First-principles study of phonon anomalies and the BCC-HCP Martensitic phase transition

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:6371859

Chen, Y

First principles total energy calculations were performed for Zr in the omega, bcc, hcp, fcc structures and for Ba in the bcc, fcc structures. From the calculations equilibrium lattice constants, cohesive energies, bulk moduli, and energy difference between the bcc and the hcp phases were obtained that are in good agreement with experiment. The total energy of the 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 revealed that the longitudinal branch along the (100) directions is lower than the transverse branch. This anomalous behavior was 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 was determined as a function of the atomic displacements corresponding to the T/sub 1/ N-point phonon mode and a long-wavelength shear. 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/sub 1/ N-point phonon indicate an instability toward the formation of the hcp phase at T = 0 K.

• Research Organization: Iowa State Univ. of Science and Technology, Ames (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 6371859
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
ALKALINE EARTH METALS
BARIUM
CALCULATION METHODS
COHERENT SCATTERING
DIFFRACTION
ELEMENTS
METALS
NEUTRON DIFFRACTION
PHASE STUDIES
PHONONS
QUASI PARTICLES
SCATTERING
SHEAR
TRANSITION ELEMENTS
ZIRCONIUM