Figure 5: Mechanism of the pressure-induced phase transition based on a thermodynamic model.

(a) Gibbs free energy (G) versus λ-Ti₃O₅ fraction (x) for every 10 K between 250 K to 500 K calculated using the Slichter–Drickamer mean-field model at P=0.1 MPa (i) and 60 MPa (ii). Blue and red circles indicate λ-Ti₃O₅ and β-Ti₃O₅, respectively. λ-Ti₃O₅ undergoes a pressure-induced phase transition to β-Ti₃O₅ because the energy barrier (shown by brown shadows) disappears by the application of external pressure above ∼60 MPa as shown in the insets (see Supplementary Movie 6). (b) Calculated x versus temperature curves at P=0.1 MPa (blue) and 60 MPa (red). (c) Calculated x versus pressure curve at 300 K indicating a threshold pressure of ∼60 MPa.