Despite the great success that theoretical approaches based on density functional theory have in describing properties of solid compounds, accurate predictions of the enthalpies of formation (�H f ) of insulating and semiconducting solids still remain a challenge. This is mainly due to incomplete error cancellation when computing the total energy differences between the compound total energy and the total energies of its elemental constituents. In this paper we present an approach based on GGA + U calculations, including the spin-orbit coupling, which involves fitted elemental-phase reference energies (FERE) and which significantly improves the error cancellation resulting in accurate values for the compound enthalpies of formation. We use an extensive set

http://absimage.aps.org/image/MAR12/MWS_MAR12-2011-007942.pdf

Correcting Density Functional Theory for Accurate Predictions of Compound Enthalpies of Formation:Fitted elemental-phase Reference Energies (FERE)

Gd3+ (gadolinium)-doped ZnSe thin films (1 to 5 mol%) are grown onto indium-doped tin oxide (ITO) glass substrate by single-step electrochemical deposition process. X-ray diffraction analysis confirms the formation of hexagonal wurtzite structure with preferred growth orientation along (101) plane. A new antistructural modeling for describing active surface centers for ZnSe:Gd system is discussed for the first time. The new antistructural modeling shows that the dissolution of Gd cations increases the concentration of surface active centers $$ {\mathrm{Gd}}_{\mathrm{Zn}}^{\bullet } $$
 and $$ {\mathrm{V}}_{\mathrm{Zn}}^{\prime \prime } $$
 , which are located in the cationic sublattice. The surface morphology of thin films investigated using scanning electron microscopy reveals some agglomeration of grains with significant changes in particle size with varying Gd3+ concentrations. UV-vis and photoluminescence studies indicate a blue shift due to the incorporation of Gd3+ into ZnSe host lattice. Electrochemical impedance spectroscopy and photoelectrochemical measurements reveal that the 3 mol% Gd3+-doped ZnSe thin film possesses low charge transfer resistance (25.42 Ω) and faster migration of photoinduced electrons, resulting in high conductivity. Therefore, the optimum doping concentration, 3 mol% Gd3+-doped ZnSe, offers a positive synergistic effect for photoelectrochemical devices.

Physicochemical and electrochemical properties of Gd3+-doped ZnSe thin films fabricated by single-step electrochemical deposition process

Thermoelectric conversion of waste heat from IC engine‐driven vehicles: A review of its application, issues, and solutions

In this work, we show the simultaneous enhancement of electrical transport and reduction of phonon propagation in p-type PbTe codoped with Tl and Na. The effective use of advanced electronic structure engineering improves the thermoelectric power factor S2σ over the temperature range from 300 to 825 K. A rise in the Seebeck coefficient S was obtained due to the enhanced effective mass m*, coming from the Tl resonance state in PbTe. Due to the presence of additional carriers brought by Na codoping, electrical conductivity became significantly improved. Furthermore, Tl and Na impurities induced crystal lattice softening, remarkably reducing lattice thermal conductivity, which was confirmed by a measured low speed of sound vm and high internal strain CeXRD. Eventually, the combination of both the attuned electronic structure and the lattice softening effects led to a very high ZT value of up to ∼2.1 for the Pb1-x-yTlxNayTe samples. The estimated energy conversion efficiency shows the extraordinary value of 15.4% (Tc = 300 K, Th = 825 K), due to the significantly improved average thermoelectric figure of merit ZTave = 1.05. This work demonstrates that the combination of impurity resonance scattering and crystal lattice softening can be a breakthrough concept for advancing thermoelectrics.

High Thermoelectric Performance of p-Type PbTe Enabled by the Synergy of Resonance Scattering and Lattice Softening.

Insight into the transport properties and enhanced thermoelectric performance of n-type Pb1−xSbxTe

The defect subsystem of PbCdTe crystals was analyzed using the method of thermodynamic potential. The predominant type of point defects and their effect on the concentration of free charge carriers have been estimated. It was established that the electroneutral substitution defect CdPb is the dominant point defect in the investigated system. Furthermore, the carrier concentration of a solid solution is determined by the concentration of single-ionized interstitial cadmium atoms and single- and double-ionized vacancies of lead. The donor effect of cadmium in lead telluride is rather weak due to the efficient self-compensation processes. Consequently, n- or p-type conductivity materials with the optimal composition for thermoelectric application carrier concentrations (1018–1019 cm−3) could be obtained by introducing the stoichiometric metal/chalcogenide component of the base material (Pb/Te) or by the implementation of additional donor/acceptor impurities.The defect subsystem of PbCdTe crystals was analyzed using the method of thermodynamic potential. The predominant type of point defects and their effect on the concentration of free charge carriers have been estimated. It was established that the electroneutral substitution defect CdPb is the dominant point defect in the investigated system. Furthermore, the carrier concentration of a solid solution is determined by the concentration of single-ionized interstitial cadmium atoms and single- and double-ionized vacancies of lead. The donor effect of cadmium in lead telluride is rather weak due to the efficient self-compensation processes. Consequently, n- or p-type conductivity materials with the optimal composition for thermoelectric application carrier concentrations (1018–1019 cm−3) could be obtained by introducing the stoichiometric metal/chalcogenide component of the base material (Pb/Te) or by the implementation of additional donor/acceptor impurities.

Point defects in PbCdTe solid solutions

Development of the high performance thermoelectric unicouple based on Bi2Te3 compounds

Results of x-ray studies and measurements of thermoelectric parameters (Seebeck coefficient S, specific electrical conductivity σ, and thermal conductivity χ) of materials based on lead telluride, such as PbTe, PbTe:Sb, PbTe-Sb2Te3, Pb18Ag1Sb1Te20, Pb18Ag2Te20, and PbTe-Ag2Te, are presented. It was found that PbTe:Sb (with 0.3 at.% Sb) as well as Pb18Ag1Sb1Te20 and Pb18Ag2Te20 systems have the highest thermoelectric figure of merit values. In the case of PbTe:Sb, this is due to a significant increase of the electrical conductivity. In the cases of Pb18Ag1Sb1Te20 and Pb18Ag2Te20, it is due to an increase of the Seebeck coefficient and a significant reduction in the thermal conductivity compared with pure PbTe.

Phase Content and Thermoelectric Properties of Optimized Thermoelectric Structures Based on the Ag-Pb-Sb-Te System

GeTe crystallizes with a strong deviation from the stoichiometric composition (in the direction of Te excess), which results in a growth of free carrier concentration (holes) up to p ~ 1021 cm−3. Such concentration is too high from the viewpoint of thermoelectric applications (maximum value of the figure of merit Z). The work demonstrates the possibility of increasing the thermoelectric efficiency of the GeTe-based material, used for the p-type leg of the thermoelectric couple over the temperature range of 600–825 K. The samples were prepared using Spark Plasma Sintering (SPS) technique. A systematic analysis of thermoelectric properties for Ge1-xPbxTe alloys (x up to 5 at.%) has been performed. An increase in the lead content in Ge1-xPbxTe alloys creates two parallel processes. The first process is a decrease of the lattice thermal conductivity κlat, which acts up to T ≈ 550 K, when the lead content in Ge1-xPbxTe alloys increases up to 5 at. %. However, the main process is to reduce deviation from the stoichiometric composition, which consequently leads to lower hole concentration p. Therefore, at a high temperature of T ≥ 550 K Fermi level EF is approaching the edge of the valence band Ev. As a result, the thermoelectric dimensionless figure of merit ZT increases up to 1.1 at the temperature of 825 K.

I.V. Horichok

Papers

Insight into the transport properties and enhanced thermoelectric performance of n-type Pb1−xSbxTe

Point defects in PbCdTe solid solutions

Development of the high performance thermoelectric unicouple based on Bi2Te3 compounds

Phase Content and Thermoelectric Properties of Optimized Thermoelectric Structures Based on the Ag-Pb-Sb-Te System

Origins of the enhanced thermoelectric performance for p-type Ge1-xPbxTe alloys