PbTe Bi2Te3 Research Articles

3D MODELING OF PHASE DIAGRAM OF THE TERNARY SnTe-PbTe-Bi2Te3 SYSTEM

For the SnTe–PbTe–Bi2Te3 system, an analytical model of the temperature-composition dependencies of the crystallization surfaces of the SnTe, PbTe, Bi2Te3, compounds and the ternary PB(Sn)Bi2Te4, Pb(Sn)Bi4Te7, PB(Sn)Bi6Te10 phases formed on based on them was developed and visualized using the 3D analytical function of OriginLab software. The analytical multi-3D model of the phase diagram of the SnTe–PbTe–Bi2Te3 system allows drawing a three-dimensional image of the phases in equilibrium from different angles, obtaining 2D projections, and tabulating the coordinates of the phase diagram. These coordinates as form of matrices – 100x100 = 10.000 and 50x50 = 2500 tabular data create chance for selecting optimal composition and temperature values for the synthesis of alloys, and crystal growth

EXPERIMENTAL REINVESTIGATION OF THE PbTe–Bi2Te3 PSEUDO-BINARY SYSTEM

A newly refined version of the phase diagram of the PbTe–Bi2Te3 pseudo-binary system was construc-ted using differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. It was established that the system forms three tetradymite-type layered ternary compounds, namely PbBi2Te4, PbBi4Te7, and PbBi6Te10, and all these phases melt with peritectic decomposition. However, earlier reported Pb3Bi4Te9, Pb2Bi6Te11, and PbBi8Te13 compounds were not confirmed in our XRD studies. The existence of homogeneity areas based on all ternary compounds and the starting phases PbTe and Bi2Te3 was detected. The crystal structure of the ternary compounds was solved by Rietveld refinement. The newly constructed phase diagram provides very valuable information for choosing appropriate conditions for the synthesis of bulk samples or single crystals growth

PHASE EQUILIBRIA OF THE PbBi2Te4–"PbSb2Te4" SECTION OF THE PbTe–Bi2Te3–Sb2Te3 SYSTEM AND SOME PROPERTIES OF THE SOLID SOLUTIONS

PbTe–Bi2Te3–Sb2Te3 system has been studied by DTA and X-ray diffraction methods along the PbBi2Te4 – "PbSb2Te4" section. It was found that the compound of the composition PbSb2Te4, specified in the literature does not exist. On the basis of the latter a wide (more than 50 mol%) area of solid solution (γ) was detected. By using obtained experimental results, a fragment of the solid-phase equilibrium diagram of the PbTe–Bi2Te3–Sb2Te3 system was constructed and boundaries of the heterogeneous areas α+γ, α+β, α+β+γ (α- and β- are solid solutions based on PbTe and Sb2Te3, respectively) have been determined

Creating Zipper-Like van der Waals Gap Discontinuity in Low-Temperature-Processed Nanostructured PbBi2n Te1+3n : Enhanced Phonon Scattering and Improved Thermoelectric Performance.

Nanoengineered materials can embody distinct atomic structures which deviate from that of the bulk-grain counterpart and induce significantly modified electronic structures and physical/chemical properties. The phonon structure and thermal properties, which can also be potentially modulated by the modified atomic structure in nanostructured materials, however, are seldom investigated. Employed here is a mild approach to fabricate nanostructured PbBi2n Te1+3n using a solution-synthesized PbTe-Bi2 Te3 nano-heterostructure as a precursor. The as-obtained monoliths have unprecedented atomic structure, differing from that of the bulk counterpart, especially the zipper-like van der Waals gap discontinuity and the random arrangement of septuple-quintuple layers. These structural motifs break the lattice periodicity and coherence of phonon transport, leading to ultralow thermal conductivity and excellent thermoelectric z T.

Thermoelectric Properties of Layered Compounds and Multicomponent Solid Solutions in the Pseudoternary System Sb2Te3–PbTe–Bi2Te3

The thermoelectric properties of layered compounds and solid solutions in the Sb2Te3–PbTe–Bi2Te3 system have been studied in a wide temperature range. The quaternary compounds and multicomponent solid solutions in this system have been shown to have a very low lattice thermal conductivity. The electrical conductivity of all the materials decreases with increasing temperature. All of the materials have been shown to be n-type. The layered compounds and multicomponent solid solutions have high thermoelectric efficiency, which makes them promising n-type thermoelectric materials.

Solid solutions based on laminated chalcogenides of bismuth and lead in ternary reciprocal Pb, Bi||Se, Te system

X-ray diffraction and metallographic studies of solid solution alloys are carried out in the PbSe–Bi2Se3 and PbTe–Bi2Te3 quasi-binary systems. Also, the alloys in the PbTe–Bi2Se3 and PbSe–Bi2Te3 diagonal cross sections of the reciprocal ternary system Pb, Bi||Se, Te are studied in the range of compositions near the solid solution PbTe1-xSex (δ). The PbSe–Bi2Se3 phase diagram is refined and it is shown that the phases with orthorhombic lattices existing in the PbS–Bi2S3 system do not form in the PbSe–Bi2Se3 system. In the Pb, Bi||Se, Te ternary reciprocal system, the presence of extended ranges of quadruple solid solutions of trigonal symmetry based on seven compounds is detected: Pb2Bi2Te5, Pb3Bi4Te9, PbBi2Te4, Pb2Bi6Te11, PbBi4Te7, PbBi6Te10, and PbBi8Te13 from the homologous series [PbTe]m[Bi2Te3]n. The extent of the δ range of the solid solution with NaCl cubic structure is established at the PbTe–PbSe side. It is found that the extent of the δ-solid solution region decreases as the PbTe content increases. The phase diagram of the PbSe–PbTe–Bi2Te3–Bi2Se3 reciprocal system illustrates the phase composition of the alloys after homogenizing at 770 K.

Mechanisms of Structure and Thermoelectric Properties of Vapor-Phase Condensates Solid Solution PbTe–Bi2Te3 on Ceramics

Based on analysis of AFM-images, presents the results of complex research the mechanisms of nucleation and growth processes, surface topology and thermoelectric properties of vapor-phase condensates PbTe-Bi2Te3, grown on polycrystalline ceramics at constant temperatures evaporation TE = 970 K and deposition TS = 470 K. Deposition time τ = (15-75) s, and the percentage of Bi2Te3 was 1-5 mol.%. The dependence of structural characteristics (average size of nanocrystals, their rate of change in the lateral (Dc, Dc/τ) and normal (hc, hc/τ) directions to the substrate surface) and thermoelectric parameters (electrical conductivity (σ), Hall concentration (n) and mobility media (μ) thermo-EMF (S) and thermoelectric power (S2σ)) condensates PbTe–Bi2Te3 the conditions of their receipt.

Oscillations of transport properties in PbTe–Bi2Te3 solid solutions

The concentration dependences of the electrical conductivity σ, Hall coefficient RH, charge carrier mobility μH, and Seebeck coefficient S for (PbTe)100−x(Bi2Te3)x semiconductor alloys were obtained at room temperature. It was found that within the PbTe-based solid solution region (x=0–6), the concentration dependences of σ, RH, μH, and S exhibit unusual for solid solutions non-monotonic oscillatory behavior, which indicates qualitative changes in the defect subsystem of the crystal occurring under increasing Bi2Te3 concentration. The observed peculiarities are attributed to the percolation effects and to the self-organization processes in the solid solutions caused by the interactions of impurity atoms among themselves and with atoms of the host lattice. It is suggested that the observed effects are typical for solid solutions, and the probability of their manifestation depends on the crystal structure, elastic and other properties of the solid solution constituents.

Design Principle of Telluride-Based Nanowire Heterostructures for Potential Thermoelectric Applications

We present a design principle to develop new categories of telluride-based thermoelectric nanowire heterostructures through rational solution-phase reactions. The catalyst-free synthesis yields Te-Bi(2)Te(3) "barbell" nanowire heterostructures with a narrow diameter and length distribution as well as a rough control over the density of the hexagonal Bi(2)Te(3) plates on the Te nanowire bodies, which can be further converted to other telluride-based compositional-modulated nanowire heterostructures such as PbTe-Bi(2)Te(3). Initial characterizations of the hot-pressed nanostructured bulk pellets of the Te-Bi(2)Te(3) heterostructure show a largely enhanced Seebeck coefficient and greatly reduced thermal conductivity, which lead to an improved thermoelectric figure of merit. This approach opens up new platforms to investigate the phonon scattering and energy filtering.

Solubility and formation of ternary Widmanstätten precipitates in PbTe in the pseudo-binary PbTe–Bi2Te3 system

A unidirectional solidification experiment by Bridgman method has been performed for the Pb_(14)Bi_(28.8)Te_(57.2) composition, which lies on the pseudo-binary PbTe–Bi_2Te_3 system, resulting in the formation of Widmanstatten precipitates of a ternary compound, most likely with the structure of PbBi_2Te_4 in the PbTe matrix. The formation of the precipitates is caused by the decrease of bismuth solubility in the PbTe phase with decreasing temperature. The PbTe-rich part of the PbTe–Bi_2Te_3 phase diagram was investigated from the compositional variations in the unidirectionally solidified sample and the diffusion couples. This proved that the solubility decreases with decreasing temperature: 15.6 ± 0.9 (583 °C) to 62^(+21)_(−17) (450 °C) at.% Bi. The orientation relationship between the matrix and precipitates has been examined by electron backscatter diffraction technique; precipitation occurs on {111} habit planes in PbTe with orientation relationship (0001)_(precipitate)//{111}_(PbTe) and _(precipitate)// _(PbTe). The thermoelectric properties in PbTe with Widmanstatten precipitates as examined by the scanning Seebeck probe method is –46 ± 2 μVK^(−1).

Crystal Structures and Thermoelectric Properties of Layered Compounds in the ATe–Bi2Te3(A = Ge, Sn, Pb) Systems

Single-crystal and powder x-ray diffraction studies of compounds in the nATe · mBi2Te3 (A = Ge, Sn, Pb) homologous series in the pseudobinary systems ATe–Bi2Te3 reveal a marked dissimilarity of the GeTe–Bi2Te3 system from SnTe–Bi2Te3 and PbTe–Bi2Te3. The GeTe–Bi2Te3 system contains, along with GeBi2Te4 (n/m = 1), GeTe-rich (n/m > 1) and Bi2Te3-rich (n/m < 1) members of the nGeTe · mBi2Te3 series. In contrast, the Sn and Pb systems contain only Bi2Te3-rich compounds (n/m < 1). This dissimilarity is interpreted in terms of the crystal structures of GeTe, SnTe, and PbTe. The thermoelectric properties of nPbTe · mBi2Te3 compounds are studied in a broad temperature range. The thermoelectric figures of merit of unoptimized n-type PbBi4Te7 and PbBi2Te4 are ZT= 0.5 and 0.4 at 600 and 650 K, respectively. Comparison of the thermoelectric properties of the isostructural 12-layer compounds GeBi4Te7, SnBi4Te7, and PbBi4Te7 indicates that the maximum in thermopower shifts to higher temperatures in going from the Ge to Sn and Pb compounds.

Thermoelectric properties and crystal structure of ternary compounds in the Ge(Sn,Pb)Te–Bi2Te3 systems

Polycrystalline samples of stoichiometric ternary compounds in the quasi-binary systems GeTe–Bi2Te3, SnTe–Bi2Te3 and PbTe–Bi2Te3 have been prepared and characterised by X-ray powder diffraction analysis. Lattice parameters have been determined and compared with literature data. At room temperature all the samples exhibit a high carrier concentration in the range 3.4×1019–2.6×1020cm−3. All AIVBi4Te7 and PbBi2Te4 compounds possess negative type of conductivity, while for other compounds it is positive. The Seebeck coefficient and electrical resistivity have been measured over the temperature range 100–800K. The calculated values of the energy band gap of Ge(Sn)Bi4Te7 and Ge(Sn)Bi2Te4 compounds were 0.19–0.22eV as determined from the temperature dependence of electrical resistivity in the intrinsic region. The density of state effective masses m∗ have been estimated for Ge- and Pb-based ternary compounds and are in the range 0.6–1.1m0. An assessment of the potential of these materials for thermoelectric application has also been made.