V. Goian, S. Kamba, O. Pacherova, J. Drahokoupil, L. Palatinus, M. Dusek, J. Rohlicek, F. Laufek, W. Schranz, A. Fuith, M. Kachlik, K. Maca, A. Shkabko, L. Sagarna, A. Weidenkaff, A. A. Belik
X-ray diffraction, dynamical mechanical analysis and infrared reflectivity studies revealed an antiferrodistortive phase transition in EuTiO3 ceramics. Near 300K the perovskite structure changes from cubic Pm-3m to tetragonal I4/mcm due to antiphase tilting of oxygen octahedra along the c axis (a0a0c- in Glazer notation). The phase transition is analogous to SrTiO3. However, some ceramics as well as single crystals of EuTiO3 show different infrared reflectivity spectra bringing evidence of a different crystal structure. In such samples electron diffraction revealed an incommensurate tetragonal structure with modulation wavevector q ~ 0.38 a*. Extra phonons in samples with modulated structure are activated in the IR spectra due to folding of the Brillouin zone. All our extensive studies give evidence that temperatures of the phase transitions to antiferrodistortive and existence of incommensurately modulated phase in EuTiO3 depend on method of samples preparation.
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http://arxiv.org/abs/1206.4137
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