First-Principles Study of Sc_1-xTi_xF₃ (x ≤ 0.375): Negative Thermal Expansion, Phase Transition, and Compressibility

We present the first-principles investigation of Sc1-xTixF3 (x ≤ 0.375). Controllable thermal expansion of Sc1-xTixF3 is achieved by different Ti contents. The negative thermal expansion (NTE) behavior is weakened gradually with increasing Ti content, which is consistent with experimental measurements. The Jahn-Teller effect plays an important role in the cubic-to-rhombohedral phase transition, which stems from the enhanced energy stability when the 3d orbitals of Ti3+ cation split into triply degenerate t2g and eg sets. The unusual thermal stiffening of Sc1-xTixF3 is found, which is similar to that of Sc1-xYxF3 and Sc1-xAlxF3 but contrary to other NTE materials.