MPB Region Research Articles

Phase Structure and Electrical Properties of 0.28PIN-0.32PZN–(0.4-x) PT-xPZ Piezoelectric Ceramics

Piezoelectric constant and Curie temperature are two important parameters of piezoelectric materials, but currently most piezoelectric materials have the problem of obtaining both high piezoelectric coefficient and Curie temperature. In this work, quaternary piezoelectric ceramics of 0.28Pb(In1/2Nb1/2)O3-0.32Pb(Zn1/3Nb2/3)O3–(0.4-x)PbTiO3-xPbZrO3 (x = 0~0.25) were designed and prepared by a solid-phase method, and the phase structure, dielectric, piezoelectric and ferroelectric properties of 0.28PIN-0.32PZN-(0.4-x)PT-xPZ piezoelectric ceramics were investigated by regulating the Zr/Ti ratio. The results show that the selected compositions are located in the MPB region, and the ceramic samples of each component display high density, the piezoelectric constant (d33) and the electromechanical coupling coefficient (kp) increase and then decrease with the increase of x. The optimum piezoelectric properties are found in compositions at x = 0.1, which showed a high piezoelectric coefficient d33 of 450 pC/N and high Curie temperature Tc of 272 °C. It is promising for use in high-temperature piezoelectric transducers.

Enhanced bipolar fatigue resistance by few oxygen vacancies of PZN-PNN-PZT ceramics near MPB

The bipolar fatigue behavior for Mn-doped PZN-PNN-PZT ceramics with composition near the MPB region was investigated at both 0.6 Ec and 2 Ec (where Ec is a coercive field). It was found that fatigue behavior depends on both the Mn doping content (or oxygen vacancies and the amplitude of the applied electric fields. Compared to no Mn doping ceramics, enhanced bipolar fatigue resistance was observed in 0.1 wt% Mn doping samples by nearly no variation of remnant polarization up to 106 cycles. The enhanced fatigue behavior is proposed to the weak pinning effect of few oxygen vacancies on domain walls, which hinders the microcrack propagation and stabilizes the domain structure. As Mn doping content increased, rich oxygen vacancies exist in ceramics, and the remnant polarization deteriorated due to the severe pinning effect of defect dipoles. Besides, different fatigue behaviors at 0.6 Ec and 2 Ec indicate that fatigue behavior can be controlled by the orientation of defect dipoles under repeated fatigue cycling.

Optimizing piezoelectric performance of complex perovskite through increasing diversity of B-site cations

Piezoelectric materials with unique properties are hugely appealing for high sensitivity sensors and ultrasonic transducers. Here, Pb(Ni1/3Nb2/3)O3-Pb(Yb1/2Nb1/2)O3-PbTiO3 piezoelectric system was designed and investigated in detail. The optimized piezoelectric response (d33 = 826 pC/N, d33* = 1017 pm/V) together with good temperature stability and negligible performance degradation up to 106 cycles was achieved in 0.58PNN-0.10PYN-0.32PT composition. Rayleigh analysis revealed the amplification of intrinsic and extrinsic contributions in MPB region due to more spontaneous polarization orientations and an increase in chemical disorder of system after the introduction of PYN. The origin of high piezoelectric response was investigated through the combination of scanning electron microscopy and piezoresponse force microscopy. The diversity of B-site cations was shown to enhance local structural heterogeneity, weaken long-range ferroelectric ordered domains, and lower free energy barrier via the formation of nanodomain configuration that promoted polarization rotation, thereby improving piezoelectric properties of the material. Therefore, it is suggested that increasing the diversity of B-site cations is an effective strategy for achieving outstanding piezoelectric performance.

Temperature-dependent energy storage performance of the ceramics in MPB region identified from the 1−(x + y) (Bi0.5Na0.5)TiO3-xBaTiO3-yBaZrO3 ternary ceramics

Temperature-dependent energy storage performance of the ceramics in MPB region identified from the 1−(x + y) (Bi0.5Na0.5)TiO3-xBaTiO3-yBaZrO3 ternary ceramics

Observation of the phase evolution and associated dielectric properties of K0.47Na0.47Li0.06NbO3 + (x)Bi0.5Na0.5ZrO3 lead free piezoceramic under varying frequency

Lead free piezoceramics K0.47Na0.47Li0.06NbO3 + (x)Bi0.5Na0.5ZrO3 where (x = 0.0 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) sintered at 1000 °C for 2 h with 0.4 wt% ≤ × ≤ 0.5 wt% possessed O and T phases coexistence with an MPB region. The structural as well as electrical metrics such as Nyquist plot, dielectric loss, dielectric constant, and a.c. conductivity were examined. The paper study discusses the outcomes of the various observation.

Achieving high Curie temperature and prominent piezoelectric response via site engineering for BiFeO3-BaTiO3 ceramics

In this paper, we proposed an effective strategy to overcome the trade-off between piezoelectric coefficient and the Curie temperature via co-doping of K+ and Nb5+ ions at A/B sites, achieving a combination of high TC and d33 in BiFeO3-BaTiO3-based ceramics. The MPB region was confirmed in a very narrow range of x = 0.0075–0.01 by the Rietveld refinement of XRD patterns and Raman spectroscopy deconvolution. An optimized composition with 1 mol% K/Nb co-dopants possesses a high Curie temperature (TC = 604 °C) along with d33 = 163 pC/N, kp = 43 %, Pr = 57.94 μC/cm2， and Ps = 68.18 μC/cm2. An outstanding thermal stability to 540 °C was verified via the temperature dependence of d33 and in situ Raman spectroscopy. This work not only affords a potential lead-free candidate material for the high-temperature piezoelectric application, but also provides a feasible strategy to design high-temperature dielectrics by exploiting the site engineering.

Synthesis, structural stability and phase diagram of BiFeO3–CaSnO3 ceramics

BiFeO 3 -based materials have received extensive attention in electronic device applications due to their high Curie temperature and large electromechanical response. In this study, new solid solutions of (1- x )BiFeO 3 - x CaSnO 3 (BF-CS) ceramics were successfully synthesized via conventional solid-state reaction method. With increasing CS content, the ceramics exhibit a single-phase perovskite and the structure changes from a main rhombohedral phase with a small amount of impurity phase to a stable rhombohedral phase and then to MPB region separating the rhombohedral and orthorhombic phases in the composition of 0 ≤ x ≤ 0.15, indicating that introducing CS can stabilize the perovskite structure formed in the sintering process. Unfortunately, the solid solubility limit of CS into BF perovskite structure is reached when x > 0.15. The dielectric peak associated with oxygen vacancies become weaker and finally disappear at x = 0.15. Moreover, the ceramics with x = 0.12–0.15 feature saturated and square-shaped P - E hysteresis loops with increased polarization can be attributed to effectively promote domain switching process at MPB, in which the highest piezoelectric coefficient d 33 = 259 pC/N can be ascribed to the combined effect of coexistence phases, high relative bulk density and low leakage current. In particular, a partial phase diagram is constructed in terms of temperature and composition, which helps to understand the structure-property relations. The distinct structures and phase transition behavior on each side of the vertical MPB line offer the guidelines and strategy to design other BF-based binary or ternary solid solutions with enhanced piezoelectric property in high temperature application.

Heterogeneous phase transformation pathways in additively manufactured Al-Ce-Mn alloys

Heat treatment of additively manufactured Al-Ce based multicomponent alloys leads to complex microstructure evolution. In this research, the ability to extend the phase transformation theories involving nucleation of a product phase from a heterogeneous multi-phase microstructure typical to that of additively manufactured samples is explored. The Al-10Ce-8Mn (wt%) was used as a model alloy system. Under additive manufacturing conditions different solidification microstructures were obtained due to spatial and temporal variations of thermal gradients (G) and liquid-solid interface velocities (R) within a given melt pool. Near the melt pool boundary (high G and low R, referred as MPB region), initially, Al20Mn2Ce forms from the liquid followed by a eutectic of FCC Al and Al11Ce3. In the melt pool interiors (low G and high R referred as ES region) a eutectic structure between FCC Al and Al20Mn2Ce is observed. During subsequent heat treatments, the MPB and ES regions transform into different sets of microstructures. In the MPB region, a fine globular microstructure containing FCC Al, Al11Ce3, Al6Mn, and Al12Mn results from the decomposition of Al20Mn2Ce. In the ES region a faceted Al51Mn7Ce4 plate phase results from the decomposition of Al20Mn2Ce. The formation of the Al51Mn7Ce4 phase within the eutectic microstructure at the boundaries of FCC Al and Al20Mn2Ce has not been reported in the literature. These two distinct phase transformation pathways are rationalized based on the role of driving force on the nucleation of (Al6Mn) and/or metastable intermetallic (Al51Mn7Ce4) phases at the interface of aluminum (FCC) and the non-equilibrium intermetallic (Al20Mn2Ce) phases.

Structural Evolution and Enhanced Piezoelectric Activity in Novel Lead-Free BaTiO3-Ca(Sn1/2Zr1/2)O3 Solid Solutions

In this study, a series of solid solutions of (1−x)BaTiO3-xCa(Sn1/2Zr1/2)O3 (abbreviated as (1−x)BT-xCSZ, x = 0.00–0.15) ceramics have been prepared by the conventional solid-state reaction method to search for high performance lead-free piezoelectric materials. The structural evolution, microstructure, and piezoelectric properties are investigated. X-ray diffraction (XRD) results indicate that the phase symmetry strongly depends on the CSZ content. A tetragonal phase is well-maintained in the compositions of 0 ≤ x ≤ 0.03, and coexistence of tetragonal and cubic phases is obtained in the range of x = 0.06–0.09, beyond which a pure cubic phase becomes stable. More importantly, a significantly enhanced piezoelectric coefficient of d33 = 388 ± 9 pC/N is attained in the composition of x = 0.06 in the MPB region, where a tetragonal ferroelectric phase and an ergodic relaxor phase with average cubic symmetry coexist. Based on the analysis of crystal structure and dielectric properties, a temperature-composition phase diagram consisting of four phase regions is established. This study indicates that the lead-free BT-CSZ binary system has great potential for use in electromechanical transducer applications.

Pressure-induced room temperature electrocaloric effect in BiFeO3-PbTiO3 solid solution based on Landau-Devonshire theory

The electrocaloric effect cooling is a promising next-generation cooling technology due to its high energy efficiency. In this work, the phase diagrams of BiFeO3-PbTiO3 solid solution have been investigated via Landau-Devonshire theory. Here, in the vicinity of morphotropic phase boundary, a relatively low electric field of 5 MV/m induces a giant electrocaloric temperature change (ΔT = 23.56 K) in a 0.81BiFeO3-0.19PbTiO3 solid solution at 630 K. It is found that the range of temperature change of ECE is broader with the increase of BiFeO3 mole fraction. In addition, a broader ECE working temperature range can be obtained near the MPB region by applying hydrostatic pressure of 1 GPa. These results suggest that this system is a potential candidate for practical electrocaloric materials.

Electric field-induced photoluminescence quenching in Pr-doped BNT ceramics across the MPB region

Piezophotonics is a great interesting field of physics that has led to a number of important technologies, such as light source, smart sensors, and mechatronics. In this work, we reported Pr-doped (Bi0·5Na0.5)TiO3-based lead-free ceramics with strong red photoluminescence emission and large strain response (d33∗ = 460 pm/V, S = 0.32 %). The PL emission can be quenched by decreasing the intensity by 93 % after electrical polarization (E = 50 kV/cm). The local structure and electric field-induced structural changes were systematically investigated to reveal the significant distinction in photoluminescence properties caused by electrical polarization. The results indicated that polarization treatment eliminates the structural inhomogeneities and establishes a long-range ferroelectric tetragonal and rhombohedral distortion. The crystal structure transformed irreversibly from a non-ergodic to a normal ferroelectric state. PL quenching originated from the decreased distortion of octahedral due to the transition from a non-ergodic state to a highly ordered symmetrical structure. Meanwhile, the enlarged domain structure contributed to the photoluminescence quenching effect. Our findings demonstrate that an electric field can be a robust tool for adjusting the photoluminescence property and provide insights into the relationship between the structure and PL properties of BNT-based ceramics under an external stimulus.

Proposing a phase diagram for BNT-BKT-KNN and finding a new MPB and large strain region in the system

Detailed investigation on “1-x-yBNT-xBKT-yKNN” was done for better understanding of its phase diagram which is crucial for estimating a useful composition range for actuation applications. A phase diagram is proposed along with a MPB between “rhombohedral ferroelectric and tetragonal ferroelectric” phases in the range x = 0.05 (0.04 ≤ y < 0.08) and x = 0.10 (0.02 ≤ y < 0.06). However addition of KNN above the critical value y ≥ 0.12 is observed to drive the system toward cubic structure. A region having large “electric field induced strain (EFIS)” value (∼0.45%) is also identified in the phase diagram.

Observation of dielectric anomalies and enhanced multiferroic properties in (1-x) Ba0.80Sr0.20TiO3-(x) LaFeO3 ceramics near at MPB region

Polycrystalline solid solution of (1-x)Ba0.8Sr0.2TiO3 - xLaFeO3 (0 ≤ x ≤ 0.50) samples were prepared by a conventional solid state process. The crystal structure of the samples transformed from tetragonal structure with P4mm space group (for x < 0.15) to orthorhombic structure with Pbnm space group (x > 0.35) alongside Morphotropic phase boundary region of 0.2 ≤x ≤ 0.35 samples. The evolution in Raman modes also indicated structural phase transition of the samples and corroborated the XRD findings. An increase in grain size with increase of LaFeO3 concentration up to x = 0.30 was observed. The ferroelectric properties were strongly dependent on composition and were correlated to the crystal structure of the samples. An enhancement in magnetization along with weak ferromagnetic hysteresis loops could be the presence of long range superexchange interaction via Fe3+−O−Ti−O−Fe3+ along the pathway. Dielectric anomalies near magnetic transitions were observed for the samples with x = 0.25 and 0.35 at temperatures 293 °C and 318 °C respectively, were ascribed to presence of strong magnetoelectric coupling. The observed dielectric relaxation in loss data attributed to hopping of oxygen vacancies.

Effects of Sintering Temperature on Structural and Electrical Properties of Fe3+ Doping PZT Ceramics

Abstract The influence of the sintering temperature on the structure and on the hysteresis loops of Fe3+ doped Pb(ZrxTi1-x)O3 system has been investigated. Three compositions have been selected in the following mode: one in rhombohedral region, one in MPB region and one in tetragonal region have been obtained by solid state reaction technique. Sintering has been carried out at 12000C and 12500C respectively. The nature of the phases has been investigated in detail using X-ray diffraction analysis (XRD). All the sintered samples reveal a perovskite type structure. The surfaces have been lapped and metalized in order to obtaine the hysteresis loops at room temperature. The results showed a similar behaviour with “hard” PZT ceramics.

Densification and properties of oxygen sintered CuO-doped PIN-PMN-PT ceramics

Relationships between sintering temperature and annealing atmosphere on microstructure and dielectric, ferroelectric, and piezoelectric properties of reactively sintered CuO-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics were investigated. Uniform 2−3 μm grain size, dense CuO-doped PIN-PMN-PT ceramics are obtained when oxygen sintered versus a bimodal grain size microstructure when sintered in air. Oxygen sintered ceramics have excellent properties including d33 = 300–315 pC/N, EC = 7.7–8 kV/cm, and tan δ < 1.5%. The MPB region was mapped for ternary compositions doped with 0.5 mol% CuO and sintered in O2. MPB 25PIN-40PMN-35PT demonstrated the maximum piezoelectric properties with d33 = 565 +/− 23 pC/N and kp = 0.64 +/− 0.01. Sintering from 1050 °C to 1200 °C increased the coercive field from 8.5 to 11.5 kV/cm and reduced dielectric losses from tan δ = 1.8% to 0.8% by facilitating diffusion of CuO into the lattice and creating domain wall pinning defect dipoles as evidenced by an increase in the internal field bias of P-E loops.

Phenomenological theory of phase transitions in the MPB region of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

ABSTRACTA higher-order Landau–Ginzburg–Devonshire theory is proposed to describe phenomenologically the complex phase transitions in the MPB region of the relaxor ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3(PMN-PT) single crystals. Using the singularity theory, a structurally stable 10th-order potential with four varying expansion coefficients (a1, a11, a2 and a12) depending on temperature and composition is found out. By studying on two- and three-dimensional sections of a four-dimensional phase diagram a1-a11-a2-a12 in the space of phenomenological parameters, the range of coefficient parameters by which the structural stability of the potential model can be guaranteed is determined. The theoretical temperature-composition phase diagram is constructed and it is shown that this is in good agreement with both recent experimental data and first-principle calculation for the symmetry change. Moreover, temperature dependence of dielectric constants for various compositions is studied.

Impact of K-compensation on phase fraction, dielectric permittivity, remnant polarization and piezoelectric constant of sodium potassium bismuth titanate ceramics

Sodium potassium bismuth titanate ceramics (NKBTx) has been considered as a potential replacement material to lead-based one due to its moderate piezoelectric constant and high Curie temperature. Recently, the piezoelectric constant and remnant polarization of NKBTx ceramics with x = 0.20 mol fraction has been improved by considering the hygroscopic nature and volatility of K2CO3. In the present work, detailed structural information of K-compensated NKBTx ceramics has been examined using Rietveld refinement program. Samples with three different mole fractions (x = 0.10, 0.20 and 0.30) were synthesized using solid-state reaction method. Not like in earlier reports, x = 0.10 and 0.30 mol fraction samples also have a mixture of rhombohedral and tetragonal phases which are revealed from Rietveld refinement. The presence of superlattice reflection $$\tfrac{1}{2}{\left\{ {311} \right\}_{pc}}$$ near 38° indicated that the existing rhombohedral phase has R3c symmetry in x = 0.10 mol fraction. Where as in x = 0.20 and 0.30 mol fraction samples, satisfactory profile fitting is obtained with rhombohedral (R3m) + tetragonal (P4mm) mixed phase structural model due to the absence of superlattice reflection. Grain growth is suppressed with the addition of xmole fraction and it is evidenced from the microstructure. Reduction of dielectric permittivity and slight shifting of phase transition temperature toward high temperature with increase in frequency indicates, all the samples have relaxor in nature. Temperature at which the dielectric permittivity maximum (T m ) increased from 325 to 345 °C with increase in x-mole fraction from 0.10 to 0.30 respectively. It is revealed from the modified Curie–Weiss law that the degree of diffusion (γ) is reduced from 1.95 to 1.71 with increase in x-mole fraction. Large remnant polarization, relative permittivity and piezoelectric constant are obtained for x = 0.20 composition and they are 21 μC/cm2, 4530 (at 5 KHz) and 215 pC/N respectively. Consolidated results reveals the extension of MPB region is strongly attributed to the K+ and Bi3+ compensation and the obtained electrical properties are associated with the phase fraction of end members as exhibited in lead-based piezoelectric ceramics.

Dielectric, Ferroelectric and Piezoelectric study of BNT-BT solid solutions around the MPB region

The (1-x)(Bi0.5Na0.5)TiO3- xBaTiO3 (x=0.01-0.1) has been prepared by solid state reaction route. The structural characterizations of the solid solutions were done by X-ray diffraction and Raman spectroscopy, which shows that the morphotropic phase boundary exist between x=0.05-0.1. The dielectric, ferroelectric and piezoelectric properties were studied around the MPB region. It is observed from the temperature and frequency dependent dielectric study that the dielectric constant increase with x values up to x=0.08 and then after decreases with x values. The variation of polarization with electric field for all compositions have been done and it is observed that polarization value is high at x=0.08. The electric displacement of the compositions having MPB with various electric field has been carried out and highest piezoelectric coefficient has been observed at x=0.08. All the characterizations concluded that the composition x=0.08 will be very suitable for actuator application.

Piezoelectric and ferroelectric properties of lead-free Bi0.5(Na0.80K0.20)0.5TiO3-(Ba0.98Nd0.20)TiO3 binary system

ABSTRACTThis research was conducted to investigate the effect of (Ba0.98Nd0.20)TiO3 addition on properties of Bi0.5(Na0.80K0.20)0.5TiO3 ceramic. The binary system having composition of(1-x)Bi0.5(Na0.80K0.20)0.5TiO3-x(Ba0.98Nd0.20)TiO3 or (1-x)BNKT-xBNdT (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06 mol fraction) was prepared by a conventional mixed oxide and sintering method. From the characterization results, the ceramics sintered at 1125°C had relative density of more than 98% of their theoretical values regardless of BNdT content. X-ray diffraction pattern of the ceramics showed a single perovskite structure with mixed rhombohedral and tetragonal phases (i.e. within MPB region). Scanning electron micrographs showed a cubic-like grain shape and the grain size decreased with increasing BNdT content. The ceramic with x = 0.04 showed relatively high room temperature dielectric constant with low loss (ϵr = 1670, tanδ = 0.0532), high piezoelectric coefficient (d33 = 192 pC/N) and good ferroelectric properties (Pr = 19.12 µC/cm2, Ec = 13.54 kV/cm and Rsq = 1.52) which may be suitable for transducer and actuator applications.

Evolution of crystalline phases and morphotropic phase boundary of the (Bi,Na)TiO3-(Bi,K)TiO3-BaTiO3 lead-free ceramic system

In this work, high density Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-BaTiO3 (BNBK) lead-free ceramics with nominal compositions crossing the morphotropic phase boundary region were prepared and their crystalline phases were investigated by a combination of the X-ray diffraction and Raman spectroscopy techniques, at room temperature. Results show that the BNBK82 sample has a single tetragonal phase (P4mm) and the BNBK91 and BNBK93 samples, single rhombohedral phase (R3c), while the BNBK88 and BNBK86 compositions showed coexistence of the above two phases with a not previously reported additional tetragonal P4bm phase. The Raman spectra deconvolution, for the BNBK86 and BNBK88 samples, also demonstrates the coexistence of rhombohedral and tetragonal phases, with phase fractions in very good agreement with the Rietveld refinement results, evidencing these compositions are located in the MPB region of the BNBK system. Results in this work suggest the MPB region proposed by Takenaka, for the BNBK system, is more appropriate than the one proposed by Trelcat.