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Anomalous polarization switching related to grain size in Pb(Zr,Ti)O3 polycrystalline films

Pb(Zr,Ti)O3 films of various grain size were prepared by the sol–gel technique. X-ray diffraction results show that these films are of single tetragonal phase with no evidence of preferential orientation. Anomalous polarization switching (APS) was induced in the films with average grain size ~150 nm by using the tip of a scanning force microscope. After scanning an area by the tip with constant poling parameter, the polarization of some grains orient opposite to the applied electric field irrespective of applied field polarity, exhibiting APS; while the rest switch in a normal way. The ratio of the APS grains to the total number decreases with the decrease of average grain size. Pulse poling experiments reveal that APS is likely to be related to the intrinsic characteristic of grains. Control experiments of poling (during and after) exclude backswitching after the removal of the external field due to the charge injection effect or the built-in field; both of which are possible reasons for APS. It is suggested that coupling between the temporary stress created in grains during field-induced normal switching and the applied field probably plays a key role in APS.