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Two-dimensional (2D) materials within the hematene-type binary oxides and perovskites family have recently gathered huge research interest for nanoelectronic devices. However, the exploration of their fascinating topological properties remains limited. Herein, through first-principles calculations, we systematically examine the electronic, magnetic, and topological properties of substitutionally doped 2D ABO _3 (A = As, Sb, or Bi, and B = V, Nb, or Ta) perovskite structures at the B site of a B _2 O _3 system. Interestingly, the atomic substitution makes the 2D ABO _3 structures dynamically stable. Our detailed calculations show the ferromagnetic (FM) and antiferromagnetic phases of these materials. The calculated Chern number ( C ) for the FM 2D ABO _3 (A = As, Sb, or Bi, B = Nb or Ta) suggests their topologically non-trivial phases. Furthermore, the computed nontrivial Berry curvature highlights the topological properties in AsNbO _3 . These findings highlight opportunities in 2D-ABO _3 materials, for applications in spintronics.

We report a detailed first principles density functional calculations to understand the electronic structure and transport properties of Zn-based pnictides ZnXPn2 (X: Si, Ge, and Sn; Pn: P and As) and ZnSiSb2. The electronic properties calculated using Tran-Blaha modified Becke-Johnson functional reveals the semi-conducting nature, and the resulting band gaps are in good agreement with experimental and other theoretical reports. We find a mixture of heavy and light bands in the band structure which is an advantage for good thermoelectric (TE) properties. The calculated transport properties unveils the favour p-type conduction in ZnXP2 (X: Si, Ge, and Sn) and n-type conduction in ZnGeP2 and ZnSiAs2. Comparison of transport properties of Zn-based pnictides with the prototype chalcopyrite thermoelectric materials implies that the thermopower values of the investigated compounds to be higher when compared with the prototype chalcopyrite thermoelectric materials, together with the comparable values for electrical conductivity scaled by relaxation time. In addition to this, Zn-based pnictides are found to possess higher thermopower than well known traditional TE materials at room temperature and above which motivates further research in these compounds. [ABSTRACT FROM AUTHOR]

First principles calculations predict the promising thermoelectric material ZnGeSb2 with a huge power factor (S2σ/τ) on the order of 3 × 1017 W m−1 K−2 s−1, due to the ultra-high electrical conductivity scaled by a relaxation time of around 8.5 × 1025Ω−1 m−1 s−1, observed in its massive Dirac state. The observed electrical conductivity is higher than the well-established Dirac materials, and is almost carrier concentration independent with similar behaviour of both n and p type carriers, which may certainly attract device applications. The low range of thermal conductivity is also evident from the phonon dispersion. Our present study further reports the gradual phase change of ZnGeSb2 from a normal semiconducting state, through massive Dirac states, to a topological semi-metal. The maximum power factor is observed in the massive Dirac states compared to the other two states. [ABSTRACT FROM AUTHOR]

The present study unveils the topological insulating nature of Th-based oxy-chalcogenides and their transport properties which are less explored. A systematic analysis of electronic, topological, mechanical, dynamical and thermoelectric properties of ThOCh (Ch: S, Se and Te) in bulk and monolayer is presented. The effect of spin-orbit coupling is found to be appreciable in ThOTe compared to ThOS and ThOSe, causing a strong topological nature in bulk ThOTe. The detailed analysis of electronic structure, Z 2 topological invariant and conducting surface states support the strong topological nature in bulk ThOTe. From thermoelectric studies, ThOS and ThOSe are found to be good thermoelectric candidates with heavy carrier doping (around 10 20 cm -3 ). To explore further, we have applied hydrostatic strain on bulk ThOCh and found that all the compounds are dynamically stable and show topological metallic behavior. The appearance of highly linearized Dirac points in the same energy range at different high symmetry points in the BZ indicate the presence of nodal line in ThOS and ThOSe without spin-orbit coupling and with the inclusion of spin-orbit coupling, the nodal line is found to be disappear. This variation in bands with and without spin-orbit coupling might indicate the topological nature in monolayer ThOCh. The thermoelectric calculations for monolayer shows an enhancement in electrical conductivity scaled by relaxation time by an order of ten compared to bulk and the carrier independent thermoelectric properties in monolayer might fetch good thermoelectric device applications. Overall, the present study explores yet another series of potential candidates for topological and thermoelectric properties in both bulk and layer forms.

The present density functional calculations propose the compounds CaSrX (X: Si, Ge, Sn, Pb) as strong topological insulators, with appreciable thermoelectric properties. Emergence of Dirac semi-metallic states has been observed in CaSrX (X: Si, Ge, Sn, Pb), which is induced by uni-axial strain along 'b' axis. CaSrSi and CaSrGe evolved as normal semiconductors with uni-axial strain. The trivial and non-trivial topological phases are evaluated by band inversion and Z 2 topological invariants. A comprehensive analysis of thermopower, electrical conductivity scaled by relaxation time at these Dirac semi-metallic states exposes the highly oscillating behaviour, which gives insight to quantum oscillations driven by uni-axial strain. Further the thermoelectric properties at strong topological insulating states and normal insulating states have been summarized, which reveals the potential thermoelectric properties of these materials.

We report the electronic structure and thermoelectric (TE) properties of OsX 2 (X: S, Se, Te), and find a giant value of thermopower of magnitude 600 μV K -1 -800 μV K -1 for a wide temperature range of 100 K-500 K for hole doping (at 10 18 cm -3 ), which is higher than the value found for well established TE materials. The optimized structural parameters are in good agreement with available experimental reports. The mechanical stability of all the compounds are confirmed from the computed elastic constants. The band gap of the investigated compounds is examined by several exchange correlation functionals, and TB-mBJ with modified parameters is found to be the best. The heavy valence bands stimulate the thermopower value for hole doping and light conduction bands intensifies the electrical conductivity values for electron doping, enabling both 'n' and 'p' type doping favourable for TE applications at higher concentrations (10 20 cm -3 ), which brings out the device application. Our results unveil the possibility of TE applications for all the examined compounds for a wide temperature range (100 K-500 K), and OsS 2 specifically is quite alternative with the performing temperature ranging from 100 K-900 K.

First principles calculations predict the promising thermoelectric material ZnGeSb 2 with a huge power factor (S 2 σ/τ) on the order of 3 × 10 17 W m -1 K -2 s -1 , due to the ultra-high electrical conductivity scaled by a relaxation time of around 8.5 × 10 25 Ω -1 m -1 s -1 , observed in its massive Dirac state. The observed electrical conductivity is higher than the well-established Dirac materials, and is almost carrier concentration independent with similar behaviour of both n and p type carriers, which may certainly attract device applications. The low range of thermal conductivity is also evident from the phonon dispersion. Our present study further reports the gradual phase change of ZnGeSb 2 from a normal semiconducting state, through massive Dirac states, to a topological semi-metal. The maximum power factor is observed in the massive Dirac states compared to the other two states.