Accession Number : ADA141235

Title :   Developing New Materials at Elevated Temperatures and Pressures.

Descriptive Note : Final rept. Sep 82-Feb 84,


Personal Author(s) : DeRaad,L ; Gell-Mann,M ; Latter,R

PDF Url : ADA141235

Report Date : Apr 1984

Pagination or Media Count : 43

Abstract : The simple application of pressure and temperature is known to cause phase (structural) changes in crystals. The changes will not generally occur if the phases are relatively metastable, as in the case of graphite and diamond. Special techniques are required to induce these changes. Thus, it is quite possible that phases exist that have gone undetected experimentally. To find such metastable phases will require in general a priori knowledge of their existence, that is, at least a crude theoretical prediction of phase diagrams as a function of pressure and temperature. Limited progress toward this goal is described. The basic approach used a crystal model closely related to the KKR method and an atomic potential described by the Thomas-Fermi statistical atom. Only the ion-ion interaction energy and the band energy are treated based on the conjecture that they are most sensitive to crystal structure. Within the KKR method for determining band energy, a new approach to the calculation of the structure constants is proposed and discussed. (Author)

Descriptors :   *Crystal structure, Metastable state, Phase transformations, High pressure, High temperature, Mathematical prediction, Potential energy, Ion ion interactions, Diamonds, Graphite, Melting, Solidification, Solvents, Precipitation, Mathematical models, Computer programs

Subject Categories : Numerical Mathematics

Distribution Statement : APPROVED FOR PUBLIC RELEASE