Search Results (12)

Cu-based ternary oxides with delafossite structure have received considerable attention in recent years for their versatility in a wide range of applications, among which is the possibility to use them in heterostructure solar cells as hole transport layers, due to their promising behavior as p-type conducting oxides. Ab initio calculations have been performed with density functional theory to investigate the role of the trivalent metal within the CuMO₂ structure and the dependence of structural and electronic properties with the species (M = Al, Ga, In, Fe, Cr, Co, Sc, Y) occupying the site of the metal. Generalized Gradient Approximation also including a Hubbard term and nonlocal Heyd–Scuseria–Enzerhof screened hybrid functional schemes were tested and their results were compared. Excellent agreement with experimental lattice parameters and measured gaps have been found. The use of hybrid functionals in HSE approximation considerably improves the bandgaps when compared with the experimental results but takes considerable time to converge, hence the need to explore less demanding methodologies. Trends in the geometry as well as in the electronic properties are discussed, and the effect of mixing different metals (CuM_xN_1−xO₂, M, N being the aforementioned elements) in the geometry and electronic properties of these delafossite materials is investigated. Due to the high cost of HSE calculations, especially when supercells are needed to model several x concentrations, statistical models and techniques based on machine learning have also been explored to predict HSE bandgap values from GGA and structural information. Full article

The cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu¹⁺Fe³⁺O₂) from a spinel solid solution (magnetite, Fe₃O₄) and understand why cuprospinel (CuFe₂O₄) is never observed, even though, as a species isostructural with magnetite, it might be expected to form. Flash furnace slags produced in the direct-to-blister copper smelter at Olympic Dam contain four Cu-bearing phases: Cu-bearing magnetite, delafossite, metallic copper, and cuprite. Delafossite coexists with magnetite as rims and lamellar exsolutions, as well as bladed aggregates, associated with cuprite within Si-rich glass. The empirical compositions of magnetite and rim delafossite are (Fe²⁺_6.89Cu²⁺_0.86Co_0.13Mg_0.15Si_0.02)_8.05 (Fe³⁺_15.52Al_0.41Ti_0.01Cr_0.01)_15.95O₃₂, and (Cu¹⁺_0.993Co_0.002Mg_0.002)_0.997(Fe³⁺_0.957Al_0.027Ti_0.005Si_0.004)_0.993O₂, respectively. The measured Cu content of magnetite represents a combination of a solid solution (~6 mol.% cuprospinel endmember) and exsolved delafossite lamellae. Atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) imaging shows epitaxial relationships between delafossite lamellae and host magnetite. Defects promoting the formation of copper nanoparticles towards the lamellae margins suggest rapid kinetics. Dynamic crystallization under locally induced stress in a supercooled system (glass) is recognized from misorientation lamellae in delafossite formed outside magnetite grains. The observations are concordant with crystallization during the cooling of molten slag from 1300 °C to <1080 °C. Melt separation through an immiscibility gap below the solvus in the system Cu-Fe-O is invoked to form the two distinct delafossite associations: (i) melt-1 from which magnetite + delafossite form; and (ii) melt-2 from which delafossite + cuprite form. Such a path also corroborates the published data explaining the lack of cuprospinel as a discrete phase in the slag. Delafossite rims form on magnetite at a peritectic temperature of ~1150 °C via a reaction between the magnetite and copper incorporated in the oxide/Si-rich melt. The confirmation of such a reaction is supported by the observed misfit orientation (~10°) between the rim delafossite and magnetite. HAADF STEM imaging represents a hitherto underutilized tool for understanding pyrometallurgical processes, and offers a direct visualization of phase relationships at the smallest scale that can complement both experimental approaches and theoretical studies based on thermodynamic modelling. Full article

For the first time, the effect of Cuprous Oxide (Cu₂O) sputtering power variation on the radio frequency sputtered Copper Chromium Oxide (CuCrO₂) thin films was studied. In this work, the sputtering power of Cr₂O₃ was held constant at 200 W while the sputtering power of the Cu₂O target was varied from 10 to 100 W. The films were subsequently annealed at 650 °C in N₂ ambiance. The effects of Cu₂O sputtering power variation on the structural, optical, and electrical properties of the films have been reported in this work. X-ray diffractometer (XRD) study revealed that the single-phase delafossite structure of CuCrO₂ was only obtained at Cu₂O sputtering power of 50 W. X-ray photoelectron spectroscopy (XPS) analysis further established the results of XRD study where Cu in 1+ oxidation state was identified in thin films obtained at 50 W of Cu₂O sputtering power. The optical studies were conducted in this work on all the post-deposition annealed films in the wavelength range of 200–800 nm. The energy dispersive x-ray spectroscopy (EDS) study revealed a near stoichiometric composition ratio of 1:1.06 of Cu:Cr at% obtained in the films sputtered with 50 W of Cu₂O sputtering power. The highest optical transmission of ~81% and the highest optical bandgap of 3.21 eV were observed for single-phase CuCrO₂ thin films. The optical transmission and the optical bandgap were found to decrease with an increase in the Cu₂O sputtering power. The electrical study performed on all the post-deposition annealed films revealed that the lowest resistivity of 0.652 Ω-cm was identified for single-phase CuCrO₂ thin films obtained at 50 W of Cu₂O sputtering power. Full article

For the first time, the deposition of CuCrO₂ thin films was carried out using a dual-target RF magnetron sputtering technique using Cu₂O and Cr₂O₃ targets. The deposited films were subsequently annealed in N₂ ambiance from 600–900 °C. This work reports that the electrical, optical, structural, and morphological properties of CuCrO₂ thin films are significantly affected due to the variation in the annealing temperature. XRD analysis confirms the presence of single-phase CuCrO₂ in the films annealed at 650 °C. The presence of Cu in the 1+ oxidation state in the phase pure CuCrO₂ thin films was confirmed through XPS analysis. Further, through XPS analysis, the oxidation states of Cu and Cr, the full-width half maximum (FWHM), the peak positions, and their respective binding energies have been elucidated. SEM analysis confirms the promotion of nanocrystalline growth in the thin films as the annealing temperature was increased from 600 °C. The average grain size increased from 40.22 nm to 105.31 nm as the annealing temperature was increased from 600 to 900 °C. Optical studies conducted in the wavelength range of 200 nm to 800 nm revealed a decrease in the optical transmission and optical bandgap with an increase in the annealing temperature. The highest optical transmission of ~81% and an optical bandgap of 3.21 eV were obtained for the films depicting the delafossite nature of CuCrO₂. The optical bandgap was found to vary between 3.16 eV and 3.74 eV for the films studied in this research. The lowest resistivity of 0.652 Ω cm was obtained for the films annealed at 650 °C. Transparent heterojunction diodes involving p-type delafossite copper chromium oxide (CuCrO₂) and n-type indium tin oxide (ITO) were fabricated. The best diode depicted a cut-in voltage of 0.85 V, a very low leakage current of 1.24 x 10-8, an ideality factor of 4.13, and a rectification ratio of 2375. Full article

In this research, we studied the functional properties of CuCrO₂, which is the most promising p-type transparent conductive oxide (TCO). The thin films were fabricated using a spin coating technique. The diffraction patterns were obtained with the help of X-ray diffractions, and the optical properties of absorption characteristics were studied using UV-visible absorption. The physical properties of film formation and surface morphology were analyzed using FESEM analysis. The aging properties were also analyzed with the help of various precursors with different aging times. The CuCrO₂ thin films’ functional properties were determined by using chelating agent and precursor solution aging times. The CuCrO₂ thin films have better transmittance, resistance, figure of merit (FOM), and electrical conductivity. Moreover, the resistivity values of the CuCrO₂ thin films are 7.01, 9.90, 12.54, 4.10, 2.42, and 0.35 Ω cm. The current research article covers the preparation of copper chromium delafossite thin films. These thin films can be suitable for hole transport layers in transparent optoelectronic devices. Full article

Hydrogen is the alternative renewable energy source for addressing the energy crisis, global warming, and climate change. Hydrogen is mostly obtained in the industrial process by steam reforming of natural gas. In the present work, CuCrO₂ particles were attached to the surfaces of electrospun CeO₂ nanofibers to form CeO₂-CuCrO₂ nanofibers. However, the CuCrO₂ particles did not readily adhere to the surfaces of the CeO₂ nanofibers, so a trace amount of SiO₂ was added to the surfaces to make them hydrophilic. After the SiO₂ modification, the CeO₂ nanofibers were immersed in Cu-Cr-O precursor and annealed in a vacuum atmosphere to form CeO₂-CuCrO₂ nanofibers. The CuCrO₂, CeO₂, and CeO₂-CuCrO₂ nanofibers were examined by X-ray diffraction analysis, transmission electron microscopy, field emission scanning electron microscopy, scanning transmission electron microscope, thermogravimetric analysis, and Brunauer–Emmett–Teller studies (BET). The BET surface area of the CeO₂-CuCrO₂ nanofibers was 15.06 m²/g. The CeO₂-CuCrO₂ nanofibers exhibited hydrogen generation rates of up to 1335.16 mL min⁻¹ g-cat⁻¹ at 773 K. Furthermore, the CeO₂-CuCrO₂ nanofibers produced more hydrogen at lower temperatures. The hydrogen generation performance of these CeO₂-CuCrO₂ nanofibers could be of great importance in industry and have an economic impact. Full article

Groundwater contamination by potentially harmful elements (PHEs) originating from the weathering of granitic and gneissic rock dissolution poses a public health concern worldwide. This study investigated physicochemical variables and PHEs in the groundwater system and mine water of the Adenzai flood plain region, in Pakistan, emphasizing the fate distribution, source provenance, chemical speciation, and health hazard using the human health risk assessment HHRA-model. The average concentrations of the PHEs, viz., Ni, Mn, Cr, Cu, Cd, Pb, Co, Fe, and Zn 0.23, were 0.27, 0.07, 0.30, 0.07, 0.06, 0.08, 0.68, and 0.23 mg/L, respectively. The average values of chemical species in the groundwater system, viz., H⁺, OH⁻, Ni²⁺, Mn²⁺, Mn³⁺, Cr³⁺, Cr⁶⁺, Cu⁺, Cu²⁺, Cd²⁺, Pb²⁺, Pb⁴⁺, Co²⁺, Co³⁺, Fe²⁺, Fe³⁺, and Zn²⁺, were 1.0 × 10⁻⁴ ± 1.0 × 10⁻⁶, 1.0 × 10⁻⁴ ± 9.0 × 10⁻⁷, 2.0 × 10⁻¹ ± 1.0 × 10⁻³, 3.0 × 10⁻¹ ± 1.0 × 10⁻³, 1.0 × 10⁻²² ± 1.0 × 10⁻²³, 4.0 × 10⁻⁶ ± 2.0 × 10⁻⁶, 4.0 × 10⁻¹¹ ± 2.0 × 10⁻¹¹, 9.0 × 10⁻³ ± 1.0 × 10⁻², 2.0 × 10⁻¹ ± 2.0 × 10⁻³, 7.0 × 10⁻² ± 6.0 × 10⁻², 5.0 × 10⁻² ± 5.0 × 10⁻², 2.0 × 10⁻² ± 1.5 × 10⁻², 6.0 × 10⁻² ± 4.0 × 10⁻², 8.0 × 10⁻³¹ ± 6.0 × 10⁻³¹, 3.0 × 10⁻¹ ± 2.0 × 10⁻⁴, 4.0 × 10⁻¹⁰ ± 3.0 × 10⁻¹⁰, and 2.0 × 10⁻¹ ± 1.0 × 10⁻¹. The mineral compositions of PHEs, viz. Ni, were bunsenite, Ni(OH)₂, and trevorite; Mn viz., birnessite, bixbyite, hausmannite, manganite, manganosite, pyrolusite, and todorokite; Cr viz., chromite and eskolaite; Cu viz., CuCr₂O₄, cuprite, delafossite, ferrite-Cu, and tenorite; Cd viz., monteponite; Pb viz, crocoite, litharge, massicot, minium, plattnerite, Co viz., spinel-Co; Fe viz., goethite, hematite, magnetite, wustite, and ferrite-Zn; and Zn viz., zincite, and ZnCr₂O₄ demarcated undersaturation and supersaturation. However, EC, Ca²⁺, K⁺, Na⁺, HCO₃⁻, Cr, Cd, Pb, Co, and Fe had exceeded the WHO guideline. The Nemerow’s pollution index (NPI) showed that EC, Ca²⁺, K⁺, Na⁺, HCO₃⁻, Mn, Cd, Pb, Co, and Fe had worse water quality. Principal component analysis multilinear regression (PCAMLR) and cluster analysis (CA) revealed that 75% of the groundwater contamination originated from geogenic inputs and 18% mixed geogenic-anthropogenic and 7% anthropogenic sources. The HHRA-model suggested potential non-carcinogenic risks, except for Fe, and substantial carcinogenic risks for evaluated PHEs. The women and infants are extremely exposed to PHEs hazards. The non-carcinogenic and carcinogenic risks in children, males, and females had exceeded their desired level. The HHRA values of PHEs exhibited the following increasing pattern: Co > Cu > Mn > Zn > Fe, and Cd > Pb > Ni > Cr. The higher THI values of PHEs in children and adults suggested that the groundwater consumption in the entire region is unfit for drinking, domestic, and agricultural purposes. Thus, all groundwater sources need immediate remedial measures to secure health safety and public health concerns. Full article

Anisotropic CuCrO₂ thin films were successfully prepared on glass substrate by the electrospinning method followed by annealing at 600 °C. The directionality of the nanowires increased with increases in rotation speed. In addition, the structural formation and optoelectronic behavior of the CuCrO₂ thin films have been studied by X-ray powder diffraction studies, transmission electron microscopy, field emission scanning electron microscopy, and UV-vis spectroscopy. The X-ray diffraction studies revealed a delafossite properties of the CuCrO₂. The electrical conductivity in the parallel and vertical directions of the films produced at 2000–3000 rpm differed by two to three orders of magnitude. The optical transmittance properties of the CuCrO₂ thin films were improved by increasing the rotation speed. Full article

A glassy carbon electrode (GCE) coated with delafossite CuCrO₂ loading on the nitrogen-doped reduced graphene oxide (N-rGO) and multiwalled carbon nanotubes (MWCNT) composite (N-rGO-MWCNT/CuCrO₂) was applied to the hydrogen evolution reaction and Bisphenol-A (BPA) detection. First, the N-rGO-MWCNT composite was prepared by in situ chemical reduction with caffeic acid as a reducing agent. Then, CuCrO₂ was accumulated on the N-rGO-MWCNT surface to form N-rGO-MWCNT/CuCrO₂ composite. The morphology structure of the N-rGO-MWCNT/ CuCrO₂ composite was analyzed by different characterization techniques. Besides, the GCE/N-rGO-MWCNT/CuCrO₂ composite electrode was investigated for hydrogen evolution reaction (HER), which shows an excellent electrocatalytic activity with a low over-potential, increasing reduction current, and a small Tafel slope of 62 mV·dec⁻¹ at 10 mA·cm⁻² with long-term stability. Moreover, the electrochemical determination of BPA was in the range of 0.1-110 µM, and low detection limit of 0.033 µM (S/N = 3) with a higher sensitivity of 1.3726 µA µM⁻¹ cm⁻². Furthermore, the prepared GCE/N-rGO-MWCNT/CuCrO₂ electrode shows effective detection of BPA in food samples with acceptable recoveries. Hence, the finding of GCE/N-rGO-MWCNT/CuCrO₂ can be observed as an impressive catalyst to the electrocatalytic activity of HER and BPA oxidation. Full article

Delafossites, with a unique combination of electrical conductivity and optical transparency constitute an important class of materials with their wide range of applications in different fields. In this article, we review the high pressure studies on copper based semiconducting delafossites with special emphasis on their structural and vibrational properties by synchrotron based powder X-ray diffraction and Raman spectroscopic measurements. Though all the investigated compounds undergo pressure induced structural phase transition, the structure of high pressure phase has been reported only for CuFeO₂. Based on X-ray diffraction data, one of the common features observed in all the studied compounds is the anisotropic compression of cell parameters in ambient rhombohedral structure. Ambient pressure bulk modulus obtained by fitting the pressure volume data lies between 135 to 200 GPa. Two allowed Raman mode frequencies E_g and A_1g are observed in all the compounds in ambient phase with splitting of E_g mode at the transition except for CuCrO₂ where along with splitting of E_g mode, A_1g mode disappears and a strong mode appears which softens with pressure. Observed transition pressure scales exponentially with radii of trivalent cation being lowest for CuLaO₂ and highest for CuAlO₂. The present review will help materials researchers to have an overview of the subject and reviewed results are relevant for fundamental science as well as possessing potential technological applications in synthesis of new materials with tailored physical properties. Full article

P-type Mg doped CuCrO₂ thin films have been deposited on fused silica substrates by Radio-Frequency (RF) magnetron sputtering. The as-deposited CuCrO₂:Mg thin films have been annealed at different temperatures (from 450 to 650 °C) under primary vacuum to obtain the delafossite phase. The annealed samples exhibit 3R delafossite structure. Electrical conductivity σ and Seebeck coefficient S of all annealed films have been measured from 40 to 220 °C. The optimized properties have been obtained for CuCrO₂:Mg thin film annealed at 550 °C. At a measurement temperature of 40 °C, this sample exhibited the highest electrical conductivity of 0.60 S·cm⁻¹ with a Seebeck coefficient of +329 µV·K⁻¹. The calculated power factor (PF = σS²) was 6 µW·m⁻¹·K⁻² at 40 °C and due to the constant Seebeck coefficient and the increasing electrical conductivity with measurement temperature, it reached 38 µW·m⁻¹·K⁻² at 220 °C. Moreover, according to measurement of the Seebeck coefficient and electrical conductivity in temperature, we confirmed that CuCrO₂:Mg exhibits hopping conduction and degenerates semiconductor behavior. Carrier concentration, Fermi level, and hole effective mass have been discussed. Full article