Abstract
We present a computational study of the electronic structure and lattice dynamics of IrTe2 that sheds light on the debated mechanism of the temperature-induced phase transitions of this material. At ambient temperature, IrTe2 adopts a hexagonal crystal structure typical of metal chalcogenides. Upon cooling, some Ir–Ir distances shorten, thus inducing lattice modulations. We demonstrate that this is due to the formation of multicenter bonds involving both Ir and Te atoms. We show how the formation of these bonds is energetically favorable but lowers the vibrational entropy; therefore, they are destabilized by temperature. The obtained model is exploited to rationalize the effect of Se doping and other experimental results from the literature.
Highlights
We present a computational study of the electronic structure and lattice dynamics of IrTe2 that sheds light on the debated mechanism of the temperature-induced phase transitions of this material
They were originally thought to originate from charge density waves (CDWs), but it was later recognized that IrTe2 lacks the typical CDW signatures such as sinusoidal structure modulation[7] and band gap opening.[8]
Numerous explanations were put forward: in-plane intralayer the role played by interlayer (Te−Te) (p orbitals) bond formation,[11] interlayer Te−Te depolymerization,[7] Jahn−Teller-like distortion,[12] Ir charge ordering/disproportionation,[5] and naturally Ir−Ir bond formation.[13−15] Understanding the electronic structure of IrTe2, and what factors drive the phase transitions, represents a fundamental step to rationalize these types of phenomena and to exploit them for technological applications
Summary
We present a computational study of the electronic structure and lattice dynamics of IrTe2 that sheds light on the debated mechanism of the temperature-induced phase transitions of this material. The formation of stronger (stiffer) bonds such as the “dimers” of IrTe2 shifts the vibrational modes toward higher frequencies, thereby decreasing the entropy of the system.[24] This effect is clearly visible in the phonons density of states of IrTe2 (Figure 2), and it explains the entropy lowering upon dimer formation.
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