Theoretical Study of a Thermophysical Property of Molten Semiconductors

This paper deals with theoretical approach to surface tension of molten silicon and germanium, and contributes to this field, which is very important. A theoretical calculation for determining the surface tension of high-temperature semiconductor melts, such as molten silicon and germanium, in the temperature range 1687–1825 K and 1211–1400 K, respectively, is described. The calculated temperature-dependence surface tension data for both Si and Ge are expressed as and (mJ m−2), respectively. These values are in consistence with the reported experimental data (720–875 for Si and 560–632 mJ m−2 for Ge). The calculated surface tension for both elements decreases linearly with temperature.

Investigation of photoconductivity in n-type Galium doped PbTe

Persistent photoconductivity at low temperature in PbTe + 0.4 at.% Ga has been investigated using kinetic equations which describe the transport process on DX-like impurity centers. Measured and calculated photoconductivity as a function of illumination and temperature is presented. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with negative correlation energy. Numeric values of the mathematical model constant at steady state are calculated by comparing the measured and calculated temperature dependence of the resistivity and carrier concentrations for illuminated and unilluminated n-type samples. Thus, the positions and concentrations of different impurity states are determined. .

A simplified approach to the vibrational self-relaxation of simple molecules through convolution of their velocities

A theoretical approach has been developed for computing collisional self-relaxation probabilities of the first excited level in the lowest vibrational mode of simple molecules. The bending (n2) vibration in triatomic molecules, in which the average translational and rotational velocities are of the same order of magnitude, was examined. The approach was based on the assumption that both the velocities should be taken into account as a convolution of the corresponding Maxwell's distribution functions. The model was checked for the SO2 molecule in the temperature range from 130.1100 K. The calculated temperature dependence curve (the Landau-Teller plot) exhibits a minimumat about 150K.The data obtained is discussed in relation to some experimental results. The comparison indicates that the problem was treated in correct manner. Some additional aspects of the relaxation, like intermolecular interactions and the steric factor, are also briefly considered. It is believed that this approach offers quite a good basis for further improvements of theoretical treatments.

Thermodynamic Properties of Coherent Interphase Boundaries in Substitutional Fcc Alloys

ABSTRACTThermodynamic and structural properties of coherent interphase boundaries (IPBs) in the Al-Li and Ag-Al alloy systems are studied using the cluster variation method (CVM) and low-temperature expansion (LTE) techniques. The energy parameters required as input for the CVM and LTE calculations were obtained by fitting to phase diagram data in the case of Al-Li alloys and from a fit to the results of first-principles total energy calculations for Ag-Al. Interphase energies are calculated as a function of temperature and composition profiles across coherent IPBs are computed for high-symmetry crystallographic orientations. It is demonstrated that the calculated temperature dependence of interphase energies and the “widths” associated with compositionally diffuse IPBs can be appreciable even at temperatures well away from critical points.

Order-Disorder Transformation in Cu3AAu: A Molecular Dynamics Study

ABSTRACTThe order-disorder transformation in CU3Au has been investigated using a combined Molecular Dynamics and Cluster Variation Method approach. Free energy minimization has been performed using the Natural Iteration technique. The calculated temperature dependence of enthalpy, lattice dynamics, short-range and long-range order parameters have been successfully compared with experimental data.

The Thermal Emission of Iodine

The temperature dependence of emission from iodine, heated in a shock wave to 1000 K–2000 K, has been measured at 4550, 5550, 6950, 7550, and 7820 Å. Preliminary measurements of the emission at 6380 Å were also made. The temperature dependence of the emission was calculated at these wavelengths for transitions to the ground electronic state X(1Σg+) of iodine from the excited electronic states, A(3Π1u), (1Π1u), and [Formula: see text]. The calculated results are in a reasonable agreement with experimental data. For the banded emission due to the B → X transition, a theory of the temperature dependence of emission was developed. At 6950, 7550, and 7820 Å, the results of this theory agree with the experimental data thus identifying the B → X transition as the source of emission at these wavelengths. The temperature dependence of emission at 4550 Å is consistent with calculated temperature dependence for either (1Π1u) → X or [Formula: see text] transitions. The temperature dependence of the emission at 5550 Å is consistent with calculated temperature dependence for the above two transitions, as well as for the A(3Π1u) → X transition.