Abstract
The local structures around Co and Fe in (BCFO) have been determined element-selectively by means of extended x-ray absorption fine structure (EXAFS) measurements at the Co and Fe edges. In the tetragonal (T) phase at , both Fe and Co ions are trivalent and locate in the pyramidal coordination. The four in-plane Fe bonds with transverse oxygen (Fe-O2) split into bonds in the monoclinic (M) phase at whereas the Co-O2 bonds do not show a split exceeding the resolution of our EXAFS analysis. This result is an element-specific interpretation of the polarization rotation in the M phase around the morphotropic phase boundary. The components of thermal vibration and static disorder are evaluated separately from the temperature dependence of the Debye Waller factor from to 300 K. The static disorder of the Fe site is large compared to that of the Co site, thereby indicating that Fe is unstable in the pyramidal coordination of the T and M phases. This study demonstrates that the instability of Fe ions plays an important role in the sequential structural distortion of the BCFO system.
4 More- Received 29 January 2015
- Revised 12 June 2015
DOI:https://doi.org/10.1103/PhysRevB.92.054108
©2015 American Physical Society