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Bulat L.P.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Osvenskii V.B.,GIREDMET Ltd. | Pshenay-Severin D.A.,RAS Ioffe Physical - Technical Institute
Materials Today: Proceedings | Year: 2015

In the present work the influence of porosity on the thermoelectric figure of merit of bulk nanostructured n-SiGe solid solution is considered. The model for transport coefficients in the solid solution was based on that by Minnich et al. [1]. It took into account acoustic, nonpolar optical phonon scattering, alloy and ionized impurity scattering of electrons. The phonon transport was described taking into account both Umklapp and normal phonon-phonon scattering, defect scattering and scattering on electrons. Grain boundary scattering was taken into account using constant mean free path equal to the grain size both for electrons and phonons. The estimations based on this model correlate quite well with the experimental data and calculations in Ref. [1] and showed the increase of the thermoelectric efficiency by 25-35% at the grain size about 20 nm. The impact of porosity was estimated using the model by Lee et al. [2] with the following differences. The electron scattering in Born approximation was replaced by more accurate phase shift method. The scattering of phonons on pores was considered. Finally, corrections were added to the effective medium theory used in estimations. The results of estimations showed the possibility to improve the thermoelectric efficiency at the pore size less than several tens of nanometers. The increase of the thermoelectric efficiency due to porosity is comparable with the increase due to grain boundary scattering at the volume pore fraction greater than 10%. © 2015 Elsevier Ltd. Source


Bulat L.P.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Osvenskii V.B.,GIREDMET Ltd. | Parkhomenko Y.N.,GIREDMET Ltd. | Pshenay-Severin D.A.,RAS Ioffe Physical - Technical Institute
Journal of Solid State Chemistry | Year: 2012

One of the possible ways to increase the thermoelectric figure of merit is the use of bulk nanostructured materials fabricated by melt spinning with subsequent hot pressing or spark plasma sintering. Among a variety of nanostructure types these materials contain regions of initial solid solution with nanometer sized inclusions of different compositions. In the present work the scattering of holes and phonons on nanoinclusions in such p-Bi xSb 1-xTe 3 based materials is considered. The change of transport coefficients due to this scattering mechanism is theoretically estimated. The estimations showed that the reduction of lattice thermal conductivity (about 12-13%) for nanoinclusions of Bi 2Te 3-Sb 2Te 3 solid solution with different compositions is much greater than the change in power factor. Therefore the corresponding increase of the thermoelectric figure of merit for this case is determined mainly by phonon scattering. Also it is shown that the results of estimations depend on phonon spectrum approximation, e.g. in the case of sine-shaped instead of linear phonon spectrum the estimations give two times higher thermal conductivity reduction. © 2012 Elsevier Inc. Source


Burlakov I.D.,Orion R and P Association | Denisov I.A.,GIREDMET Ltd. | Sizov A.L.,Orion R and P Association | Silina A.A.,Moscow State University | Smirnova N.A.,GIREDMET Ltd.
Applied Physics | Year: 2014

The root mean square (rms) values comparison of CdZnTe substrate surface obtained by confocal microscopy (CM), atomic force microscopy (AFM) and X-ray reflectometry (XRR) has been made. It has been found that CM gives largest rms parameter values, AFM occupies an intermediate position, and values, obtained by XRR, give an order of magnitude smaller than the other two methods. It has been shown that rms values significantly differ with the use of various objectives in CM. Possible reasons of results disagreement have been discussed. Source


Bulat L.P.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Novotelnova A.V.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Asach A.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Tukmakova A.S.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | And 4 more authors.
Journal of Electronic Materials | Year: 2016

Spark plasma sintering (SPS) enables preparation of bulk homogeneous nanothermoelectrics with improved figure of merit, offering a potential route to production of segmented legs from layerwise powder in one sintering cycle. However, it is rather difficult to create appropriate thermal, electric, and pressure conditions to obtain optimal sample parameters. The sintering process of an example segmented leg with Bi2Te3, PbTe, and Mg2(Si0.4Sn0.6)0.993Sb0.007 parts using an SPS-511S installation has been simulated. The temperature distribution in the volume of a segmented sample with the stated composition has been obtained as a function of its geometry, as parameterized by the diameter-to-height ratio. The optimal ratio values, correlating with greater temperature difference along the sample length, have been determined. The results can be used to formulate recommendations for achieving better SPS processing conditions for fabrication of segmented thermoelectric legs. These legs have good performance due to the significant temperature difference in the leg during sintering. © 2016 The Minerals, Metals & Materials Society Source


Bulat L.P.,Saint Petersburg State University of Information Technologies, Mechanics and Optics | Drabkin I.A.,GIREDMET Ltd. | Karatayev V.V.,GIREDMET Ltd. | Osvenskii V.B.,GIREDMET Ltd. | And 3 more authors.
Journal of Electronic Materials | Year: 2014

Two factors that are important for proper estimation of the thermoelectric figure of merit of bulk nanostructured materials based on bismuth telluride and its solid solutions have been investigated. First, the anisotropy of the thermoelectric properties of nanostructured (Bi,Sb)2Te3 fabricated by the spark plasma sintering (SPS) method was studied experimentally as a function of sintering temperature and pressure. Two measuring methods were used: (a) the Harman method and (b) separate measurements of electrical conductivity, Seebeck coefficient, and thermal conductivity (laser flash method). Anisotropy and transport property values obtained by these methods are compared. Secondly, the influence of the nanoparticle size distribution on the lattice thermal conductivity was taken into account theoretically for scattering of phonons both on nanoprecipitates with different compositions and orientations and on grain boundaries. The results of estimations based on different theoretical approaches (relaxation-time approximation, Monte Carlo simulations, and effective medium method) are compared using typical size distribution parameters from available experimental data. © 2014 TMS. Source

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