Metastable piezoelectric group-IV monochalcogenide monolayers with a buckled honeycomb structure

Journal Article · Fri Jan 29 00:00:00 EST 2021 · Physical Review. B

DOI:https://doi.org/10.1103/physrevb.103.024107· OSTI ID:1763368

Poudel, Shiva P.  ^[1]; Barraza-Lopez, Salvador  ^[1]

---

1. Univ. of Arkansas, Fayetteville, AR (United States)

Multiple two-dimensional materials are being naïvely termed stable on the grounds of displaying phonon dispersions with no negative frequencies and of not collapsing on molecular dynamics calculations at fixed volume. But, if these phases do not possess the smallest possible structural energy, how does one understand and establish their actual meta stability? To answer this question, twelve two-dimensional group-IV monochalcogenide monolayers (SiS, SiSe, SiTe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, and PbTe) with a buckled honeycomb atomistic structure—belonging to symmetry group P3m1—displaying an out-of-plane intrinsic electric polarization are shown to be metastable by three independent methods. First, we uncover a coordination-preserving structural transformation from the low-buckled honeycomb structure onto the lower-energy Pnm2₁ (or Pmmn for PbS, PbSe, and PbTe) phase to estimate energy barriers E_B that must be overcome during such structural transformation. Using the curvature of the local minima and E_B as inputs to Kramers escape formula, large escape times are found, implying the structural metastability of the buckled honeycomb phase (with the exception of PbS and PbSe, these phases display escape times ranging from 700 years to multiple times the age of the universe and can be considered “stable” for practical purposes in that relative sense). The second demonstration is provided by phonon dispersion relations that include the effect of long-range Coulomb forces and display no negative vibrational modes. The third and final demonstration of structural metastability is furnished by room-temperature ab initio molecular dynamics for selected compounds. Here, the magnitude of the electronic band gap evolves with chemical composition. Different from other binary two-dimensional compounds such as transition metal dichalcogenide monolayers and hexagonal boron nitride monolayers which only develop an in-plane piezoelectric response, the twelve group-IV monochalcogenide monolayers with a buckled honeycomb structure also display out-of-plane piezoelectric properties.

• Research Organization: Univ. of Arkansas, Fayetteville, AR (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
• Grant/Contract Number: SC0016139; AC02-05CH11231
• OSTI ID: 1763368
• Journal Information: Physical Review. B, Vol. 103, Issue 2; Related Information: https://journals.aps.org/prb/supplemental/10.1103/PhysRevB.103.024107; ISSN 2469-9950
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
Ferroelasticity
Ferroelectricity
Mechanical & acoustical properties
Phase transitions
Phonons
Chalcogenides
Monolayer films
Piezoelectrics
Density functional calculations