Rabih Al Rahal Al Orabi

Prediction of high thermoelectric potential in AMN2 layered nitrides: electronic structure, phonons, and anharmonic effects

Band structures, electronic transport coefficients, harmonic and anharmonic vibrational properties of novel layered nitrides have been studied to evaluate the potential for thermoelectric applications. Using first principles theoretical methods we predict that AMN2 compounds with A = Ca, Sr, and Ba, and M = Ti, Zr, Hf may exhibit Seebeck coefficients in excess of 150 μV K−1 and good electrical conductivities. The phonon dispersions indicate the presence of low lying optic modes that can lead to low thermal conductivity. The analysis of the mode resolved Gruneisen parameter points to large anharmonicity. In addition, we show that the A-site substitution controls the degeneracies at the top of the valence band and the anisotropy of the Seebeck tensors.

Cu Insertion Into the Mo12 Cluster Compound Cs2Mo12Se14: Synthesis, Crystal and Electronic Structures, and Physical Properties.

Mo-based cluster compounds are promising materials for high-temperature thermoelectric applications due to their intrinsic, extremely low thermal conductivity values. In this study, polycrystalline cluster compounds Cs2CuxMo12Se14 were prepared for a wide range of Cu contents (0 ≤ x ≤ 2). All samples crystallize isostructurally in the trigonal space group R3̅. The position of the Cu atoms in the unit cell was determined by X-ray diffraction on a single-crystalline specimen indicating that these atoms fill the empty space between the Mo-Se clusters. Density functional theory calculations predict a metallic ground state for all compositions, in good agreement with the experimental findings. Magnetization measurements indicate a rapid suppression of the superconducting state that develops in the x = 0.0 sample upon Cu insertion. Transport properties measurements, performed in a wide temperature range (2-630 K) on the two end-member compounds x = 0 and x = 2, revealed a multiband electrical conduction as shown by sign reversal of the thermopower as a function of temperature.

Enhancement of thermoelectric properties by effective K-doping and nano precipitation in quaternary compounds of (Pb1−xKxTe)0.70(PbSe)0.25(PbS)0.05

We investigated thermoelectric properties in K-doped quaternary compounds of (Pb1−xKxTe)0.70(PbSe)0.25(PbS)0.05 (x ≤ 0.03). In terms of two valence bands model, we argue that the L-band approaches to the Σ-band with increasing the K-doping concentration resulting in the increase of carrier concentration and effective mass of carrier due to the increase of band degeneracy. The effective K-doping by x = 0.02 and PbS substitution causes high power factor and low thermal conductivity, resulting in the comparatively high ZT value of 1.72 at 800 K. The low thermal conductivity for (Pb0.98K0.02Te)0.70(PbSe)0.25(PbS)0.05 compound is attributed from the lattice distortion and line dislocation in a phase of nano precipitation. By optimizing K-doping and PbS substitution, we achieved the enhancement of practical thermoelectric performance such as average ZTavg = 1.08, engineering (ZT)eng = 0.81, maximum efficiency ηmax = 11.63%, and output power density Pd = 6.3 W cm−2, with temperature difference ΔT = 500 K, which has practical applicability in waste heat power generation technologies.

High-Performance Thermoelectric Bulk Colusite by Process Controlled Structural Disordering

High-performance thermoelectric bulk sulfide with the colusite structure is achieved by controlling the densification process and forming short-to-medium range structural defects. A simple and powerful way to adjust carrier concentration combined with enhanced phonon scattering through point defects and disordered regions is described. By combining experiments with band structure and phonons calculations, we elucidate, for the first time, the underlying mechanism at the origin of intrinsically low thermal conductivity in colusite samples as well as the effect of S vacancies and antisite defects on the carrier concentration. Our approach provides a controlled and scalable method to engineer high power factors and remarkable figures of merit near the unity in complex bulk sulfide such as Cu26V2Sn6S32 colusites.

Improved electronic structure and magnetic exchange interactions in transition metal oxides

We discuss the application of the Agapito Curtarolo and Buongiorno Nardelli (ACBN0) pseudo-hybrid Hubbard density functional to several transition metal oxides. For simple binary metal oxides, ACBN0 is found to be a fast, reasonably accurate and parameter-free alternative to traditional DFT  +  U and hybrid exact exchange methods. In ACBN0, the Hubbard energy of DFT  +  U is calculated via the direct evaluation of the local Coulomb and exchange integrals in which the screening of the bare Coulomb potential is accounted for by a renormalization of the density matrix. We demonstrate the success of the ACBN0 approach for the electronic properties of a series technologically relevant mono-oxides (MnO, CoO, NiO, FeO, both at equilibrium and under pressure). We also present results on two mixed valence compounds, Co3O4 and Mn3O4. Our results for these binary oxides and all the materials we have investigated, obtained at the computational cost of a standard LDA/PBE calculation, are in excellent agreement with hybrid functionals, the GW approximation and experimental measurements.

Enhancement of the Thermoelectric Properties of FeGa3-type Structures with Group 6 Transition Metals: A Computational Exploration

The possible existence of group 6 TM3 compounds with T = Cr, Mo, W and M = Ga, In is investigated with the aid of density functional theory calculations. Their most probable crystal structure is expected to be of the FeGa3 type tetragonal space group P42/mnm. All compounds are computed to be semiconductors with a band gap ranging from 0.08 to 0.43 eV, at the modified Becke-Johnson level of theory. The thermoelectric properties are analyzed via calculations based on Boltzmann transport equation under a constant relaxation time approximation. Promising power factors are computed for both n- and p-type WGa3 because of a band degeneracy around the Fermi level similar to that of heavily doped PbTe and SnTe materials. If the optimal chemical potential can be reached, a thermoelectric figure of merit up to 0.6 at 800 K for both n- and p-type may be expected for WGa3.

Research data supporting "Lead-Free Polycrystalline Ferroelectric Nanowires with Enhanced Curie Temperature"

Figures.zip file contains original SEM images and graphical images included in the main text and the supporting information of the manuscript. The original SEM images contain original scales and beam conditions at which SEM images were taken. SEM images in the manuscript and supporting information may have been taken as a whole or a part of the original images wherever apply. Likewise the scale in the manuscript images have been re‐drawn in order to enhance the clarity of the images, but depict true scale as they were in original. Data Files.zip contains data files for the graphs discussed in the main text and supporting information of the manuscript. Theoretical data. zip contains data file for the XRD plots and DFT theory for figure 5c and figure S1 asap

Dataset on the electronic and thermal transport properties of quaternary compounds of (PbTe)0.95−x(PbSe)x(PbS)0.05

The data presented in this article are related to the research article entitled “High thermoelectric performance in pseudo quaternary compounds of (PbTe)0.95−x(PbSe)x(PbS)0.05 by simultaneous band convergence and nano precipitation” (Ginting et al., 2017) [1]. We measured electrical and thermal transport properties such as temperature-dependent Hall carrier density nH, Hall mobility μH, thermal diffusivity D, heat capacity Cp, and power factor S2σ in (PbTe)0.95−x(PbSe)x(PbS)0.05 (x=0.0, 0.05, 0.10, 0.15, 0.20, 0.35, and 0.95) compounds with other related compounds from references. From the theoretical fitting of thermal conductivity κ, we found that the temperature-dependent thermal conductivity follows nano-structure model as well as alloy scattering. Transmission electron microscopy images shows that there are numerous nano-scale precipitates in a matrix. Owing to the low thermal conductivity and high power factor, we report high thermoelectric performances such as the high ZT, engineering ZTeng, efficiency η.