Synthesis and Room Temperature Ferromagnetism in Fe-Doped CuAlO_2 Semiconductor

The synthesis and characterization of Fe-doped CuA102 semiconductor were reported. The samples were synthesized by a simple and cost effective spin-on technique from solid state reaction of Cu20 and A1203 on sapphire （001） substrate. Appropriate ethyl-cellulose （EC） and terpineol are useful for the formation of Fe-doped CuA102 films. X-ray diffraction （XRD） revealed the growth of pure delafossite CuA102 phase ruled out elemental metallic Fe clusters in all the Fe incorporated CuA102 films. The existence of ferromagnetism at room temperature is evidenced by well-defined hysteresis loops. Specially, the saturation magnetization （Ms） values at room temperature have been monotonously enhanced with the increase of Fe composition from 1% to 5%.

Catalytic Removal of PM by Li-Co Delafossite Catalysts

By using solution combustion synthesis method, several Li-Co delafossite catalysts were prepared via a highly exothermic and self-sustaining reaction. The prepared catalysts were characterized by XRD, SEM and the catalytic activities of the catalysts were evaluated by small sample experiment. It is shown that under loose contact conditions this catalyst can catalyze soot combustion at 360 ℃, and the best prepared catalyst Li Co0.9O2 can ignite soot combustion below 300 ℃. In the incompletely synthesized catalysts the Co cations shift to higher electrovalence, so the number of the surface adsorbed oxygen（O-） of the prepared delafossite catalysts increase and Li Co0.9O2 has the optimum catalytic activity.

Preparation of CuGaO₂Thin Film by a Sol-Gel Method Using Two Kinds of Metal Source Combination

We prepare CuGaO2 thin films on SiO2 substrates by using the sol-gel spin-coating method with two combinations of Cu and a Ga source, Cu and Ga nitrate, or acetylacetonate. X-ray diffraction analysis reveals that the thin films prepared using nitrate sol that are annealed at a temperature of 850°C - 950°C show both c-axis-orientated peaks, (006) and a non-c-axis-oriented peak (012) with similar intensity;little dependence of signal intensity on annealing temperature is also shown. The films are opaque in appearance at these annealing temperatures. Scanning electron microscope observation reveals that the opaque appearance is due to the texture or cracks on the surface of the films. In contrast, the films prepared using acetylacetonate show a (006) peak with higher signal intensity than the (012) peaks. The films show more transparent appearance than that of the films by nitrate. The highest conductivity of the film is 5.7 × 10-4Ω-1·cm-1, obtained in the films by nitrate annealed at 850°C.

Structural and Magnetic Properties of Substituted Delafossite-Type Oxides CuCr_{1 - x}Sc_xO₂

This work describes the scandium doping effect on the structural and magnetic properties of delafossite-type oxides CuCr1?- xScxO2. The lattice parameters were found to vary according to Vegard’s low. A reflection broadening is observed, that is ascribed to local lattice distortion due to the ionic radius difference between Cr3+ and the non-magnetic dopants. Magnetic susceptibility measurements show that the dominant interactions are antiferromagnetic (AFM) but that doping induces significant changes. The coupling between the local spins at the Cr sites and doped metal transition may enhance spin fluctuations at the Cr sites, which break the residual magnetic degeneracy as fluctuation-induced symmetry breaking in a highly magnetic degenerate ground state manifold of some frustrated systems.

Preparation of CuYO2 Thin Films by Sol-Gel Method Using Copper Acetate and Yttrium Acetate as Metal Sources

Delafossite structured p-type wide bandgap semiconductor, CuYO2 thin films were prepared on SiO2 substrate by sol-gel method using copper (II) acetate and yttrium (III) acetate as source materials. The films preparation process was studied by varying annealing temperature after the preparation of gel films by spin coating, followed by thermal annealing at higher temperature. In the present work, one step annealing directly from Cu-Y-gel under nitrogen flow was used. X-ray diffraction (XRD) revealed that the film annealed at 800。C is significantly c-axis oriented, shows only (002) and (004) peaks at 15.6。 and 31.5。, respectively. The optical bandgap of 3.7 - 3.8 eV is estimated by (αhν)2 plot which is higher than previous works. In addition, the films with highly c-axis orientation showed photoluminescence (PL) at room temperature with very broad peak at 2.3 eV. The films annealed at different temperature showed different structural properties.

Effects of electrochemical synthetic conditions on surface property and photocatalytic performance of copper and iron-mixed p-type oxide electrodes

Earth-abundant copper and iron-mixed oxide（CuO/CuFeO_2; CFO） film electrodes are synthesized using an electrochemical deposition（ED） technique at two different ED potentials（-0.36 and-0.66 V vs saturated calomel electrode（SCE）; denoted as ED-1 and ED-2, respectively）. Then, their surface morphologies are compared, and the photo（electro）catalytic activities for the reduction of Cr（VI） are examined in aqueous solutions at pH 7 under simulated sunlight（AM 1.5 G; 100 mW cm（-2））. The degree of the electrical potential applied to the ED process significantly affects the thickness of the synthesized electrode film and the intensity ratio of the diffraction peaks of CuO（111） and CuFeO_2（012）. A 200 μm thick ED-2 sample with a distinct stacking of CuO on CuFeO_2 exhibits a larger broadband absorption spectrum than the 50-μm thick ED-1 with less separate stacking. Furthermore, the ED-2 sample has a higher intensity ratio of the diffraction peaks of CuO（111） and CuFe02（012） than ED-1. As-synthesized ED-2 samples produce larger photocurrents, leading to faster Cr（VI） reduction on the surface under given potential bias（-0.5 V vs SCE）or bias-free conditions. The energy levels（i.e., flatband potential） for the two samples are almost the same（only 10 mV difference）, presumably supposing that the enhanced photoactivity of the ED-2 sample for Cr（VI） reduction is due to the facilitated charge transfer. The time-resolved photoluminescence emission spectra analysis reveal that the lifetime（r） of the charge carriers in the ED-1 sample is 0.103 ns, which decreases to 0.0876 ns in the ED-2. The ED-2 sample synthesized at a high negative potential is expected to contribute greatly to the application of other solar-to-fuel energy conversion fields as a highly efficient electrode material.

Novel Silver-Copper Mixed Oxides:A Success of Soft-Chemistry Methods

1 Results The discovery of thefamily of mercury cupratesinthe eighties ,which present the highest Curie Temper-ature (Tc) among all known High Temperature Super-Conductors (HTSC) 。

Preparation,characterization and application of CuCrO_2/ZnO photocatalysts for the reduction of Cr(VI)

The delafossite CuCrO2 elaborated by sol-gel from 40 nm diameter colloid is optically active in the visible region. It is characterized physically and photoelectrochemically. The microstrncture is fairly homogenous with a mean crystallite size of ca. 2 Ixm. The optical gap （1.30 eV）, determined from the diffuse reflectance, is well suited to the sunlight spectrum. The Mott Schottky plot is characteristic of P-type conductivity with a flat band potential of-0.26 VscE. As application, the photoreduction of chromate is successfully achieved in air-equilibrated suspension CuCrO2/ZnO （1/1）. CuCrO2 is photoactivated by visible light and the electrons in the conduction band （-1.34 VscE） are injected to ZnO. In the presence of salicylic acid, a conversion of Cr（VI） to Cr（III） of 57% is obtained under optimal conditions （pH 3 at 25~C, 5x 10-4 mol/L） because of the HCrO4- dark adsorption onto ZnO （4HCrO4- ＋ 3C7H603 ＋ 1802 ＋ 16H~ 4Cr3＋ ＋ 21CO2 ＋ 19H20, AGO = -557 kcal/mol）. Prolonged illumination is accompanied by a deceleration in the photoactivity owing to the competitive water reduction, an issue of energetic concern. The hetero-system exhibits self sensitization for hydrogen production with an evolution rate of 149 Ixmol/（hr.g）.

The role of phase impurities and lattice defects on the electron dynamics and photochemistry of CuFeO2 solar photocathodes

CuFeO2 is a promising photocathode for H2 evolution and CO2 reduction reactions.To better understand the complex defect chemistry and role of impurity phases in this material and their effect on the photochemical performance,we employ visible light transient absorption spectroscopy and density functional theory(DFT)calculations to investigate the electron dynamics in electrochemically deposited Cu-Fe oxide thin films.Kinetic analysis of carrier lifetime shows a fast,sub-ps contribution to relaxation followed by persistence of a Iong-lived state to time delays greater than 2 ns.Increasing amplitude of the Iong-lived state is shown to correlate with the rate of fast initial relaxation,and this is explained in terms of a competition between charge carrier trapping and charge separation.Charge separation in CuFeO2 occurs via hole thermalizati on from O 2p to Cu 3d vale nee band states leadi ng to segregatio n of electr ons and holes across layers in the CuFeO2 lattice.Correlation between transient absorption measurements and DFT calculations suggest that Cu vacancies enhanee photochemical performance by facilitating charge separation kinetics.In contrast,O interstitials are predicted to switch the relative positions of O 2p and Cu 3d vale nee band states,which would in hibit charge separatio n by in ter-band hole thermal izatio n.Fin ally,we find no evide nee for electron in jecti on from CuFeO2 to CuO suggest!ng that charge separati on at this heterostructure in terface does not play a role in the carrier lifetime or photochemical performance of the catalysts studied here.

Enhanced electrochemical performance and mechanism study of AgLi1/3Sn2/3O2 for lithium storage

Herein,AgLi1/3Sn2/3O2 with delafossite structure was prepared by treating the layered compound Li2 SnO3 with molten AgN03 via ion exchange of Li^+for Ag^+.The structure characterization and the electrochemical performance of AgLi1/3Sn2/3O2 was thoroughly investigated.AgLi1/3Sn2/3O2 is found to possess stacking lamellar morphology,which means small electrochemical impedance and so facilitates charge transfer kinetics during the cycling.Compared with Li2 Sn03,due to the introducing of excellent electrical conductivity of silver,AgLi1/3Sn2/3O2 exhibits improved electrochemical performance in terms of capacity,cycling stability and coulombic efficiency.The results show AgLi1/3Sn2/3O2 presents favorable specific capacity of 339 mAh/g at current density of 200 mA/g after 50 cycles and initial coulombic efficiency of 96%.Exsitu XRD analysis revealed the reaction mechanism of AgLi1/3Sn2/3O2 as an anode for lithium ion batteries.

Hydrothermal synthesized delafossite CuGaO_(2) as an electrocatalyst for water oxidation

Hydrogen production from water splitting provides an effective method to alleviate the ever-growing global energy crisis.In this work,delafossite CuGaO_(2)(CGO)crystal was synthesized through hydrothermal routes with Cu(NO_(3))_(2)·3H_(2)O and Ga(NO_(3))_(3)·xH_(2)O used as reactants.The addition of cetyltrimethylammonium bromide(CTAB)was found to play an important role in modifying the morphology of CuGaO_(2)(CGO-CTAB).With the addition of CTAB,the morphology of CGO-CTAB samples changed from irregular flake to typical hexagonal sheet microstructure,with an average size of 1-2μm and a thick-ness of around 100 nm.Furthermore,the electrocatalytic activity of CGO-CTAB crystals for oxygen evolution reaction(OER)was also studied and compared with that of CGO crystals.CGO-CTAB samples exhibited better activity than CGO.An overpotential of 391.5 mV was shown to be able to generate a current density of 10 mA/cm^(2).The as-prepared samples also demonstrate good stability for water oxidation and relatively fast OER kinetics with a Tafel slope of 56.4 mV/dec.This work highlights the significant role of modification of CTAB surfactants in preparing CGO related crystals,and the introduc-tion of CTAB was found to help to improve their electrocatalytic activity for OER.