Experimental setup: AFM head and sample holder are placed in a dry nitrogen atmosphere. A peltier element connected to an external temperature controller cools the brass sample plate equipped with a temperature sensor at the bottom. A closed fluid cycle (water, respectively ethanol) transports the waste heat of the peltier element to a cold reservoir (air, respectively dry ice), so that temperatures down to −30 °C and −80 °C, respectively, can be reached.
Temperature-ramp-synchronized PFM scan on the z-face of periodically poled LiNbO3 with a continuous decrease of the temperature from +30°C to −80°C. The PFM contrast is constant across the full temperature range which verifies the reliability of our SRT-PFM setup.
Morphology of single crystals of RbHSO4, grown from aqueous solution. Crystallographic axes a, b, c are indicated. The piezoelectric tensor components are related to the Cartesian reference system e i , with e 2 || b, e 3 || c and e 1 = e 2 × e 3. The cleavage plane is indicated in gray. The normal h of the cleavage plane nearly coincides with the c-axis (∠(h, c) = 0.14°).
(a) Lateral PFM scan of c-axis oriented RbHSO4 where the temperature is decreased in steps of 1 K from −5 °C to −30 °C. For each step the temperature is fixed for a couple of scan lines. The ferroelectric phase transition is clearly visible due to the rapid onset of the piezoresponse at −9 °C. (b) Top: lateral PFM scan with plane domain contrast due to torsion of the cantilever. Bottom: vertical PFM with domain wall contrast due to buckling of the cantilever. (c) Temporal evolution of a ferroelectric domain pattern recorded at −25 °C for different times after passing the phase transition. The domain structure shows a strong relaxation reducing the total domain walls length. Image size 100 × 100 μm2; bright domains correspond to a +P s orientation.
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