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 permittivity as a function of temperature. It is believed that point and planar defects in thin ATN films disrupt the complex sequence of in-phase and antiphase rotations around cp thereby reducing the effective strength of interactions between the tilting and cation displacements.
Epitaxial silver tantalate niobate, Ag(Ta0.5Nb0.5)O3 (ATN), thin films on (001)SrRuO3∕(001)LaAlO3 substrates were deposited by a chemical solution deposition route. The solution was prepared using niobium ethoxide, tantalum ethoxide, and silver nitrate precursors in a 2-methoxyethanol and pyridine solvents. Films were crystallized between 450 and 800°C in O2 ambient. X-ray diffraction data demonstrated cube-on-cube epitaxy, with a limited reaction between the ATN thin films and the SrRuO3. The dielectric constants of the epitaxial films improved from 260 to 360 at 100kHz with an increase in the crystallization temperatures from 500to800°C. It is speculated that the phase transition between the orthorhombic M2 and M3 phases (which occurs at ∼330K in ceramics) is shifted to lower temperatures (⩽99K) for the films. For a film that was crystallized at 750°C, the frequency dependence was small (⩽20.3%) within the range of 1Hz–100kHz, the capacitance change, ΔC∕C, was small (⩽12.1%) over the temperature range of −20–120°C with a corresponding temperature coefficient of capacitance of −0.11%∕°C at room temperature at 100kHz, and the dc field tunability was not hysteretic, but was limited to 4.8% with a 150kV∕cm bias.
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