Fatigue-resistant,temperature-insensitive strain behavior and strong red photoluminescence in Pr-modified 0.92(Bi0.5Na0.5)TiO3–0.08(Ba0.90Ca0.10)(Ti0.92Sn0.08)O3 lead-free ceramics

An electric-field-induced large strain and strong photoluminescence was achieved by introducing trivalent Pr³⁺ as the activator into 0.92(Bi_0.5Na_0.5)TiO₃ − 0.08(Ba_0.90Ca_0.10)(Ti_0.92Sn_0.08)O₃ (BNT−8BCST) ceramics. Around a critical composition of 0.4 mol% Pr³⁺, a large strain of ∼0.39% with a relatively small hysteresis compared with existing lead-free Bi-perovskite ceramics was obtained. In particular, the strain is very resistant to field cycling and thermal shock, giving the materials attractive for its exceptionally good fatigue resistance and high temperature stability. Besides the excellent electrical properties, Pr³⁺-modified BNT−8BCST host exhibits a strong photoluminescence with a bright red emission at 610 nm assigned to ¹D₂ → ³H₄ transitions of the Pr³⁺ ions upon a blue light excitation of 400–500 nm. The photoluminescence can be enhanced through poling treatment of the samples. Moreover, samples have a superior water resistance property which almost maintaining the same photoluminescence intensity after 40 h water immersion time. These results suggest the material may have potential application as a multifunctional device such as “on-off” actuator and electric field-controlled photoluminescence devices by integrating its excellent luminescence and electrical properties.     

Crystal growth and characterization of Deuterated Glycine Phosphite single crystals

Deuterated Glycine Phosphite single crystals were grown by low temperature solution growth method using high purity deuterated water as solvent. Deuteration content of the as grown crystals was improved by repeated recrystallisation process. Structural perfection, transparency and the functional groups present in the grown crystals were identified using different characterization analyses. Dielectric behaviors of the as grown specimens were examined through thermal and impedance analysis. Partial deuteration of the grown crystal was confirmed from the DSC and dielectric results.     

Electrical Properties and Local Domain Structure of LiNbO3 Thin Film Grown by Ion Beam Sputtering Method

The nanocrystalline ferroelectric LiNbO3 films on（001） Si substrates with the random orientation of polycrystalline grains and the predominance of the grains with lateral orientation of the polar axis were grown using the ion beam sputtering method. The remanent polarization and the coercive field are 12 μC/cm2and 29 kV/cm, respectively. The thermal annealing leads to the coarsening of the grains. The appearance of the ＂local texture,＂ which gives rise to the unipolarity of the heterostructures caused by the predominance of the one direction in the vertical component of the spontaneous polarization, is investigated.     

Preparation of polycrystalline BaTi2O5 ferroelectric ceramics

Polycrystalline BaTi₂O₅ (BT₂) was prepared by solid state sintering in air using BaCO₃ and TiO₂ as starting materials. A rod-like BT₂ sintered bodies in a single phase were obtained above 1025 °C by adding 5 wt.% B₂O₃. The densification of BT₂ sintered bodies decreased with increasing sintering temperature. The maximum permittivity of BT₂ sintered body was 640 at the Curie temperature (T_c) of 461 °C and the frequency of 100 kHz. The addition of B₂O₃ was effective to obtain BT₂ in a single phase at low temperatures with elongated microstructure and to improve the permittivity, indicating the formation of preferred orientation at low temperature was related with liquid-phase sintering mechanism.     

Fractality and dielectric spectra of ferroic materials

 The character of low-infralow-frequency dielectric spectra of ferroelectrics and related materials, their transformation with temperature, electric field and aging time, the temperature dependencies of relaxation times at phase and structural transitions are evidence of their fractality. The analysis of optical microscope research brought to light the fractal features of domain boundaries and their temporal evolution. The kinetic equations modified by introducing of the fractional derivatives, percolation and fractal models describe the preponderance of the dielectric spectra and explain the critical slowdown of relaxation. The fractal dimensionalities evaluated by experiments and their change at phase transitions have being discussed in comparison with the percolation models and the dynamic scaling theory. Received: 23 December 1998/Reviewed and accepted: 7 January 1999     

Enhancing properties of lead-free ferroelectric BaTiO3 through doping

The substitution on either the A- or B-site of ferroelectric perovskites by aliovalent elements has a profound influence on their properties. Donor doping “softens” ferroelectrics, whereas acceptor doping “hardens” them. The charge compensation mechanisms are reviewed, as well as the models describing their effects. The focus of this review is doped-BaTiO₃, a model lead-free ferroelectric. The effects of aliovalent doping on its dielectric, ferroelectric, and piezoelectric properties are reviewed and illustrated in the case of Cu (acceptor) doping.     

Ultrasound studies of phase transitions in tungsten bronze ferroelectric materials

Attenuation and velocity measurements at ultrasonic frequencies were performed in two ferroelectric solid solutions with tungsten bronze structure type, SBN and PBN, as a function of temperature (from 200 to 380 K). Both materials, in polycrystalline form, presented sensitive changes in the temperature dependence curves of attenuation and velocity. One of these anomalies (at 350 K for SBN and 323 K for PBN) was associated with a second-order phase transition, confirming the ferroelectric orthorhombic–ferroelectric tetragonal phase transition suggested for both systems in this temperature range.     

Piezoelectric shear-mode properties of Pb(Yb1/2Nb1/2)O3-PbTiO3 ceramics

A Pb(Yb_1/2Nb_1/2)O₃-PbTiO₃ [PYNT] solid solution was synthesized and characterized for its potential use. The shear-mode dielectric and piezoelectric behaviors of PYNT with a morphotropic phase boundary (MPB) composition were studied as a function of temperature. Dielectric permittivity K₁₁^T and loss were found to be 2310 and 2.5%, respectively, at room temperature. Piezoelectric coefficient d₁₅ and electromechanical coupling factor k₁₅ were calculated to be 710 pC/N and 0.70, respectively, maintaining nearly constant up to 300 °C, resistivity and RC time constant were observed to be 2.4 × 10⁹ Ω cm and 1.07 s, respectively, at 350 °C. These good piezoelectric properties, together with the high Curie temperature (T_c ∼ 370 °C), indicate that PYNT is a promising candidate for high temperature-shear sensor and inkjet actuator applications.     

Synthesis and characterizations of BNT–BT and BNT–BT–KNN ceramics for actuator and energy storage applications

Dielectric and ferroelectric properties of 0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃ (BNT–BT) and 0.93Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.01K_0.5Na_0.5NbO₃ (BNT–BT–KNN) ceramics were studied in detail. An XRD analysis confirmed the single perovskite phase formation in both the samples. Room temperature (RT) dielectric constant (ε_r) ~1020 and 1370, respectively at 1 kHz frequency were obtained in the BNT–BT and BNT–BT–KNN ceramics. Temperature dependent dielectric and the polarization vs. electric field (P–E) studies confirmed the coexistence of ferroelectric (FE) and anti-ferroelectric (AFE) phases in the BNT–BT and BNT–BT–KNN ceramics. Substitution of KNN into the BNT–BT system decreased the remnant polarization, coercive field and the maximum strain percentage. The energy storage density values ~0.485 J/cm³ and 0.598 J/cm³ were obtained in the BNT–BT and BNT–BT–KNN ceramics, respectively. High induced strain% in the BNT–BT ceramics and the high energy storage density in the BNT–BT–KNN ceramics suggested about the usefulness of these systems for the actuator and the energy storage applications, respectively.     

Piezoelectric and dielectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Ba(Zr0.04Ti0.96)O3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–xBa(Zr_0.04Ti_0.96)O₃ (abbreviated as BNBT–BZT100x, wherein x from 0 to 10 mol%) were fabricated. We have studied effects of amount of BZT content on the electrical properties and microstructures. X-ray diffraction analysis indicates that a solid solution is formed when BZT diffuses into the BNBT lattice, and further the crystal structure of sintered hybrid changes from rhombohedral to tetragonal symmetry along with increasing BZT content. Piezoelectric property measurements reveal that the BNBT–BZT4 ceramics has the highest piezoelectric performance, for example, the piezoelectric constant d₃₃ reaches to 167 pC/N and planar electromechanical coupling factor k_p is up to 0.27. In addition, the effect of Bi₂O₃ on the electrical properties and microstructure of the BNBT–BZT4 ceramics have also been studied, and found that the doping of Bi enhances the piezoelectric properties of ceramics.