  We consider a standard Ginzburg-Landau model of a ferroelectric whose
electrical polarization is coupled to gradients of elastic strain. At the
harmonic level, such flexoelectric interaction is known to hybridize acoustic
and optic phonon modes and lead to phases with modulated lattice structures
that precede the symmetry broken state for sufficiently large couplings. Here,
we use the we use the self-consistent phonon approximation to calculate the
effects of thermal and quantum polarization fluctuations on the bare modes to
show that such long-range modulated order is unstable at all temperatures. We
discuss the implications for the nearly ferroelectric SrTiO$_3$ and KTaO$_3$,
and propose that these systems are melted versions of an underlying modulated
state which is dominated by non-zero momentum thermal fluctuations except at
the very lowest temperatures.
