Papers by Keyword: CuAlO₂

Abstract: Oxide ceramic is a kind of environmental friendly materials, which has attracted more and more interests for its bunch of advantages such as sound chemical, thermal stability, simple synthetic process, cheap price, harmless and safety. Therefore, Oxide ceramic will be a promising material in the future. In this work, polycrystalline samples of CuAlO₂ were prepared by a solid state reaction method. The mixture of pure CuO and Al₂O₃ powders was firstly pressed under the pressure of 60 MPa, and then 200 MPa to prepare pellets of 5 mm thick and 10 mm in diameter. The green compacts were sintered at five different temperatures (1273 K, 1323 K, 1373 K, 1423 K, 1473 K) for various holding times (5 h, 10 h and 15 h) in the air and then the furnace cooled. The crystalline and microstructures of the sintered CuAlO₂ bodies were detected by XRD and SEM. The properties of density, thermal conductivity were also investigated in detail. The experimental results show that CuAlO₂ bodies were rhombohedral, belonging to R3m space group. It is found that the density and the thermal conductivity of CuAlO₂ ceramics were significantly dependent on the sintering temperatures. The density and thermal conductivity increased with increasing the sintering temperatures. The thermal conductivity of samples sintered at 1273 and 1473 K with the same holding time (10 h) were 9.70 and 35.53 W/mk at the room temperature, 3.41 and 8.29 W/mk at 1100 K, respectively.

Abstract: In this study, we investigated a CuAl_0.9Fe_0.1O₂ compound prepared at two different sintering temperatures in order to find out the effect of sintering temperature on the compound's figure of merit of thermoelectric properties. The thermoelectric CuAl_0.9Fe_0.1O₂ compound was prepared from high purity grade Cu₂O, Al₂O₃ and Fe₂O₃ powders. The mixture of these powders were ground and then pressed with uniaxial pressure into pellets. The pellets obtained were sintered in the air at 1423 K and 1473 K. X-ray diffraction (XRD) patterns showed a single phase of CuAl_0.9Fe_0.1O₂ with rhombohedral structure, , along with a trace of CuO second phase. Moreover, the XRD peaks of the sample sintered at 1423 K indicated that more Fe³⁺ atoms replaced Al³⁺ atoms in this sample than they did in the sample sintered at 1473 K. The average grain size of the CuAl_0.9Fe_0.1O₂ compound prepared increased with increasing sintering temperature, whereas its mean pore size and porosity decreased with increasing sintering temperature. The dispersed small pores markedly decreased the thermal conductivity of the compound, while the Fe³⁺ substitution of Al³⁺ increased its electrical conductivity. The highest figure of merit (ZT) found was 0.021 at 973 K in the CuAl_0.9Fe_0.1O₂ sample sintered at 1423 K. Our findings show that this low-cost material with a reasonable figure of merit is a good candidate for thermoelectric applications at high-temperature.

Abstract: The P-type transparent conductive oxide CuAlO₂ was prepared by solid state reaction in this paper. The chemical state, phase structure, microstructure and optical properties were characterized by Differential Thermal Analysis ( DTA),X-ray diffraction ( XRD),Scanning Electron Microscope ( SEM) and Infrared Spectroscopy ( IR) respectively. Testing results show that the product is really p-type transparent conductive oxide CuAlO₂. CuAlO₂ phase began to form at about 1047.7 °C.It can be formed with high density and a high infrared light transmittance of the conductive oxide at 1150 °C.

Abstract: CuAlO₂ microcrystallites were synthesized by Sol-gel method at 1200°C with Cu (CH₃COO)₂·H₂O, Al (NO₃)₃·9H₂O and ethylene glycol as raw materials. The phase composition,morphology,and optical properties of CuAlO₂ microcrystallites were chatacterized by X-ray diffraction, Scanning electron microscope,Photoluminescence and UV-visible spectroscopy respectively. The results of XRD show that CuAlO₂ with delafossite crystal structure is obtained. The defect emission were observed through PL spectrum test. It can be concluded that Cu-vacancy may be the possible reason of the observed activated p-type conductivity of CuAlO₂. Can be found three characterized peak (λ₁=290nm, λ₂=410nm, λ₃=430 nm) on the spectra.

Abstract: The reaction behavior of CuAlO₂ during the annealing at high temperatures was investigated. The relationship between thermoelectric properties including electrical resistivity, excess oxygen doping and decomposition of CuAlO₂ was discussed. The evolution of CuAlO₂ compact during the annealing mainly included excess oxygen doping, decomposition of CuAlO₂ into CuAl₂O₄ and CuO and complete decomposition of CuAlO₂ as following pattern : CuAlO₂ → CuAlO_2+x → CuAlO₂+CuO+ CuAl₂O₄ → CuAl₂O₄+CuO. Electrical resistivity of the compacts was decreased with excess oxygen doping, but increased when CuO and CuAl₂O₄ were formed. Thermoelectric performance of the compacts was improved due to the excess oxygen doping.

Abstract: Structural, electronic and optical properties of 2H-CuAlO₂ were computed, using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The equilibrium lattice parameters, band structure, densities of states (DOS) and charge densities of 2H-CuAlO₂ have been obtained. The equilibrium lattice parameters, band structure and DOS are found to be in good agreement with the available experimental and calculational values. The charge densities and the chemical bonding of 2H-CuAlO₂ are analyzed, which show that bonding between Cu and O is mainly covalent due to Cu 3d and O 2p hybridization and that bonding between Al and O is mainly ionic. The complex dielectric function, refractive index and absorption coefficient of 2H-CuAlO₂ have been predicted. The calculated static dielectric constant and static refractive index of 2H-CuAlO₂ is 7.1 and 2.66, respectively.

Abstract: Transparent conducting oxides (TCOs) are well known and have been widely used for a long time in optoelectronics industries. The most popular TCOs have n-type characteristics. However p-type material is not well established and examined. The delafossite-CuAlO₂ is one of the p-type TCOs. In this paper, amorphous Cu-Al-O films were deposited onto (100) p-type silicon substrate by magnetron sputtering. After that, the films were annealed at 800°C for 2 h in different partial oxygen levels ranging from 5*10^-5 to 1 atm with N₂, air, and O₂. X-ray diffraction patterns showed that as-deposited films were amorphous. In addition, delafossite-CuAlO₂ (R m and P6₃/mmc phase) appeared at 800°C in N₂, but monoclinic-CuO and spinel-CuAl₂O₄ phases existed in air and O2. The formation of delafossite-CuAlO₂ phase can be explained with thermodynamics. The optoelectronic properties of delafossite-CuAlO₂ films were also measured. The direct optical bandgap was around at 3.3 eV, which is comparable with literature data. The electrical conductivity was obtained to be 6.8*10^-3 S/cm. The hot-probe method employed to measure the electrical property of the films, which indicates that delafossite-CuAlO₂ films have p-type characteristics.