Jarrier, R.; Marti, X.; Herrero-Albillos, J.; Ferrer, P.; Haumont, R.; Gemeiner, P.; Geneste, G.; Berthet, P.; Schülli, T.; Cevc, P.; Blinc, R.; Wong, S.S.; Park, T.-J.; Alexe, M.; Carpenter, M.A.; Scott, J.F.; Catalan, G.; Dkhil, B.: Surface phase transitions in BiFeO3 below room temperature. Physical Review B 85 (2012), p. 184104/1-10
10.1103/PhysRevB.85.184104

Abstract:
We combine awide variety of experimental techniques to analyze two heretofore mysterious phase transitions in multiferroic bismuth ferrite at low temperature. Raman spectroscopy, resonant ultrasound spectroscopy, electron paraelectric resonance, x-ray lattice constant measurements, conductivity and dielectric response, and specific heat and pyroelectric data have been collected for two different types of samples: single crystals and, in order to maximize surface/volume ratio to enhance surface phase transition effects, BiFeO3 nanotubes were also studied. The transition at T =140.3K is shown to be a surface phase transition, with an associated sharp change in lattice parameter and charge density at the surface. Meanwhile, the 201Kanomaly appears to signal the onset of glassy behavior.