Phase transitions sequence in pyrochlore Cd2 Nb2O7 studied by IR reflectivity
Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic
2 A.F. Ioffe Physico-Technical Institute, RAS, Politechnicheskaya 26, 194021 St. Petersburg, Russia
Corresponding author: a email@example.com
Published online: 15 January 2001
The infrared reflectivity of Cd2Nb2O7 single crystal was studied in the temperature interval of 10-540 K, together with complementary dielectric measurements. A ferroelectric soft mode was revealed above the ferroelectric phase transition at Tc = 196 K coupled with a central-mode type dispersion in the near-millimetre range. This proves the mixed displacive and order-disorder nature of the transition. Below Tc many new modes were detected due to lowering of the symmetry, especially below the previously suggested incommensurate transition at 85 K. Discussion of the possible phase transitions based on symmetry considerations is presented with the conclusion that the ferroelectric transition is proper with the symmetry of the order parameter, whereas the intermediate ferroelastic transition is improper and triggered by the coupling with the ferroelectric order parameter.
PACS: 78.30-j – Infrared and Raman spectra / 63.20-e – Phonons in crystal lattices / 77.80.Bh – Phase transitions and Curie point
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001