The pressure induced twisted distortion in the flexible oxide Tc₂O₇

The pressure induced twisted distortion of the diagonal-double tetrahedrons (DDTs) in Tc₂O₇ and the corresponding anomalous lattice variation under pressure were unraveled based on van der Waals (vdW) corrected density functional theory calculations. We show that the optPBE functional precisely represents the crystal structure of Tc₂O₇ with less than 0.5% volume overestimation. The flexibility of the Tc₂O₇ cell originating from the weak vdW interactions between the Tc₂O₇ DDTs is confirmed. On the contrary, we have found that the strong ionic bonding in the Tc₂O₇ DDT leads to the rigidity of the Tc₂O₇ DDT. According to the analysis of chemical bonding characterization, the pressure induced distortion of the Tc₂O₇ DDT leads to inhomogeneous Tc-O bonding distributions.