Fig. 1

Schematic of the measurement set-up and explanation of the proposed experiments. a Set-up used to record the piezoelectric charge generated by the material through the use of a special current-to-voltage transimpedance amplifier. The amplifier maintains a reasonable bandwidth of 4–5 Hz with an ultralow input-bias current consumption of <0.1 fA. b When a single domain polarization is scanned, there is no current flowing, as the force is kept constant. However, when the tip crosses different domains, there will be a current flowing as the force is kept constant, but the d₃₃ value will invert its sign. c At the domain wall, the generated current can be modeled as the tip will enter into one domain, loading it, and will leave an opposite domain, unloading it. The sign of charge generation depends on the scan direction or more precisely on whether the tip crosses from and Up to a Down domain (generation of Q < 0) or from an Down to an Up domain (generation of Q > 0). d Spectroscopy sweep model obtained when the tip performs a force-vs-distance sweep. While the tip exerts a force on the sample a strain is created. Once the force is released, unstraining occurs. The straining and unstraining processes generate positive or negative charges depending on the polarization of the domain