Bulk Nanocrystalline Thermoelectrics Based on Bi-Sb-Te Solid Solution

A nanopowder from p-Bi-Sb-Te with particles ~ 10 nm were fabricated by the ball milling using different technological modes. Cold and hot pressing at different conditions and also SPS process were used for consolidation of the powder into a bulk nanostructure and nanocomposites. The main factors allowing slowing-down of the growth of nanograins as a result of recrystallization are the reduction of the temperature and of the duration of the pressing, the increase of the pressure, as well as addition of small value additives (like MoS2, thermally expanded graphite or fullerenes). It was reached the thermoelectric figure of merit ZT=1.22 (at 360 K) in the bulk nanostructure Bi0,4Sb1,6Te3 fabricated by SPS method. Some mechanisms of the improvement of the thermoelectric efficiency in bulk nanocrystalline semiconductors based on BixSb2-xTe3 are studied theoretically. The reduction of nanograin size can lead to improvement of the thermoelectric figure of merit. The theoretical dependence of the electric and heat conductivities and the thermoelectric power as the function of nanograins size in BixSb2-xTe3 bulk nanostructure are quite accurately correlates with the experimental data.Comment: 35 pages, 24 figures, 4 tables, 52 reference

Integral Equations for Heat Kernel in Compound Media

By making use of the potentials of the heat conduction equation the integral equations are derived which determine the heat kernel for the Laplace operator $-a^2\Delta$ in the case of compound media. In each of the media the parameter $a^2$ acquires a certain constant value. At the interface of the media the conditions are imposed which demand the continuity of the `temperature' and the `heat flows'. The integration in the equations is spread out only over the interface of the media. As a result the dimension of the initial problem is reduced by 1. The perturbation series for the integral equations derived are nothing else as the multiple scattering expansions for the relevant heat kernels. Thus a rigorous derivation of these expansions is given. In the one dimensional case the integral equations at hand are solved explicitly (Abel equations) and the exact expressions for the regarding heat kernels are obtained for diverse matching conditions. Derivation of the asymptotic expansion of the integrated heat kernel for a compound media is considered by making use of the perturbation series for the integral equations obtained. The method proposed is also applicable to the configurations when the same medium is divided, by a smooth compact surface, into internal and external regions, or when only the region inside (or outside) this surface is considered with appropriate boundary conditions.Comment: 26 pages, no figures, no tables, REVTeX4; two items are added into the Reference List; a new section is added, a version that will be published in J. Math. Phy

ВЛИЯНИЕ ПАРАМЕТРОВ ПЛАСТИЧЕСКОГО ФОРМОВАНИЯ НА СТРУКТУРНЫЕ ХАРАКТЕРИСТИКИ ТЕРМОЭЛЕКТРИЧЕСКОГО МАТЕРИАЛА В ПРОЦЕССЕ ГОРЯЧЕЙ ЭКСТРУЗИИ

We used mathematical modeling to compare the stress and deformation in a Bi0.4Sb1.6Te3 solid solution base thermoelectric material for extrusion through different diameter dies. The results show that extrusion through a 20 mm diameter die produces a more inhomogeneous deformation compared with extrusion through a 30 mm diameter die. Extrusion through a die of a larger diameter produces a structure that is coarser but has a more homogeneous grain size distribution. The degree of preferential grain orientation is higher for extrusion through a larger diameter die. We found a change in the lattice parameter of the solid solution along the extruded rod, correlating with detect formation during extrusion. The concentration of vacancies is higher for extrusion through a smaller diameter die. This difference between the structures results from a more intense dynamic recrystallization for a smaller diameter die. Increasing the die diameter and lowering the extrusion temperature allow retaining the thermoelectric properties of the material due to a better texture.С помощью математического моделирования проведено сравнение напряжений и деформаций в термоэлектрическом материале на основе твердого раствора Bi0,4Sb1,6Te3 при экструзии через фильеры с разным диаметром. Показано, что при экструзии через фильеру диаметром 20 мм возникает более неоднородная деформация, чем при экструзии через фильеру 30 мм. Установлено, что при увеличении диаметра фильеры структура материала получается менее дисперсная, но более однородная по размерам. Степень преимущественной ориентации зерен при экструзии через фильеру большего диаметра более высокая. Обнаружено изменение параметра решетки твердого раствора по длине экструдированного стержня, связанного с дефектообразованием в процессе экструзии. Выявлено, что концентрация вакансий больше при экструзии через фильеру меньшего диаметра. Это является следствием более интенсивного протекания процессов динамической рекристаллизации. При переходе к большему диаметру фильеры и более низкой температуре экструзии термоэлектрические свойства материала сохраняются за счет лучшей текстуры

Influence of plastic formation parameters on structural characteristics of thermoelectric material during hot extrusion

We used mathematical modeling to compare the stress and deformation in a Bi0.4Sb1.6Te3 solid solution base thermoelectric material for extrusion through different diameter dies. The results show that extrusion through a 20 mm diameter die produces a more inhomogeneous deformation compared with extrusion through a 30 mm diameter die. Extrusion through a die of a larger diameter produces a structure that is coarser but has a more homogeneous grain size distribution. The degree of preferential grain orientation is higher for extrusion through a larger diameter die. We found a change in the lattice parameter of the solid solution along the extruded rod, correlating with detect formation during extrusion. The concentration of vacancies is higher for extrusion through a smaller diameter die. This difference between the structures results from a more intense dynamic recrystallization for a smaller diameter die. Increasing the die diameter and lowering the extrusion temperature allow retaining the thermoelectric properties of the material due to a better texture

Periodic Self-Assembly of Poly(ethyleneimine)–poly(4-styrenesulfonate) Complex Coacervate Membranes

Coacervation is a self-assembly strategy based on the complexation of polyelectrolytes, which is utilized in biomedicine and agriculture, as well as automotive and textile industries. In this paper, we developed a new approach to the on-demand periodic formation of polyelectrolyte complexes through a Liesegang-type hierarchical organization. Adjustment of reaction conditions allows us to assemble materials with a tunable spatiotemporal geometry and establish materials’ production cycles with a regulated periodicity. The proposed methodology allows the membrane to self-assemble when striving to reach balance and self-heal after exposure to external stimuli, such as potential difference and high pH. Using chronopotentiometry, K+ ion permeability behavior of the PEI–PSS coacervate membranes was demonstrated. The periodically self-assembled polyelectrolyte nanomembranes could further be integrated into novel energy storage devices and intelligent biocompatible membranes for bionics, soft nanorobotics, biosensing, and biocomputing