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The Origin of the Giant Hall Effect in Metal-Insulator Composites

Open Journal of Composite Materials 2016年第3期6卷 78-90页

作者： joachim sonntag MEAS Deutschland GmbH a TE Connectivity LTD Company Dortmund Germany

Near the metal-insulator transition, the Hall coefficient R of metal-insulator composites (M-I composite) can be up to 104 times larger than that in the pure metal called Giant Hall effect. Applying the physical model for alloys with phase separation developed in [1] [2], we conclude that the Giant Hall effect is caused by an electron transfer away from the metallic phase to the insulating phase occupying surface states. These surface states are the reason for the granular structure typical for M-I composites. This electron transfer can be described by [1] [2], provided that long-range diffusion does not happen during film production (n is the electron density in the phase A. uA and uB are the volume fractions of the phase A (metallic phase) and phase B (insulator phase). β is a measure for the average potential difference between the phases A and B). A formula for calculation of R of composites is derived and applied to experimental data of granular Cu1-y(SiO2)y and Ni1-y(SiO2)y films.

关键词： Metal-Insulator Composites Granular Metals Hall Coefficient Conductivity Electron Density

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Electronic Transport in Alloys with Phase Separation (Composites)

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Open Journal of Composite Materials 2019年第1期9卷 21-56页

作者： joachim sonntag Bertrand Lenoir Pawel Ziolkowski TE Connectivity Sensors Germany GmbH Dortmund Germany Institut Jean Lamour UMR 7198 CNRS-Université de Lorraine 2 Allée André Guinier-Campus ARTEM Nancy Cedex France German Aerospace Center Institute of Materials Research Koln Germany

A measure for the efficiency of a thermoelectric material is the figure of merit defined by ZT = S2T/ρκ, where S, ρ and κ are the electronic transport coefficients, Seebeck coefficient, electrical resistivity and thermal conductiviy, respectively. T is the absolute temperature. Large values for ZT have been realized in nanostructured materials such as superlattices, quantum dots, nanocomposites, and nanowires. In order to achieve further progress, (1) a fundamental understanding of the carrier transport in nanocomposites is necessary, and (2) effective experimental methods for designing, producing and measuring new material compositions with nanocomposite-structures are to be applied. During the last decades, a series of formulas has been derived for calculation of the electronic transport coefficients in composites and disordered alloys. Along the way, some puzzling phenomenons have been solved as why there are simple metals with positive thermopower? and what is the reason for the phenomenon of the “Giant Hall effect”? and what is the reason for the fact that amorphous composites can exist at all? In the present review article, (1), formulas will be presented for calculation of σ = (1/ρ), κ, S, and R in composites. R, the Hall coefficient, provides additional informations about the type of the dominant electronic carriers and their densities. It will be shown that these formulas can also be applied successfully for calculation of S, ρ, κ and R in nanocomposites if certain conditions are taken into account. Regarding point (2) we shall show that the combinatorial development of materials can provide unfeasible results if applied noncritically.

关键词： Hall Effect Giant Hall Effect Seebeck Coefficient (Thermopower) Electron Density Conductivity Thermal Conductivity Composites Nanocomposites Percolation Theory

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