Electric-field-induced dipole reorientation characteristics in paraelectric KTN crystals

Local dipoles significantly influence the properties of paraelectric perovskites. Potassium tantalate niobate (KTa_1−xNb_xO₃, abbreviated as KTN) is a perovskite with excellent electro-optic and piezoelectric properties. Manipulating dipoles via electric fields in paraelectric KTN demonstrates significant application potential. Therefore, such dipole dynamics under electric fields are essential to research. In this work, we investigated dipole reorientation under electric fields in paraelectric KTN crystals. We found that, under an electric field of 10 kV/cm, local polarization opposing the direction of the applied field still exists in the KTa_0.62Nb_0.38O₃ (T_C = 13 °C) crystal. Additionally, a macroscopic piezoelectric coefficient of ∼40 pC/N was achieved in the paraelectric KTa_0.62Nb_0.38O₃ crystal by applying a 12.5 kV/cm electric field for 24 h. This phenomenon is attributed to the maintainable field-induced reorientation state of the dipoles after the removal of the electric field. Furthermore, since complete dipole reorientation requires strong fields, in the case of a KTa_0.61Nb_0.39O₃ crystal with a T_C (23 °C) approaching room temperature, a field-induced phase transition (at 2.1 kV/cm) occurs prior to the complete switching of dipoles in the paraelectric phase. This results in a multi-domain state in the recently phase-transformed crystal. Our findings help in understanding the performance exhibited under electric fields and can facilitate the optimization of paraelectric perovskites.