Soft-phonon mediated structural phase transition in GeTe

Wdowik, U. D.; Parliński, K.; Rols, S.; Chatterji, Tapan

doi:10.1103/physrevb.89.224306

Cited by 73 publications

(74 citation statements)

References 60 publications

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“…However, the recent experimental study on bulk polycrystalline α-GeTe specimen reveals that the Raman modes of E and A 1 occur at 95 and 125 cm −1 along with additional bands with lesser intensity at high frequencies. 22 On the basis of ab initio results [17][18][19][20] and earlier Raman spectroscopy observations, 21,22 we confirm that the observed vibrational modes in 10µm crystal size are intrinsic part of bulk α-GeTe structure. Furthermore, the decrease in crystal size leads to downshift of phonon modes in addition to the peak broadening of the Raman spectra as shown in inset of Figure 3.…”

Section: Resultssupporting

confidence: 62%

“…It is interesting to note that there is large disparity in calculated phonon frequencies by different theoretical methods because different approaches have been followed for introducing the screening effects on long range dipole-dipole interactions by the free charge carriers in these calculations. However, all these theoretical calculations carried by ab initio methods [17][18][19][20] lead to phonon modes corresponding to E T O and A LO 1 at 73 -88 cm −1 and 121 -143 cm −1 . In Figure 3, we show the Raman spectra of α-GeTe single crystals with various sizes and clearly demonstrate effect of crystal size on the intrinsic vibrational modes, i.e.…”

Section: Resultsmentioning

confidence: 99%

“…The lattice dynamical calculation on α-GeTe structure reveals the Raman active vibrational symmetries and tensor components consists of three optical phonon modes, i.e., A1(Z), E(Y), and E(-X), where X, Y, Z denote the phonon polarization directions in the C 3v coordinate system and Z is the trigonal axis. 17,18 It is worthwhile to mention that α-GeTe is a nonstoichiometric compound due to the presence of significant amount of Ge vacancies at its sub-lattice and it leads to the very high concentration of free charge carriers, i.e. holes (10 20 -10 22 cm −3 ).…”

Section: Resultsmentioning

confidence: 99%

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The role of atomic vacancies on phonon confinement in α-GeTe

Kalra

Murugavel

2015

AIP Advances

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Atomic defects and their dynamics play a vital role in controlling the behavior of non-volatile phase change memory materials used in advanced optical storage devices. Synthesis and structural analysis by XRD and Raman spectroscopy on α-GeTe single crystal with different sizes are reported. The spectroscopic measurements on micron and nano sized α-GeTe single crystal reveal the evolution of phonon confinement with crystal sizes of few hundred nanometers. The characteristic vibrational modes of bulk α-GeTe structure are found to downshift and asymmetrically broaden to lower frequency with decreasing the single crystal size. We attribute the observed downshift of Raman lines in α-GeTe is largely due to the presence of high concentration of atomic vacancies. The crystal size and temperature dependent Raman spectra provide explicitly the dynamics of vacancies on optical phonon confinement in α-GeTe structure. Thus, the observed large concentration of vacancies and their size dependency might influence the phase change phenomenon in GeTe based alloys.

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Section: Resultssupporting

confidence: 62%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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The role of atomic vacancies on phonon confinement in α-GeTe

Kalra

Murugavel

2015

AIP Advances

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“…Another controversial issue is whether Pb 1−x Ge x Te alloys undergo a displacive second-order [36,37] or an orderdisorder [50,59,82,83] phase transition with composition and temperature. Resolving these questions is beyond the scope of this work.…”

Section: Discussionmentioning

confidence: 99%

“…Anharmonic phonon lifetimes are calculated taking into account the contribution of three-phonon scattering processes [29,34,35]. Pb 1−x Ge x Te alloys are treated using the virtual crystal approximation, thus assuming a displacive second-order phase transition [36,37]. Mass disorder is modeled via an effective phonon lifetime given as [38,39] …”

Section: Methodsmentioning

confidence: 99%

Ferroelectric phase transition and the lattice thermal conductivity of Pb1−xGexTe alloys

et al. 2017

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Type of publicationArticle (peer-reviewed) We show how tuning the proximity to the soft optical mode phase transition via chemical composition affects the lattice thermal conductivity κ of Pb 1−x Ge x Te alloys. Using first-principles virtual-crystal simulations, we find that the anharmonic contribution to κ is minimized at the phase transition due to the maximized acoustic-optical anharmonic interaction. Mass disorder significantly lowers and flattens the dip in the anharmonic κ over a wide composition range, thus shifting the κ minimum away from the phase transition. The total κ and its anharmonic contribution vary continuously between the rocksalt and rhombohedral phases as expected for the second-order phase transition. The actual phase and its strength of resonant bonding play a less prominent role in reducing the κ of Pb 1−x Ge x Te alloys than the proximity to the phase transition and the atomic mass. Our results show that alloys with soft optical mode transitions are promising materials for achieving low thermal conductivity and possibly high thermoelectric efficiency.

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Microscopic Complexity in Phase‐Change Materials and its Role for Applications

Deringer

Dronskowski

Wuttig

2015

Adv Funct Materials

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Phase‐change materials (PCMs) are widely used for data storage and in other functional devices. Despite their seemingly simple compositions, these materials exhibit intriguing microscopic complexity and a portfolio of interesting properties. In this Feature Article, it is shown that structural and electronic peculiarities on the atomic scale are key determinants for the technological success of PCMs. Particular emphasis is put on the interplay of different experimental and theoretical methods, on the bonding nature of crystalline and amorphous PCMs, and on the role of surfaces and nanostructures. Then, unconventional transport properties of the crystalline phases are highlighted, both with regard to electrical and heat conduction. Finally, perspectives and future directions are drawn: for finding new PCMs based on microscopic understanding, and also for new applications of these materials in emerging fields.

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Soft-phonon mediated structural phase transition in GeTe

Cited by 73 publications

References 60 publications

The role of atomic vacancies on phonon confinement in α-GeTe

The role of atomic vacancies on phonon confinement in α-GeTe

Ferroelectric phase transition and the lattice thermal conductivity of Pb1−xGexTe alloys

Microscopic Complexity in Phase‐Change Materials and its Role for Applications

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