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Abstract
We combine infrared absorption and Raman scattering spectroscopies to explore the properties of the heavy transition metal dichalcogenide 1T-HfS2. We employ the LO–TO splitting of the Eu vibrational mode along with a reevaluation of mode mass, unit cell volume, and dielectric constant to reveal the Born effective charge. We find {Z}_{{rm{B}}}^{* } = 5.3e, in excellent agreement with complementary first-principles calculations. In addition to resolving the controversy over the nature of chemical bonding in this system, we decompose Born charge into polarizability and local charge. We find α = 5.07 Å3 and Z* = 5.2e, respectively. Polar displacement-induced charge transfer from sulfur p to hafnium d is responsible for the enhanced Born charge compared to the nominal 4+ in hafnium. 1T-HfS2 is thus an ionic crystal with strong and dynamic covalent effects. Taken together, our work places the vibrational properties of 1T-HfS2 on a firm foundation and opens the door to understanding the properties of tubes and sheets.
Highlights
While 3d transition metal oxides and chalcogenides display strong electronic correlations, narrow bandwidths, and robust magnetism, 4 and 5d systems are recognized for strong spin–orbit coupling, increased hybridization, and more diffuse orbitals
The arrows are not scaled to real displacement amplitudes
Polarizability entails the sum of all cationic and anionic electron cloud volume contributions, whereas local effective charge is related to short-range interactions indicative of ionic displacement and chemical bonding
Summary
While 3d transition metal oxides and chalcogenides display strong electronic correlations, narrow bandwidths, and robust magnetism, 4 and 5d systems are recognized for strong spin–orbit coupling, increased hybridization, and more diffuse orbitals. Despite the apparent ionicity of the density of states, the dynamical Born effective charges in 1T-HfS2 are anomalous.
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