Stress-induced suppression of piezoelectric properties in PbTiO3:La thin films via scanning force microscopy

Abstract

Sol-gel derived polycrystalline La-doped PbTiO3 films are investigated by scanning force microscopy (SFM) in a piezoelectric contact mode. The SFM signal proportional to the effective piezoelectric coefficient, deff, is measured inside individual domains as a function of the mechanical force exerted by the SFM tip on the film’s surface. It is found that the piezoelectric signal can be fully suppressed under sufficiently high force (∼20–22 μN). The suppression is qualitatively different for domains of opposite polarities where deff may change its sign depending on the orientation of polarization vector. The piezoelectric hysteresis loops acquired under increasing force gradually shrink with an asymmetric decrease of the piezoelectric coefficients. This leads to a pronounced vertical shift of the loops (deff offset). The obtained results are discussed in terms of the competing electrostatic and piezoelectric contributions to the measured signal and stress-induced polarization instabilities in the vicinity of the SFM tip.

Nanoelectromechanics of polarization switching in piezoresponse force microscopy

“…The stages of the polarization switching process, such as domain nucleation and early stages of growth, which are most relevant to applications in highdensity ferroelectric data storage devices, cannot be described using a point charge approximation. Moreover, even though it has been shown that strains produced by the tip may suppress local polarization 12 or induce local ferroelectroelastic polarization switching, electrostatic models do not take into account strain effects. 13,14 Here, we analyze the microscopic mechanisms for electric field-and mechanical stress-induced polarization switching phenomena using recently obtained expressions for the electroelastic fields under the PFM tip, 15 for strong and weak indentation regimes.…”

Abnormal domain switching in Pb(Zr,Ti)O3 thin film capacitors

“…7 The mechanical load exerted by the tip may change the sign of the effective piezocoefficient. 8 While specific field configuration beneath the tip and spontaneous domain backswitching was suggested by another group 9 as the reason for abnormal domain formation. Similar effect was reported in lithium tantalate crystals but no explanation was proposed.…”

“…Electrical switching between the oblique and normal domains is usually constrained due to high mechanical stress associated with this type of switching. 8 However, given eight possible polarization directions in rhombohedral grains versus six directions for tetragonal grains, additional possibilities for switching without overcoming mechanical stress exist in rhombohedral grains. Thus, we propose that the abnormal switching effect can be explained by switching between oblique domains in rhombohedral grains, where the final orientation of the out-of-plane polarization component is determined by the charge compensation at the grain boundaries.…”

“…However, in some cases this trend is disrupted, i.e., after the external field is turned off the resulting domains exhibit polarization opposite to the direction of the applied field. [7][8][9][10][11][12][13] Different mechanisms have been proposed to explain this effect which is basically a consequence of asymmetric mechanical and electrical boundary conditions in the PFM experiments. In thin films the formation of domains with polarization opposite to the applied field related to high-order ferroelastoelectric switching induced by compressive stress of the probing tip has been suggested.…”

Dynamic piezoresponse force microscopy: Spatially resolved probing of polarization dynamics in time and voltage domains

“…Note that in all locations the offset component shows pronounced hysteresis with an "ideal" loop shape. However, the hysteresis loops are significantly shifted in the vertical direction, either due to the presence of frozen polarization layers, 84,85,108 non-uniform stress effects, 106,[109][110][111][112] or contribution of nonlocal bimorph modes. 113 The relaxing part shows almost complete lack of hysteresis, similar to the tip-electrode data in Sec.…”