Ferroelastic 90 degrees a-domain dynamics in epitaxial Pb(Zr0.2Ti0.8)O-3 (lead zirconium titanate, PZT) films is investigated using lateral and vertical piezoelectric force microscopies. The PZT film consists of out-of-plane polarized c-domains separated by a cross-hatch network of in-plane polarized a-domains. When an electric field is applied across the PZT film, the a-domains are rearranged on the nanoscale. Depending on the direction of the electric field, this results either in larger or more fragmented c-domains. Both lateral and vertical piezoelectric force signals demonstrate the importance of ferroelastic a-domain movement since their dynamics will determine the final polarization retention time and stability of ferroelectric capacitors. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3442802]