Pyroelectric hysteresis loops measured on as-grown films. The initial response is positive in the 10 nm thick sample (a), while it is negative in the thicker samples [(b)–(d)].
Polarization hysteresis loops measured on films. The solid curves are the measured polarization (left ordinate axis) and the broken curves the measured current (right ordinate axis).
The measured pyroelectric response vs time after polarization for two film thicknesses, 19 nm (solid curves) and 10 nm (dashed curves). The 10 nm thick film reverts to a net positive polarization after being switched to a negative state. For thicker films the response is symmetric.
The relationship between film thickness and displacement field, as obtained from a Landau–Ginzburg–Devonshire model at room temperature (solid line). The open circles mark the experimental initial pyroelectric response (right ordinate axis) and the open squares shows the displacement field calculated from the measured lattice constant (left ordinate axis).
The measured offset voltage of the pyroelectric (filled circles) and ferroelectric (open circles) hysteresis loops. The voltage offset is negative in thin films, going positive and increasing with film thickness to saturate at .
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