Abstract
X-ray diffraction, dynamical mechanical analysis, and infrared reflectivity studies revealed an antiferrodistortive phase transition in EuTiO ceramics. Near 300 K, the perovskite structure changes from cubic to tetragonal due to antiphase tilting of oxygen octahedra along the axis ( in Glazer notation). The phase transition is analogous to SrTiO. However, some ceramics as well as single crystals of EuTiO show different infrared reflectivity spectra bringing evidence of a different crystal structure. In such samples, electron diffraction revealed an incommensurate tetragonal structure with modulation wave vector q 0.38 a. Extra phonons in samples with modulated structure are activated in the IR spectra due to folding of the Brillouin zone. We propose that defects such as Eu and oxygen vacancies strongly influence the temperature of the phase transition to antiferrodistortive phase as well as the tendency to incommensurate modulation in EuTiO.
3 More- Received 28 May 2012
DOI:https://doi.org/10.1103/PhysRevB.86.054112
©2012 American Physical Society