Study of the pressure effects in TiOCl by ab initio calculations

TL;DR

This study uses ab initio calculations to explore how pressure influences the electronic and magnetic properties of TiOCl, revealing a pressure-induced transition to a room-temperature spin-Peierls insulator-insulator phase.

Contribution

It provides detailed insights into pressure effects on TiOCl's structure, magnetic coupling, and phase transitions, including the prediction of a room-temperature transition at around 10 GPa.

Findings

Pressure increases transition temperature linearly.

At ~10 GPa, TiOCl undergoes a spin-Peierls transition near room temperature.

Different dimerized structures are stable at high pressures.

Abstract

Electronic structure calculations on the low dimensional spin-1/2 compound TiOCl were performed at several pressures in the orthorhombic phase, finding that the structure is quasi-one-dimensional. The Ti3+ (d1) ions have one t2g orbital occupied (dyz) with a large hopping integral along the b direction of the crystal. The most important magnetic coupling is Ti-Ti along the b axis. The transition temperature (Tc) has a linear evolution with pressure, and at about 10 GPa this Tc is close to room temperature, leading to a room temperature spin-Peierls insulator-insulator transition, with an important reduction of the charge gap in agreement with the experiment. On the high-pressure monoclinic phase, TiOCl presents two possible dimerized structures, with a long or short dimerization. Long dimerized state occurs above 15 GPa, and below this pressure the short dimerized structure is the more stable phase.