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Evidence and Influence of Copper Vacancies in p-Type CuGaO <sub/>2</sub> Mesoporous Films
摘要： Delafossite CuGaO2 nanocrystals were hydrothermally synthesized and characterized spectroscopically and electrochemically as mesoporous thin films. The nanocrystals demonstrate a preferred orientation within the film structure, as shown by enhancement of the (00l) peaks via two-dimensional powder X-ray diffraction. Annealing conditions of low and high temperature (i.e., 100?300 °C), with oxygen and/or argon atmospheres, were investigated, and the resulting effect on the thin film electrochemistry was measured. Cyclic voltammetry showed an increase in non-faradaic current with higher annealing temperatures and demonstrated a quasi-reversible redox feature (E1/2 = 0.1 V vs Fc+1/0). This feature is assigned to a CuII/CuI redox couple associated with surface defects. X-ray photoelectron and energy dispersive spectroscopies provide evidence for CuII surface defects and copper vacancies. Electrochemical impedance spectroscopy revealed that CuGaO2 films were highly conductive with σ ～ 10?5 Ω?1 cm?1, consistent with a large density of hole carriers induced by copper vacancies. The significance of synthesis, film preparation, and annealing conditions on the presence of surface defects and large hole densities is discussed. The prevalence of such defects in delafossite CuGaO2 is expected to have a large impact on the use of this material as a hole transport layer in solar cell architectures.
关键词： p-type metal oxide,delafossite,hole transport,heterojunction solar cell,CuGaO2
更新于2025-09-23 15:23:52
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Pulsed-laser epitaxy of metallic delafossite PdCrO <sub/>2</sub> films
摘要： Alternate stacking of a highly conducting metallic layer with a magnetic triangular layer found in delafossite PdCrO2 provides an excellent platform for discovering intriguing correlated quantum phenomena. Thin film growth of delafossites may enable not only the tuning of the basic physical properties beyond what bulk materials can exhibit, but also the development of novel hybrid materials by interfacing with dissimilar materials, yet this has proven to be extremely challenging. Here, we report the epitaxial growth of metallic delafossite PdCrO2 films by pulsed laser epitaxy (PLE). The fundamental role of the PLE growth conditions, epitaxial strain, and chemical and structural characteristics of the substrate is investigated by growing under various growth conditions and on various types of substrates. While strain plays a large role in improving the crystallinity, the direct growth of epitaxial PdCrO2 films without impurity phases was not successful. We attribute this difficulty to both the chemical and structural dissimilarities with the substrate and volatile nature of the PdO sublayer, which make nucleation of the right phase difficult. This difficulty was overcome by growing CuCrO2 buffer layers before PdCrO2 films were grown. Unlike PdCrO2, CuCrO2 films were readily grown with a relatively wide growth window. Only a monolayer thick buffer layer was sufficient to grow the correct PdCrO2 phase. This result indicates that the epitaxy of Pd-based delafossites is extremely sensitive to the chemistry and structure of the interface, necessitating near perfect substrate materials. The resulting films are commensurately strained and show an antiferromagnetic transition at 40 K that persists down to as thin as 3.6 nm in thickness. This work provides key insights into advancing the epitaxial growth of the broader class of metallic delafossites for both studying the basic physical properties and developing new spintronic and computing devices.
关键词： delafossite,pulsed laser epitaxy,thin film growth,antiferromagnetic transition,PdCrO2
更新于2025-09-23 15:21:01
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: <i>Ab initio</i> and Monte Carlo approaches
摘要： The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to 30% of Cr3+ ions by Ga3+ ones does not significantly affect the remaining Cr-Cr superexchange interactions. Monte Carlo simulations show that CuCr1?xGaxO2 preserves its magnetoelectric properties up to x ≈ 0.15 with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing x and eventually disappears at x ≈ 0.2. Our simulations show that Ga3+ doping increases the Curie-Weiss temperature of CuCr1?xGaxO2, which agrees well with experimental observations. Moreover, our results show that the incommensurate ground-state configuration is destabilized by Ga3+ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for x ≤ 0.15 through simulating P -E hysteresis loops, which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model.
关键词： CuCrO2,multiferroic,Monte Carlo simulations,ferroelectric properties,magnetic properties,density functional theory,delafossite,Ga doping
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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Inorganic CuFeO2 Delafossite Nanoparticles as Effective Hole Transport Material for Highly Efficient and Long-Term Stable Perovskite Solar Cells
摘要： The regular architecture (n-i-p) of perovskite solar cells (PSCs) has an ascendant interest in the renewable energy field, owing to high certified efficiencies in the recent years. However, there are still serious obstacles of PSCs associated with spiro-OMeTAD hole transport material (HTM), such as: i-) prohibitively expensive material cost (~150-500 $/g) and ii-) operational instability at elevated temperatures and high humidity levels. Herein, we have reported the highly photo-, thermal- and moisture-stable and cost-effective PSCs employing inorganic CuFeO2 delafossite nanoparticles as HTM layer, for the first time. By exhibiting superior hole mobility and additive-free nature, the best-performing cell achieved a power conversion efficiency (PCE) of 15.6% with a negligible hysteresis. Despite exhibiting the lower PCE as compared to spiro-OMeTAD-based control cell (19.1%), non-encapsulated CuFeO2-based cells maintained above 85% of their initial efficiency, while the PCE of control cells dropped to ~10% under continuous illumination at maximum power point (MPP) tracking after 1000 h. More importantly, the performance of control cells was quickly degraded at above 70 oC whereas CuFeO2-based cells, retaining ~80% of their initial efficiency after 200 h, was highly stable even at 85 oC in ambient air under dark conditions. Besides appearing on significant improvement in stability against light soaking and thermal stress, CuFeO2-based cells exhibited superior shelf stability even at 80 ± 5% relative humidity and retained over 90% of their initial PCE. Overall, we strongly believe that this study highlights the potential of inorganic HTMs for the commercial deployment of long-term stable and low-cost PSCs.
关键词： Perovskite solar cell (PSC),Operational stability,CuFeO2 delafossite nanoparticles,Inorganic hole transport material (HTM),Thermal and moisture stability
更新于2025-09-12 10:27:22
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Transparent p-Cu0.66Cr1.33O2/n-ZnO heterojunction prepared in a five-step scalable process
摘要： Transparent and electrical conducting p-type off-stoichiometric copper–chromium oxide thin films were used to build p-Cu0.66Cr1.33O2/n-ZnO heterojunctions. The junctions were fabricated in a novel and simple five step process including metal organic chemical vapour deposition, atomic layer deposition, chemical wet etching, and optical lithography. One last step of thermal annealing, with varying temperatures of 650 and 700 °C, is added in order to tune the electrical properties of delafossite and consequently the electrical features of p–n junctions. This work was developed to address the lack of transparent and industrially scalable rectifying p–n junctions that can open multiple application paths in transparent electronics. A competitive ideality factor η of 6.6 and a transmittance in the visible range of 50% were achieved. An understanding of the electronic response of junctions is presented herein as well as a deepening comprehension of the physical properties of materials, with the bands alignment and the Fermi level tuning.
关键词： Atomic layer deposition,Optical lithography,Thermal annealing,Delafossite,Metal organic chemical vapour deposition,p-Cu0.66Cr1.33O2/n-ZnO heterojunctions,Transparent electronics,Chemical wet etching,Fermi level tuning
更新于2025-09-10 09:29:36
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PVP assisted hydrothermal synthesis of CuCoO2 nanoplates with enhanced oxygen evolution reaction performance
摘要： Tuning size and morphology and exploiting new catalytic materials are several important strategies commonly used to develop highly efficient oxygen evolution reaction (OER) electrocatalysts. In this work, we report the synthesis of CuCoO2 (CCO) nanoplates through a facile one-step PVP assisted hydrothermal process. The influence of hydrothermal reaction parameters, including the precursor composition, reaction temperature and duration, on the morphology, size and crystal phase of CCO crystals has been investigated in detail. In addition, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to comprehensively characterize CCO’s crystal structure, morphology, composition and chemical states of elements. Furthermore, the electrocatalytic performance of CCO nanoplates towards the OER is studied and compared to that of CCO micrometer-sized crystals. The CCO nanoplates only require a low overpotential of 390 mV to attain an anodic current density 10 mA cm-2 in alkaline solution, and show comparatively fast OER kinetics with a Tafel slope of 70 mV dec-1 and reasonably good long-term catalytic stability, substantially outperforming CCO micro-crystals, which highlights the importance of size and morphology of CCO for use in OER electrocatalysis.
关键词： Water splitting,Oxygen evolution reaction,CuCoO2,Delafossite,Electrocatalyst
更新于2025-09-10 09:29:36
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Photo-electrochemical properties of p-type AgCoO2 prepared by low temperature method
摘要： AgCoO2 prepared by co-precipitation at low temperature (~ 80 °C) is characterized by physical and photo-electrochemical techniques. The X-ray diffraction shows broad peaks with a particle size of ~ 20 nm and a specific surface area of ～ 28 m2 g?1. The forbidden band (1.33 eV) is due to Ag+: d → d transition, further transition at 4.50 eV is assigned to the charge transfer. The transport properties, measured up to 650 K, indicate intrinsic conductivity: σ = σo exp{? 0.24 eV/kT (Ω-cm)?1}, supporting a phonon assisted conduction mechanism. An exchange current density of 1.27 mA cm?2 in Na2SO4 (0.1 M) solution is consistent with the electrochemical stability up to 0.8 VSCE. The capacitance measurement (C?2 - E) indicates p type conduction, with a flat band potential (Efb) of 0.26 VSCE and a holes density (NA) of 7.38 × 1019 cm?3 due to the oxygen insertion in the layered lattice. The electrochemical impedance spectroscopy (EIS) data, recorded in the range (1 mHz - Hz), reveals a predominant bulk contribution with a low depletion angle of 3° and a pseudo capacitive behavior. As application, AgCoO2 is tested for the hydrogen production upon visible illumination owing to the potential of its conduction band (?0.83 VSCE), less cathodic than that of H2O/H2 (~ ?0.5 VSCE). H2 evolution rate of 79 μmol g?1 min?1 is determined at neutral pH with a quantum yield of 1.92% in presence of NO2? as hole scavenger; no Ag deposition was observed after photocatalysis.
关键词： Delafossite AgCoO2,Co-precipitation,Nano sized,Hydrogen,Photo electrochemistry
更新于2025-09-09 09:28:46
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Structural stability and electronic properties of XTO2 (X= Cu, Ag; T=Al, Cr): an ab initio study including X vacancies and Mg doping
摘要： Ab initio density functional theory-based calculations are used to study the structural and electronic properties of CuAlO2, AgAlO2, CuCrO2, and AgCrO2 transparent conducting oxides (TCOs). The hexagonal 2H delafossite polymorph is determined here to be one of the most stable polymorphs, by comparing total energies for different structural phases. The simple antiferromagnetic configuration is chosen to model magnetic effects in CuCrO2 and AgCrO2 due to it having one of the lowest ground state total energies and containing the most semiconductor like behavior of the magnetic configurations considered. Electronic structures of 2H CuAlO2 and AgAlO2 obtained from different approximations for the exchange-correlation functional, GGA (PBE), PBE+U, PBE+mBJ, PBE+mBJ+U, and the Hybrid HSE06 are compared. Supercells are employed to model 6.25% Cu and Ag vacancies, 3.13% O vacancies, and 6.25% Mg doping replacing Al and Cr, from which structural and electronic properties are obtained and used to predict on the effectiveness of these native defects and dopant on increasing the conductivity in all TCOs studied in this work. The obtained partial density of states for the pristine systems supports a model of hole conduction in the a – b plane, perpendicular to the O – X – O dumbbells of the delafossite structure. Additionally, the partial density of states of the defective and doped systems suggest a growth environment deficient in X and saturated in O may increase conductivity in these materials.
关键词： Delafossite,Density functional theory,Transparent conducting oxides,Mg doping,Structural stability,Ab initio,Vacancies,Electronic properties
更新于2025-09-04 15:30:14