A novel lead-free relaxor ferroelectric ceramic of (0.67 -x)BiFeO 3 -0.33BaTiO 3 -xBa(Mg 1/3 Nb 2/3 )O 3 [(0.67 -x)BF-0.33BT-xBMN, x = 0-0.1] was prepared by a solid-state reaction method. A relatively high maximum polarization P max of 38 lC/cm 2 and a low remanent polarization P r of 5.7 lC/cm 2 were attained under 12.5 kV/mm in the x = 0.06 sample, leading to an excellent energy-storage density of W~1.56 J/cm 3 and a moderate energy-storage efficiency of g~75%. Moreover, a good temperature stability of the energy storage was obtained in the x = 0.06 sample from 25°C to 190°C. The achievement of these characteristics was basically attributed to an electric field induced reversible ergodic to ferroelectric phase transition owing to similar free energies near a critical freezing temperature. The results indicate that the (0.67 -x)BF-0.33BT-xBMN lead-free realxor ferroelectric ceramic could be a promising dielectric material for energy-storage capacitors.

No abstract

New lead‐free perovskite solid solution ceramics of (1 − x)(Bi1/2Na1/2)TiO3–xBa(Ni1/2Nb1/2)O3[(1−x)BNT–xBNN,x = 0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X‐ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x = 0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x = 0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d33~121 pC/N and kp~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x = 0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long‐range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.

A novel (0.67−x)BiFeO3–0.33BaTiO3–xBaZrO3 lead‐free relaxor ferroelectric ceramic was developed by a solid‐state reaction method. Measurements of temperature‐dependent dielectric permittivity and the polarization/strain hysteresis loops demonstrated an obvious evolution of dielectric relaxor behavior at room temperature (RT) from nonergodic to ergodic states. A significantly enhanced electrostrain of ~0.37% at 7 kV/mm with a relatively small hysteresis of ~39% and a low‐frequency sensitivity was found at x = 0.04, showing large potential for actuator applications. This was basically attributed to a rapid response of forward and backward switching between ergodic and ferroelectric phases owing to similar free energies and large local random fields.

The 0.45Bi(Mg0.5Ti0.5)O3–(0.55 − x)PbTiO3–x(Bi0.5Na0.5)TiO3 (BMT–PT–xBNT) ternary solid solution ceramics were prepared via a conventional solid‐state reaction method; the evolution of dielectric relaxor behavior and the electrostrain features were investigated. The XRD and dielectric measurements showed that all studied compositions own a single pseudocubic perovskite structure and undergo a diffuse‐to‐relaxor phase transition owing to the evolution of the domain from a frozen state to a dynamic state. The formation of the above dielectric relaxor behavior was further confirmed by a couple of measurements such as polarization loops, polarization current density curves, as well as bipolar strain loops. A large strain value of ~0.41% at a driving field of 7 kV/mm (normalized strain d33* of ~590 pm/V) was obtained at room temperature for the composition with x = 0.32, which is located near the boundary between ergodic and nonergodic relaxor. Moreover, this electric field‐induced large strain was found to own a frequency‐insensitive characteristic.