Investigation of Dielectric, Ferroelectric, and Strain Responses of (1 - x)[0.90(Bi0.5Na0.5)TiO3 - 0.10SrTiO3] - xCuO Ceramics

The low-temperature sintering of (Bi_0.5Na_0.5)TiO₃-based ceramics can be achieved by sintering aid CuO. Piezoelectric ceramics (1 - x)[0.90(Bi_0.5Na_0.5)TiO₃ - 0.10SrTiO₃] - xCuO (BNT-ST-Cu) with x = 0, 0.01, 0.02, 0.03, and 0.04 were prepared through the mixed oxide route. A tetragonal structure was indexed for the undoped sample. Its structure was found to be changed to a pseudocubic when Cu was added. For undoped Cu samples, the sintering temperature (T _s) for sufficient densification was 1160 °C. However, T _s was reduced to 1090-1120 °C for Cu-added specimens. Field emission scanning electron microscopy (FE-SEM) showed a uniform and dense grain morphology for all samples. The maximum dielectric constant temperature (T _m) was decreased with the doping concentration of Cu and applied frequency. The strain was increased with Cu concentration and had the maximum value of 500 pm/V for the sample x = 0.02 with symmetric and slim strain loops.

Improvement of electric field-induced strain and energy storage density properties in lead-free BNKT-based ceramics modified by BFT doping

In this research, the effects of Ba(Fe_0.5Ta_0.5)O₃ (BFT) additive on the phase evolution, the dielectric, ferroelectric, piezoelectric, electric field-induced strain responses, and energy storage density of the Bi_0.5(Na_0.80K_0.20)_0.5TiO₃–0.03(Ba_0.70Sr_0.03)TiO₃ (BNKT–0.03BSrT) ceramics have been systematically investigated. The ceramics have been prepared by a solid-state reaction method accompanied by two calcination steps. X-ray diffraction indicates that all ceramics coexist between rhombohedral and tetragonal phases, where the tetragonal phase becomes dominant at higher BFT contents. The addition of BFT also promotes the diffuse phase transition in this system. A significant enhancement of electric field-induced strain response (S_max = 0.42% and = 840 pm V⁻¹) is noted for the x = 0.01 ceramic. Furthermore, the giant electrostrictive coefficient (Q₃₃ = 0.0404 m⁴ C⁻²) with a giant normalized electrostrictive coefficient (Q₃₃/E = 8.08 × 10⁻⁹ m⁵ C⁻² V⁻¹) are also observed for this composition (x = 0.01). In addition, the x = 0.03 ceramic shows good energy storage properties, i.e. it has a high energy storage density (W = 0.65 J cm⁻³ @ 120 °C) with very high normalized storage energy density (W/E = 0.13 μC mm⁻²), and good energy storage efficiency (η = 90.4% @ 120 °C). Overall, these results indicate that these ceramics are one of the promising candidate piezoelectric materials for further development for actuator and high electric power pulse energy storage applications.

The effects of Ba(Fe_0.5Ta_0.5)O₃ additive on phase, dielectric, ferroelectric, piezoelectric, electric field-induced strain, and energy storage density of the Bi_0.5(Na_0.80K_0.20)_0.5TiO₃–0.03(Ba_0.70Sr_0.03)TiO₃ ceramics have been investigated.

Electric field-responsive photoluminescence color switching and reversible properties via Tb/Eu co-doped ergodic relaxor ferroelectrics

A facile strategy of color switching has been developed through reversibly multicolored photoluminescence modulation in dual rare-earth element modified 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (BNT6BT-Tb/Eu-x) relaxor ferroelectrics via the application of in situ electric fields. By virtue of the chemical and charge disorder induced by the trivalent rare earth ions, more dynamic and weakly correlated polar nanoregions are formed, which facilitate a reversible transition between the randomly oriented polar nanoregions and unstable ordered ferroelectric domains under an electric field. The electroceramics thus become more ergodic, exhibiting giant and reversible electric field-induced strain as well as structural symmetry changes around the luminescent centers and the BNT6BT-Tb/Eu-0.04 sample reveals the highest ergodicity degree. Accordingly, the overall emission color can be modulated reversibly between orange and green by purely physical stimuli (an electric field). The design of the color modulation elucidated in this work should inspire similar research expanded to other soft ferroelectrics for optical tuning and displays at ambient temperature. This should also be helpful for the realization of regulating the physical coupling (photoluminescence color switching-ergodic relaxor ferroelectrics) in multifunctional inorganic materials.

Room-Temperature Large and Reversible Modulation of Photoluminescence by in Situ Electric Field in Ergodic Relaxor Ferroelectrics

Ferroelectric oxides with luminescent ions hold great promise in future optoelectronic devices because of their unique photoluminescence and inherent ferroelectric properties. Intriguingly, the photoluminescence performance of ferroelectric ceramics could be modulated by an external electric field. However, researchers face a current challenge of the diminutive extent and degree of reversibility of the field-driven modification that hinder their use in room-temperature practical applications. Within the scope of current contribution in rare-earth-doped bismuth sodium titanate relaxors, the most important information to be noted is the shifting of the depolarization temperature toward room temperature and the resulting considerable enhancement in ergodicity, as evidenced by the dielectric properties, polarization, and strain hysteresis, as well as the in situ Raman/X-ray diffraction studies. After the introduction of 1 mol % Eu, the induced composition and charge disorders disrupt the original long-range ferroelectric macrodomains into randomly dynamic and weakly correlated polar nanoregions, which facilitates a reversible transformation between polar nanoregions and unstable ferroelectric state under an electric field, engendering a large strain. By virtue of this, both the extent and degree of reversibility of photoluminescence modulation are enhanced (∼60%) considerably, and room-temperature in situ tunable photoluminescence response is then achieved under electric field. These should be helpful for the realization of regulating the physical couplings (photoluminescent-ferroelectrics) in multifunctional inorganic ferroelectrics with a high ergodic state by reversibly tuning the structural symmetry.

High energy storage density over a broad temperature range in sodium bismuth titanate-based lead-free ceramics

A series of (1-x)Bi_0.48La_0.02Na_0.48Li_0.02Ti_0.98Zr_0.02O₃-xNa_0.73Bi_0.09NbO₃ ((1-x)LLBNTZ-xNBN) (x = 0-0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The phase structure, microstructure, dielectric, ferroelectric and energy storage properties of the ceramics were systematically investigated. The results indicate that the addition of Na_0.73Bi_0.09NbO₃ (NBN) could decrease the remnant polarization (P_r) and improve the temperature stability of dielectric constant obviously. The working temperature range satisfying TCC_150 °C ≤±15% of this work spans over 400 °C with the compositions of x ≥ 0.06. The maximum energy storage density can be obtained for the sample with x = 0.10 at room temperature, with an energy storage density of 2.04 J/cm³ at 178 kV/cm. In addition, the (1-x)LLBNTZ-xNBN ceramics exhibit excellent energy storage properties over a wide temperature range from room temperature to 90 °C. The values of energy storage density and energy storage efficiency is 0.91 J/cm³ and 79.51%, respectively, for the 0.90LLBNTZ-0.10NBN ceramic at the condition of 100 kV/cm and 90 °C. It can be concluded that the (1-x)LLBNTZ-xNBN ceramics are promising lead-free candidate materials for energy storage devices over a broad temperature range.

Structure and electrical properties of lead-free Bi0.5Na0.5TiO3-based ceramics for energy-storage applications

A new energy-storage ceramic system based on (1 − x)(Bi_0.5Na_0.5TiO₃–BaTiO₃)–xNaTaO₃ ((1 − x)(BNT–BT)–xNT) is reported in this study.

High strain response in ternary Bi0.5Na0.5TiO3–BaTiO3–Bi(Mn0.5Ti0.5)O3 solid solutions

In this study, a ternary solid solution (0.935 − x)BNT–0.065BT–xBi(Mn_0.5Ti_0.5)O₃ (BNT–BT–BMnT; x = 0–0.030) was designed and fabricated by means of a conventional fabrication process.