Disordered electronic systems: Concentration dependence of the dc conductivity in amorphous transition-metal–metalloid alloys (metallic regime) (original) (raw)
Related papers
Physical Review B, 2005
The electronic transport in the phase separated regime is determined by both the different local band structure in the phases ͑called phases A and B͒ and electron redistribution (electron transfer) to the phase with the deeper average potential ͑phase B͒. Equations for the dependence of the electronic conductivity on metalloid concentration x are derived. In amorphous metal-metalloid alloys the metal-insulator transition ͑M-I transition͒ characterized by the transition from Ͼ 0 to = 0 at temperature T =0 at x = x c takes place in the phase separated regime. The M-I transition in S 1−x M x alloys is determined by the conduction band ͑phase A͒, whereas in N 1−x M x , and in many T 1−x M x alloys, it is determined by the valence band ͑phase B͒ ͑N and T stand for a transition metal with completely and incompletely occupied d band, respectively, S for a simple metal as Al, Ga, In,. . ., and M for a metalloid element as Si or Ge͒. ͑1͒ Granular structure, ͑2͒ rapid decrease of the average metal grain size with increasing x, and ͑3͒ relatively small x c are characteristic features for S 1−x M x thin films deposited under extreme deposition conditions and are caused by the fact that a considerable part of electrons transferred occupy surface states leading to charged phase boundaries. The fractal structure found in Al 1−x Ge x alloys after annealing is related with the formation of a maximum of phase boundary faces for acceptance of the transferred electrons. For strong scattering in a single phase, there are a minimum metallic conductivity min Ӎ͑c * /6͒͑e 2 / h͒͑1/d͒ and mobility edges at density of states 4c * m / h 2 d, where c * =1/4 ͑d is the average atomic distance. e and m are the elementary charge and effective mass of the electrons, respectively, and ប = h /2 is Plancks constant͒.
Temperature dependent electronic transport in concentrated solid solutions of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">mml:mrowmml:mn3mml:mid -transition metals Ni, Fe, Co and Cr from first principles
Physical review, 2018
An approach previously developed for the calculation of transport coefficients via the Mott relations is applied to the calculation of finite temperature transport properties of disordered alloys-electrical resistivity and the electronic part of thermal conductivity. The coherent potential approximation (CPA) is used to treat chemical disorder as well as other sources of electron scattering, i.e. temperature induced magnetic moment fluctuations and lattice vibrations via the alloy analogy model. This approach, which treats all forms of disorder on an equal first principles footing, is applied to the calculation of transport properties of a series of face-centered crystal cubic (fcc) concentrated solid solutions of the 3d-transition metals Ni, Fe, Co and Cr. For the nonmagnetic alloys, Ni 0.8 Cr 0.2 , and Ni 0.33 Co 0.33 Cr 0.3 the combined effects of chemical disorder and electron-lattice vibrations scattering result in a monotonic increase in the resistivity as a function of temperature from an already large, T=0, residual resistivity. For magnetic Ni 0.5 Co 0.5 , Ni 0.5 Fe 0.5 , Ni 0.33 Fe 0.33 Co 0.33 , whose residual resistivity is small, additional electron scattering from temperature induced magnetic moment fluctuations results in a further rapid increase of the resistivity as a function of temperature. The electronic part of the thermal conductivity in nonmagnetic, Ni 0.8 Cr 0.2 , and Ni 0.33 Co 0.33 Cr 0.33 , monotonically increases with temperature. This behavior is a result of the competition between a reduction in the conductivity due to electron-lattice vibrations scattering and temperature induced increase in the number of carriers. In the magnetic alloys, electron scattering from magnetic fluctuations leads to an initial rapid decrease in thermal conductivity until this is overcome by an increasing number of carriers at temperatures slightly below the Curie temperature. Similar to the resistivity above T C , the electronic part of the thermal conductivities are close to each other in all alloys studied.
Physical review, 1972
A model calculation of the temperature dependence of the electronic density of states and the electrical conductivity of disordered binary alloys, based on the coherent-potential approximation (CPA) is made by introducing thermal disorder in the single-band model (Velic@ and others). Thermal disorder is found to broaden and smear the static-alloy density of states. The electrical resistivity in weak-scattering alloys always increases with temperature. However, in the strong-scattering case, the temperature coefficient of resistivity can be positive, zero, or negative, depending on the location of the Fermi energy.
Electronic Transport in Alloys with Phase Separation (Composites)
Open Journal of Composite Materials, 2019
A measure for the efficiency of a thermoelectric material is the figure of merit defined by 2 ZT S T 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 () 1 σ 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.
Electrons in non-crystalline metals ?Still a challenging problem
Zeitschrift f�r Physik B Condensed Matter, 1987
The following aspects of the electronic properties of liquid and amorphous metals are studied: (i) density of states of polyvalent liquid metals by means of finite cluster calculations, (ii) the Hall coefficient of simple metals by the use of a generalised transport equation, (iii) the effect of multiple scattering on the electrical resistivity. Measuring electronic densities of states (DOS) and electrical transport coefficients in liquid and amorphous metals is an everyday activity of the Basel solid state group. Therefore any condensed matter theoretician working there is exposed to the question how to calculate such quantities in a simple but well founded theoretical framework. It is the purpose of this contribution to summarize some recent calculcations aiming at a better understanding and a more quantitative description of the electronic properties in non-crystalline metals-a fascinating problem of condensed matter physics on which the first author has had many stimulating discussions with H. Thomas.
Physical Review B
An approach previously developed for the calculation of transport coefficients via the Mott relations is applied to the calculation of finite temperature transport properties of disordered alloys-electrical resistivity and the electronic part of thermal conductivity. The coherent potential approximation (CPA) is used to treat chemical disorder as well as other sources of electron scattering, i.e. temperature induced magnetic moment fluctuations and lattice vibrations via the alloy analogy model. This approach, which treats all forms of disorder on an equal first principles footing, is applied to the calculation of transport properties of a series of face-centered crystal cubic (fcc) concentrated solid solutions of the 3d-transition metals Ni, Fe, Co and Cr. For the nonmagnetic alloys, Ni 0.8 Cr 0.2 , and Ni 0.33 Co 0.33 Cr 0.3 the combined effects of chemical disorder and electron-lattice vibrations scattering result in a monotonic increase in the resistivity as a function of temperature from an already large, T=0, residual resistivity. For magnetic Ni 0.5 Co 0.5 , Ni 0.5 Fe 0.5 , Ni 0.33 Fe 0.33 Co 0.33 , whose residual resistivity is small, additional electron scattering from temperature induced magnetic moment fluctuations results in a further rapid increase of the resistivity as a function of temperature. The electronic part of the thermal conductivity in nonmagnetic, Ni 0.8 Cr 0.2 , and Ni 0.33 Co 0.33 Cr 0.33 , monotonically increases with temperature. This behavior is a result of the competition between a reduction in the conductivity due to electron-lattice vibrations scattering and temperature induced increase in the number of carriers. In the magnetic alloys, electron scattering from magnetic fluctuations leads to an initial rapid decrease in thermal conductivity until this is overcome by an increasing number of carriers at temperatures slightly below the Curie temperature. Similar to the resistivity above T C , the electronic part of the thermal conductivities are close to each other in all alloys studied.
Anomalous electronic transport in quasicrystals and related complex metallic alloys
Comptes Rendus Physique, 2014
We analyze the transport properties in approximants of quasicrystals α-AlMnSi, 1/1-AlCuFe and for the complex metallic phase λ-AlMn. These phases presents strong analogies in their local atomic structures and are related to existing quasicrystalline phases. Experimentally they present unusual transport properties with low conductivities and a mix of metallic-like and insulating-like characteristics. We compute the band structure and the quantum diffusion in the perfect structure without disorder and introduce simple approximations that allow to treat the effect of disorder. Our results demonstrate that the standard Bloch-Boltzmann theory is not applicable to these intermetallic phases. Indeed their dispersion relation are flat indicating small band velocities and corrections to quantum diffusion that are not taken into account in the semi-classical Bloch-Boltzmann scheme become dominant. We call this regime the small velocity regime. A simple Relaxation Time Approximation to treat the effect of disorder allows us to reproduce the main experimental facts on conductivity qualitatively and even quantitatively. To cite this article: Guy Trambly de Laissardière, D. Mayou, C. R. Physique XXXX (20XX). Résumé Transportélectronique anormal dans les quasicristaux et les alliages métalliques complexes reliés. Nous analysons les propriétés de transportélectronique dans les approximants de quasicristaux α-AlMnSi, 1/1-AlCuFe et pour la phase complexe reliée λ-AlMn. Ces phases présentent de fortes analogies de leurs structures atomiques locales et sont reliéesà des phases quasicrystallines existantes. Expérimentallement elles présentent des propriétés de transport inhabituelles avec une faible conductivité et un mélange de propriétés de type métallique et de type isolant. Nous calculons la structure de bande et la diffusion quantique de la structure parfaite et introduisons une approximation simple qui permet de traiter l'effet du désordre. Nos résultats démontrent que la théorie standard de Bloch-Boltzmann n'est pas applicableà ces systèmes intermétalliques. En effet leurs relations de dispersion sont plates indiquant une faible vitesse de bande et les correctionsà la diffusion quantique qui ne sont pas prises en compte par la théorie semi-classique deviennent dominantes. Nous appelons ce régime le régime de faible vitesse. Une simple approximation de temps de relaxation pour traiter l'effet du désordre permet de reproduire les principaux résultats expérimentaux sur la conductivité qualitativement et même quantitativement.
Electron transport in liquid metals and alloys
Canadian Journal of Physics, 1987
This paper deals with a number of selected topics from the field of electric transport properties in liquid metals and alloys. First, some nearly free electron systems are considered; it appears that some problems associated with the properties of liquid Na–Cs alloys and of amalgams are still unsolved. Then, systems exhibiting strong compound formation, particularly alkali–nonalkali alloys with a large electronegativity difference between the components, are reviewed. A qualitative interpretation in terms of chemical-valence rules, based upon our knowledge of the solid state, is given. Next, recently developed theories dealing with transport properties in disordered media are critically discussed. Some models for the interpretation of the alkali – group IV alloys are presented. The basic ideas derived from these models are used also as guidelines for a more qualitative discussion of the alkali – group III and alkali – group V alloy systems.
On the Electronic Structure and Thermodynamics of Alloys
1986
I would also like to thank all the students of the department for their friendship and their support. They have made my stay at Columbia very enjoyable. I am indebted to my parents, Paul and Paulette, who have always supported and encouraged me in all aspects of my life.
Anomalous electronic behaviour of crystalline phases close to quasicrystals
Physica B: Condensed Matter, 1995
The crystalline approximant phases ~-AIMnSi and R-AICuFe present for alloys of metallic elements anomalou electronic transport properties, with low conductivity values and strong temperature dependences of both the conductiv ity and the Hall coefficient. In both the ct-and R-phases, the high field magnetoconductivity can be analysed by quantur interference effects. The transport behaviours are very similar to those of the high structural quality icosahedral phase~ Moreover, the R-AICuFe phase properties are identical to those of the AICuFe icosahedral phases of the sam composition. Surprisingly, the ct-AlMnSi phase, of a much simpler structure than R-AICuFe, presents the sam anomalous behaviours. Approximants are very different from the icosahedral AIMnSi counterparts which behave lik amorphous metals. The results indicate that the relevant length scale for understanding the transport properties is abo~ the size of these crystalline unit cells, i.e. one or two nanometers. * Corresponding author.