Structural phase transitions in AgTa0.5Nb0.5O3 thin films

Octahedral tilt transitions in epitaxial AgTa0.5Nb0.5O3 (ATN) films grown on (001)p (where p=pseudocubic) oriented SrRuO3/LaAlO3 and LaAlO3 substrates were characterized by electron diffraction and high resolution x-ray diffraction. It was found that the ATN films exhibited octahedral rotations characteristic of the Pbcm space group, similar to those seen in bulk materials; however, the temperature of the M3↔M2 phase transition has been suppressed by ∼250 K due to the fact that the correlation length for rotations about cp was significantly reduced. The average off-center B-cation displacements, which signify the degree of long-range order for these local cation positions, were negligibly small compared to bulk materials, as inferred from the near-zero intensity of the 1/4(00l)p-type reflections. On cooling, pronounced ordering of B-cation displacements occurred at ≈60 K which is significantly lower compared to bulk (≈310 K). The onset of this ordering coincides with a broad maximum in relative permittivi...