Synthesis and thermoelectric properties of Re3As6.6In0.4 with Ir3Ge7 crystal structure

The Re3As7−xInx solid solution was prepared for x ≤ 0.5 by heating the elements in stoichiometric ratios in evacuated silica tubes at 1073 K. It crystallizes with the Ir3Ge7 crystal structure, space group Im−3m, with a unit-cell parameter a ranging from 8.716 to 8.747 Å. The crystal structure and properties were investigated for a composition with x = 0.4. It is shown that indium substitutes arsenic exclusively at one crystallographic site, such that the As–As dumbbells with dAs–As = 2.54 Å remain intact. Re3As6.6In0.4 behaves as a bad metal or heavily doped semiconductor, with electrons being the dominant charge carriers. It possesses high values of Seebeck coefficient and low thermal conductivity, but relatively low electrical conductivity, which leads to rather low values of the thermoelectric figure of merit

Relaxation of Photogenerated Carriers in P3HT:PCBM Organic Blends

Relaxing in the sunlight. Long time-transient decays of photogenerated carriers in P3HT:PCBM blends for organic solar cells are interpreted in terms of the relaxation of hole carriers in a broad density of states. The after-pulse time-resolved microwave conductivity (TRMC) decays observed in P3HT:PCBM blends display a dependence on time close to t−β, independent of excitation intensity, in the 10 ns–1 μs range. This is explained in terms of the relaxation of carriers in a Gaussian density of states (DOS). The model is based on a demarcation level that moves with time by thermal release and retrapping of initially trapped carriers. The model shows that when the disorder is large the after-pulse decay of the type t−β is obtained, while at low disorder and large temperature the carrier distribution becomes independent of time. In the measurements different β values were observed depending on the solvent used for spin-coating: 0.4–0.6 for chlorobenzene and 0.3–0.4 for toluene. The model was applied to extract the shape of the DOS from the TRMC decays, giving a dispersion parameter of about 120 meV for blends with high P3HT content

Superparamagnetic behavior of MOCVD grown ZnO:Co films

Temperature and field dependences of magnetization have been measured for Co-doped ZnO films with different Co content grown by MOCVD on sapphire substrates. Measured field dependences of magnetization show ferromagnetic-like hysteresis loops and paramagnetic contribution. Coercive field decreases with an increase of Co content and temperature. The difference between temperature dependences of magnetization measured in zero field cooling and field cooling conditions was observed in the temperature range from 2 K to 300 K indicating superparamagnetic behaviour of the films. The distribution of blocking temperatures extracted from the temperature dependences of magnetization is broad and shifts to the low blocking temperatures with an increase of Co conten

Superparamagnetic behavior of MOCVD grown ZnO:Co films

Temperature and field dependences of magnetization have been measured for Co-doped ZnO films with different Co content grown by MOCVD on sapphire substrates. Measured field dependences of magnetization show ferromagnetic-like hysteresis loops and paramagnetic contribution. Coercive field decreases with an increase of Co content and temperature. The difference between temperature dependences of magnetization measured in zero field cooling and field cooling conditions was observed in the temperature range from 2 K to 300 K indicating superparamagnetic behaviour of the films. The distribution of blocking temperatures extracted from the temperature dependences of magnetization is broad and shifts to the low blocking temperatures with an increase of Co conten

Photocatalytic CO2 Conversion Using Anodic TiO2 Nanotube-CuxO Composites

Nanosized titanium dioxide (TiO2) is currently being actively studied by the global scientific community, since it has a number of properties that are important from a practical point of view. One of these properties is a large specific surface, which makes this material promising for use in photocatalysts, sensors, solar cells, etc. In this work, we prepared photocatalysts based on TiO2 nanotubes for converting carbon dioxide (CO2) into energy-intensive hydrocarbon compounds. Efficient gas-phase CO2 conversion in the prepared single-walled TiO2 nanotube-CuxO composites was investigated. Parameters of defects (radicals) in composites were studied. Methanol and methane were detected during the CO2 photoreduction process. In single-walled TiO2 nanotubes, only Ti3+/oxygen vacancy defects were detected. The Cu2+ centers and O2− radicals were found in TiO2 nanotube-CuxO composites using the EPR technique. It has been established that copper oxide nanoparticles are present in the TiO2 nanotube-CuxO composites in the form of the CuO phase. A phase transformation of CuO to Cu2O takes place during illumination, as has been shown by EPR spectroscopy. It is shown that defects accumulate photoinduced charge carriers. The mechanism of methane and methanol formation is discussed. The results obtained are completely original and show high promise for the use of TiO2-CuxO nanotube composites as photocatalysts for CO2 conversion into hydrocarbon fuel precursors

Photocatalytic CO₂ Conversion Using Anodic TiO₂ Nanotube-Cu_xO Composites

Nanosized titanium dioxide (TiO2) is currently being actively studied by the global scientific community, since it has a number of properties that are important from a practical point of view. One of these properties is a large specific surface, which makes this material promising for use in photocatalysts, sensors, solar cells, etc. In this work, we prepared photocatalysts based on TiO2 nanotubes for converting carbon dioxide (CO2) into energy-intensive hydrocarbon compounds. Efficient gas-phase CO2 conversion in the prepared single-walled TiO2 nanotube-CuxO composites was investigated. Parameters of defects (radicals) in composites were studied. Methanol and methane were detected during the CO2 photoreduction process. In single-walled TiO2 nanotubes, only Ti3+/oxygen vacancy defects were detected. The Cu2+ centers and O2− radicals were found in TiO2 nanotube-CuxO composites using the EPR technique. It has been established that copper oxide nanoparticles are present in the TiO2 nanotube-CuxO composites in the form of the CuO phase. A phase transformation of CuO to Cu2O takes place during illumination, as has been shown by EPR spectroscopy. It is shown that defects accumulate photoinduced charge carriers. The mechanism of methane and methanol formation is discussed. The results obtained are completely original and show high promise for the use of TiO2-CuxO nanotube composites as photocatalysts for CO2 conversion into hydrocarbon fuel precursors

Doping nature of group V elements in ZnO single crystals grown from melts at high pressure

ZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO