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Doping is one of the possible ways to significantly increase the thermoelectric properties of many different materials. It has been confirmed that by introducing bismuth atoms into Mg sites in the Mg2Si compound, it is possible to increase career concentration and intensify the effect of phonon scattering, which results in remarkable enhancement in the figure of merit (ZT) value. Magnesium silicide has gained scientists’ attention due to its nontoxicity, low density, and inexpensiveness. This paper reports on our latest attempt to employ ultrafast self-propagating high-temperature synthesis (SHS) followed by the spark plasma sintering (SPS) as a synthesis process of doped Mg2Si. Materials with varied bismuth doping were fabricated and then thoroughly analyzed with the laser flash method (LFA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with an integrated energy-dispersive spectrometer (EDS). For density measurement, the Archimedes method was used. The electrical conductivity was measured using a standard four-probe method. The See-beck coefficient was calculated from measured See-beck voltage in the sample subjected to a temperature gradient. The structural analyses showed the Mg2Si phase as dominant and Bi2Mg3 located at grain boundaries. Bismuth doping enhanced ZT for every dopant concentration. ZT = 0.44 and ZT=0.38 were obtained for 3wt% and 2wt% at 770 K, respectively [ABSTRACT FROM AUTHOR]

The device processing, dopant diffusion and activation of the intrinsic point defects in germanium are analyzed. The analysis of the formation and migration energies of the vacancy and self-interstitial in germanium shows that the lattice defect formation and activation is highly controlled by the intrinsic defects in the semiconductor.

The plasficity of hexagonal fitanium is reexamined based on the split slip modes phenomenon, revealing the existence of subslip modes in prismatic and pyramidal hep slip systems. The energetics of dislocation emission and motions were described using all-dimension relaxed atomic models of crystal slip, calculated with density functional theory. The proposed computafional methodology is based on the generalized stacking fault energy concept and respects all elastic effects arising within dislocation nucleation. As a result, improved accuracy has been obtained with regard to ductility prediction and a breach has been discovered in the fundamental Peierls-Nabarro rule. This approach is essential for the Rice and Peierls-Nabarro models and can be used as an effective tool for ducfility predictions when designing new hexagonal alloys. [ABSTRACT FROM AUTHOR]

Phonon and electronic transport of buckled structured SiGe monolayer and halogenated SiGe monolayers (X 2 -SiGe, X = F, Cl, and Br) are investigated for the first-time using ab initio density functional theory (DFT). The phonon calculations reveal complete dynamical stability of SiGe and fluorinated (F 2 -SiGe) monolayers in contrast to earlier reported works, where a small magnitude of imaginary frequency in SiGe monolayer near the zone centre of the Brillouin zone (BZ) is observed. The phonon calculations of chlorinated and brominated SiGe reveal no dynamical stability even with very high convergence parameters and better computational accuracy. The lower value of lattice thermal conductivity in the case of F 2 -SiGe is attributed to the strong phonon anharmonic scattering and larger contribution of the three phonon process to anharmonic scattering. The semimetallic nature of the SiGe monolayer turns to semiconducting after halogenation. We have also calculated the electron relaxation time to study their precise thermoelectric parameters. The enhancement of the Seebeck coefficient and reduction in lattice thermal conductivity in the SiGe monolayer is observed after halogenation which results in the improvement of the thermoelectric figure of merit (ZT). The room temperature figure of merit, ZT, which is 0.112 for the SiGe monolayer, enhances significantly to 0.737 after addition of fluorine atoms. Our study suggests that the halogenation of two-dimensional materials can improve their thermoelectric properties.

Intrinsically hydrophobic rare-earth oxides (REOs) have emerged as a robust class of ceramics for a variety of applications. Recently, the hydrophobicity of REOs has been observed experimentally and subsequently scrutinized using electronic structure density functional theory (DFT) calculations. In this work, we applied the DFT method to analyze the possibility of tuning the wettability of commonly used hydrophilic Al 2 O 3 and TiO 2 by surface doping with Ce. The calculations indicate that Ce can preferentially segregate to the surface of Al 2 O 3 and TiO 2 and form a Ce-rich oxide layer, which is stable under a wide range of oxygen chemical potentials. A remarkable increase in the water contact angle is predicted for Ce-doped Al 2 O 3 (0001), whereas the water contact angle calculated for Ce-doped TiO 2 (110) remains unchanged, regardless of the Ce concentration. The wetting properties of Ce-doped Al 2 O 3 are governed by two factors: (1) the unique electronic structure of the rare-earth metal promotes hydrogen bond formation between H 2 O and surface oxygen; (2) significant relaxation of the surface Ce and O atoms hampers direct interaction between H 2 O and Al cations, preventing dissociative water adsorption. These results provide a valuable opportunity for Al 2 O 3 surface modification, in terms of achieving hydrophobicity.