First-principles thermoelasticity of transition metals at high pressure I. Tantalum prototype in the quasi-harmonic limit
The thermoelastic properties of bcc tantalum have been investigated over a broad range of pressures (up to 10 Mbar) and temperatures (up to 26,000 K) using a new first-principles approach that accurately accounts for cold, electron-thermal, and ion-thermal contributions in materials where anharmonic effects are small. Specifically, we have combined ab initio full-potential linear-muffin-tin-orbital (FP-LMTO) electronic-structure calculations for the cold and electron-thermal contributions to the elastic moduli with phonon contributions for the ion-thermal part calculated using model generalized pseudopotential theory (MGPT). For the latter, a summation of terms over the Brillouin zone is performed within the quasi-harmonic approximation, where each term is composed of a strain derivative of the phonon frequency at a particular k point. At ambient pressure, the resulting temperature dependence of the Ta elastic moduli is in excellent agreement with ultrasonic measurements. The experimentally observed anomalous behavior of C{sub 44} at low temperatures is shown to originate from the electron-thermal contribution. At higher temperatures, the main contribution to the temperature dependence of the elastic moduli comes from thermal expansion, but inclusion of the electron- and ion-thermal contributions is essential to obtain quantitative agreement with experiment. In addition, the pressure dependence of the moduli at ambient temperature compares well with recent diamond-anvil cell measurements to 1.05 Mbar. Moreover, the calculated longitudinal and bulk sound velocities in polycrystalline Ta at higher pressure and temperature in the vicinity of shock melting ({approx} 3 Mbar) agree well with data obtained from shock experiments. However, at high temperatures along the melt curve above 1 Mbar, the B{prime} shear modulus becomes negative indicating the onset of unexpectedly strong anharmonic effects. Finally, the assumed temperature dependence of the Steinberg-Guinan strength model obtained from scaling with the bulk shear modulus is examined at ambient pressure.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 897927
- Report Number(s):
- UCRL-JRNL-220868; TRN: US200706%%129
- Journal Information:
- Physical Review B, vol. 76, N/A, August 23, 2006, pp. 054109, Journal Name: Physical Review B, vol. 76, N/A, August 23, 2006, pp. 054109
- Country of Publication:
- United States
- Language:
- English
Similar Records
First Principles Thermoelasticity of Tantalum at High Pressures
Thermoelasticity at High Temperatures and Pressures for Ta
Related Subjects
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
AMBIENT TEMPERATURE
BRILLOUIN ZONES
ELECTRONIC STRUCTURE
MELTING
PHONONS
PRESSURE DEPENDENCE
SHEAR
STRAINS
TANTALUM
TEMPERATURE DEPENDENCE
THERMAL EXPANSION
THERMOELASTICITY
TRANSITION ELEMENTS
ULTRASONIC WAVES