P21to the nonpolar space group P21/mwas elucidated using single-crystal X-ray diffraction. Room-temperature (RT) hysteresis loop reveals the intrinsic ferroelectricity of [C4N2H14][BiI5] with a relative small coercive field (Ec∼ 0.27 kV/cm), saturation polarization (Ps∼ 1.87 μC/cm2), and remanent polarization (Pr∼ 1.61 μC/cm2). [C4N2H14][BiI5]-based solar device exhibits significant PV effects with a steady-state photocurrent (Jsc) of 3.54 μA/cm2and a photovoltage (Voc) of 0.34 V under AM 1.5 G illumination, which can be significantly improved by adjusting the ferroelectric polarization, reaching a maximum Jscof 140 μA/cm2and Vocof 0.51 V. This work offers a promising avenue for lead-free molecular ferroelectric materials in the field of optoelectronic devices.

Single-component white-light luminescent materials are considered an economical and facile choice for phosphor-converted white light-emitting diodes (pc-WLEDs). Here, a new single-component white-light-emitting material Cs2MnCl4:Eu2+based on the combination of a lead-free halide structure and a rare-earth ion is first reported. Benefiting from the smart dilution–sensitization design strategy, white light composed of dual broad emission originating from Eu2+(blue light, 444 nm, 4f65d1→ 4f7) and Mn2+(yellow light, 566 nm, 4T1g→ 6A1g) was successfully realized under near-ultraviolet light (404 nm) radiation with a high photoluminescence quantum yield of 66%. Based on the single-source Cs2MnCl4:Eu2+phosphor, a pc-WLEDs device with “eye-friendly” white light production was successfully fabricated. The pc-WLEDs exhibit suitable color coordinates of (0.3294, 0.2746) and a high color rendering index of 82.3, demonstrating the potential in the future health-conscious illumination application by reducing the risk of eye strain and high-energy blue-light damage. This work achieves a new single-component white-light-emitting Mn-based halide phosphor and provides a new path for the design of single-component white light sources in Mn-based halides.

TiO2-based photocatalysts have been extensively studied owing to their economic affordability, sensitive photo-responsivity, excellent chemical and thermal stability, abundance in nature, and other properties. However, insufficient visible-light absorption and photoelectrode efficiency greatly impede the practical application of TiO2-based photoelectrochemical (PEC) devices. Herein, a novel oxygen-deficient TiO2/black-BaTiO3(B-BTO)/CdS composite film was successfully fabricated by combining a hydrothermal method and Al-reduction and chemical bath deposition (CBD) techniques. A superior photocurrent density of 7.14 mA cm−2was achieved in the TiO2/B-BTO/CdS photoanode at 0 V vs.Ag/AgCl, which was approximately 35.7-fold and 2.2-fold higher than that of TiO2/BaTiO3(TiO2/BTO) and CdS photoanodes, respectively. The improved PEC performance of the prepared nanocomposite can be attributed to the synergistic effect of the increased surface area of nanorod arrays, promoted light-harvesting capacity of oxygen-deficient B-BTO, spontaneous polarization of BTO, and TiO2/B-BTO/CdS multiple heterojunction structures. This work is expected to offer a new avenue for designing new oxygen-deficient TiO2-based nanocomposites with outstanding PEC activity.

The push-pull DC autotransformer (PPDAT) is a potential power equipment to interconnect the MMC and LCC HVDC systems. However, the harmonic stability of the PPDAT remains an unsolved challenge. In this article, considering the dual closed-loop control and bidirectional DC voltage operation of the PPDAT, its DC impedance models are proposed using the harmonic transfer function (HTF) method. Both the DC impedance models at the high/low voltage side considering the harmonic coupling and internal dynamics of the hybrid MMC/LCC HVDC system are deduced. The accuracy of the detailed DC impedance models is validated in PSCAD/EMTDC simulations. The impedance analysis under bidirectional DC voltage operation scenarios reveals that the DC voltage polarity affects the low frequency region. Besides, the main impact of PPDAT's parameters on the wideband impedance characteristics is disclosed. It shows that unreasonable parameter design will bring negative damping characteristics near the resonance point (RP). Moreover, stability analysis considering the interaction of PPDAT and LCC-HVDC at the high-voltage side is conducted. The results indicate that the potential resonances can be readily predicted through the Nyquist diagrams and the negative damping of the PPDAT may cause instability at RP.

Synthesizing highly luminescent active iondoped phosphors is desirable for many related applications but, remains challenging when a conventional solid-state reaction method is used for this purpose. In this contribution, we demonstrate the transformation of a poorly luminescent phase with a photoluminescence quantum yield (PLQY) of 3.1% to highly luminescent cousins with a PLQY of 58.9%, through a post-synthetically topochemical reaction treatment, as illustrated in a Mn4+-doped Sr3WO6model system. Detailed structural analyses, combined with spectroscopic results, revealed that the highly luminescent treated samples have larger W–O distances, and the volume of the [(W/Mn)O6] octahedron in the structure was expanded with respect to the precursor, as a result of the formation of oxygen vacancies. We find that topochemical reduction causes the conversion of W6+ions to W5+, while it does not impact the oxidation state of Mn4+ions. These changes lead to the release of the chemical pressure around the Mn4+ions, resulting in significant suppression of non-radiative recombination and thus greatly enhanced luminescence. We believe that our concept proposed here has the potential to be extended to tuning the properties of other functional materials that are sensitive to the local crystal environments of dopants.

Hybrid organic–inorganic molecular ferroelectrics (HOIMFs) have garnered significant attention owing to their potential applications in optoelectronic and spintronic devices. However, HOIMFs with high Curie temperature (Tc), narrow bandgap (Eg), excellent stability, and high breakdown voltage are still very rare. Herein, we present a novel lead-halide molecular ferroelectric, (1,4-butanediammonium)PbI4(1), synthesized hydrothermally. 1exhibits a ferroelectric-to-paraelectric phase transition with a high Curie temperature of 485 K, a room temperature ferroelectric hysteresis loop with a robust saturation polarization of 3.9 μC/cm2and strong coercivity of 33 kV/cm, and a typical semiconductor behavior with a direct bandgap of 2.28 eV. Switchable photovoltaic effect was observed in 1-based device with a fast response time of ∼2 ms and high breakdown electric field of 80 kV/cm. Dramatically enhanced photovoltaic performance has been achieved by manipulating the ferroelectric polarization, resulting in a maximum photovoltage of Voc∼ 0.84 V and a photocurrent of Jsc∼ 33.31 nA/cm2under standard AM 1.5 G illumination. This study offers a bright avenue for advancing high-Tclead-halide molecular ferroelectrics with promising potentials in photodetectors, data storage, and logical switching devices.

A universal and facile strategy is proposed to fabricate polarized Bi2WO6nanoparticles with the assistance of a soluble organic–inorganic composite film. After electric poling, there is no significant change in the crystal structure or morphology as confirmed by XRD, SEM and TEM studies. By combining piezoresponse force microscopy (PFM), photoinduced silver deposition and time-resolved photoluminescence (PL) testing, it can be revealed that the promoted separation and prolonged lifetime of photogenerated carriers are unambiguously caused by ferroelectric polarization. The visible-light-driven photocatalytic activity of the polarized Bi2WO6nanosheets was significantly improved by 2-fold compared to that of pristine Bi2WO6. This electric poling strategy offers a new route for large-scale fabrication of various polarized ferroelectric nanoparticles, and has immense potential for practical applications in catalysis, optoelectronics and energy storage devices.

A new series of mixed valence perovskites, La0.75K0.25AMnTiO6(A = Sr and Ba) nanocubes, have been synthesized by a mild hydrothermal route. From powder X-ray diffraction (XRD) analysis, the crystal structure of La0.75K0.25AMnTiO6was solved as the orthorhombic symmetry (space group Pbnm) with a random A-site or B-site arrangement. The phase purity of the products was confirmed by ICP, SEM, and EDS analyses, and the oxidation states of the B-site metal atoms were determined to be +4 for Ti and +3/+4 for Mn from XPS results. The soft ferromagnetic behavior is present in both samples. The Curie point TChas been detected as high as 309 K in La0.75K0.25SrMnTiO6and 217 K in La0.75K0.25BaMnTiO6. A Griffiths phase can be observed at the high temperature region, which is related to the magnetic inhomogeneity induced by the existence of short-range ferromagnetic clusters. The resistivity measurements indicate that the semiconducting properties of the samples can be depicted better by variable range hopping (VRH) due to a diluted double-exchange interaction of Mn3+-O-Mn4+with Ti4+doping.

With the addition of oxygen into the chain-like bismuth sulfide of Bi2S3, there are two interesting functional compounds of Bi2O2S (photoelectric) and Bi4O4S3(superconducting) containing the PbO-like [Bi2O2] layers. Nanoscale Bi2O2S crystals with an indirect band gap of 1.12 eV are synthesized via a facile hydrothermal method. This semiconductor shows excellent photoelectric response under the irradiation of visible light lamp at room temperature. Theoretical calculations and packing factor model both indicate that the loosely packed Bi2O2S is an excellent photoelectric material. When the Bi2O2S phase was annealed at 500 °C in an evacuated quartz tube, nanocrystals of Bi4O4S3were obtained. The powder X-ray diffraction and electron microscope analyses (SEM, TEM, EDX) confirmed the thermal decomposition from orthorhombic Bi2O2S to tetragonal Bi4O4S3. The superconducting transition temperature of Bi4O4S3was observed to be 4.6 K from the temperature-dependence measurements of electrical resistivity and magnetic susceptibility. Our results also provide a new method utilizing thermal decomposition to prepare a new phase without high temperature reaction.

A series of double B mixed perovskite oxides La0.75K0.25Mn1-xFexO3(x= 0.2–0.5) were synthesized under mild hydrothermal conditions and characterized by powder X-ray diffraction, SEM, ICP, XPS, iodometric titration, and SQUID. All the compounds corresponded to orthorhombic structure of space group Pnmaand presented a cuboid morphology. The oxidation state of Fe is +3 whereas Mn is a mixed valence of Mn3+/Mn4+. The curves Mvs. Tfor all the compositions indicated the coexistence of ferro- and antiferromagnetic contribution.

Ba1‐xKxBiO3(x = 0.05, 0.35, 0.5,0.55), BaBi0.75Na0.25O3, and Ba0.85K0.15Bi0.83Na0.17 O3are hydrothermally synthesized from aqueous solutions of Bi(NO3)3, Ba(NO3)2, NaBiO3, and KOH (autoclave, 180 °C, 1—5 d) and characterized by SEM, powder XRD, and magnetization measurements.

Title compounds with x = 0.2—0.5 are hydrothermally synthesized from aqueous solutions of La(NO3)3, MnCl2, Fe(NO3)3, and KOH (autoclave, 260 °C, 3 d).

The title compounds are hydrothermally synthesized from aqueous solutions of La(NO3)3, CrCl3, Fe(NO3)3, and KOH with various initial Fe/Cr ratios and KOH contents (autoclave, 513 K, 5 d) and characterized by powder XRD, SEM, and magnetization measurements.

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