Antiferrodistortive phase transition in EuTiO3

TL;DR

This study investigates the antiferrodistortive phase transition in EuTiO3 ceramics, revealing structural changes near 300K and the influence of defects on the transition and incommensurate modulation.

Contribution

It provides detailed experimental evidence of phase transition mechanisms in EuTiO3 and highlights the role of defects in structural variations and incommensurate phases.

Findings

EuTiO3 undergoes a cubic to tetragonal phase transition near 300K.

Defects like Eu3+ and oxygen vacancies affect transition temperature and structure.

In some samples, an incommensurate tetragonal structure is observed.

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.