  We report that an energetic plasma process is extremely effective in
enlarging the unit cell volume and ferroelectric distortion of the
ferroelectric oxides, resulting in a significant increase in its Tc. We
demonstrate experimentally that c-axis oriented BaTiO3 films can be deposited
directly on quartz glass and Si substrates using such a process and that the
material shows an approximately 5% expansion of its unit cell volume and
approximately 4 times the ferroelectric tetragonal distortion of the bulk
crystals. Such a frozen negative pressure results in a Tc value that is
approximately 580 K higher than that of bulk single crystals, providing a wide
range of operating temperatures for the devices. The present results suggest an
approach to producing ferroelectric oxides with unique properties that might be
extended to ferromagnetic or superconductor oxides and demonstrate a route to a
lead-free ferroelectric oxide for capacitive, ferroelectric memory, and
electro-optical devices.
