The quasiharmonic Debye approximation has been implemented within the aflow and Materials Project frameworks for high-throughput computational materials science (Automatic Gibbs Library, agl), in order to calculate thermal properties such as the Debye temperature and the thermal conductivity of materials. We demonstrate that the agl method, which is significantly cheaper computationally compared to the fully ab initio approach, can reliably predict the ordinal ranking of the thermal conductivity for several different classes of semiconductor materials. In particular, a high Pearson (i.e., linear) correlation is obtained between the experimental and agl computed values of the lattice thermal conductivity for a set of 75 compounds including materials with cubic, hexagonal, rhombohedral, and tetragonal symmetry.

High-throughput computational screening of thermal conductivity, Debye temperature, and Grüneisen parameter using a quasiharmonic Debye model

Thorough characterization of the thermo-mechanical properties of materials requires difficult and time-consuming experiments. This severely limits the availability of data and it is one of the main obstacles for the development of effective accelerated materials design strategies. The rapid screening of new potential systems requires highly integrated, sophisticated and robust computational approaches. We tackled the challenge by surveying more than 3,000 crystalline solids within the AFLOW framework with the newly developed "Automatic Elasticity Library" combined with the previously implemented GIBBS method. The first extracts the mechanical properties from automatic self-consistent stress-strain calculations, while the latter employs those mechanical properties to evaluate the thermodynamics within the Debye model. The new thermo-elastic library is benchmarked against a set of 74 experimentally characterized systems to pinpoint a robust computational methodology for the evaluation of bulk and shear moduli, Poisson ratios, Debye temperatures, Gruneisen parameters, and thermal conductivities of a wide variety of materials. The effect of different choices of equations of state is examined and the optimum combination of properties for the Leibfried-Schlomann prediction of thermal conductivity is identified, leading to improved agreement with experimental results than the GIBBS-only approach.

Combining the AFLOW GIBBS and Elastic Libraries for efficiently and robustly screening thermo-mechanical properties of solids

The electrical properties between 80 and 300 K and the optical absorption at room temperature of both n- and p-type CuInTe2 are studied. The n-type sample is obtained by annealing p-type CuInTe2 in the presence of indium for a prolonged period of time. The p-type samples are grown by programmed directional freezing technique with slight excess of indium in the stoichiometry. Two defect levels with ED = 58 meV and EA around 15 meV are identified from the analysis of the temperature dependence of the carrier concentration. The origin of these levels, consistent with the covalent bonding model, is attributed to InCu and VTe, respectively. From a theoretical fit to the experimental data, the density of states effective mass of the electrons is found to be m = 0.16me. The estimated values of the conduction and valence-band deformation potentials are in agreement with the general trend observed in other I–III–VI2 compounds. Using the model proposed for the band-gap shrinkage, the energy gap of n-type CuInTe2 in the dilute limit is calculated to be 1.026 eV.



On a etudie les proprietes electriques entre 80 et 300 K, et l'absorption optique a temperature ambiante de CuInTe2 type n et type p. L'echantillon type n a ete obtenu par recuit et celuit type p par mise en presence de l'Indium durant une periode de temps prolonge. On a fait croǐtre les echantillons type p par la technique de refroidissement directionnel programme avec un leger exces d'Indium dans la stoechiometrie. Par l'analyse de la dependance de la temperature de concentration des porteurs, on a identifie deux niveaux de defauts avec ED = 58 meV et EA environ 15 meV. L'origine de ces niveaux, compatible avec le modele de liaison covalente, est attribue it a InCu et a VTe, respectivement. Apres un ajustement theorique aux donnees experimentales, la densite des etats de la masse effective des electrons est de m★ = 0,16me. Les valeurs estimees des potentiels de deformation des bandes de conduction et de valence sont en accord avec la tendance generale observee dans les composes I–III–VI2. En utilisant le modele propose pour la contraction de la bande du gap, le resultat de gap d'energie de CuInTe2 type n dans la limite diluee est de 1,026 eV.

Electrical and optical properties of n- and p-type CuInTe2

A dynamic pulse-echo overlap method is used to measure the longitudinal and transverse sound velocities of polycrystalline samples of CuInTe2 and CuInSe2 between 4.2 and 300 K. From these measurements the temperature dependence of the elastic moduli is obtained. From the low temperature value of the average sound velocity, the Debye temperature is calculated to be 197.5 and 243.7 K for CuInTe2 and CuInSe2, respectively. Using the Szigeti relationships the ionicities are estimated to be 0.39 and 0.34 for CuInSe2 and CuInTe2, respectively.



Une methode dynamique de recouvrement de poulsation-echo a ete utilisee pour mesurer la vitesse du son longitudinale et transverse dans des echantillons polycristallins de CuInTe2 et CuInSe2 entre 4,2 et 300 K. Nous avons obtenu la dependence vis a vis de la temperature des modules elastiques. D'autre part a partir des valeurs moyennes de la vitesse du son a basses temperatures nous avons calcule la temperature de Debye et on a trouve 197,5 et 243,7 K pour le CuInTe2 et CuInSe2 respectivement. Au moyen des relations de Szigeti les ionicites ont ete estimees en 0,39 et 0,34 pour le CuInTe2 et CuInSe2, respectivement.

Sound Velocities and Elastic Moduli in CuInTe2 and CuInSe2

Rough sets applied to materials data

The specific heat Cv of the ternary semiconducting compounds CuGaSe2, CuGaTe2, and CuInTe2 is determined experimentally in a temperature region within 2 and 30 K. From the results the Debye temperatures and standard entropies are calculated. By dividing Cv into a Debye and two Einstein contributions the approximate shape of the low frequency phonon modes is estimated.



Die spezifische Warmekapazitat CV der ternaren halbleitenden Verbindungen CuGaSe2, CuGaTe2 und CuInTe2 wird experimentell in einem Temperaturbereich von 2 bis 30 K bestimmt. Aus den Mesergebnissen werden Debyetemperaturen und Standardentropien berechnet. Durch Aufteilen von Cv in einen Debyeteil und zwei Einsteinteile last sich der genaherte Verlauf der niedrigfrequenten Phononenmoden abschatzen.

G. Kühn

Papers

Specific heat, debye temperature, and belated properties of chalcopyrite semiconducting compounds CuGaSe2, CuGaTe2, and CuInTe2