First-principles study of the structural energetics of PdTi and PtTi

Abstract

The structural energetics of PdTi and PtTi have been studied using first-principles densityfunctional theory with pseudopotentials and a plane-wave basis. We predict that in both materials, the experimentally reported orthorhombic B19 phase will undergo a low-temperature phase transition to a monoclinic B19 ′ ground state. Within a soft-mode framework, we relate the B19 structure to the cubic B2 structure, observed at high temperature, and the B19 ′ structure to B19 via phonon modes strongly coupled to strain. In contrast to NiTi, the B19 structure is extremely close to hcp. We draw on the analogy to the bcc-hcp transition to suggest likely transition mechanisms in the present case.

The electronic, elastic, and structural properties of Ti–Pd intermetallics and associated hydrides from first principles calculations

“…These studies include the elastic constants of the B2 phase [25], the structural properties of the B2, B19, and B19 0 phases [26], the optical properties of the B2 phase [27], and the structural energies and phonon dispersion of the B2 phase [28]. More recently, Curtarolo et al calculated structural stabilities and enthalpies of formation for five intermetallics (Ti 3 Pd, Ti 2 Pd, TiPd, TiPd 2 , TiPd 3 ) using an ultrasoft pseudopotential within the local density approximation (LDA) [30].…”

Preferential growth of Pt on rutileTiO2

“…In addition to the increased coordination of Pt, the other significant difference between the two cases is the Pt-Ti interatomic distance, which increases to an average of 2.78Å on anatase (101). Examination of the Pt-Ti interatomic distance in various PtTi compounds, such as in B2 and B19 structures, [13] shows that the preferred nearest-neighbor Pt-Ti distance is near 2.75Å (the same analysis for Pt oxides shows a preferred Pt-O bond near 2.0Å). Therefore, on anatase (101) Pt not only has a higher coordination than on rutile (110), which indicates increased binding, it can also position itself at preferred distances from both O and Ti due to the larger spacings between the bridging oxygen rows.…”

First-principles thermodynamics of transition metals: W, NiAl, and PdTi

“…3 and about 0.34% larger than the cold curve minimum [13] which excludes zero-point vibrations. The upper insert shows the free energy difference between the two phases as a function of temperature, with the phase transition at 140K.…”

“…The upper insert shows the free energy difference between the two phases as a function of temperature, with the phase transition at 140K. This is very much larger than the estimate taken from the Landau barrier height [13] …”