Polarization effect for dielectric and mechanical behaviors in Pb(Mg1/3,Nb2/3)0.71Ti0.29O3 crystal

• The <0 0 1>-poled PMNT29% crystal showed electric-field-induced monoclinic symmetry at room temperature.
• The Young’s modulus of poled sample was 15% higher than that of unpoled sample.
• The phase transition was studied by dielectric and mechanical tests.
• Compared with the dielectric measurement during the phase transitions, mechanical measurement was more sensitive to reflecting the phase transition and relaxation process.
• A relaxation process emerged below phase transition temperature, while it disappeared after polarization.

The relative permittivity and dissipation factor of (0 0 1)-cut Pb(Mg1/3Nb2/3)0.71Ti0.29O3 (PMNT29%) single crystal as functions of temperature were characterized at different frequencies by a LCR meter. From 280 K to 480 K, the unpoled sample showed three phase transitions: rhombohedral → tetragonal macro-domain → tetragonal micro-domain → cubic. The <0 0 1>-poled sample showed electric-field-induced monoclinic symmetry at room temperature, and also exhibited three phase transitions from 280 K to 480 K: monoclinic → tetragonal macro-domain → tetragonal micro-domain → cubic. The Young’s modulus and internal friction of PMNT29% crystal as functions of temperature at different vibration frequencies were tested by a dynamic mechanical analysis (DMA) system. Compared with the dielectric measurement during the phase transitions, mechanical measurement was more sensitive to reflecting the phase transition and relaxation process. On average, the Young’s modulus of the poled sample was 15% higher than that of unpoled sample, which is probably due to the changes of structure and internal stress induced by polling. Besides, a relaxation process caused by the interaction between domain walls and lattice defects emerged in the unpoled sample, while it disappeared in the poled sample due to the enhanced long-range domain order by field-induced phase transition.

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