Electrical Properties of Lead-Free Relaxor Ferroelectric Solid Solution Single Crystal (Na1/2Bi1/2)TiO3–BaTiO3 Grown by Bridgman Method

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Lead-free relaxor ferroelectric solid solution single crystals of (Na1/2Bi1/2)TiO3–BaTiO3 (NBT-BT) grown by the Bridgman method without the flux of Bi2O3 and Na2O have good optical quality and electrical properties. It was found that their transition from the rhombohedral phase to the tetragonal phase occurs at about 250 °C, accompanied by isotropization. Moreover, the domain wall structure changes with heating, and dielectric dispersion gradually disappears at 250 °C. Relative permittivity increases with further heating and shows a peak at $T_{\text{a}}$ of 340 °C with the appearance of brightness in a polarizing microscope, accompanied by a small frequency dispersion in $\tan\delta$. Polarization–electric field ($P$–$E$) hysteresis loops reveal a narrow shape without saturation with increasing electric field due to random fields based on defects at A-sites in perovskite compounds. Strain ($S$) versus electric field curves under bipolar fields reveal a slightly piezoelectric behavior without polarization reversal. The value of $d_{33}$ ($S_{\text{max}}/E_{\text{max}}$) was estimated to be about 250 pm/V at room temperature.
2009-09-25