ab initio Energetics and Thermoelectric Profiles of Gallium Pnictide Polytypes

First-Principles Investigations of Thermoelectric Behavior of RuCrX (X = Si, Ge, Sn)

The half-Heusler alloys have not only been recognized for spintronic and memory devices but also for thermoelectric applications. In this research work, the detailed study for thermoelectric parameters of RuCrX (X = Si, Ge, Sn) half-Heusler alloys has been carried out by using the pseudopotential approach alongside the Boltzmann transport theory. The RuCrX (X= Si, Ge, Sn) was reported stable in C1 _b -type structure by means of energy-volume optimization, elastic stability criteria, positive phonon frequencies in phonon dispersion curves, and formation energies. The all important thermoelectric properties of these alloys have not yet been explored. The thermoelectric properties such as Seebeck coefficient, electronic part of thermal conductivity, electrical conductivity, and power factor have been discussed within a specific temperature range (300-1200 K). The calculated value of the power factor was found to be 5.11 × 10¹¹ W/(m K² s) for RuCrSi, 3.42 × 10¹¹ W/(m K² s) for RuCrGe, and 1.85 × 10¹¹ W/(m K² s) for RuCrSn at 1200 K.

Emergence of -s, -p-dband inversion in zincblende gold iodide topological insulator and its thermoelectric properties

We employfirst-principlescalculations to investigate the topological states (TS) and thermoelectric (TE) transport properties of three dimensional (3D) gold iodide (AuI) which belongs to the zincblende family. We explore, semi-metal (SM) to topological conductor (TC) and topological insulator (TI) phase transitions. Under pristine conditions, AuI exhibits Dirac SM nature but, under the influence of mild isotropic compressive pressure the system undergoes electronic quantum phase transition driving it into non-trivial topological state. This state exhibits Dresselhaus like band spin splitting leading to a TC state. In order to realize TI state from the SM state, we break the cubic symmetry of the system by introducing a compressive pressure along (001) crystal direction. The non-trivial TI nature of the system is characterized by the emergence of robust surface states and theZ2invariantν0= 1 which indicates a strong TI nature. A novel facet of the phase transition discussed here is, the -sand -p, -dorbital band inversion mechanism which is unconventional as compared to previously explored TI families. This mechanism unravels new path by which TI materials can be predicted. Also, we investigated the lattice and electronic contributions to the TE transport properties. We characterize the TE performance by calculating the figure of merit (zT) and find that, at room temperature (300 K) and for a fixed doping concentration (i.e.,n= 1 × 1019 cm-3) the zT is 0.55 and 0.53 for electrons and holes respectively. This is quite remarkable since, higher values of zT are generally predicted at higher temperature scales whereas, zT values as in the present case are desired at room temperatures for various energy applications. The manifestation of non-trivial TS governed by the unconventional band inversion mechanism and the TE properties of AuI make it a unique multi-functional candidate with probable thermoelectric and spintronic applications.

Thermal transport properties of novel two-dimensional CSe

Recently, as a novel member of the IV-VI group compounds, two-dimensional (2D) buckled monolayer CSe has been discovered for use in high-performance light-emitting devices (Q. Zhang, Y. Feng, X. Chen, W. Zhang, L. Wu and Y. Wang, Nanomaterials, 2019, 9, 598). However, to date, the heat transport properties of this novel CSe is still lacking, which would hinder its potential application in electronic devices and thermoelectric materials that can generate electricity from waste heat. Here we systematically study the heat transport properties of monolayer CSe based on ab initio calculations and phonon Boltzmann transport theory. We find that the lattice thermal conductivity κlat of monolayer CSe is around 42 W m-1 K-1 at room temperature, which is much lower than those of black phosphorene, buckled phosphorene, MoS2, and buckled arsenene. Moreover, the longitudinal acoustic phonon mode contributes the most to the κlat, which is much larger than those of the out-of-plane phonon mode and transverse acoustic branches. The calculated size-dependent κlat shows that the sample size can significantly reduce the κlat of monolayer CSe and can persist up to 10 μm. These discoveries provide new insight into the size-dependent thermal transport in nanomaterials and guide the design of CSe-based low-dimensional quantum devices, such as thermoelectric devices.