Search results for "Electrical resistivity and conductivity"
showing 10 items of 317 documents
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…
Soot particle properties in the microwave range
1993
This paper outlines the study of Diesel soot particle properties in the frequency band 2.0-40.0 GHz. Using a transmission/reflection as well as a cavity perturbation method, the complex dielectric constant ?* = ?1 - j?2 was measured for multiple of samples (soot particles produced in a Diesel engine and deposited on paper filter). From the analysis of the experimental data the following conclusions appear: The complex dielectric constant - i.e. the HF electrical conductivity and the microwave power absorption efficiency - are dependent on the frequency and the soot particle thickness. Increasing the soot particle thickness causes the reflection to be stronger and results in less influence o…
Unification of the electrical behavior of defects, impurities, and surface states in semiconductors: Virtual gap states in CdO
2009
In contrast to conventional semiconductors, native defects, hydrogen impurities, and surface states are all found to be donors in $n$-type CdO. Using this as a model system, the electrical behaviors of defects, dopants, and surface states in semiconductors are unified by a single energy level, the charge neutrality level, giving much insight into current materials and allowing a band-structure engineering scheme for obtaining desired custom electronic properties in new compound semiconductors.
Superior energy density through tailored dopant strategies in multilayer ceramic capacitors
2020
The Gerson–Marshall (1959) relationship predicts an increase in dielectric breakdown strength (BDS) and therefore, recoverable energy density (Wrec) with decreasing dielectric layer thickness. This relationship only operates however, if the total resistivity of the dielectric is sufficiently high and the electrical microstructure is homogeneous (no short circuit diffusion paths). BiFeO3–SrTiO3 (BF–ST) is a promising base for developing high energy density capacitors but Bi-rich compositions which have the highest polarisability per unit volume are ferroelectric rather than relaxor and are electrically too conductive. Here, we present a systematic strategy to optimise BDS and maximum polaris…
Optimization of the carrier concentration in phase-separated half-Heusler compounds
2014
Inspired by the promising thermoelectric properties of phase-separated half-Heusler materials, we investigated the influence of electron doping in the n-type Ti_(0.3−x)Zr_(0.35)Hf_(0.35)NiSn compound. The addition of Nb to this compound led to a significant increase in its electrical conductivity, and shifted the maximum Seebeck coefficient to higher temperatures owing to the suppression of intrinsic carriers. This resulted in an enhancement of both the power factor α^2σ and figure of merit, zT. The applicability of an average effective mass model revealed the optimized electron properties for samples containing Nb. There is evidence in the literature that the average effective mass model i…