  We combine a wide variety of experimental techniques to analyze two
heretofore mysterious phase transitions in multiferroic bismuth ferrite at low
temperature. Raman spectroscopy, resonant ultrasound spectroscopy, EPR, X-ray
lattice constant measurements, conductivity and dielectric response, 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 201K anomaly appears to signal the onset of glassy behaviour.
