Comprehensive investigation of the extremely low lattice thermal conductivity and thermoelectric properties of BaIn2Te4

Recently, an extremely low lattice thermal conductivity value has been reported for the alkali-based telluride material BaIn2Te4. The value is comparable with low-thermal conductivity metal chalcogenides, and the glass limit is highly intriguing. Therefore, to shed light on this issue, we performed first-principles phonon thermal transport calculations. We predicted highly anisotropic lattice thermal conductivity along different directions via the solution of the linearized phonon Boltzmann transport equation. More importantly, we determined several different factors as the main sources of the predicted ultralow lattice thermal conductivity of this crystal, such as the strong interactions between low-frequency optical phonons and acoustic phonons, small phonon group velocities, and lattice anharmonicity indicated by large negative mode Gruneisen parameters. Along with thermal transport calculations, we also investigated the electronic transport properties by accurately calculating the scattering mechanisms, namely the acoustic deformation potential, ionized impurity, and polar optical scatterings. The inclusion of spin-orbit coupling (SOC) for electronic structure is found to strongly affect the p-type Seebeck coefficients. Finally, we calculated the thermoelectric properties accurately, and the optimal ZT value of p-type doping, which originated from high Seebeck coefficients, was predicted to exceed unity after 700 K and have a direction averaged value of 1.63 (1.76 in the y-direction) at 1000 K around 2 x 1020 cm-3 hole concentration. For n-type doping, a ZT around 3.2 x 1019 cm-3 concentration was predicted to be a direction-averaged value of 1.40 (1.76 in the z-direction) at 1000 K, mostly originating from its high electron mobility. With the experimental evidence of high thermal stability, we showed that the BaIn2Te4 compound has the potential to be a promising mid- to high-temperature thermoelectric material for both p-type and n-type systems with appropriate doping.Eskisehir Technical University [ESTU-BAP 22ADP150]C.S. acknowledges the support from the Eskisehir Technical University (ESTU-BAP 22ADP150). The numerical calculations reported in this paper were partially performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA resources)

Investigation of the structural, electronic, thermoelectric, and thermal transport properties of zıntl BaIn2Te4 material from first principles

Bu çalışmada tellür tabanlı BaIn2Te4 malzemesinin yapısal, elektronik, örgü dinamiksel, termoelektrik ve termal taşınım özellikleri kuramsal olarak incelenmiştir. Toplam enerji ve örgü dinamiksel hesaplamalar yoğunluk fonksiyonel kuramı (YFK) temelinde ve genelleştirilmiş gradyan yaklaşımı (GGY) kullanılarak gerçekleştirilmiştir. Termolektrik katsayıların hesabı gevşeme zamanı yaklaşımı altında elektronik Boltzmann taşınım denklemi çözülerek elde edilmiştir. Fonon taşınım özellikleri ise doğrusallaştırılmış fonon Boltzmann taşınım denkleminden elde edilmiştir. Deneysel parametre kullanmadan elde edilen denge örgü parametreleri ve iç parametreler deneysel ölçümlerle uyumludur. Elektronik bant yapısı hesaplamalarında doğrusal-olmayan bant aralığı bulunmuş olup aralık değeri GGY limitlerinde 0,963 eV olarak elde edilmiştir. Fonon dağılım eğrileri pozitif çıkmış olup yapının dinamik olarak stabil olduğunu göstermektedir. Hesaplamış olduğumuz termoelektrik katsayılardan Seebeck katsayısının benzer taşıyıcı konsantrasyonlarda p-tipi katkılamanın, n-tipi katkılamaya göre daha yüksek değerler aldığı görülmüştür. BaIn2Te4 malzemesinin örgü termal iletkenliğinin anizotropik davranış sergilediği, ortalamasının ise deneyle mükemmel biçimde uyumlu olduğu bulunmuştur. Tamamı kuramsal olarak elde edilen niceliklerle hesaplanmış ZT değerinin oda sıcaklığında 0.25 ve altında olduğu görülmüş, orta ve yüksek sıcaklıklarda ise yüksek değerlere ulaştığı gözlenmiştir. Özellikle p-tipi katkılamada 500K'den itibaren ZT>1 değerinden daha yüksek değerlere ulaşılmıştır. n-tipi katkılamada ise ZT>1 değerine yaklaşık 700K sıcaklıktan itibaren ulaşılmıştır.In this study, the structural, electronic, lattice dynamical, thermoelectric and thermal transport properties of the tellurium-based BaIn2Te4 material were investigated theoretically. Total energy and lattice dynamical calculations have been performed on the basis of density functional theory (DFT) and using the generalized gradient approach (GGA). The calculation of the thermoelectric coefficients was obtained by solving the electronic Boltzmann transport equation under the relaxation time approximation. Phonon transport properties are also obtained from the linearized phonon Boltzmann transport equation. Equilibrium lattice parameters obtained without using experimental parameters are in good agreement with the experiment together with internal parameters. The indirect band-gap was found in the electronic band structure calculations and the gap value was obtained as 0.963 eV at the GGA limits. Phonon distribution curves are positive, showing that the structure is dynamically stable. Among the thermoelectric coefficients we have calculated, the Seebeck coefficient has been found to have higher values for p-type doping compared to n-type at similar carrier concentrations. The lattice thermal conductivity of BaIn2Te4 was found to be anisotropic, and its average was found to be in perfect agreement with the experiment. It was observed that the ZT value, all calculated with the theoretically obtained quantities, was 0.25 and below at room temperature, and it reached high values at medium and high temperatures. Especially in p-type doping, values higher than ZT>1 have been reached starting from 500K. In n-type doping, on the other hand, ZT>1 value is reached starting from about 700K temperature