Search results for "temperature"
showing 10 items of 3798 documents
Comparison of the F-type center thermal annealing in heavy-ion and neutron irradiated Al2O3 single crystals
2018
Abstract The optical absorption and thermally stimulated luminescence of Al2O3 (sapphire) single crystals irradiated with swift heavy ions (SHI) 238U with energy 2.4 GeV is studied with the focus on the thermal annealing of the F-type centers in a wide temperature range of 400–1500 K. Its theoretical analysis allows us to obtain activation energies and pre-exponentials of the interstitial oxygen ion migration, which recombine with both types of immobile electron centers (F and F+ centers). A comparison of these kinetics parameters with literature data for a neutron-irradiated sapphire shows their similarity and thus supports the use of SHI-irradiation for modeling the neutron irradiation.
Lattice sites of diffused gold and platinum in epitaxial ZnSe layers
2000
Abstract The lattice location of diffused gold and platinum in zinc selenide (ZnSe) epitaxial layers was studied using the Rutherford backscattering (RBS) channeling technique. Thin Au and Pt films were evaporated onto ZnSe samples. The Au/ZnSe samples were annealed at 525°C and the residual Au film was removed by etching. Channeling angular scan measurements showed that about 30% of Au atoms were close to substitutional site (displaced about 0.2 A). In the case of the Pt/ZnSe samples the annealing temperatures ranged from 600°C to 800°C. The Pt minimum yields along 〈1 0 0〉 direction were close to the random value, varying from 80% to 90%. The measured Pt angular scans along 〈1 0 0〉 and 〈1 …
Radiation-induced defects in sapphire single crystals irradiated by a pulsed ion beam
2020
Abstract The luminescence and thermal stability of defects formed in α-Al2O3 single crystals after powerful (300 keV) pulsed irradiation with C+/H+ ion beam were investigated. It was found by measuring of optical density, photoluminescence, and pulsed cathodoluminescence that ion irradiation induces both single F-, F+-centers and F2-type aggregate centers. An intense thermoluminescence band with a complex shape was observed in the broad temperature range of 350–700 K, its intensity decreases with increasing of the energy density of the ion beam. The thermal stability of the F-type defects produced in α-Al2O3 after irradiation with a pulsed ion beam is comparable to that in neutron-irradiate…
Relaxation of polarization in (K0.5Na0.5)(Nb0.93Sb0.07)O3 ferroelectric ceramics modified by BaTiO3
2017
ABSTRACTA study of low-frequency relaxation of polarization in conventionally prepared ceramic compounds of (1-x)(K0.5Na0.5)(Nb0.93Sb0.07)O3+xBaTiO3+0.5mol.%MnO2 (x = 0.02, 0.04) examined over a wide temperature range is reported. Anomalous behavior of the temperature dependence of the coercive field Ec(T) is detected in the temperature range of the orthorhombic to tetragonal phase transition. The observed features of polarization are assigned to dynamics of the domain structure at the temperature range of phase coexistence.
Study of the thermochromic phase transition in CuMo1−xWxO4 solid solutions at the W L3-edge by resonant X-ray emission spectroscopy
2021
Abstract Polycrystalline CuMo 1 − x W x O 4 solid solutions were studied by resonant X-ray emission spectroscopy (RXES) at the W L 3 -edge to follow a variation of the tungsten local atomic and electronic structures across thermochromic phase transition as a function of sample composition and temperature. The experimental results were interpreted using ab initio calculations. The crystal-field splitting parameter Δ for the 5d(W)-states was obtained from the analysis of the RXES plane and was used to evaluate the coordination of tungsten atoms. Temperature-dependent RXES measurements were successfully employed to determine the hysteretic behaviour of the structural phase transition between t…
Dielectric behaviour of BaTi1-xZrxO3ceramics obtained by means of a solid state and mechanochemical synthesis
2016
ABSTRACTIn this study the comparison of dielectric behaviour of BaTi1-xZrxO3 (BTZx) ceramic samples prepared by means of a solid state and mechanochemical synthesis was presented. A single phase of perovskite structure was identified in the samples at room temperature. No significant impurities were detected in an EDS spectrum and the samples had a good stoichiometric ratio. The morphology of the investigated samples was characterized by a scanning electron microscopy (SEM). The investigation of dielectric properties of the BTZx samples within the temperature range from 140 K to 600 K was performed by means of a dielectric spectroscopy method at the frequency ranging from 0.1 Hz to 10 MHz. …
Correlation between in situ structural and optical characterization of the semiconductor-to-metal phase transition of VO2 thin films on sapphire
2020
A detailed structural investigation of the semiconductor-to-metal transition (SMT) in vanadium dioxide thin films deposited on sapphire substrates by pulsed laser deposition was performed by in situ temperature-dependent X-ray diffraction (XRD) measurements. The structural results are correlated with those of infrared radiometry measurements in the SWIR (2.5-5 μm) and LWIR (8-10.6 μm) spectral ranges. The main results indicate a good agreement between XRD and optical analysis, therefore demonstrating that the structural transition from monoclinic to tetragonal phases is the dominating mechanism for controlling the global properties of the SMT transition. The picture that emerges is a SMT tr…
Temperature Coefficients of Solar Cell Parameters at Maximum Power Point
2020
Analytical expressions for the temperature coefficients of the maximum power point voltage and current are presented. The temperature coefficients are calculated assuming the bandgap to be a linear function of the temperature and accounting for energy losses of non-radiative nature. The latter are introduced in the model through the External Radiative Efficiency. The so-called $\gamma$ parameter, which has been shown to account for the thermal sensitivity of all mechanisms determining the open-circuit voltage, appears to also play a role in the temperature coefficient of the maximum power point voltage and current. Numerical results and a comparison with experimental measurements are also p…
Investigation on partial discharges in HVDC cables after polarity reversal events
2020
Due to the accumulation of space charge inside the insulating layer of HVDC cables, the electric field under load conditions may be altered compared to what is established in HVAC cables. For example, a high thermal gradient leads to the inversion of the electric field pattern until the maximum value is reached in proximity of the dielectric-semicon interfaces. These maximum values can be further increased due to transient overvoltages and polarity reversal events until reaching electric field values higher than the rated ones. The main goal of this research is to investigate the possibility that, during these transient phenomena, conditions are created that favor the occurrence of partial …
Polarity reversal in HVDC joints - The effect of the axial thermal conduction
2020
It has been shown that the establishment of a thermal gradient over the radius of HVDC cables involves the accumulation of space charge within the dielectric layer. High thermal gradients over the insulation thickness of loaded cables can lead to the inversion of the radial electric field pattern. In this scenarios, transient overvoltages and polarity reversal can lead to local and transitory peaks of electric field. Since the temperature distribution plays an important role in reaching critical values of the electric field, it has been considered interesting to have a more in-depth view of the thermal behavior of HVDC systems close the discontinuities of the geometry along the cable axis. …