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Thermoelectric properties of two stacking sequences of crystalline GST-225 W.Ibarra-Hern´ andez, Jean-Yves Raty March 11, 2014 abstract Figure 1: The two proposed stacking sequences for GST-225. The stacking proposed by Kooi and De Hosson is Te-Ge-Te-Sb-Te- Te-Sb-Te-Ge-[1] (left) and the one proposed by Petrov et al.[2] derives from the previous one by the exchange of Sb and Ge layers (right). Green, violet and light blue represent Te, Ge and Sb atoms respectively. Pseudobinary GeTe-Sb 2 Te 3 compounds are widely used as phase-change optical materials for DVD-RAM.[3] Ge 2 Sb 2 Te 5 (GST-225) is used for this propose but the stacking sequence of the stable crystal structure is motive of debate. Pseudobinary compounds there are claimed to be good thermoelectric materials due the large number of intrinsic structural vacancies.[4] Thermoelectric properties for two proposed stacking sequences of GST-225 are computed us- ing DFT[5, 6] and Boltzmann trans- port equation in the constant relax- ation time approximation. After phonon calculations, no dynamic instabilities were found in the Irreducible Brillouin Zone for either of the proposed stacking sequences. One of the stacking sequences shows semiconductor-like density of states (DOS) with a computed gap of 190 meV unlike the other stacking sequence which has a metallic-like DOS. Thermoelectric properties calculation reveals that semiconductor-like structure has the highest value of Seebeck co- eﬃcient (SC)(at 650K S xx ≈ 100 against 45μV/K of the metallic-like). Our theoretical results of SC are in good agreement with experimental data. References [1] Kooi, B. J. and De Hosson, J. T. M., Journal of Applied Physics 92 (2002) 3584. [2] Petrov I I, I. R. M. and G, P. Z., Soviet Physics - Crystallography 13 (1968) 339. [3] Kolobov, A. et al., Nature Materials 3 (2004) 703. [4] Konstantinov, P., Shelimova, L., Avilov, E., Kretova, M., and Zemskov, V., Inorganic Materials 37 (2001) 662. [5] Hohenberg, P. and Kohn, W., Phys. Rev. 136 (1964) B864. [6] Kohn, W. and Sham, L. J., Phys. Rev. 140 (1965) A1133. 1

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Thermoelectric properties of two stacking

sequences of crystalline GST-225

W.Ibarra-Hernandez, Jean-Yves Raty

March 11, 2014

abstract

Figure 1: The two proposed stacking se-quences for GST-225. The stacking proposedby Kooi and De Hosson is Te-Ge-Te-Sb-Te-Te-Sb-Te-Ge-[1] (left) and the one proposed byPetrov et al.[2] derives from the previous oneby the exchange of Sb and Ge layers (right).Green, violet and light blue represent Te, Geand Sb atoms respectively.

Pseudobinary GeTe-Sb2Te3 compoundsare widely used as phase-changeoptical materials for DVD-RAM.[3]Ge2Sb2Te5 (GST-225) is used forthis propose but the stacking se-quence of the stable crystal structureis motive of debate. Pseudobinarycompounds there are claimed to begood thermoelectric materials due thelarge number of intrinsic structuralvacancies.[4] Thermoelectric proper-ties for two proposed stacking se-quences of GST-225 are computed us-ing DFT[5, 6] and Boltzmann trans-port equation in the constant relax-ation time approximation. After phonon calculations, no dynamic instabilitieswere found in the Irreducible Brillouin Zone for either of the proposed stack-ing sequences. One of the stacking sequences shows semiconductor-like densityof states (DOS) with a computed gap of 190 meV unlike the other stackingsequence which has a metallic-like DOS. Thermoelectric properties calculationreveals that semiconductor-like structure has the highest value of Seebeck co-efficient (SC)(at 650K Sxx ≈ 100 against 45µV/K of the metallic-like). Ourtheoretical results of SC are in good agreement with experimental data.

References

[1] Kooi, B. J. and De Hosson, J. T. M., Journal of Applied Physics 92 (2002)3584.

[2] Petrov I I, I. R. M. and G, P. Z., Soviet Physics - Crystallography 13 (1968)339.

[3] Kolobov, A. et al., Nature Materials 3 (2004) 703.

[4] Konstantinov, P., Shelimova, L., Avilov, E., Kretova, M., and Zemskov, V.,Inorganic Materials 37 (2001) 662.

[5] Hohenberg, P. and Kohn, W., Phys. Rev. 136 (1964) B864.

[6] Kohn, W. and Sham, L. J., Phys. Rev. 140 (1965) A1133.

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