Structural, elastic, electronic, andoptical properties of layered TiNX (X = F, Cl, Br, I) compounds: a density functional theory study

Abstract

Titanium nitride halides, TiNX (X = F, Cl, Br, I) in the α-phase (orthorhombic) are exciting quasi two-dimensional (2D) electronic systems exhibiting a fascinating series of electronic ground states under different conditions. Pristine TiNX are semiconductors with varying energy gaps and possess attractive properties for potential applications in the fields of optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated TiNCl becomes superconducting at reasonably high temperature in the α-phase. We have revisited the electronic band structure of these compounds using density functional theory (DFT) based first-principles calculations. The atomic species and orbital resolved partial electronic energy density of states are calculated together with the total density of states (TDOS). The structural and elastic properties have been investigated in details for these layered compounds for the first time. The elastic anisotropy has been explored. The optical properties, including energy dependent real and imaginary parts of the dielectric constant, optical conductivity, reflectivity, and loss function of TiNX are studied for the first time. The Debye temperatures of these compounds have been calculated and the related thermal and phonon parameters are discussed. The calculated physical parameters are compared with existing theoretical and experimental results and show fair agreement, where available. All these compounds are found to reflect electromagnetic radiation strongly in the mid ultraviolet region. The elastic properties show high degree of anisotropy. The lattice is highly compressible along the crystallographic c-direction. The effect of halogen atoms on various structural, elastic, electronic, and thermal properties in TiNX are also discussed in detail.

An ab-initio study on structural, elastic, electronic, bonding, thermal, and optical properties of topological Weyl semimetal TaX (X = P, As)

“…It is instructive to note that the machinability indices of Ta X ( X = P, As) are comparable to widely mentioned MAX phase nanolaminates and other layered ternary and binary compounds including topological systems 5 – 7 , 125 – 130 . The high hardness of TaP is quite remarkable and exceeds that for many MAX phase compounds and related systems 120 , 125 – 134 . The high bond hardness of TaP found from bond hardness calculations supports the findings from the analysis of elastic constants and moduli of this WSM.…”

“…TaP is significantly harder than TaAs but TaAs shows better machinability compared to TaP. It is instructive to note that the machinability indices of TaX (X = P, As) are comparable to widely mentioned MAX phase nanolaminates and other layered ternary and binary compounds including topological systems [5][6][7][125][126][127][128][129][130] . The high hardness of TaP is quite remarkable and exceeds that for many MAX phase compounds and related systems 120,[125][126][127][128][129][130][131][132][133][134] .…”

An Ab Initio Approach to Understand the Structural, Thermophysical, Electronic, and Optical Properties of Binary Silicide Srsi2: A Double Weyl Semimetal

“…We have further calculated the Cauchy pressure, 𝐶 (= 𝐶 − 𝐶 ) that reflects the nature of bonding in a compound at the atomic level [51,52]. A material with positive Cauchy pressure is typically characterized to be a ductile material while the material's brittleness is represented by a negative value [53].…”

The TiNI monolayer: a two-dimensional system with promising ferroelastic, topological, and thermoelectric properties

“…[16][17][18][19][20][21][22][23] Among many possible 2D materials, a new kind of system with a rectangular structure has been widely investigated due to its favorable physical properties including high carrier mobility, sensitive mechanical response, large optical absorption coefficient, and good catalytic and thermoelectric performance. [24][25][26][27][28][29][30][31][32][33][34][35][36] For example, Zhang et al predicted that the TiC monolayer has an indirect band gap of B0.2 eV and exhibits anisotropic electronic transport. 24 Zhou et al found that the band inversion in the ZrC monolayer can lead to the quantum spin Hall effect.…”