First-principles study of phonon anomalies and the bcc-hcp martensitic phase transition

Technical Report · Sat Nov 01 04:00:00 EST 1986

OSTI ID:6986884

Chen, Y

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 difference between the bcc and the hcp phases which are in good agreement 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) direction 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 displacements corresponding to the T/sub 1/ N-point phonon mode and a long wavelength shear. Results from frozen phonon calculations for Zr indicate an instability toward the hcp phase at t = 0 K in the bcc-hcp transition and determine the third and fourth order anharmonic coupling strengths which were used to evaluate the temperature dependence of selected frequencies. 135 refs., 29 figs., 13 tabs.

• Research Organization: Ames Lab., IA (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 6986884
• Report Number(s): IS-T-1275; ON: DE87003050
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
656002* -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALINE EARTH METALS
BARIUM
COUPLING CONSTANTS
CRYSTAL-PHASE TRANSFORMATIONS
DATA
EIGENVALUES
ELEMENTS
ENERGY-LEVEL TRANSITIONS
EXCITATION
INFORMATION
LATTICE PARAMETERS
MATHEMATICAL MODELS
METALS
NUMERICAL DATA
PHASE TRANSFORMATIONS
PHONONS
QUASI PARTICLES
TEMPERATURE DEPENDENCE
THEORETICAL DATA
TRANSITION ELEMENTS
VALENCE
ZIRCONIUM