V, Rajaji and Dutta, Utpal and P C, Sreeparvathy and Sarma, Saurav Ch and Sorb, Y A and Joseph, B and Sahoo, Subodha and Peter, Sebastian C and V, Kanchana and Narayana, Chandrabhas
(2018)
Structural, vibrational, and electrical properties of 1T-TiTe2 under hydrostatic pressure: Experiments and theory.
Physical review B, 97.
pp. 1-13.
ISSN 1098-0121
Abstract
We report the structural, vibrational, and electrical transport properties up to ∼16 GPa of 1T -TiTe2, a prominent
layered 2D system. We clearly show signatures of two isostructural transitions at ∼2 GPa and ∼4 GPa obtained
from the minima in c/a ratio concomitant with the phonon linewidth anomalies of Eg and A1g modes around
the same pressures, providing a strong indication of unusual electron-phonon coupling associated with these
transitions. Resistance measurements present nonlinear behavior over similar pressure ranges shedding light on
the electronic origin of these pressure-driven isostructural transitions. These multiple indirect signatures of an
electronic transition at ∼2 GPa and ∼4 GPa are discussed in connection with the recent theoretical proposal
for 1T -TiTe2 and also the possibility of an electronic topological transition from our electronic Fermi surface
calculations. Between 4 GPa and ∼8 GPa, the c/a ratio shows a plateau suggesting a transformation from an
anisotropic 2D layer to a quasi-3D crystal network. First-principles calculations suggest that the 2D to quasi-3D
evolution without any structural phase transitions is mainly due to the increased interlayer Te-Te interactions
(bridging) via the charge density overlap. In addition, we observed a first-order structural phase transition from
the trigonal (P3¯m1) to monoclinic (C2/m) phase at higher pressure regions. We estimate the start of this structural
phase transition to be ∼8 GPa and also the coexistence of two phases [trigonal (P3¯m1) and monoclinic (C2/m)]
was observed from ∼8 GPa to ∼16 GPa.
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