Electronic topological transitions and mechanical properties of hafnium dioxide allotrope at high pressure: Evolutionary first-principles techniques

Allotrope of HfO2 is explored by using first-principles evolutionary algorithm technique, based on density functional theory. The tetragonal structure with a space group of P4/nmm is found to be thermodynamically stable within the harmonic level. Arising particularly from the relative enthalpy, hafnium dioxide allotrope is taken into account in appraising the dynamic stability. Following this, the phonon calculations display that hafnium dioxide allotrope is dynamically stable under compressed conditions. Along with, the density of states suggests that hafnium dioxide allotrope is demonstrated that it is a semiconductor. Besides, the more significant change in the shape of density of states is observed when the pressure increased, by adopting an effect of this electronic topological transition, resulting in the energy gap is falling down monotonically. By inspecting their elastic constants and Vicker's hardness, the P4/nmm structure displayed the Vicker's hardness of 26.1GPa at a pressure of 200GPa. These findings suggest HfO2 is more likely to be attained experimentally and theoretically in the metal oxides family.

Enthalpic analysis of the CaTiSiO5 system

The relative enthalpy of titanite and enthalpy of CaTiSiO5 melt have been measured using drop calorimetry between 823 K and 1843 K. Enthalpies of solution of titanite and CaTiSiO5 glass have been measured by the use of hydrofluoric acid solution calorimetry at 298 K. Enthalpy of vitrification at 298 K, δvitr H(298 K) = (80.7 ± 3.4) kJ mol−1, and enthalpy of fusion at the temperature of fusion 1656 K, δfus H(1656 K) = (139 ± 3) kJ mol−1, of titanite have been determined from experimental data. The obtained enthalpy of fusion is considerably higher than up to the present published values of this quantity.

Theory of Schottky-Contact Formation on GaAs (110)

ABSTRACTA phenomenological theory of Schottky contact formation to GaAs (110) surfaces at room temperature is discussed. The theory splits into two regimes, low- and high-metal coverages. In the low-coverage regime the movement of the Fermi level is proposed to occur because of universal derelaxation of the GaAs (110) surface. For large metal depositions, the resulting barrier heights are hypothesized to be determined by the interaction of either free (not involved in compound formation with other species) metal or free As with the GaAs surface region. It is shown that based on simple considerations of the relative enthalpy of metal-arsenide formation, it is possible to decide which species is responsible for the barrier height and, thus, to account for the majority of barrier heights to the GaAs (110) surface.

Steps on (001) Si Surfaces

ABSTRACTPrimitive (001) surfaces contain only biatomic (ao/2) steps and thereby provide a topological way of suppressing antiphase domain formation in polar materials heteroepitaxially grown on nonpolar (001) substrates. We show that thermodynamic equilibrium is a necessary and sufficient condition to form primitive (001) Si surfaces due to a π-bonded step reconstruction that lowers the relative enthalpy of reconstructed [110] biatomic steps by 0.04 eV per step atom, and to correlation, which freezes out the step configurational entropy thereby suppressing the formation of all other types of steps. Implications for general vicinal (001) Si surfaces are discussed.