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Metal-insulator Transition (metal-insulator + transition)

Distribution by Scientific Domains
Physics and Astronomy60%
Polymers and Materials Science40%

Selected Abstracts

Traversing the Metal-Insulator Transition in a Zintl Phase: Rational Enhancement of Thermoelectric Efficiency in Yb14Mn1,xAlxSb11,

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2008
Eric S. Toberer
Abstract For high temperature thermoelectric applications, Yb14MnSb11 has a maximum thermoelectric figure of merit (zT) of ,1.0 at 1273,K. Such a high zT is found despite a carrier concentration that is higher than typical thermoelectric materials. Here, we reduce the carrier concentration with the discovery of a continuous transition between metallic Yb14MnSb11 and semiconducting Yb14AlSb11. Yb14Mn1-xAlxSb11 forms a solid solution where the free carrier concentration gradually changes as expected from the Zintl valence formalism. Throughout this transition the electronic properties are found to obey a rigid band model with a band gap of 0.5,eV and an effective mass of 3 me. As the carrier concentration decreases, an increase in the Seebeck coefficient is observed at the expense of an increased electrical resistivity. At the optimum carrier concentration, a maximum zT of 1.3 at 1223,K is obtained, which is more than twice that of the state-of-the-art Si0.8Ge0.2 flown by NASA. [source]

Colossal Electroresistance and Giant Magnetoresistance in Doped PbPdO2 Thin Films

ADVANCED MATERIALS, Issue 21 2009
Xiaolin Wang
Observations on colossal electroresistance (ER) and giant magnetoresistance in doped PbPdO2, one of the candidates of a new class of materials, spin gap-less semiconductors, are reported. The resistivity is strongly suppressed by electrical current below a metal-insulator transition with the ER values of up to 107, which is much greater than that achieved in colossal magnetoresistance materials. [source]

Influence of electronic correlations on the frequency-dependent hopping transport in Si:P

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008
Elvira Ritz
Abstract At low energy scales charge transport in the insulating Si:P is dominated by activated hopping between the localized donor electron states. Thus, theoretical models for a disordered system with electron-electron interaction are appropriate to interpret the electric conductivity spectra. With a newly developed technique we have measured the complex broadband microwave conductivity of Si:P from 100 MHz to 5 GHz in a broad range of phosphorus concentration n /nc from 0.56 to 0.95 relative to the critical value nc = 3:5 × 1018 cm,3 corresponding to the metal-insulator transition driven by doping. At our base temperature of T = 1.1 K the samples are in the zero-phonon regime where they show a super-linear frequency dependence of the conductivity indicating the influence of the Coulomb gap in the density of the impurity states. At higher doping n , nc, an abrupt drop in the conductivity power law ,1(,) , ,, is observed. The dielectric function ,1 increases upon doping following a power law in (1 , n /nc). Dynamic response at elevated temperatures has also been investigated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Intensified spin-dependent-transport and localized-spin freezing in magnetite sinter made from low size-dispersion hematite nanoparticles with low temperature calcination

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006
H. Kobori
Abstract The spin-dependent-transport (SDT) has been studied for magnetite (Fe3O4) nano-particle sinter (MNPS) made from low size-dispersion hematite (,-Fe2O3) nanoparticles (LSDHN's) with low temperature calcination. Two kinds of LSDHN's are grown by the hydrothermal synthesis. The average sizes of them are 30 nm and 60 nm. The MNPS is produced by calcining the LSDHN's at 500 °C for 5 hours in the atmosphere of Ar(90%)/H2(10%) mixed gases. As compared with a bulk single crystal, the considerable intensification of negative-differential-magnetoresistance (ND-MR) has been observed for the MNPS. We have not observed abrupt change of the electrical resistivity in the vicinity of the temperature of the Verwey transition (which is the metal-insulator transition) appeared for a bulk single crystal. The ND-MR for 30 nm shows larger values than that of 60 nm on the temperature dependence. From the X-ray diffraction experiment, the MNPS is found to include crystalline magnetite regions. We consider that the MNPS is composed of large amorphous-like grain-boundaries and small crystalline grains. The electrical current is inferred to flow in grain-boundary regions. In grain-boundary regions, since the localized spins are relatively random distributed, the spin-polarized conduction electrons show the SDT. Below the Verwey temperature, we have observed the magnetization difference between zero-field cooling (ZFC) and field-cooling (FC). This phenomenon indicates that the localized spins in the amorphous-like grain-boundaries are frozen in some degree. Above the Verwey temperature, the magnetoresistance is well fitted by the square of the Langevin function. We consider that the localized spins in the amorphous-like grain-boundaries do not form perfectly random configuration and are somewhat ordered in a short range region. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The vanadium Magnéli phases VnO2n -1

ANNALEN DER PHYSIK, Issue 9 2004
U. Schwingenschlögl
Abstract To compare the metal-insulator transitions (MITs) of VO2 and V2O3 we analyze the relations between the structural and electronic properties of the vanadium Magnéli phases. These materials set up the homologous series VnO2n -1 (3 , n , 9) and have crystal structures comprising typical dioxide-like and sesquioxide-like regions. As the MITs of the vanadium Magnéli phases are accompanied by structural transformations, we are able to discuss the effects of characteristic changes in the local atomic environments. The systematic investigation of the transport properties is based on a new and unifying description of the crystal structures of the Magnéli phases including VO2 and V2O3. Our results lead to a comprehensive understanding of the MITs in the Magnéli class and shed new light on the role of particular electronic states for the MIT of V2O3. [source]