Integrating multiple functions in a single compound is still attractive and necessary to meet the demand of device miniaturization. In this work, we systemically modulate multifunctional properties in the 0.74BiFeO3–0.26(Ba0.85Ca0.15)TiO3–x wt. % MnO2 solid solution with the addition of MnO2. A highly rectangular and saturated polarization–hysteresis (P–E) loop is obtained with a large remanent polarization Pr of 49.5 μC/cm2 as x=0.8. Furthermore, the piezoelectric coefficient d33 also obviously improved with an optimized d33=137 pC/N by the introduction of MnO2 due to the grain size effect, the improvement of insulation, and relaxation regulation. With the addition of MnO2, the remanent magnetization Mr increases monotonically because of the enhanced exchange interactions between Fe2+and Fe3+. The results may provide an effective way to explore promising multifunctional materials in BiFeO3-based ceramics.
Searching for lead-free piezoelectric thin films with a high piezoelectric coefficient is beneficial for applications in microelectromechanical systems. The solid solution method is verified as an effective route to largely improve the piezoelectric performance. Herein, we report the piezoelectric properties in polycrystalline (1 − x)BiFe 0.975 Ti 0.025 O 3 −xCaTiO 3 thin films. A giant effective piezoelectric coefficient of 542 pm/V has been achieved in 0.76BiFe 0.975 Ti 0.025 O 3 −0.24CaTiO 3 thin films because of the enhanced dielectric constant as well as remanent polarization, which originated from the coexistence of rhombohedral and pseudo-cubic phases and enhanced growth kinetics. The results indicate a type of lead-free piezoelectric thin film based on BiFeO 3 with the effective piezoelectric coefficient larger than 500 pm/V.
We investigate the effect of Jahn-Teller (JT) active Cu2+ ions on the structural, magnetic, and ferroelectric properties of Co1–xCuxCr2O4 (0 ≤x≤ 0.4). All the samples can be indexed with a cubic lattice with space group Fd3¯m at room temperature. All the samples undergo a paramagnetic-ferrimagnetic transition at TC and spiral ferrimagnetic ordering at TS. The magnetization measurements manifest that magnetization reversal occurs in the x = 0.2 and 0.3 samples. The x = 0.3 sample possesses a rather large polarization of 14 μC/m2, which is 7 times in magnitude compared with the CoCr2O4 single crystal. The analysis of the infrared active phonon modes implies that two T1u(IR) optical phonon modes are gradually split into a doublet at around 40 K, implying the lowering of lattice symmetry. The presence of a low-symmetry tetragonal phase becomes polar and enhances the electric polarization of Co0.7Cu0.3Cr2O4.
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