Phonons of Phase‐Change Materials

Gaspard, Jean-Pierre

doi:10.1002/pssr.202200111

Cited by 4 publications

(24 citation statements)

References 31 publications

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“…when MMBs are formed, a hardening of the low-energy acoustic phonons is experimentally observed [106]. The soft (hard) behavior of optical (acoustic) phonons has been also encountered in pnictogens at HP [108,109] and it has been recently understood in the light of a simple model of three-center "covalentlike" interactions, which supports the multicenter character of bonds in PCMs, as already pointed out [52]. As regards the Ah phase of As above 25 GPa (As-II), it exhibits only acoustic phonon modes (see blue line in Fig.…”

Section: Unconventional Bonding In Group-15 and -16 Elements At High ...mentioning

confidence: 65%

“…The disagreement could likely be caused by anharmonic effects that are not included in our simulations. In this context, it is well known that anharmonic effects are notable in PCMs and important for the description of the vibrational properties as the MMB formation is approached [13,52,85,86,106,107]. The presence of strong anharmonic interactions in As-I close to Pt is also evidenced by the large values of the absolute phonon Grüneisen parameter, |γi|, of the A1g mode (inset of Fig.…”

Section: Unconventional Bonding In Group-15 and -16 Elements At High ...mentioning

confidence: 82%

“…In particular, Dronkowski and coworkers demonstrated the electron delocalization and multicenter character of bonding in PCMs by calculations of the projected force constants along several atoms and of the crystal-orbital bond index (COBI), together with its integrated values for two-center and three-center bonds, ICOBI(2c) and ICOBI(3c), respectively [39][40][41]. The multicenter character of bonding in PCMs has also been recently justified on the basis of a three-center "covalent-like" interaction [52].…”

Section: Introductionmentioning

confidence: 99%

“…Pressure is the perfect tool to distinguish between the pre-MMB and MMB scenarios. The importance of applying high pressure (HP) to understand the unconventional bond present in PCMs has been highlighted in several works [13,31,34,52]. Unfortunately, the importance of pressure has not been fully exploited despite examples of the pressure-induced MMB formation in IV-VI and V2-VI3 chalcogenides, such as GeSe, SnSe, GeTe, and As2S3 [84][85][86][87], have been published.…”

Section: Introductionmentioning

confidence: 99%

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Metavalent multicenter bonding in pnictogens and chalcogens: nature and mechanism of formation

Osman,

Otero-de-la-Roza,

Rodríguez-Hernández

et al. 2023

Preprint

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Due to the exceptional property portfolio and technological applications of phase change materials, mostly chalcogens related to IV-VI and V2-VI3 families, which are in turn related to pnictogens (group V or 15) and chalcogens (group VI or 16), the nature of the unconventional chemical bonding in these materials has been debated for almost 70 years. This unconventional bond, which has been quoted in the literature as resonant, hypervalent, electron-rich multicenter, three-center-four-electron (3c-4e), and metavalent, is believed to be responsible for the exceptional properties of phase change materials. In the last decade, two bonding models, the metavalent and the electron-rich multicenter models, have competed to explain the nature of this unconventional bond, which we have here renamed as metavalent multicenter bond (MMB) for the sake of clarity. In this comprehensive work, we address the nature of MMB and propose that MMB is an electron-deficient multicenter bond (EDMB), related to the threecenter-two-electron (3c-2e) bond. For that purpose, we explore the pressure-induced mechanism of MMB formation in the some of the simplest possible systems, pnictogens (As, Sb, Bi) and chalcogens (Se, Te, Po), with density-functional theory calculations. In the way, we find that polonium is the only element among chalcogens and pnictogens with crystalline α and β structures already exhibiting MMBs at RP. We find that the mechanism of MMB formation in pnictogens (chalcogens) is comprised of three (two) stages, is similar to that of the EDMB formation in B2H6, in some Zintl phases, intermetallics, and cluster compounds, and in atomic/polymeric nitrogen and hydrogen at high pressures. On the other hand, the mechanism of EDMB formation is completely different from that of the 3c-4e bond formation in molecules. Finally, we propose the simplest geometries of EDMBs that can be found in solids along one, two, and three dimensions and comment on the validity of the doublet/octet rules in the hypercoordinated multicenter units with EDMBs.

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Section: Unconventional Bonding In Group-15 and -16 Elements At High ...mentioning

confidence: 65%

Section: Unconventional Bonding In Group-15 and -16 Elements At High ...mentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Metavalent multicenter bonding in pnictogens and chalcogens: nature and mechanism of formation

Osman,

Otero-de-la-Roza,

Rodríguez-Hernández

et al. 2023

Preprint

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show abstract

“…The optical difference between rhombohedral and monoclinic As 2 Te 3 would be explained here by the reduction in coordination number and the reinforced Peierls distortion, which weakens the MVB in the monoclinic phase. Peierls distortion drive the metal‐semiconductor transition in PCM as described by Jean‐Pierre Gaspard in his paper [ 7 ] in which a minimal model of covalent bonding is involved to explain the remarkable properties of PCMs with a particular emphasis on the vibrational properties.…”

mentioning

confidence: 99%