CuO Phase Research Articles

Epitaxial mist chemical vapor deposition growth and characterization of Cu3N films on (0001)α-Al2O3 substrates

Epitaxial growth of Cu3N films on (0001)α-Al2O3 substrates was performed by mist chemical vapor deposition. As a source solution, 0.10 mol l−1 of copper (II) acetylacetonate dissolved in 28% aqueous ammonia was used. Even though an aqueous solution was used as the source solution, the epitaxial Cu3N film was realized without the incorporation of CuO and Cu2O phases in the growth of 300 °C. The film was also found to have limited O incorporation from the results of scanning transmission electron microscopy and Rutherford back-scattering spectroscopy. The optical property of the Cu3N film was also investigated.

Andean Sacha Inchi (Plukenetia Volubilis L.) Leaf-Mediated Synthesis of Cu2O Nanoparticles: A Low-Cost Approach.

In this work, Andean sacha inchi (Plukenetia volubilis L.) leaves were used to prepare monodispersed cuprous oxide (Cu2O) nanoparticles under heating. Visual color changes and UV-visible spectroscopy of colloidal nanoparticles showed λmax at 255 nm, revealing the formation of copper oxide nanoparticles. Transmission electron microscopy and dynamic light scattering analysis indicated that the prepared nanoparticles were spherical with an average size of 6–10 nm. The semi-crystalline nature and Cu2O phase of as-prepared nanoparticles were examined by X-ray diffraction. Fourier-transform infrared spectroscopy confirmed the presence of polyphenols, alkaloids and sugar in the sacha inchi leaf, allowing the formation of Cu2O nanoparticles from Cu2+. Additionally, as-synthesized Cu2O nanoparticles exhibited good photocatalytic degradation activity against methylene blue (>78%, 150 min) with rate constant 0.0219106 min−1. The results suggested that the adopted method is low-cost, simple, ecofriendly and highly selective for the synthesis of small Cu2O nanoparticles and may be used as a nanocatalyst in the future in the efficient treatment of organic pollutants in water.

Pulsed laser deposition of single phase n- and p-type Cu2O thin films with low resistivity

Low resistivity (ρ ~ 3–24 mΩ·cm) with tunable n- and p-type single phase Cu2O thin films have been grown by pulsed laser deposition at 25–200 °C by varying the background oxygen partial pressure (O2pp). Capacitance data obtained by electrochemical impedance spectroscopy was used to determine the conductivity (n- or p-type), carrier density, and flat band potentials for samples grown on indium tin oxide (ITO) at 25 °C. The Hall mobility (μH) of the n- and p-type Cu2O was estimated to be ~0.85 cm2/V.s and ~ 4.78 cm2/V.s respectively for samples grown on quartz substrate at 25 °C. An elevated substrate temperature ~ 200 °C with O2pp = 2–3 mTorr yielded p-type Cu2O films with six orders of magnitude higher resistivities in the range, ρ ~ 9–49 kΩ.cm and mobilities in the range, μH ~ 13.5–22.2 cm2/V.s. UV–Vis-NIR diffuse reflectance spectroscopy showed optical bandgaps of Cu2O films in the range of 1.76 to 2.15 eV depending on O2pp. Thin films grown at oxygen rich conditions O2pp ≥ 7 mTorr yielded mixed phase copper oxide irrespective of the substrate temperatures and upon air annealing at 550 °C for 1 h completely converted to CuO phase with n-type semiconducting properties (ρ ~ 12 Ω.cm, μH ~ 1.50 cm2/V.s). The as-grown p- and n-type Cu2O showed rectification and a photovoltaic response in solid junctions with n-ZnO and p-Si electrodes respectively. Our findings may create new opportunities for devising Cu2O based junctions requiring low process temperatures.

Low-Temperature Propylene Epoxidation Activity of CuO–CeO2 Catalyst with CO + O2: Role of Metal–Support Interaction on the Reducibility and Catalytic Property of CuOx Species

Epoxidation of propylene into propylene oxide (PO) in the gas phase is a highly challenging reaction. Cu-based catalysts have been active for this reaction, but the state of Cu as an active species is still debatable. In this paper, we report the propylene epoxidation activity of solution combustion synthesized Cu/CeO2 catalysts with the CO + O2 mixture at low temperatures (50–100 °C) peaking at ∼80 °C. The highest PO yield was obtained with 20–25% Cu loading in CeO2. In contrast, the reaction over the catalyst containing nonreducible support such as Cu/SiO2 occurred above 170 °C. Detailed structural characterization indicated two types of Cu species such as Cu2+ partly (∼3%) dissolved in CeO2 forming a CuxCe1–xO2−δ phase and the remaining amount formed highly dispersed CuO as a separate phase. Thus, the highest activity relates to the optimum presence of CuO along with Ce1–xCuxO2−δ. The reducibility of the Cu species in two phases was significantly shifted toward lower temperatures, indicating strong electronic interaction between the two phases. The substituted Cu2+ was reduced first, and then, the bulk CuO reduction was initiated. In situ spectroscopic studies showed Cu+ formation from Cu2+ over Cu/CeO2 catalysts even at room temperature unlike in CeO2 or CuO + CeO2 physical mixtures, indicating strong electronic interaction between Ce1–xCuxO2−δ and CuO phases on CO adsorption in the Cu/CeO2 catalyst. It is proposed that substituted Cu2+ along with Ce4+ is reduced easily, and then, Ce3+ promotes the reduction of the interfacial CuO phase that might donate active oxygen species for epoxidation reaction.

Surface‐enhanced resonance Raman scattering in partially oxidized thin copper film

AbstractBroad and low‐intensity Raman peaks are usually expected from nanocrystalline thin semiconductor films. The inherently weak Raman scattering phenomenon can be further deteriorated by unwanted background signals preventing the successful Raman analysis of an analyte. In this study, the resonant and surface‐enhanced Raman scattering techniques were combined to detect CuO and Cu2O phases in the partially oxidized nanocrystalline copper film that were otherwise undetectable. Heat treatment resulted in increased oxidation and phase transition from multiphase to single CuO phase that was in situ observed by temperature‐dependent Raman measurements. Detailed understanding of the film properties and substrate interaction was made by using several characterization techniques.

Low annealing temperature effect on Structural, and optical properties of CuO nanostructure thin films

In present work, the modified chemical bath deposition method (CBD) called successive ionic layer adsorption and reaction effective coast method was used for deposited copper oxide CuO nanostructured thin films. Structural, surface texture and optical characteristics of the deposited films were studied as a function of low annealing temperature (150, 200 and 250) °C. X-ray diffraction studies showed that the as-deposited and annealed films exhibited low crystallinity of polycrystalline nature in the monoclinic phase. It is observed a fixed or very little increment of peaks intensity and the crystallinity of the deposited films with the increase of annealing temperature to 250 °C. The lattice constants were calculated and show good agreement with the standard values. The crystallite size was decreased, whereas the dislocation density and the number of crystallites were increased with the increment of annealing temperature. The average grain diameter was increased and the average surface roughness decreased with the increment of annealing temperature. The optical energy gap for the as-deposited film is 1.87eV and increased to (2.03, 2.06 and 2.09) eV with the increment of annealing temperatures. The Urbach tails energy width decreased from 0.91 eV to (0.73, 0.54 and 0.46) eV for as-deposited and annealed films at low temperatures (150, 200 and 250) °C respectively. The low annealing temperatures was used because the deposition process was performs at low temperatures below 100 °C, therefore_it can be concluded that the low annealing temperatures used in this work are not suitable temperatures for the growth of CuO films and it can be above 300 °C to enhance the film crystallinity and formation of CuO phase.

Urea–nitrate combustion synthesis of CuO/CeO2 nanocatalysts toward low-temperature oxidation of CO: the effect of Red/Ox ratio

The low-temperature catalytic oxidation of carbon monoxide (CO) is the key process to overcome incomplete combustion of fossil fuels for both commercial (e.g., lowering automotive emissions) and domestic (e.g., indoor air quality improvement) applications. So the development of cost-effective and high-active catalysts made from non-noble metals is an actual material science challenge. Ce–Cu–O oxide system is one of the most prospective to investigate due to the feasibility of the Langmuir–Hinshelwood dual-site oxidation mechanism, and, in our previous work, it was shown that solution combustion synthesis using the urea as fuel in stoichiometric ratio with metal nitrates is a most reasonable fuel choice toward the synthesis of CuO/CeO2 nanocatalysts for effective CO oxidation. In this work, the effect of the Red/Ox (urea to nitrates or U/N) ratio on the catalytic oxidation activity of resulting CuO/CeO2 composites is in the spotlight. Series of CuO/CeO2 nanocatalysts were successfully synthesized via the urea–nitrate combustion method with U/N ratios from 0.2 to 1.4 and then were applied for CO oxidation. The samples before and after catalysis were characterized by EDX, SEM, PXRD, N2-ASA, H2-TPR, etc. It was shown that the U/N ratio strongly affects the qualitative and quantitative X-ray phase composition (c-CeO2, m-CuO, and am-CuO, in general), CeO2 and CuO crystallite sizes (4.9–63.0 nm and 14.7–28.3 nm, correspondently), specific surface area (4–46 m2/g) and porosity (0.009–0.033 cm3/g), as well as the morphology of nanocomposites and their catalytic characteristics (t50% = 113–199 °C and t100% = 137–348 °C). The sample synthesized at U/N = 0.2 shows the best oxidative performance (t50% = 113 °C and t100% = 137 °C) explained by the highest surface (46 m2/g), the lowest CeO2 crystallite size (4.9 nm), and the lowest degree of agglomeration of nanocrystals in the CuO/CeO2 composite. Besides, cyclic and water resistivity tests of this sample confirm the high stability of its catalytic activity in the CO oxidation process due to the close conjugation of the CeO2 and CuO components in the resulting nanocomposite, confirmed by the H2-TPR analysis results. Thus, it was shown that the optimization of Red/Ox ratio in the urea–nitrate combustion process contributes to obtaining the stable CuO/CeO2 nanocatalyst with gradual conversion of CO at quite low temperatures (ti ~ 50 °C). We believe that the subsequent reduction of CuO loading in the Ce–Cu–O system allows creating a cost-effective and stable composite nanocatalyst with high activity even at room temperature.

Optimizing reaction conditions and experimental studies of selective catalytic reduction of NO by CO over supported SBA-15 catalyst

Selective catalytic reduction of NO with CO (CO-SCR) was investigated based on optimizing the operating conditions by response surface methodology (RSM) and by appropriately choosing the supported SBA-15 catalysts. The effects of the CO-SCR reaction parameters such as NO:CO molar ratios and oxygen concentrations on the catalytic performance were determined by RSM to evaluate the NO conversion using a first-order polynomial model. The CuO/SBA-15 and Fe2O3/SBA-15 catalysts were synthesized by a hydrothermal method and characterized by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), N2 adsorption-desorption (BET), scanning electron microscopy coupled to energy dispersive X-Ray spectroscopy (SEM-EDS), and Fourier transform infrared spectroscopy (FTIR) to investigate the physicochemical properties of the solids. The RSM showed a very good agreement between predicted values and experimental results with the Pareto analysis confirming the accuracy and reliability of the model. The optimized results indicated the maximum NO conversion at 500°C with using the NO to CO molar ratio of 1:2 (500:1000ppm) in the absence of oxygen. Under these conditions, CuO/SBA-15 catalyst achieved 99.7% of NO conversion, whereas Fe2O3/SBA-15 had 98.1% of the catalytic parameter. Catalytic tests in CO-SCR reaction were performed on both catalysts at optimum operating conditions with CuO/SBA-15 exhibiting better performance compared to that of Fe2O3/SBA-15. The results revealed that CuO/SBA-15 was a promising catalyst for CO-SCR of NO due to the well-dispersed CuO phase on SBA-15 surface that allows the solid being more tolerant to the presence of oxygen.

Investigation of the Quenching Rate Effect on the Ferromagnetic Properties of CuO Nanoparticles

We studied the effect of pressure in a plasma-chemical reactor on the magnetic properties of copper oxide nanoparticles. Plasma-chemical synthesis of copper oxide nanopowders was carried out using an oxygen plasma of an arc discharge at pressures of 40 Pa and 200 Pa. Transmission electron microscopy showed that the obtained samples were made up of highly agglomerated particles with average particle sizes of 31 nm and 27 nm, respectively. X-ray diffraction showed the presence of a single crystalline phase of CuO. Despite the insignificant difference in the average sizes, the nanoparticles exhibited radically different magnetic behavior. Using a vibrating superconducting quantum interference device magnetometer, it was shown that the magnetic properties of nanoparticles obtained at 40 Pa were close to the bulk material and exhibited weak ferromagnetism. The nanoparticles obtained at 200 Pa demonstrated a significant deviation from the properties of the bulk material, showed magnetic hardness, and shifts in the hysteresis loops.

Wetting and spreading of Ca‐Y‐Ba‐Cu‐O solution on Y2O3 and CaSZ crucible in growing Y1‐xCaxBa2Cu3O7‐δ single crystal

AbstractSizable and uniform Y1‐xCaxBa2Cu3O7‐δ single crystals are of significant importance to study high‐temperature superconductivity. However, the severe liquid loss resulting from intrinsic wetting property during top‐seeded solution‐growth (TSSG), makes it difficult to obtain such crystals. Here the reactive wetting performance of the Ca‐Y‐Ba‐Cu‐O solution on two types of crucibles was studied. It was identified that the spreading process on the Y2O3 crucible is characterized by forming double‐layer of Y2BaCuO5 and YBa2Cu3O7‐δ, while that on the CaSZ crucible (Ca‐stabilized ZrO2) produces the BaZrO3 layer with CuO phase. In the former case, the liquid has a low energy interface with the top layer of YBa2Cu3O7‐δ, leading to strong spreading and creeping behaviors. Conversely, due to a high interfacial energy between solution and BaZrO3, the CaSZ crucible has a low wettability, particularly beneficial to solve the liquid loss problem. Consequently, with negligible liquid creeping out of CaSZ crucibles, we succeeded in growing a series of homogeneous Y1‐xCaxBa2Cu3O7‐δ single crystals with an acceptable size up to a × b × c = 11.2 × 11 × 4.8 mm3. Moreover the wetting modes of solution on various kinds of crucibles for TSSG in growing doped YBa2Cu3O7‐δ single crystals were also elucidated. Most importantly, the understanding gained from this work is broadly applicable for producing other desirable doped‐crystals.

Processing influence in the CaCu3Ti4O12 electrical properties

CaCu3Ti4O12 (CCTO) is a complex oxide with a perovskite structure that is widely studied due to its dielectric and non-ohmic properties. The formation and composition of grains and grain boundaries are very important factors to improve these electrical properties. In this work, CCTO-based ceramics were processed by solid-state reaction at different calcination temperatures (700 °C to 1000 °C, for 4 h) and sintering at 1100 °C for 6 h aiming optimization in capacitor–varistor properties. The changes in crystal phase composition observed via XRD and chemical contrasts visualized by SEM/EDS point out that the disappearance of the secondary CuO phase of calcined powders is linked to complete Cu ion incorporation to the crystal structure of CCTO. This phenomenon culminated in sinterization via liquid phase formation, with abnormal grain growth for samples calcined at temperatures higher than 900 °C. The calcination occurring at 800 °C for 4 h, to produce CCTO with a more homogeneous microstructure, with apparent porosity of 2.67%, α of 5.49, EB of 1505 V cm−1, e′ (1 kHz) of 7506 and ΦB of 0.754 eV, was considered the best processing condition.

Effect of Co and Mn doping on the morphological, optical and magnetic properties of CuO nanostructures

Copper oxide (CuO) is an exciting semiconducting material with interesting structural and optical properties. Transition metal doped-CuO nanostructures have great potential to use in memory device applications. In the present work, we describe in detail, the synthesis of pure CuO, cobalt (Co) and manganese (Mn) doped CuO via low temperature co-precipitation method. Various techniques like; X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Superconducting Quantum Interference Device (SQUID) magnetometer have been utilized to characterize the synthesized nanoparticles. XRD data exhibits a pure monoclinic phase of CuO for all synthesized samples. Surface morphology obtained from FE-SEM clearly shows the presence of cluster-like structure of grains. The magnetic investigations suggest that pure CuO nanoparticles exhibit the superparamagnetic state, which further transforms to antiferromagnetic state with Co doping. However, a peak of sharp intensity (maxima) at T = Tf in ZFC curve in Mn-doped sample gives the evidence of spin glass (SG) behavior.

The Optoelectronic Properties of p-Type Cr-Deficient Cu[Cr0.95-xMg0.05]O2 Films Deposited by Reactive Magnetron Sputtering.

CuCrO2 is one of the most promising p-type transparent conductive oxide (TCO) materials. Its electrical properties can be considerably improved by Mg doping. In this work, Cr-deficient CuCrO2 thin films were deposited by reactive magnetron sputtering based on 5 at.% Mg doping. The influence of Cr deficiency on the film’s optoelectronic properties was investigated. As the film’s composition varied, CuO impurity phases appeared in the film. The mixed valency of Cu+/Cu2+ led to an enhancement of the hybridization between the Cu3d and O2p orbitals, which further reduced the localization of the holes by oxygen. As a result, the carrier concentration significantly improved. However, since the impurity phase of CuO introduced more grain boundaries in Cu[Cr0.95−xMg0.05]O2, impeding the transport of the carrier and incident light in the film, the carrier mobility and the film’s transmittance reduced accordingly. In this work, the optimal optoelectronic performance is realized where the film’s composition is Cu[Cr0.78Mg0.05]O2. Its Haacke’s figure of merit is about 1.23 × 10−7 Ω−1.

Effect of Cu substitution on the structure and reactivity of CuxCo3-xO4 spinel catalysts for direct NOx decomposition

A Cu-substituted, Co-based spinel catalyst (CuxCo3-xO4) is introduced for direct NO decomposition to N2 and O2. A series of CuxCo3-xO4 catalysts with varying Cu content (0 ≤ × ≤ 1) were synthesized via a co-precipitation method. Reactivity for direct NO decomposition was measured at 450 °C, with the maximum activity of 2.8 × 10−2 [(μmol NO to N2) g-1 s-1] and selectivity to N2 of 61 % occurring over the Cu0.4Co2.6O4 (x = 0.4) catalyst. Additionally, the CuxCo3-xO4 catalysts demonstrated the ability to mitigate N2O formation as all traces of this greenhouse gas were decomposed regardless of Cu content. Characterization by X-ray diffraction and X-ray absorption spectroscopy revealed the effects of Cu substitution on the occupancies and valencies of the Co and Cu ions in the spinel structure. Activity was shown to correlate with increasing incorporation of Cu2+ into the tetrahedral sites of the normal spinel structure; however, significant formation of a segregated CuO phase caused the activity to decrease when x ≥ 0.4. The bulk structure-activity relationships we elucidate are expected to provide a guide for the design of improved direct NO decomposition catalysts and other bulk oxide catalyst systems based on careful design of the cation arrangements in oxides.

Enhanced Magnetic and Magnetocaloric Properties of La0.45Nd0.25Sr0.3MnO3/CuO Composite

This work is devoted to investigating the magnetic and magnetocaloric properties of La0.45Nd0.25Sr0.3MnO3-CuO composite prepared by the solid-state reaction with various concentration of CuO (2 wt.%, 5 wt.%, and 10 wt.%). The X-ray diffraction (XRD) and the scanning electron microscopy (SEM) techniques were used to identify the obtained structural phases and microstructural morphologies in the prepared pellets. A second-order transition was observed with critical a temperature around 294 K for 2 wt.% and 10 wt.% and 321 K for 5 wt.% of the CuO phase in the composite. Magnetic entropy changes in La0.45Nd0.25Sr0.3MnO3-CuO composites were calculated using the Maxwell approximation around the magnetic transition. The highest values of magnetic entropy change were found for 5 wt.% of CuO in La0.45Nd0.25Sr0.3MnO3-CuO pellet composites which is attributed to the localization of the copper oxide in the grains boundaries of La0.45Nd0.25Sr0.3MnO3 perovskite.

Influence of copper on the compositions, microstructure and room and elevated temperature tribological properties of the molybdenum nitride film

Molybdenum nitride ceramic films, exhibiting excellent mechanical and frictional properties, have a great prospect for the application of high speed cutting tools and precision dies. However, the formation of lubricating tribofilm MoO3 with a layer structure always weakens the wear-resistance. In this paper, copper was added into the molybdenum nitride matrix using RF magnetron sputtering system to improve the tribological properties at room temperature (RT) and elevated temperatures. The results showed that face-centered cubic (fcc) Mo2N, fcc-Cu and CuO phases co-existed in the molybdenum nitride and copper films. As the Cu/(Cu + Mo) ratio increased, RT average friction coefficient (Cof.) dropped gradually due to the lubricating Cu and CuO phases, while wear rate (WR) initially decreased and then increased gradually after reaching a minimum value of ~1.2 × 10−6 mm3/N·mm. WR at RT was mainly attributed by the soft lubricating phases, hardness and H/E ratio. The tribofilm changed from CuO to CuMoO4 and MoO3 as the testing temperature increased from 100 to 600 °C, this led to the drop in Cof. at the cost of WR.

Catalytic Abatement of VOCs: Aerobic Combustion of Methane or Ethane over Alumina-Supported Metal Oxides Recovered from Spent Catalysts

γ-Al2O3 supported Cu, Cu-Zn and Cu-Ni-Fe-Zn oxide catalysts were prepared using leachate transition metal nitrate and sulfate aqueous solutions from commercial spent catalysts. A bench-scale rig was used to investigate the combustion activity of these catalysts toward methane or ethane in the air stream (1000 ppmv) at a space velocity of 20,000 h-1. The Cu-Ni-Fe-Zn oxides/γ-Al2O3 catalyst proved to be the most active catalyst for the combustion of methane in the temperature range 290-575°C and of ethane in the lower temperature range of 275-525oC as compared to Cu and Cu-Zn oxide loaded catalysts. X-ray powder diffractograms indicated that the metal oxide species were highly dispersed or amorphous on the alumina surface in all the catalysts except for the detection of a minority phase of monoclinic CuO on the Cu-containing mono-metallic catalysts. The co-existence of ZnO in the CuO catalysts suppresses the activity of the copper oxide species and, therefore, the conversion of methane or ethane was reduced. The present research endeavor provides proof-of-concept that relatively inexpensive metal oxide-based heterogeneous catalysts for VOCs abatement can be recovered from spent catalysts. Hence, environmental and health threats of improper handling of VOCs or spent catalysts may be alleviated.

Texture and Bandgap Tuning of Phase Pure Cu2o Thin Films Grown By a Simple Potentiostatic Electrodeposition Technique

Phase pure Cu2O is one of the most desirable p-type absorber materials for ZnO based all-oxide solar cell because of its reported direct bandgap(~2.17 eV) and a suitable band alignment with n-type ZnO electrodes. Highly textured phase pure Cu2O thin films have been grown by a simple electrodeposition technique with varying cathodic potentials (-0.3 to -1.0 V) using Fluorine-doped Tin Oxide (FTO) substrates as working electrodes and a carbon rod as a counter electrode immersed in an alkaline aqueous electrolyte held at ~60 0C for 40 min. The surface morphology, structural, optical properties of the as-deposited Cu2O thin films were characterized by Scanning Electron Microscopy (SEM), Surface profiler, X-ray diffraction (XRD), and UV-Vis-NIR Spectroscopy respectively. SEM micrographs revealed that the deposited thin films coherently carpet the underlying substrate and composed of sharp faceted well-define grains having size in the range of 0.5 – 1.0 µm . XRD analyses showed that all films are composed of polycrystalline cubic Cu2O phase only and have average crystalline domain size in the range 30 – 73 nm. The preferred crystalline orientation of phase pure Cu2O films were found to be changing from (200) to (111) with increasing cathodic potentials and showed highest (111) and (200) crystalline texture coefficient while grown at -1.0 and -0.8 V respectively. The estimated optical bandgap of the as-grown samples were found in the range (2.00 – 2.20) eV consistent with the previously reported results and the variation of the optical bandgap could be attributed to the variation of the film thickness. The performance of copper oxide films was tested by estimating LED ‘ON/OFF’ modulated surface photovoltage into a photoelectrochemical cell at zero bias voltage and was found to be reasonable to integrate them into optoelectronic devices.

Structural and Dielectric Properties of Bi-Zn Substituted Calcium Copper Titanate (CCTO)

Calcium copper titanate (CCTO), an electroceramic with giant dielectric constant is useful in supercapacitor, microwave absorption, shielding of electromagnetic interference, and high frequency application. Bi3+-Zn2+ substituted CCTO with chemical composition Ca1-xBixCu3Ti4-xZnxO12 (0.0<x<0.2) was fortified using sol-gel auto combustion technique and were characterized using XRD, FESEM, and impedance analyser. XRD confirms the formation of CCTO phase with some traces of CuO and CaTiO3 phase. FESEM micrograph shows particles shapes close to cubic shape.

Effect of vacuum annealing on the structural and optical properties of sputtered Cu4O3 thin films

ABSTRACT Cu4O3 thins films were deposited by the reactive magnetron sputtering process on glass and Si (100) wafers. In order to investigate the thermal stability of the Cu4O3 phase, the films were subjected to vacuum annealing treatment for one hour at various temperatures ranging from 200°C to 500°C. The samples were characterized by using EDS, XRD, SEM and UV–VIS. The phase transformation of Cu4O3 into Cu2O was obtained from 300°C (critical temperature). Increasing annealing temperature leads to compact morphology and the grain shape changing from elongated towards spherical. Due to this annealing the film structure presentes coexistence of a Cu4O3 and Cu2O mixture where O atoms are lost in the Cu–O system. The UV–VIS analysis reveals a gradual increase in the transmittances from 55 to 70% with the increasing annealing temperature, while the band gap shows a maximum value (Eg = 2 eV) at 500°C corresponding to the Cu2O phase.