Recent experimental and theoretical progress on semiconducting CaAgP prompted us to investigate in detail the electrical and thermal transport properties of this hexagonal pnictide, using first-principles calculations based on the density functional theory. In contrast to using a standard generalized gradient approximation, employing a hybrid Heyd−Scuseria− Ernzerhof functional yields its semiconducting nature, in agreement with the experimental observation with a bandgap of ∼0.15 eV. The narrow band gap semiconductor CaAgP, which under negative (chemical) pressure has been shown to turn into a nodalline semimetal, is found to be dynamically stable, with a gapped electronic band structure when a hybrid functional is used. This is in an attractive range for applications in thermoelectric devices, and we have determined the lattice and electronic conductivity as a function of doping, which indeed predicts a promising thermoelectric performance, particularly for p-doped CaAgP.
A detailed investigation of the structure, electronic, spectroscopic, and optical properties of a series of transition metal-doped tetraphenylporphyrins (TM-TPP; TM = Fe, Co, Ni, Cu and Zn) is performed under density functional framework. The structure and stability of tetraphenylporphyrin (TPP) and TM-TPPs are understood with HOMO-LUMO gap, chemical hardness, and binding energies of the transition metals to the compound. Optical properties of TPP and TM-TPP series are assessed with relevant optical absorption spectra. A couple of visible active compounds, viz. Co-TPP and Ni-TPP, are reported for the first time for future opto-electronic applications. To gain insight on the possible synthesis of these compounds, we have analyzed frontier molecular orbitals (FMOs) as well as infra-red spectra. Graphical abstract Optical absorption spectra of TPP and TM-TPPs, and infrared spectra of TPP merged with Co-TPP.
We systematically consider the KMgX family (X = P, As, and Sb) of materials and investigate the effects of spin-orbit coupling (SOC) on thermal and electrical transport properties using a combined first-principles and Boltzmann transport equation approach. It is found that so far unexplored ternary quasi-two-dimensional KMgSb is particularly promising with SOC having a strong effect, shifting its behaviour from a p-type to n-type thermoelectric material. The transport properties of KMgSb were studied under the application of hydrostatic pressure. Our calculations show that Bi doping in KMgSb may prove to be a game changer as the lattice thermal conductivity (κL) becomes ultra-low, thereby increasing the thermoelectric figure of merit (zT) by > 280 % with SOC and by > 345 % without SOC. Through our computational investigation, we explain that the SOC plays a critical role and establish that alloy engineering may improve thermoelectric performance dramatically. * Corresponding author: hem.kandpal[at]cy.iitr.ac.in ing [24]. In the process of alloy engineering, one can fortify the strength of SOC if heavier atoms replace the lighter atoms. In such a case the inclusion of SOC becomes inescapable. In the current work, we are dealing with Sb and Bi atoms and hence SOC has been given due importance.
Spintronics is an emerging form of electronics based on the electrons' spin degree of freedom for which materials with robust half-metallic ferromagnet (HMF) character are very attractive. Here we determine the structural stability, electronic, magnetic, and mechanical properties of the half-Heusler (hH) compound CoFeGe, in particular also in its cubic form. The first-principles calculations suggest that the electronic structure is robust with 100 \% spin polarization at the Fermi level under hydrostatic pressure and uni-axial strain. Both the longitudinal and Hall current polarization are calculated and the longitudinal current polarization ($P_{L}$) is found to be $>99\%$ and extremely robust under uniform pressure and uni-axial strain. The anomalous Hall conductivity (AHC) and Spin Hall conductivity (SHC) of hH cubic CoFeGe (\textit{c}-CoFeGe) are found to be $\sim -100$ S/cm and $\sim 39~\hbar/e$ S/cm, respectively. Moreover, the Curie temperature of the alloy is calculated to be $\sim$524 K with a 3 $\mu_{B}$ magnetic moment. Lastly, the calculated mechanical properties indicate that \textit{c}-CoFeGe is ductile and mechanically stable with a bulk modulus of $\approx$ 154 GPa. Overall, this analysis reveals that cubic CoFeGe is a robust half-metallic ferromagnet and an interesting material for spintronic applications.
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