Thermodynamic and constitutional studies of the PbTe-GeTe system

Shamsuddin,; Ramachandrarao, P.; Misra, S. P.; Anantharaman, T. R.

doi:10.1007/bf00754472

Cited by 19 publications

(6 citation statements)

References 11 publications

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“…Note that Ge vacancies would also affect the phase transition temperature of GeTe as well . However, the phase diagram of GeTe-PbTe − and related literature , all indicate a low PbTe solubility of ∼10% in GeTe. Therefore, most of the existing work on the GeTe-PbTe thermoelectrics involves Pb-rich secondary phase, , and the carrier concentration seems to be not fully optimized by PbTe-alloying alone , as shown in a study involving additional Bi 2 Te 3 -alloying …”

Section: Introductionmentioning

confidence: 89%

High-Performance GeTe Thermoelectrics in Both Rhombohedral and Cubic Phases

et al. 2018

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GeTe experiences phase transition between cubic and rhombohedral through distortion along the [111] direction. Cubic GeTe shares the similarity of a two-valence-band structure (high-energy L and low-energy Σ bands) with other cubic IV–VI semiconductors such as PbTe, SnTe, and PbSe, and all show a high thermoelectric performance due to a high band degeneracy. Very recently, the two valence bands were found to switch in energy in rhombohedral GeTe and to be split due to symmetry-breaking of the crystal structure. This enables the overall band degeneracy to be manipulated either by the control of symmetry-induced degeneracy or by the design of energy-aligned orbital degeneracy. Here, we show Sb-doping for optimizing carrier concentration and manipulating the degree of rhombohedral lattice distortion to maximize the band degeneracy and then electronic performance. In addition, Sb-doping significantly promotes the solubility of PbTe, enhancing the scattering of phonons by Ge/Pb substitutional defects for minimizing the lattice thermal conductivity. This successfully realizes a superior thermoelectric figure of merit, zT of >2 in both rhombohedral and cubic GeTe, demonstrating these alloys as top candidates for thermoelectric applications at T < 800 K. This work further sheds light on the importance of crystal structure symmetry manipulation for advancing thermoelectrics.

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Section: Introductionmentioning

confidence: 89%

High-Performance GeTe Thermoelectrics in Both Rhombohedral and Cubic Phases

et al. 2018

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“…There have been numerous experimental studies of the equilibrium phase stability of these systems. [15][16][17][18][70][71][72][73][74][75][76][77][78][79][80] The first three systems mix on the anion sublattice of rocksalt, and the last three mix on the rocksalt cation sublattice. The model of coherent phase stability used here consists of three parts.…”

Section: Fig 1 (Color Online) Schematic Phase Diagram Of a Pseudo-bmentioning

confidence: 99%

Coherent and incoherent phase stabilities of thermoelectric rocksalt IV-VI semiconductor alloys

Doak

Wolverton

2012

Phys. Rev. B

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Nanostructures formed by phase separation improve the thermoelectric figure of merit in lead chalcogenide semiconductor alloys, with coherent nanostructures giving larger improvements than incoherent nanostructures. However, large coherency strains in these alloys drastically alter the thermodynamics of phase stability. Incoherent phase stability can be easily inferred from an equilibrium phase diagram, but coherent phase stability is more difficult to assess experimentally. Therefore, we use density functional theory calculations to investigate the coherent and incoherent phase stability of the IV-VI rocksalt semiconductor alloy systems Pb(S,Te), Pb(Te,Se), Pb(Se,S), (Pb,Sn)Te, (Sn,Ge)Te, and (Ge,Pb)Te. Here we use the term coherent to indicate that there is a common and unbroken lattice between the phases under consideration, and we use the term incoherent to indicate that the lattices of coexisting phases are unconstrained and allowed to take on equilibrium volumes. We find that the thermodynamic ground state of all of the IV-VI pseudo-binary systems studied is incoherent phase separation. We also find that the coherency strain energy, previously neglected in studies of these IV-VI alloys, is lowest along 111 (in contrast to most fcc metals), and is a large fraction of the thermodynamic driving force for incoherent phase separation in all systems. The driving force for coherent phase separation is significantly reduced, and we find that coherent nanostructures can only form at low temperatures where kinetics may prohibit their precipitation. Furthermore, by calculating the energies of ordered structures for these systems we find that the coherent phase stability of most IV-VI systems favors ordering over spinodal decomposition. Our results suggest that experimental reports of spinodal decomposition in the IV-VI rocksalt alloys should be re-examined. PACS number(s): 64.75. Nx, 82.60.Nh, 84.60.Rb, 64.70.kg 2

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“…This makes Pb ideal for substituting Ge, and indeed leads to an observation of a high thermoelectric performance in GeTe–PbTe alloys . However, the solubility of PbTe is limited to be only ≈13%, presumably due to the large lattice mismatch between GeTe and PbTe. This leaves possibilities for further improvements by a further reduction in the lattice thermal conductivity through alloying.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous Optimization of Carrier Concentration and Alloy Scattering for Ultrahigh Performance GeTe Thermoelectrics

et al. 2017

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In order to locate the optimal carrier concentrations for peaking the thermoelectric performance in p‐type group IV monotellurides, existing efforts focus on aliovalent doping, either to increase (in PbTe) or to decrease (in SnTe and GeTe) the hole concentration. The limited solubility of aliovalent dopants usually introduces insufficient phonon scattering for thermoelectric performance maximization. With a decrease in the size of cation, the concentration of holes, induced by cation vacancies in intrinsic compounds, increases rapidly from ≈1018 cm−3 in PbTe to ≈1020 cm−3 in SnTe and then to ≈1021 cm−3 in GeTe. This motivates a strategy here for reducing the carrier concentration in GeTe, by increasing the mean size of cations and vice‐versa decreasing the average size of anions through isovalent substitutions for increased formation energy of cation vacancy. A combination of the simultaneously resulting strong phonon scattering due to the high solubility of isovalent impurities, an ultrahigh thermoelectric figure of merit, zT of 2.2 is achieved in GeTe–PbSe alloys. This corresponds to a 300% enhancement in average zT as compared to pristine GeTe. This work not only demonstrates GeTe as a promising thermoelectric material but also paves the way for enhancing the thermoelectric performance in similar materials.

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Thermodynamic and constitutional studies of the PbTe-GeTe system

Cited by 19 publications

References 11 publications

High-Performance GeTe Thermoelectrics in Both Rhombohedral and Cubic Phases

High-Performance GeTe Thermoelectrics in Both Rhombohedral and Cubic Phases

Coherent and incoherent phase stabilities of thermoelectric rocksalt IV-VI semiconductor alloys

Simultaneous Optimization of Carrier Concentration and Alloy Scattering for Ultrahigh Performance GeTe Thermoelectrics

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