Chemical bonding and Born charge in 1T-HfS2

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 E-u 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 the controversy over the nature of chemical bonding in this system, we decompose Born charge into polarizability and local charge. We find alpha = 5.07 A(3) 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.

Automated summary

In this study, infrared absorption and Raman scattering spectroscopies were utilized to investigate the properties of 1T-HfS2. By analyzing the LO-TO splitting of the E-u vibrational mode and reevaluating the mode mass, unit cell volume, and dielectric constant, the Born effective charge was revealed to be ZB* = 5.3e, in agreement with first-principles calculations. Furthermore, the Born charge was decomposed into polarizability and local charge, with polar displacement-induced charge transfer from sulfur p to hafnium d being a key factor in the enhanced Born charge. The findings suggest that 1T-HfS2 is an ionic crystal with strong and dynamic covalent effects.