SAIP2026

The VEC effect on the electronic and lattice dynamic stability of B2 Ti50Ru50-xNix: A supercell approach

8 Jul 2026, 15:30

20m

Lecture Hall GH1 (University of the Western Cape)

Oral Presentation Track A - Physics of Condensed Matter and Materials Physics of Condensed Matter and Materials

Speaker

Bongani Ngobe (MINTEK and Wits University)

Description

TiRu forms a B2 (CsCl-type) structure at high temperature, which typically transforms to lower-symmetry phases upon cooling; however, in TiRu, B2 remains stable down to room temperature. This study investigates the effect of Ni substitution on the electronic structure and lattice dynamic stability of the B2 Ti50Ru50 phase using first-principles calculations within the supercell (SC) approach. The objective is to assess the role of valence electron count (VEC) of Ni in modifying the stability of the B2 TiRu phase and its potential to induce martensitic phase transformation (MPT). The phonon dispersion results confirm that the unalloyed B2 Ti₅₀Ru₅₀ phase is dynamically stable, exhibiting only positive vibrational frequencies. Upon alloying, Ti8Ru5Ni3 (18.75 at. % Ni) remains dynamically stable, whereas at Ti8Ru4Ni4 (25 at. % Ni) and above it shows the appearance of negative vibrational frequencies, indicating the onset of lattice dynamic instability. The electronic structure, analysed using the partial density of states (PDOS), shows that Ni-3d states contribute significantly near the Fermi level. This modifies the Ti-Ru hybridisation and shifts the electronic states towards the anti-bonding region, resulting in reduced electronic stability. The observed phonon softening is consistent with these electronic changes. These results demonstrate that Ni d-orbital filling effectively modifies the electronic structure and promotes lattice instability, providing a pathway for inducing martensitic phase transformation in the B2 TiRu phase.