Abstract
Unlike , , x∼=0.12, undergoes a structural change to a low-temperature tetragonal (LTT) phase below 60 K, and this transformation is known to suppress drastically. We present self-consistent local-density-functional calculations for this system that indicate the octahedrons are unstable to an X-point tilt in any direction, thereby leading to strongly anharmonic X-point vibrations. The LTT phase is most favored energetically, consistent with experiment. The effect of the LTT distortion on the electronic structure accounts for the suppression of in the LTT phase, and for the enhanced isotope effect at x=.
- Received 18 March 1991
DOI:https://doi.org/10.1103/PhysRevLett.67.228
©1991 American Physical Society