Jigong Hao

Switching of morphotropic phase boundary and large strain response in lead-free ternary (Bi0.5Na0.5)TiO3–(K0.5Bi0.5)TiO3–(K0.5Na0.5)NbO3 system

In this work, we report the phase diagram of lead-free ternary (1 - y)[(1 - x)(Bi0.5Na0.5) TiO3-x (Bi0.5K0.5)TiO3]-y(K0.5Na0.5)NbO3 (BNT-BKT-KNN) system and study the switching characteristics of the morphotropic phase boundary (MPB). The addition of KNN intrinsically changes the structural nature of the system with the shift of MPB from MPB(I) between ferroelectric rhombohedral and ferroelectric tetragonal phases to MPB(II) between ferroelectric rhombohedral and relaxor pseudocubic phases. As the MPB(I) switches to MPB(II), large piezoelectric response with d(33) similar to 150pC/N that obtained for BNT-0.20BKT near MPB(I) almost disappears. Instead, a significant jump of electric-filed-induced strain S up to 0.32%-0.46% (S-max/E-max = 400-575 pm/V) is achieved near MPB(II) due to the shift of the ferroelectric-relaxor transition temperature TF-R down to room temperature. In this study, giant strain similar to 0.46% occurs in a very narrow region in the BNT-BKT-KNN system with x = 0.20, y = 0.01, which lies on an underlying tricritical triple point of a rhombohedral (R), tetragonal (T), and pseudocubic (Pc) phases. In-situ high-energy X-ray scattering experiments with external electric field reveal an initial electric-field-induced distortion from the Pc structure for the MPB(II) compositions, while those with single R phase shows no such distortion, which suggests that the large strain achieved near the MPB(II) is likely to be induced by the electric-field-induced structure distortion due to its relative instability structure. We believe that the discovery of a compositional line in the pseudo-ternary system, where the strain response is consistently derivable, should be useful for designing high-performance piezoelectric materials in other BNT-based systems by searching MPBs

Phase transitions, relaxor behavior, and large strain response in LiNbO3-modified Bi0.5(Na0.80K0.20)0.5TiO3 lead-free piezoceramics

The effect of LiNbO3 (LN) addition on the ferroelectric behavior and piezoelectric properties of Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT20) lead-free piezoceramics were systematically investigated. Results showed that the LN substitution into BNKT20 induced a transition from coexistence of ferroelectric tetragonal and rhombohedral phases to relaxor pseudocubic phases, which is accompanied by the significant disruption of ferroelectric order and with the shift of the ferroelectric-relaxor transition temperature TF-R down to room temperature. Accordingly, a large accompanying normalized strain of ∼0.38% (corresponding to a large signal d33* of ∼475u2009pm/V) were obtained in BNKT20 with 2.5u2009mol. %LN addition near the phase boundary. Temperature-dependent measurements of both polarization and strain from room temperature to 120u2009°C suggested that the origin of the large strain is due to a reversible field-induced ergodic relaxor-to-ferroelectric phase transformation. Moreover, an attractive property for application as hi...

Phase transitional behavior and electric field-induced large strain in alkali niobate-modified Bi0.5(Na0.80K0.20)0.5TiO3 lead-free piezoceramics

The effect of (KyNa1-y)NbO3 (KyNN) addition on the ferroelectric stability and consequent changes in the electrical properties of lead-free Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT20) piezoceramics were systematically studied. Results showed that the KyNN substitution into BNKT20 induces a phase transition from coexistence of ferroelectric tetragonal and rhombohedral to a relaxor pseudocubic with a significant disruption of the long-range ferroelectric order, and correspondingly adjusts the ferroelectric-relaxor transition point TF-R to room temperature. Accordingly, a large electric-field-induced strain of 0.33%–0.46% (Smax/Emaxu2009=u2009413–575u2009pm/V), which is derived from a reversible field-induced ergodic relaxor to ferroelectric phase transformation, was obtained in KyNN-modified compositions near the phase boundary. Moreover, a relationship between the position of the ferroelectric-relaxor phase boundary and the tolerance factor t of the end member KyNN was found in BNKT20–xKyNN system, which is expected to provide...

Orientation dependence of the dielectric and piezoelectric properties for the Ba0.98Ca0.02Ti0.96Sn0.04O3 thin films

Lead free Ba0.98Ca0.02Ti0.96Sn0.04O3 (BCST) thin films with (110), (111) and (001) orientations were processed via chemical solution deposition, and effects of orientation on the dielectric and piezoelectric properties were investigated in some aspects. The (110) orientated BCST thin films exhibit highest Curie temperature (Tc of 85xa0°C) and lowest dielectric loss (tan δ of 0.02). While, the (111) orientated BCST thin films exhibit highest dielectric tunability (74xa0%) and largest piezoelectric coefficient (d33 of 78xa0pm/V), which indicate that it is a promising lead-free replacement for lead-based applications. The anisotropic dielectric and piezoelectric properties in the three kinds of oriented BCST films has been attributed to the difference of structure, in-plane stress and polarization rotation in orientation engineered BCST films. This work clearly reveals the dielectric and piezoelectric properties of BCST films exhibit a strong sensitivity to orientation.

Enhanced electrostricitive properties and thermal endurance of textured (Bi0.5Na0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3 ceramics

Textured 0.92(Bi0.5Na0.5)TiO3–0.06BaTiO3–0.02(K0.5Na0.5)NbO3 (BNT–BT–KNN) ceramics have been produced by tape casting with pure-phase (Bi0.5Na0.5)TiO3 templates. Through the approach of texture construction, enhanced electrostrictive response was obtained with an electrostrictive coefficient Q33 (∼0.024u2009m4/C2 at 60u2009kV/cm) and good thermostability comparable with that of traditional Pb-based electrostrictors. Even at an electric-field as low as 35u2009kV/cm or at a temperature as high as 180u2009°C, samples still possess a large electrostrictive response with Q33u2009>u20090.022u2009m4/C2, suggesting it is very promising for practical applications as a lead-free electrostrictive material owning to its wide usage range. Moreover, reducing the applied electric-filed or increasing temperature can both induce the predominant to pure electrostriction transition due to the little contributions of electrostriction strain from ferroelectric domain switching. Our work may provide a new recipe for designing high-performance BNT-based l...

The optimization of electric properties of multilayered BNT–BT–ST/BCST thin films by configuration

The 0.755Bi0.5Na0.5TiO3–0.065BaTiO3–0.18SrTiO3/Ba0.98Ca0.02Ti0.96Sn0.04O3 (BNT–BT–ST/BCST) multilayered thin films, consisting of BNT–BT–ST layers and BCST layers, were prepared by using the sol–gel processing technique. The structure, leakage current, dielectric and piezoelectric properties of the multilayered thin films were investigated. Compositionally graded elemental profiles between individual BNT–BT–ST and BCST layers were achieved. The electric properties of the BNT–BT–ST/BCST multilayered thin films could be affected by the periodic layers. As a result, with an increase in periodic layers of the BNT–BT–ST/BCST multilayered thin films, the leakage current and dielectric loss were significantly reduced; moreover, the piezoelectric responses could be maintained at a high level (d33 = 130–150 pm V−1). This demonstrated the possibility to improve certain properties of the leakage current and dielectric loss for multilayered thin films, which could be exploited for functional devices that demand high quality.

Effect of LaNiO3 Buffer Layer on Ferroelectric Properties of Ba(Zr,Ti)O3 Thin Films

BaZrxTi(1-x)O3 (x = 0∼0.15) (BZT) thin films were prepared by chemical solution deposition. LaNiO3 buffer layer was introduced to modify the structure and ferroelectric properties of the films. Results show that the BZT films deposited on Pt/Ti/SiO2/Si substrate have random orientation, but those on LaNiO3 buffered Pt/Ti/SiO2/Si substrate have highly (100) preferred orientation. Grain size and leakage current of the BZT films decrease with increase of Zr content. The BZT films with LaNiO3 buffer layer exhibit larger grain size and have higher remanent polarization, dielectric constant and tunability. This work reveals the promising application of highly (100) oriented BZT films in multifunctional ferroelectrics.