Electronic, optical and thermal properties of the hexagonal and rocksalt-like Ge2Sb2Te5 chalcogenide from first-principle calculations

Tsafack, Thierry; Jacoboni, Carlo; Lee, Bong-Sub; Pop, Eric; Rudan, Massimo

doi:10.1063/1.3639279

Cited by 57 publications

(36 citation statements)

References 43 publications

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“…Regardless, this demonstrates the relative accuracy of the harmonic force constants in our calculations. We also note that the calculated PHDOS here compares well with the previously reported PHDOS from a first-principles calculation23 with slightly different acoustic velocities. These small variations likely arise from different DFT approximations employed [LDA23 vs. GGA (this work)] as LDA (GGA) typically gives shorter (longer) bonds, thus higher (lower) sound velocities.…”

Section: Resultssupporting

confidence: 86%

Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

Mukhopadhyay

Lindsay

Singh

2016

Sci Rep

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The lattice thermal conductivity (κ) of hexagonal Ge2Sb2Te5 (h-GST) is studied via direct first-principles calculations. We find significant intrinsic anisotropy (κa/κc~2) of κ in bulk h-GST, with the dominant contribution to κ from optic phonons, ~75%. This is extremely unusual as the acoustic phonon modes are the majority heat carriers in typical semiconductors and insulators. The anisotropy derives from varying bonding along different crystal directions, specifically from weak interlayer bonding along the c-axis, which gives anisotropic phonon dispersions. The phonon spectrum of h-GST has very dispersive optic branches with higher group velocities along the a-axis as compared to flat optic bands along the c-axis. The large optic mode contributions to the thermal conductivity in low-κ h-GST is unusual, and development of fundamental physical understanding of these contributions may be critical to better understanding of thermal conduction in other complex layered materials.

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Section: Resultssupporting

confidence: 86%

Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

Mukhopadhyay

Lindsay

Singh

2016

Sci Rep

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“…Our results of the KH structure are similar to those reported in Ref. [50]. Phonon band structure has been reported for some of these structures in the works of Campi et al [31,51].…”

Section: (Gete) 2 (Sb 2 Te 3 ) (Gst225)supporting

confidence: 92%

Ab initio density functional theory study of the electronic, dynamic, and thermoelectric properties of the crystalline pseudobinary chalcogenide (GeTe)x/(Sb2Te3)
Ibarra-Hernández
¹
,
Raty
²

2018
Phys. Rev. B

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We use ab initio density functional theory calculations to understand the electronic, dynamical, and thermoelectric behavior of layered crystalline phase-change materials. We perform calculations on the pseudobinary compounds (GeTe) x /(Sb 2 Te 3 ) (GST) with x = 1, 2, and 3. Since the stable configuration of these compounds remains somehow unsettled, we study one stacking configuration for GST124 (x = 1), three for GST225 (x = 2), and two for GST326 (x = 3). A supercell approach is used to check the dynamical stability of the systems while thermoelectric properties are obtained by solving the Boltzmann transport equation. We report that the most accepted stacking configuration of GST124, GST225, and GST326 have metallic character and for the case of x = 2 and 3, those are the ones with the lowest energy. However, we find the metallic of GST326 configuration to be dynamically unstable. In general, our values of the Seebeck coefficient and thermal conductivity for compounds with x = 1 and 2 agree very well with the available experimental data. The small differences that we observe with respect to experimental data are attributed to the disorder that is present experimentally and that we have not taken into account. We do not find a Dirac cone in the electronic band structure of GST225, contrarily to previous reports. We attribute this due to the theoretical strain induced by the choice of the pseudopotential.

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“…We find a clear semiconducting behavior with a band gap of 0.17 eV. This is in good agreement with a previous theoretical investigation 36 where an indirect band gap of 0.1 eV was noted for c-GST although they used different exchangecorrelation potential (local density approximation without spin-orbit coupling) and different method (shifting of the hexagonal structure) to generate the cubic structure. Another previous study considered the cubic GST as a narrow-gap degenerate semiconductor, with E F reside inside the valence band or a defect band.…”

Section: A Electronic Structure and Optical Propertiessupporting

confidence: 91%

Transport properties of cubic crystalline Ge2Sb2Te5: A potential low-temperature thermoelectric material

Sun

Mukhopadhyay

Subedi

et al. 2015

Applied Physics Letters

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Ge2Sb2Te5 (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coefficients 200 -300 µV/K in its cubic crystalline phase (c-GST) at remarkably high p-type doping levels of ∼ 1×10 19 -6×10 19 cm −3 at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coefficient was found to exceed 200 µV/K for a doping range 1×10 19 -3.5×10 19 cm −3 . Given that the lattice thermal conductivity in this phase has already been measured to be extremely low (∼ 0.7 W/m-K at 300 K), 1 our results suggest the possibility of using c-GST as a low-temperature thermoelectric material.

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Electronic, optical and thermal properties of the hexagonal and rocksalt-like Ge2Sb2Te5 chalcogenide from first-principle calculations

Cited by 57 publications

References 43 publications

Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

Ab initio density functional theory study of the electronic, dynamic, and thermoelectric properties of the crystalline pseudobinary chalcogenide (GeTe)x/(Sb2Te3)
Ibarra-Hernández
¹
,
Raty
²

2018
Phys. Rev. B

Transport properties of cubic crystalline Ge2Sb2Te5: A potential low-temperature thermoelectric material

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Electronic, optical and thermal properties of the hexagonal and rocksalt-like Ge2Sb2Te5 chalcogenide from first-principle calculations

Cited by 57 publications

References 43 publications

Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

Ab initio density functional theory study of the electronic, dynamic, and thermoelectric properties of the crystalline pseudobinary chalcogenide (GeTe)x/(Sb2Te3)Ibarra-Hernández1, Raty2 2018Phys. Rev. B

Transport properties of cubic crystalline Ge2Sb2Te5: A potential low-temperature thermoelectric material

Contact Info

Product

Resources

About

Ab initio density functional theory study of the electronic, dynamic, and thermoelectric properties of the crystalline pseudobinary chalcogenide (GeTe)x/(Sb2Te3)
Ibarra-Hernández
¹
,
Raty
²

2018
Phys. Rev. B