Antiferrodistortive phase transition in EuTiO3

Abstract

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. We propose that defects like Eu3+ and oxygen vacancies strongly influence the temperature of the phase transition to antiferrodistortive phase as well as the tendency to incommensurate modulation in EuTiO3.Comment: PRB, in pres

Pressure-temperature phase diagram of multiferroicEuTiO3

“…On the other hand, various diffraction experiments find a lower transition temperature in the range between 160-240 K 11-13 whereas Goian et al 14 report the phase transformation near 300 K for samples sintered at ambient pressure. For samples sintered at high pressure no transition was observed 14 . This suggests that the inherent microstrain induced during the fabrication process may play a large role in the determination of the transition boundaries.…”

“…An antiferrodistortive transition to the tetragonal I4/mcm structure takes place in both systems on cooling, and is attributed to the TiO 6 octahedral rotational instability. For EuTiO 3 , this tetragonal distortion has first been detected by an anomaly in the specific heat close to room temperature (282 K) 10 and has been confirmed by other techniques, namely x-ray diffraction [11][12][13][14] , EPR 15 , muon spin rotation 16 , resonant ultrasound scattering 17 , inelastic neutron scattering 18 , thermal expansion 19 , magnetic susceptibility 20 . Among various investigations of this phase transition a strong scattering in the transition temperature (T s ) has been reported ranging from 160 to 308 K [10][11][12][13][14]17,18 , depending on the applied experimental technique, the fabrication method and the quality of the samples.…”

“…An alternative defect can also be the presence of Eu 3+ ions, which have smaller ionic radius than Eu 2+ , resulting in reduced lattice parameters, which also affect the magnetic properties. Goian et al 14 proposed that the transition temperature T s in EuTiO 3 is strongly dependent on the sample preparation: they did not observe any tetragonal distortion down to 100 K from single crystal diffraction, while powder diffraction of the same sample revealed the tetragonal structure close to room temperature, as observed by an anomaly in the thermal expansion. Eu or Ti vacancies are also possible defects for this system, contrary to SrTiO 3 40 .…”

Emergent Superstructural Dynamic Order due to Competing Antiferroelectric and Antiferrodistortive Instabilities in BulkEuTiO3

“…Samples ranged in size between 0.5 to 1mm 3 , displaying high crystallinity with a .02 • mosaicity. In addition the requisite magnetodielectric response below T N was previously published for these samples [16]. X-ray diffraction measurements were performed on the 6ID-B beamline at the Advanced Photon Source and the XMaS beamline at European Synchrotron Radiation Facility.…”

“…Thus the underlying character of the AFD order is purely a 0 a 0 c − and thus of the I4/mcm symmetry group. Incidentally, not dissimilar looking satellite modulations were recently identified by electron diffraction [16]. However their data was inconsistent, given the sensitivity of the technique, this may be a result of irreproducible sample conditions caused by the mechanical grinding of the sintered pelletized ETO samples.…”