Search results for "Resistivity"
showing 10 items of 385 documents
Finite range scattering of Ni and Zn impurities in Y-123 thin films
1997
Abstract We investigated YBa 2 (Cu 1− z M z ) 3 O 7-δ (M Ni,Zn) thin films and determined the decrease of T c and the increase of residual resistivity due to Cu-site substitution, taking into account the CuO-chain contributions to the total conductivity. Although Zn suppresses T c stronger than Ni by a factor of 2.3 the increase of resistivity differs only slightly. Furthermore the observed resistivities are too high to be explained within scattering from point-like defects. To reconcile these contradictions, we assumed finite size scattering potentials, which lead to scattering phase shifts δ l of higher angular momebtum l > 0. T c -suppression is discussed qalitatively within this picture.
Electrical Transport Properties of Lead−Free (Na0.5Bi0.5)1-xBaxZr0.04Ti0.96O3Ceramics (x = 0.06, 0.085, 0.1)
2011
Lead-free ceramics (Na0.5Bi0.5)1-xBaxZr0.04Ti0.96O3 were prepared by solid phase hot pressing sintering process. Density values of obtained samples are higher than 95% of the theoretical ones. Samples with x = 0.06, 0.085 and 0.1 were investigated in the present work. For these samples both ac and dc electric conductivity were studied. A low frequency (100 Hz-100 kHz) ac conductivity obeys the power law, characteristic for disordered materials. The dc conductivity has a thermally activated character. A barrier hopping model is found to explain the mechanism of charge transport in these materials. The (Na0.5Bi0.5)1-xBaxZr0.04Ti0.96O3 system is expected to be a new and promising candidate for…
Temperature-dependent resistivity and anomalous Hall effect in NiMnSb from first principles
2019
We present implementation of the alloy analogy model within fully relativistic density-functional theory with the coherent potential approximation for a treatment of nonzero temperatures. We calculate contributions of phonons and magnetic and chemical disorder to the temperature-dependent resistivity, anomalous Hall conductivity (AHC), and spin-resolved conductivity in ferromagnetic half-Heusler NiMnSb. Our electrical transport calculations with combined scattering effects agree well with experimental literature for Ni-rich NiMnSb with 1--2% Ni impurities on Mn sublattice. The calculated AHC is dominated by the Fermi surface term in the Kubo-Bastin formula. Moreover, the AHC as a function o…
Tailoring of the electrical and thermal properties using ultra-short period non-symmetric superlattices
2016
Thermoelectric modules based on half-Heusler compounds offer a cheap and clean way to create eco-friendly electrical energy from waste heat. Here we study the impact of the period composition on the electrical and thermal properties in non-symmetric superlattices, where the ratio of components varies according to (TiNiSn)���:(HfNiSn)���������, and 0 ��� n ��� 6 unit cells. The thermal conductivity (��) showed a strong dependence on the material content achieving a minimum value for n = 3, whereas the highest value of the figure of merit ZT was achieved for n = 4. The measured �� can be well modeled using non-symmetric strain relaxation applied to the model of the series of thermal resistanc…
Charge-carrier density collapse in and epitaxial thin films
2000
We measured the temperature dependence of the linear high field pH of La0.67Ca0.33MnO3 Tc = 232K) and La0.67Sr0.33MnO3 Tc = 345K) thin films in the temperature range from 4 K up to 360 K in magnetic fields up to 20 T. At low temperatures we find a charge-carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature Tc a dramatic drop in the number of charge-carriers n down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data due to a non saturated ma…
An analog electronic interface to measure electrical conductivity in liquids
2005
Abstract Measuring conductivity in aqueous solutions is a problem which is not easy to solve due to the differences in mass and mobility that exist between ions conduction and electrons. Additionally, it is necessary to keep in mind the interaction processes electrode-solution. As a consequence, the electrolytic conductivity cell has to be polarized with alternating voltage of adequate amplitude and frequency in order to extract the correct information. In this paper an electronic conditioning circuit is presented which converts electric conductivity into a value of continuous voltage. A hardware solution is proposed to do the conductivity temperature compensation. Experimental results obta…
Thermal conductivity of thermoelectric Al-substituted ZnO thin films
2013
ZnO:Al thin films with a low electrical resistivity were grown by magnetron sputtering on sapphire substrates. The cross-plane thermal conductivity (κ = 4.5 ± 1.3 W/mK) at room temperature is almost one order of magnitude lower than for bulk materials. The thermoelectric figure of merit ZT at elevated temperatures was estimated from in-plane power factor and the cross-plane thermal conductivity at room temperature. It is expected that the thermal conductivity drops with increasing temperature and is lower in-plane than cross-plane. Consequently, the thin film ZT is at least three times higher than for bulk samples at intermediate temperatures. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinh…
Dielectric relaxation phenomenon and conductivity in lead-free ceramics
2018
Abstract Relaxation phenomena and electric conductivity of (1-x) KNbO3-xK0.5Bi0.5TiO3 system where x = 0, 0.025, 0.05, 0.075, 0.1, 0.2, 0.3 have been studied at high temperature. A relaxation behavior was observed in temperature range 400 K ≤ T ≤ 550 K for orthorhombic solid solutions at room temperature. The activation energy (Ea) of this phenomenon was range from 0.68 eV for x = 0–0.489 eV for x = 0.075 with τ0 = 10−13 s. The relaxation was attributed to hopping of oxygen vacancies for solid solutions x ≤ 0.075. Substitution by K0.5Bi0.5TiO3 does not affect the electrical conductivity of KNbO3 too much, while the mobility of species such as oxygen vacancies and oxygen ions allow the incre…
PEDOT thin films with n-type thermopower
2019
peer-reviewed Synthesis of n-type organic semiconductors is challenging as reduced states are difficult to obtain due to their instability in air. Here, we report tailoring of semiconducting behavior through control of surfactant concentration during synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles. Nanoparticles were synthesized by mini-emulsion polymerization, where stable suspensions were used to produce polymer films by a simple casting technique on polyethylene terephthalate (PET) substrates. Electrical conductivity and Seebeck coefficients were measured as a function of surfactant concentration. It was found that conductivity decreases three orders of magnitude as s…
Capacitance study of thin film SnO2:F/p-type a-Si:H heterojunctions
2011
Abstract We characterized SnO 2 :F/p-type a-Si:H heterojunctions by current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature to determine the junction parameters. Samples with circular geometry and different diameters were characterized. The current scales with the junction area, and the current density J as a function of the voltage V is a slightly asymmetric curve with a super-linear behaviour (cubic law) for high voltages. Using a transmission line model valid for devices with circular geometry, we studied the effects of the SnO 2 :F resistivity on the measured capacitance when the SnO2:F layer works as an electrical contact. The measured C-V curve allows us t…