Degree Type

Dissertation

Date of Award

1986

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

Abstract

First-principles total energy calculations have been performed for transition metal Zr in the (omega), bcc, hcp, fcc structures and for Ba in the bcc, fcc structures. From our calculations we obtained equilibrium lattice constants, cohesive energies, bulk moduli and energy differ- ence between the bcc and the hcp phases which are in good agree- ment with experiment. The total energy of (omega) phase was found to be very close to that of hcp phase in Zr;Recent neutron scattering experiments on a single crystal of bcc Ba have revealed that the longitudinal branch along the 100 direc- tion is lower than the transverse branch. This anomalous behavior has been studied with use of the frozen-phonon method and is shown to arise from d-electron interactions;For the pressure induced bcc-hcp transition in Ba, the volume dependence of the complete energy surface from the bcc to the hcp structure has been determined as a function of the atomic displace- ments corresponding to the T(,1) N-point phonon mode and a long wavelength shear. The results predict that the frequency of this phonon mode decreases with increasing pressure;For the temperature dependent bcc-hcp transition in Zr, the frozen phonon calculation results of the T(,1) N-point phonon indicate an instability toward the formation of the hcp phase at T = 0 K. From the frozen phonon calculations the third and fourth order anharmon- ic coupling strengths have been determined and used to evaluate the temperature dependence of selected phonon frequencies in bcc Zr;It is found that phonon-phonon interactions are crucial for stabilizing the high-temperature bcc phase of Zr; *DOE Report IS-T-1275. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

DOI

https://doi.org/10.31274/rtd-180813-11893

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Yin Chen

Language

en

Proquest ID

AAI8703693

File Format

application/pdf

File Size

111 pages

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