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 ZB∗ = 5.3e, in excellent agreement with complementary first principles calculations. In addition to resolving controversy over the nature of chemical bonding in this system, we decompose Born charge into polarizability and local charge. We find α = 5.07 \AA3 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.
@article{arxiv.2104.00478,
title = {Chemical bonding and Born charge in 1T-HfS$_2$},
author = {Sabine N. Neal and Shutong Li and Turan Birol and Janice L. Musfeldt},
journal= {arXiv preprint arXiv:2104.00478},
year = {2021}
}