Electrical properties of mechanically activated zinc oxide

Microstructural properties of a commercial zinc oxide powder were modified by mechanical activation in a high-energy vibro-mill. The obtained powders were dry pressed and sintered at 1100°C for 2 h. The electrical properties of grain boundaries of obtained ZnO ceramics were studied using an ac impedance analyzer. For that purpose, the ac electrical response was measured in the temperature range from 23 to 240°C in order to determine the resistance and capacitance of grain boundaries. The activation energies of conduction were obtained using an Arrhenius equation. Donor densities were calculated from Mott-Schottky measurements. The influence of microstructure, types and concentrations of defects on electrical properties was discussed

Modification of the structural and optical properties of commercial ZnO powder by mechanical activation

Mechanical activation was used as a method for modification of the structural and optical properties of commercial ZnO powder. For this purpose zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a continual regime in air up to 300 minutes. Starting and modified ZnO samples were characterized using XRD, BET and TEM measurements. Optical properties of these samples were investigated by Raman and photoluminescence (PL) spectroscopy. The color of commercial ZnO powder was white while mechanically activated ZnO powder was dark yellow, indicating the presence of nonstoichiometry. In the Raman spectra of non-activated sample Raman modes of bulk ZnO were observed, while the spectra of modified samples point out structural and stoichiometric changes. The PL spectra of modified samples excited by 325 and 442 nm lines of a He-Cd laser show great difference with respect to the spectra of the original sample. This study confirms that change in the defect structure of the ZnO crystal lattice introduced by mechanical activation affects the optical properties of this material

P-Type copper aluminum oxide thin films for gas-sensing applications

In this study we deposited new, ternary thin films of copper aluminum oxide with p-type and n-type behavior using RF magnetron sputtering for use as chemical gas sensors. p-Type materials are known to be good catalysts and can be combined with the well-known n-type materials for chemiresistive sensors application. Copper aluminum oxide in the delafossite phase CuAlO2 is a ternary oxide that has generated interest as a transparent p-type conducting material, while in the spinel phase CuAl2O4 is known to be n-type. We demonstrated that thin films of copper aluminum oxide with the proper resistance can be successfully applied as p-and n-type resistive gas sensors for ozone detection. We have studied the sputtering deposition conditions from a CuAlO2 sintered target by changing the substrate temperature in inert Ar atmosphere. In addition, post-deposition annealing in O-2 atmospheres was also tested. XRD, SEM and Raman investigations were used to characterize the thin films. Selected films with mixed phases of CuAlO2, CuAl2O4 and CuO were tested for gas sensing as resistive chemical sensors, showing promising results with ozone, acetone and ethanol

Nanoindentation study of nickel manganite ceramics obtained by a complex polymerization method

The chemical synthesis of nickel manganite powder was performed by a complex polymerization method (CPM). The obtained fine nanoscaled powders were uniaxially pressed and sintered at different temperatures: 1000-1200 degrees C for 2 h, and different atmospheres: air and oxygen. The highest density was obtained for the sample sintered at 1200 degrees C in oxygen atmosphere. The energy for direct band gap transition (Eg) calculated from the Tauc plot decreases from 1.51 to 1.40 eV with the increase of the sintering temperature. Indentation experiments were carried out using a three-sided pyramidal (Berkovich) diamond tip, and Young's modulus of elasticity and hardness of NTC (negative temperature coefficient) ceramics at various indentation depths were calculated. The highest hardness (0.754 GPa) and elastic modulus (16.888 GPa) are exhibited by the ceramics sintered at highest temperature in oxygen atmosphere

Thermal behaviour of the TiO2-based gels obtained by microwave-assisted sol–gel method

In order to establish the influence of the preparation method on thermal behaviour of gels obtained by the sol-gel and microwave-assisted sol-gel methods, a comparative thermal analysis study was conducted by the thermogravimetric and differential thermal analysis (TG/DTG/DTA) and evolved gas analysis (EGA) on TiO2 and V2O5-doped TiO2 gels, where TiO2:V2O5 molar ratio was set to 99.95:0.05 and 98.0:2.0. In contrast to TiO2 gels, for which the thermal behaviour was not significantly influenced by the preparation method, the microwave-irradiated binary samples showed a more complex and prolonged decomposition compared to their non-irradiated counterparts. This observation was correlated with influence of microwaves in enhancing the reaction rate between the Ti and V reagents leading to formation of more complex compositions of gels. Based on TG/DTG/DTA results, the temperatures of 300 and 450 A degrees C were chosen for the processing of powders in air. All samples thermally treated at 300 and 450 A degrees C crystallized in a single anatase phase except the TiO2:V2O5 with a molar ratio 99.95:0.05, obtained by microwave-assisted sol-gel method that contains also small amount of rutile phase. At 550 A degrees C all samples contain mixture of anatase and rutile phases