  We report a Raman scattering investigation of KTa1-xNbxO3 (x = 0.35, 0.5)
thin films deposited on MgO and LaAlO3 as a function of temperature. The
observed phase sequence in the range from 90 K to 720 K is similar to the
structural phase transitions of the end-member material KNbO3. Although similar
in the phase sequence, the actual temperatures observed for phase transition
temperatures are significantly different from those observed in the literature
for bulk samples. Namely, the tetragonal (ferroelectric) to cubic
(paraelectric) phase transition is up to 50 K higher in the films when compared
to bulk samples. This enhanced ferroelectricity is attributed to biaxial strain
in the investigated thin films.
