1,720,973 research outputs found
The Charge Transport Properties of a HWCVD a-Si:H Thin Film under Bending Pressure
No full textThe transient thermoelectric effects (TTEs) method is used to measure the ambipolar space charge built up in a low-pressure hot wire chemical vapor deposition (HWCVD) technique a-Si:H layer deposited on a glass substrate. The stage 2 TTE-transients yield the trap state density difference with and without bending pressure up to 9 bars. The a-Si:H sample shows a reduction of the negative storage peaks at 0.045eV and 0.026eV with increasing pressure, while the positive (hole trap) peak and the zero crossing practically do not change with the pressure. At the maximum bending pressure, the negative peaks are almost zero and shifted into the band gap or toward the conduction band. Our result shows that it is necessary to produce and mount hydrogenated thin film solar cell stress-free
Electroresistive effect in slightly oxygen deficient Nd0.7Sr0.3MnO3-delta ceramic
No full textWe observe a strong electroresistive (ER) effect in slightly oxygen deficient Nd0.7Sr0.3MnO3-delta ceramic which behaves equivalent to the well-known magnetoresistive effect and which apparently involves both the higher insulating grain boundaries as well as parts of the domain (grain) volume, just like the MR in ceramics. While the magnetic field acts on the magnetic dipoles of the manganites (MR), the nature of the electrical dipole moments - intrinsic or extrinsic - is not fully understood as yet, but as the ER-effect increases dramatically with 6, for these compounds the evidence points to extrinsic electrical dipoles which appear together with a local restructuring when oxygen is formally missing. (c) 2005 Elsevier B.V. All rights reserved
Trap state spectroscopy in CMR manganites and spinel manganates using opto-impedance
No full textThe photo-induced AC-impedance method is used as a versatile instrumentation to study the trap state densities and the carrier
relaxation times in magneto-resistive manganites and magneto-conductive manganates and thus as a probe to check the crystal quality,
which is important for the performance of any device material. A comparative study using compounds of different defect densities is
presented. High defect concentrations in the compounds are identified through the photoresistivity and/or the photo-induced capacitive
build up
Determination of the baric coefficient using a double ac method
No full textAn apparatus has been designed which measures the baric coefficient gamma, defined as the relative change of a resistance under pressure: R=R-0(1+gamma p), using a double ac method, the pressure modulation of the resistance being obtained via compressional sound waves. First results on manganites RE(1-x)A(x)MnO(3) are obtained and compared with the pressure derivatives of R(p,T) as obtained with static methods. Good agreement was obtained at larger superimposed static pressure P-st, however, extra results are obtained in the limit P-st-> 0 and in the case of a percolation of phase separated volumes. (c) 2005 American Institute of Physics
The baric coefficient of resistance of Mn1.9Cr0.1Sb as measured by the double AC method
No full textThe baric coefficient of resistance of the magnetocaloric cycle working medium Mn1.9Cr0.1Sb, aside from the peak which is expected and related to the pressure shift of the AF-Fr transition temperature T-s(p), shows two sidebands which are probably related to the percolation of phase domains. (c) 2007 Elsevier B.V. All rights reserved
Electrical field induced order–order transitions in rare earth manganites
No full textVaristor-like electrical transport is found in Nd2/3Sr1/3MnOz, and Pr0.7Sr0.3MnO3 compounds, with evidence of magnetic order-order transitions superimposed. The transition temperatures move under a magnetic field which establishes the spin-dependent character of these phenomena. We also discuss the possibilty that the electrical field induces such transitions, as the transition appears and/or shifts at certain applied currents (or potentials). (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Boundary resistance anomalies in Nd0.7Sr0.3MnO3-delta
No full textSpin-dependent varistor-like electrical transport is found in Nd2/3Sr1/3MnO3-delta compounds for deltagreater than or equal to0.1, for which the transport through magnetic grain or phase boundaries is responsible. Specifically, electrical-field-induced changes of the spin array orientations inside of and between the domains have to be concluded. Among those, we identify an E-field-induced metamagnetic transition. (C) 2003 Elsevier B.V. All rights reserved
Comparison of the magnetic properties between Y-3(Fe, Cr)(29) and Y2Fe15Cr2 single crystals
No full textA Y-3(Fe, Cr)(29) single crystal which has a Nd-3(Fe, Ti)(29)-type monoclinic structure has been prepared using the Czochralski method followed by heat treatment of an initial Y-2(Fe, Cr)(17) crystal. The magnetization curves were measured along the easy and hard magnetization directions in the range from 1.5 to 293 K for crystals of Y-3(Fe, Cr)(29) and Y-2(Fe, Cr)(17). The saturation magnetization of Y-3(Fe, Cr)(29) decreases with increasing temperature and is in good agreement with a T-3/2 spin-wave relation law. The magnetic properties of the two crystals are compared. (C) 2002 Elsevier Science B.V. All rights reserved
Evidence of photogenerated space charges in the charge ordered state of Pr0.63Ca0.37MnO3 single crystals
No full textTime-resolved thermoelectric power measurements on bulk single crystals with composition close to charge ordered compound Pr2/3Ca1/3MnO3 show a voltage transient V-2(t) for T < T-co, which is superimposed to and faster as the quasistatic thermovoltage decay V-3(t) which is usually the only transient observed with manganite ceramic. From V-3(t) we derive the heat conductivity k and thermopower S in the temperature range 90 K < T < 350 K. The extra transient is ascribed to the decay of an ambipolar charge distribution in trap states which appears only in the charged ordered regime of x = 0.37. First data on intrinsic and/or extrinsic trap level distributions are given. (C) 2004 Elsevier B.V. All rights reserved
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