Abnormal vibrational anisotropy and thermal properties of a two-dimensional GeAs semiconductor

Abstract

The anisotropy in the crystal structure plays a striking role in the optical, electrical and thermal properties of the condensed matter. Here, we investigate the in-plane vibrational anisotropy in two-dimensional...

Anisotropy and thermal properties in GeTe semiconductor by Raman analysis

“…Where C v , V̄ , and τ T are heat capacity under constant volume, averaged acoustic phonon velocity, and the thermal transport relaxation time, respectively. Under the assumed conditions, where C v is 2 k B and V̄ is 5 km s −1 , 4,59 the thermal transport relaxation time can be approximated as the quasi-particle lifetime of the Raman optical phonon τ , . By referring to the FWHM ( Γ ) value in the range of 8–16 cm −1 , τ ranges from 0.33–0.66 ps.…”

“…Low-symmetric two-dimensional (2D) layered materials present intriguing in-plane anisotropy. [1][2][3][4] For instance, GaTe, GeSe, GeAs, and black phosphorus have been reported to have significant directional dependence of their photoemission, thermoelectricity, and mobility properties, mainly due to the anisotropic light-matter interactions, such as the electronphoton and electron-phonon couplings. 1,2,[4][5][6][7][8] As a typical binary IV-VI chalcogenide with a rhombohedral (α-phase; or pseudo-cubic) crystal structure at room temperature that is formed by distortion at high-temperature of the cubic phase, 9,10 GeTe (R3m-C 3v space group) has advantages for application in thermal-/opto-electronic devices, e.g., with a maximum thermoelectric figure-of-merit (ZT ) value of ∼0.8 that can be improved up to the currently known 2.7 at 750 K (ref.…”

“…[1][2][3][4] For instance, GaTe, GeSe, GeAs, and black phosphorus have been reported to have significant directional dependence of their photoemission, thermoelectricity, and mobility properties, mainly due to the anisotropic light-matter interactions, such as the electronphoton and electron-phonon couplings. 1,2,[4][5][6][7][8] As a typical binary IV-VI chalcogenide with a rhombohedral (α-phase; or pseudo-cubic) crystal structure at room temperature that is formed by distortion at high-temperature of the cubic phase, 9,10 GeTe (R3m-C 3v space group) has advantages for application in thermal-/opto-electronic devices, e.g., with a maximum thermoelectric figure-of-merit (ZT ) value of ∼0.8 that can be improved up to the currently known 2.7 at 750 K (ref. 11) by elemental doping, as well as substitution or alloying with other compounds.…”

Optical properties of ferroic Fe2O(SeO3)2 and Fe2(SeO3)3·3H2O

“…When these elements containing lone electrons are mixed with transition metals, the lone electron is usually a “chemical scissor”, thereby generating a layered or low-dimensional compound, as reported by Takagi et al 12 In this case, they can present more diverse crystal structures and intriguing optical/electrical/magnetic properties than common two-dimensional materials including ferroic semiconductors. 13,14…”

“…When these elements containing lone electrons are mixed with transition metals, the lone electron is usually a ''chemical scissor'', thereby generating a layered or low-dimensional compound, as reported by Takagi et al 12 In this case, they can present more diverse crystal structures and intriguing optical/electrical/magnetic properties than common two-dimensional materials including ferroic semiconductors. 13,14 Recently, a Raman study on Fe 2 O(SeO 3 ) 2 (FSO), accompanied by magnetic susceptibility measurements, found that below T N B 105 K it exhibits an antiferromagnetic behavior. 15 However, unlike other saw-tooth chain compounds, this oxoselenite shows a low-dimensional behavior above T N , which cannot be described by the Curie-Weiss law but was interpreted as an indication of the proximity of FSO to a quantum critical point (QCP).…”