Structural disordering and viedemann-franz relation in melts of some II-IV-V<Subscript>2</Subscript> semiconductors

The thermal and electrical conductivities, as well as the thermoelectric power of the CdSnAs₂, CdGeAs₂, ZnSnAs₂, and ZnGeAs₂ ternary semiconductor compounds, were studied in both solid and liquid states. It was shown that the thermal and electrical conductivities of these compounds increase, while the thermoelectric power decreases in the course of melting to the values characteristic of liquid metals. In contrast to metal melts, the electrical conductivity and the Lorentz numbers calculated from the Viedemann-Franz relation increase with temperature in II-IV-V₂ semiconductor melts. According to the Mott classification, the melts of these compounds are related to group B. Melting of II-IV-V₂ semiconductors causes their metallization.     

Interfullerene Interaction and Properties of Fullerites

The correlation is revealed between the mass of a molecule of C_cn fullerene and the properties of fcc-fullerites such as the sublimation energy, the distance between the centers of the nearest molecules, the GЬ neisen parameter, bulk modulus at zero pressure and temperature. The data of correlation dependences are used to determine the parameters of the Mie-Lennard-Jones pair potential for interfullerene interaction in fcc-fullerites. The thus determined parameters of the potential are used to calculate the properties of fullerites and obtain good agreement with known literature data. It is demonstrated that, at nc ≤ 15 to 20, crystals of C_nc fullerites are unstable. At the same time, fullerites with nc ≥ 100 will have anomalously low values of surface energy, and this must bring about the fragmentation of nanoclusters of C_nc molecules this large. The parameters of the triple and critical points of fullerenes are estimated. A study is made of the evolution of the potential parameters and of the properties identified above with the variation of the molecular mass of fullerene.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 3, 2005, pp. 385–395.Original Russian Text Copyright © 2005 by M. N. Magomedov.     

Effect of the carbon isotope composition on the properties of diamond

Parameters of the interatomic interaction potential for ¹²C and ¹³C carbon isotopes in the crystal lattice of diamond have been determined. Based on these data, the isotope dependence of the properties of diamond such as the Debye temperature, molar heat capacity, thermal expansion coefficient, vacancy formation energy, self-diffusion activation energy, surface energy, and longitudinal sound velocity is described. This approach is used for estimating a change in the bulk compression modulus of lithium crystals upon the passage from ⁷Li to ⁶Li. As the temperature increases, the isotope dependence of the heat capacity at constant volume vanishes; at a certain temperature, the isotope dependence of the thermal expansion coefficient changes from growth to decay. The expected isotope dependence of the parameters of phase transitions is predicted. It is shown that carbon condensates formed upon deposition from the gas phase must be enriched with the heavy isotope.     

Diphenylamine‐Substituted Carbazole‐Based Hole Transporting Materials for Perovskite Solar Cells: Influence of Isomeric Derivatives

A series of new branched hole transporting materials (HTMs) containing two diphenylamine‐substituted carbazole fragments linked by a nonconjugated methylenebenzene unit is synthesized and tested in perovskite solar cells. Synthesis of the investigated materials is performed by a simple two‐step synthetic procedure providing a target product in high yield. The isolated materials demonstrate good thermal stability and majority of the investigated compounds exist in an amorphous state, which is advantageous as there is no risk of crystallization directly in the film. The highest charge drift mobility of µ₀ = 4 × 10^?4 cm² V^?1 s^?1, measured at weak electric fields, is by ca. one order of magnitude higher than that of Spiro‐OMeTAD under identical conditions. From the perovskite solar cell testing results, it can be seen that performance of two new HTMs ( V885 and V911 ) is on a par with Spiro‐OMeTAD. Due to the ease of synthesis, good thermal, optical and photophysical properties, this type of molecules hold great promise for practical application in commercial perovskite solar cells.     

The correlation of the parameters of interatomic interaction in crystals with the position of atom in the periodic table

The previously obtained parameters of interatomic potential of the type of Mie-Lennard-Jones potential are used to analyze the correlation of these parameters with the position of atom in the periodic table for the purpose of estimating the parameters of interatomic potential of substances for which no experimental data are available that would enable one to calculate these parameters. The parameters of interatomic potential for promethium (Pm-61) are estimated for two versions of structure, and the parameters for lanthanides are corrected. The similarity in double periodicity for lanthanides and actinides is used for estimating the values of coordinate of the minimum of potential r _o for elements ranging from curium (Cm-96) to dubnium (Db-105). The value of r _o is estimated for roentgenium (Rg-111) proceeding from the fact that, in the case of atomic number Z _a > 60, the value of r _o decreases with increasing Z _a in elements from the same subgroup. Correct values of the parameters of potential are predicted for elements ranging from francium (Fr-87) to dubnium (Db-105). The obtained parameters of interatomic potential are used to calculate the Debye temperature and Grueneisen parameter for neptunium (Np-93) and americium (Am-95).     

A Change in the Debye Temperature of a Single-Component Substance upon Amorphization

Technical Physics Letters - A method for calculating the Debye temperature of a single-component substance in the amorphous state is proposed based on a nonlinear dependence of first coordination...     

Size dependence of the shape of a silicon nanocrystal during melting

Technical Physics Letters - Based on the experimentally established dependence of the melting temperature of a silicon nanocrystal on its size, it is shown that, as the size of a melting...     

The features of vacancy formation at low temperatures

Expressions for the calculation of the thermodynamic potential, enthalpy, entropy s _v, and volume of vacancy formation in a simple crystal at temperatures close to absolute zero are derived. It is established that the vacancy concentration Φ as a function of the temperature T exhibits a minimum at a certain temperature T ₀. At T<T ₀, the Φ(T) function increases with decreasing temperature; the s _v(T) value changes sign at T=T ₀ and is negative at T<T ₀. It is shown that the existence of the “zero-point vacancies” does not violate the third law of thermodynamics. Three new effects are predicted, and the prospects for their experimental observation are considered.