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Amorphous silicon and silicates-stabilized ZrO2 hollow fiber with low thermal conductivity and high phase stability derived from a cogon template
摘要： ZrO2 ?bers are used as refractory materials owing to their excellent thermal resistance and thermal stability. Natural cogon ?ber is a type of hollow Gramineae ?ber, and usually contains a small amount of amorphous silicon and silicates, such as SiO2, MgSiO3, CaSiO4, and Al2SiO5, which can e?ectively avoid the phase transition of ZrO2. In this study, hollow ZrO2 ?bers with remarkable thermal insulation and phase stability were synthesized using a cogon ?ber template. The results showed that the ?nal ZrO2 ?bers successfully inherited the hollow structure and amorphous substance from the cogon template. The hollow structure of the biomorphic ZrO2 ?ber helped prevent heat ?ow more e?ciently compared to solid ?bers and reduced the thermal conductivity to a signi?cant extent. In addition, the amorphous silicon and silicates played an important role in the phase stability of tetragonal ZrO2; the transformation from the tetragonal to monoclinic phase was avoided at room temperature and in humid environment.
关键词： Thermal conductivity,Amorphous silicon and silicates,Cogon ?bers,Phase stability,ZrO2 hollow ?bers
更新于2025-09-23 15:23:52
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Structural Stability of Hafnia-Based Materials at Ultra-High Temperature
摘要： This study assesses the structural stability at ultra-high temperature of the following selected compositions: 6.5 and 14 mol. % of RE2O3 (RE = Dy, Y, Er, Yb, and Lu) doped HfO2. Under thermal cycling and thermal shock, the structural stability was evaluated at 2400°C with water vapor flux using a specific test bench with a 3 kW CO2 laser. The cubic phase stability, which is theoretically important in the broad temperature range from 25 to 2800°C, was determined by a quantitative analysis of the X-ray diffractograms. Fully and partially stabilized HfO2, obtained respectively with 14 mol. % and 6.5 mol. % of dopants, showed different behaviors to thermal damage. Thermal expansion was measured up to 1650°C to anticipate dimensional changes of these stabilized samples and to be able to design an optimized material solution fitting with future combustion chamber requirements. All of these results were then considered in order to exhibit a trend on the thermal stability at 2400°C of the ionic radius of the dopants and their optimal doping rates.
关键词： Phase stability,UHTC,Thermal expansion,Spacecraft propulsion,HfO2
更新于2025-09-23 15:22:29
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High Phase Stability in CsPbI <sub/>3</sub> Enabled by Pba??I Octahedra Anchors for Efficient Inorganic Perovskite Photovoltaics
摘要： CsPbI3 inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI3 severely hinders its applications. Herein, the nature of the photoactive CsPbI3 phase transition from the perspective of PbI6 octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI3. CsPbI3 is decorated with multifunctional 4-aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films’ surface (NGBr-CsPbI3(ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI3 anchors the PbI6 octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner-sharing PbI6 octahedra and kinetically stabilizes the photoactive phase CsPbI3. Moreover, the added ABA and NGBr not only interact with shallow- or deep-level defects in CsPbI3 to significantly reduce defect density, but also lead to improved energy-level alignment at the interfaces between the CsPbI3 and the charge transport layers. Finally, the champion NGBr-CsPbI3(ABA)-based inorganic perovskite solar cell delivers 18.27% efficiency with excellent stability. Overall, this work demonstrates a promising concept to achieve highly phase-stabilized inorganic perovskite with suppressed defect density for promoting its optoelectronic applications.
关键词： inorganic perovskite,phase stability,PbI6 octahedra anchors,CsPbI3,defect density
更新于2025-09-23 15:21:01
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Mn Doping CsPbI3 Film Towards High-Efficiency Solar Cell
摘要： A doping technique that introduces suitable elements into the host material is extensively utilized to modulate perovskite lattice structure, stabilize crystallographic phases and achieve various optical and electronic properties. In this work, we substitute Pb2+ in CsPbI3 film with Mn2+ to improve the phase stability of the material. The crystalline quality of perovskite materials with Mn2+ doping is significantly improved, and the defect densitys is reduced. The power conversion efficiency (PCE) of an inorganic perovskite solar cell with optimized Mn2+ doping (2%) reached 16.52 %, which is higher than the 15.05% of the reference, with an enhancement of ~ 10%. Simultaneously, the humidity and thermal stability were boosted by the Mn doping, which is attributed to the introduction of Mn shrinking the lattice of the perovskite material and enhancing the formation energy of the CsPbI3 film.
关键词： Power Conversion Efficiency,Mn-Doping,CsPbI3,Phase Stability,Perovskite Solar cell
更新于2025-09-23 15:21:01
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Prediction of a Dynamically Stable New Half-Metallic Phase for the BaN and BaC Compounds
摘要： The structural, magnetic, elastic, mechanical, and thermodynamic properties of BaC and BaN compounds in different phases were studied using first-principle calculations based on spin-polarized density functional theory within the generalized gradient approximation (GGA-PBEsol) and the modified Becke–Johnson approach (mBJ-GGA-PBEsol) for the exchange-correlation energy and potential. The following phases—rock-salt (NaCl), CsCl, zinc blende (ZB), NiAs- and WZ-type hexagonal, tetragonal (P4/nmm), and orthorombic (Pnma) phases of BaC and BaN compounds—were considered. We obtained that Pnma phase has the lowest energy configuration as a function of the volume for both the BaN and BaC compounds. The ferromagnetic phase is energetically favored with respect to the non-magnetic phase in the BaN and BaC compounds, except for the CsCl phase in the BaC compound. Considering the phonon dynamics of BaN and BaC compounds in the Pnma, NaCl, ZB, and WZ phases, we observed that the BaN and BaC compounds in the Pnma, NaCl, and ZB phases are dynamically stable. The calculated elastic properties for the Pnma, NaCl, and ZB phases show that they are elastically stable. The Pnma phase for the BaN and BaC compounds, which is a new phase was found to be dynamically and elastically stable. The BaN and BaC compounds exhibit half-metallic behavior in the Pnma, NaCl, and ZB phases. The half-metallic and magnetic character found in the BaN and BaC compounds are attributed to the presence of spin-polarized 2p orbitals of the nitrogen and carbon atoms, respectively. We found that BaN and BaC compounds are half-metallic ferromagnets with magnetic moment of 1 μB and 2 μB per formula unit, respectively. Using the GGA-PBEsol (mBJ-GGA-PBEsol) approach, our calculated half-metallic gaps for BaN and BaC compounds are 0.22 eV (0.54 eV) and 0.32 eV (0.44 eV) in the Pnma phase, 0.23 eV (1.32 eV) and 0.35 eV (1.00 eV) in the NaCl phase, and 0.38 eV (1.54 eV) and 0.50 eV (1.57 eV) in the ZB phase, respectively.
关键词： BaN,Density functional theory,Half-metallic,BaC,Phase stability,Phonon dynamics
更新于2025-09-23 15:21:01
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Effect of Oxygen Partial Pressure on the Phase Stability of Copper–Iron Delafossites at Elevated Temperatures
摘要： Oxide-based materials are promising candidates for use in high temperature thermoelectric generators. While their thermoelectric performance is inferior to commonly used thermoelectrics, oxides are environmentally friendly and cost-effective. In this study, Cu-based delafossites (CuFeO2), a material class with promising thermoelectric properties at high temperatures, were investigated. This work focuses on the phase stability of CuFeO2 with respect to the temperature and the oxygen partial pressure. For this reason, classical material characterization methods, such as scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, were combined in order to elucidate the phase composition of delafossites at 900 ?C at various oxygen partial pressures. The experimentally obtained results are supported by the theoretical calculation of the Ellingham diagram of the copper–oxygen system. In addition, hot-stage X-ray diffraction and long-term annealing tests of CuFeO2 were performed in order to obtain a holistic review of the phase stability of delafossites at high temperatures and varying oxygen partial pressure. The results support the thermoelectric measurements in previous publications and provide a process window for the use of CuFeO2 in thermoelectric generators.
关键词： high temperature thermoelectric materials,delafossite,thermoelectric generator (TEG),phase stability,Ellingham diagram
更新于2025-09-19 17:15:36
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Intrinsic defects in and electronic properties of <i>θ</i> -Al <sub/>13</sub> Fe <sub/>4</sub> : an <i>ab initio</i> DFT study
摘要： θ-Al13Fe4 exhibits a rich variety of crystal physics. It contains twenty crystallographically different atomic species with a diversity of chemical coordination. An understanding of its structural and physical properties is a prerequisite for controlling its formation and its use. Here we investigate systematically the intrinsic defects in θ-Al13Fe4 using a ?rst-principles density-functional theory method. The calculations reveal that among the various intrinsic defects it is energetically favourable for Fe substitution of Al but on just three of the ?fteen Al sites. This results in a new structural model, Al68Fe24(Al, Fe)4(Al, Fe)2(Al, Fe)4 (the Roman numerals represent the Al sites) which updates the thermodynamic model, currently in use, which is associated with the formation of vacancies on some of the Al sites. The calculations demonstrate that the addition of Fe induces magnetism which gives rise to clustering. The calculations provide the dependence of the lattice parameters on Fe concentration and explain the experimental data in the literature. The information obtained here provides insight into the formation and properties of θ-Al13Fe4 and its role in the solidi?cation of Al alloys, in determination of the microstructure and related mechanical properties of the products, and in catalysis for organic reactions.
关键词： magnetic properties,density-functional theory calculations,intrinsic defects,θ-Al13Fe4,phase stability
更新于2025-09-19 17:15:36
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A 0D/3D Heterostructured All‐Inorganic Halide Perovskite Solar Cell with High Performance and Enhanced Phase Stability
摘要： Although organic–inorganic hybrid perovskite solar cells (PVSCs) have achieved dramatic improvement in device efficiency, their long-term stability remains a major concern prior to commercialization. To address this issue, extensive research efforts are dedicated to exploiting all-inorganic PVSCs by using cesium (Cs)-based perovskite materials, such as α-CsPbI3. However, the black-phase CsPbI3 (cubic α-CsPbI3 and orthorhombic γ-CsPbI3 phases) is not stable at room temperature, and it tends to convert to the nonperovskite δ-CsPbI3 phase. Here, a simple yet effective approach is described to prepare stable black-phase CsPbI3 by forming a heterostructure comprising 0D Cs4PbI6 and γ-CsPbI3 through tuning the stoichiometry of the precursors between CsI and PbI. Such heterostructure is manifested to enable the realization of a stable all-inorganic PVSC with a high power conversion efficiency of 16.39%. This work provides a new perspective for developing high-performance and stable all-inorganic PVSCs.
关键词： solar cell,phase stability,inorganic perovskite,high performance,0D/3D heterostructured
更新于2025-09-19 17:13:59
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Black phosphorus quantum dots in inorganic perovskite thin films for efficient photovoltaic application
摘要： Black phosphorus quantum dots (BPQDs) are proposed as effective seed-like sites to modulate the nucleation and growth of CsPbI2Br perovskite crystalline thin layers, allowing an enhanced crystallization and remarkable morphological improvement. We reveal that the lone-pair electrons of BPQDs can induce strong binding between molecules of the CsPbI2Br precursor solution and phosphorus atoms stemming from the concomitant reduction in coulombic repulsion. The four-phase transition during the annealing process yields an α-phase CsPbI2Br stabilized by BPQDs. The BPQDS/CsPbI2Br core-shell structure concomitantly reinforces a stable CsPbI2Br crystallite and suppresses the oxidation of BPQDs. Consequently, a power conversion efficiency of 15.47% can be achieved for 0.7 wt % BPQDs embedded in CsPbI2Br film-based devices, with an enhanced cell stability, under ambient conditions. Our finding is a decisive step in the exploration of crystallization and phase stability that can lead to the realization of efficient and stable inorganic perovskite solar cells.
关键词： inorganic perovskite,phase stability,Black phosphorus quantum dots,photovoltaic application,crystallization
更新于2025-09-19 17:13:59
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Recent Advances in Improving Phase Stability of Perovskite Solar Cells
摘要： Organic–inorganic hybrid perovskite solar cells (PSCs) have demonstrated high efficiency and improved stability, which shows promising potential for commercialization. However, among all challenges, the material and device instability of the methylammonium lead iodide (MAPbI3) absorber are regarded as serious obstacles to the future development of devices for long-term operation. Compared with conventional MAPbI3, formamidinium lead iodide (FAPbI3) and cesium lead iodide (CsPbI3) have attracted more attention due to their superior thermal stability. Due to their undesirable tolerant factor, however, these materials suffer from poor phase stability, which is worthy of careful investigation. This perspective highlights the recent progress on the phase stabilization of FAPbI3 and inorganic CsPbI3 materials with emphasis on the fundamental understanding of the origin of phase instability. In addition, strategies to fabricate corresponding devices toward high-efficiency and long-lifetime are discussed. This review sheds light onto the design and synthesis of FAPbI3 and inorganic CsPbI3 perovskite materials. In the end, the potential of FAPbI3 and inorganic CsPbI3 perovskite materials as stable absorbers is discussed, which promotes the development of corresponding solar cells and other optoelectronic devices for practical applications.
关键词： FAPbI3,CsPbI3,phase stability,optoelectronic devices,perovskite solar cells
更新于2025-09-19 17:13:59