Fig. 1. (a) Sketch of the experiment setup; coordinate axes are defined here. (b)–(f) Micrographs of the KTN sample under different conditions. (b) The sample in the single domain state at 25°C or 28°C. The sample in the multiple domain state (c), (d) at 25°C and (e), (f) at 28°C under positive/negative electric fields. The scale bar in (b) is 100 µm. The spots on the sample surface assure the measurement position to be the same.

Fig. 2. Raman spectra of the KTN sample (a) at 25°C and (c) at 28°C under zero/positive/negative electric fields. The enlarged Raman spectra around the TO₃ modes corresponding to the temperatures of (b) 25°C and (d) 28°C.

Fig. 3. Relative permittivity varying with increasing electric field of the KTN sample (a) at 25°C and (b) at 28°C under positive and negative electric fields.

Fig. 4. Diagram of the field-induced transition process from the single domain state to the multiple domain state. (a) Sample in the single domain state. (b) Under a relatively low electric field, the state transition begins. (c) Under a relatively high electric field, the polarization of the field-induced ferroelectric domain can bear comparison with the polarization of the spontaneous ferroelectric domain; as a result, domain boundaries form. (d) Under the reversed electric field, the domain boundaries rotate 90°.