  The current work employs a phase-field model to test the stability of
nanoscale periodic domain patterns, and to explore the application of one
pattern in an energy harvester device. At first, the stability of several
periodic domain patterns with in-plane polarizations is tested under
stress-free and electric field-free conditions. It is found that simple domain
patterns with stripe-like features are stable, while patterns with more complex
domain configurations are typically unstable at the nanoscale. Upon identifying
a stable domain pattern with suitable properties, a conceptual design of a thin
film energy harvester device is explored. The harvester is modelled as a thin
ferroelectric film bound to a substrate. In the initial state a periodic stripe
domain pattern with zero net charge on the top electrode is modelled. On
bending the substrate, a mechanical strain is induced in the film, causing
polarized domains to undergo ferroelectric switching and thus generate
electrical energy. The results demonstrate the working cycle of a conceptual
energy harvester which, on operating at kHz frequencies, such as from
vibrations in the environment, could produce an area power density of about
40W/m2.
