O3 Relaxor Ceramics Research Articles

Enhanced energy storage performance in (1-x)Bi0.85Sm0.15FeO3-xCa0.5Sr0.5Ti0.9Zr0.1O3 relaxor ceramics

Producing dielectric ceramics with favorable energy storage density, efficiency, and thermal stability has become an urgent task for developing energy storage devices. In this work, the innovative Pb-free (1-x)Bi0.85Sm0.15FeO3-xCa0.5Sr0.5Ti0.9Zr0.1O3 [(1-x)BSF-xCSTZ, x = 0.0, 0.1, 0.2, 0.3 and 0.4] ceramics were fabricated via traditional solid phase sintering approach. Their structures, electrical characteristics, and energy storage properties were researched comprehensively. The results verified that all the samples form solid solutions with pseudo-cubic perovskites structure. The density of ceramic samples is improved accompanied by gradually refined grain size upon increasing the CSTZ doping content. Interestingly, an excellent recoverable density of ∼3.3 J/cm3 with high efficiency of ∼78% is received at x = 0.3 under the average breakdown electric field of 350 kV/cm. The energy storage performances remained stable in a broad temperature range of 20 – 110 ℃, a large frequency range of 1 Hz – 1 kHz, and beyond 105 repeated charging-discharging cycles. The enhanced energy storage performances of BSF ceramics by introducing CSTZ result from the improved relaxor behavior and the increased electric breakdown strength. Our strategy for relaxor modulation with a sealed sintering method to achieve high energy storage performance can be valuable in BiFeO3-based ceramic capacitors.

High temperature A.C. conductivity analysis of ZnO nanoparticles doped BaZr0.15Ti0.85O3 relaxor ceramics

This article covers the microstructure, AC conductivity (σac) and impedance analysis of lead-free polycrystalline BaZr0.15Ti0.85O3 (BZT) piezoceramics modified by the addition of 1 wt % ZnO nanoparticles synthesized by the conventional mixed oxide route. Nanoparticles of ZnO with an average diameter of ~41 nm have been produced via direct precipitation method. XRD study confirms the hexagonal symmetry (space group P63mc) of ZnO while sintered BZT ceramic compositions consist of single phase tetragonal perovskite structure with the space group (P4mm). Role of ZnO as sintering aid is confirmed via SEM analysis since dense microstructure (with increase in the grain size) of doped BZT composition was achieved. The negative temperature coefficient of resistance (NTCR) behavior which refers to decrease in electrical resistance with increase in temperature is investigated for both compositions while high temperature AC conductivity analysis proposed that the conduction in studied compositions is due to hopping charge mechanism.

Enhanced energy storage performance of Ba0.94(Bi0.5K0.5)0.06Ti0.85Zr0.15O3 relaxor ceramics by two-step sintering method

A series of Ba0.94(Bi0.5K0.5)0.06Ti0.85Zr0.15O3 (referred to as BBK) ceramics with high density microstructure were fabricated by a two-step sintering method. A strong influence of the sintering temperature on the microstructure, dielectric properties and relaxor behavior of BBK ceramics was observed. Slim hysteresis loops could be obtained in all BBK ceramics, and the optimal sample sintered at 1250 °C for 6 h shows a high dielectric constant (εr ˜3066 at 102 Hz), a low dielectric loss (tan δ ˜0.005 at 102 Hz), a high energy density (Wdischarge ˜0.95 J/cm3 at 76 kV/cm) and a high energy efficiency (η ˜88% at 76 kV/cm). The correlation of electrical properties for BBK ceramics with sintering temperatures could be attributed to grain size effect and relaxor behavior.

Dielectric properties in lead-free (1-x)BaTiO3-xBi(Zn0.5Ti0.5)O3 relaxor ceramics under bias fields

Abstract The bias field-dependent dielectric properties of lead-free (1-x)BaTiO 3 -xBi(Zn 0.5 Ti 0.5 )O 3 ceramics with x = 0.08, 0.10, and 0.14 were investigated. It was demonstrated that the composition with x = 0.08 exhibited a high dielectric tunability of 58% with a low dielectric permittivity of 2973 under 3 MV m −1 at room temperature. Meanwhile, the x = 0.14 composition showed stable dielectric response with varying the bias field at different temperatures, which was attractive for high-performance dielectric capacitor applications. Moreover, it was found that the dielectric tunability was significantly reduced with the increase in ferroelectric relaxor degree, which was quite helpful for designing and selecting appropriate materials for dielectric tunable and dielectric capacitor applications. The related mechanism was also analyzed.

Temperature dependent polarization reversal mechanism in 0.94(Bi1/2Na1/2)TiO3-0.06Ba(Zr0.02Ti0.98)O3 relaxor ceramics

The temperature at which the electric field induced long-range ordered ferroelectric state undergoes transition into the short-range ordered relaxor state, TF-R, is commonly defined by the onset of strong dispersion of the dielectric permittivity. However, this combined macroscopic property and structural investigation of the polarization reversal process in the prototypical lead-free relaxor 0.94(Bi1/2Na1/2)TiO3-0.06Ba(Zr0.02Ti0.98)O3 reveals that an applied electric field can trigger depolarization and onset of relaxor-like behavior well below TF-R. The polarization reversal process can as such be described as a combination of (1) ferroelectric domain switching and (2) a reversible phase transition between two polar ferroelectric states mediated by a non-polar relaxor state. Furthermore, the threshold fields of the second, mediated polarization reversal mechanism depend strongly on temperature. These results are concomitant with a continuous ferroelectric to relaxor transition occurring over a broad temperature range, during which mixed behavior is observed. The nature of polarization reversal can be illustrated in electric-field-temperature (E-T) diagrams showing the electric field amplitudes associated with different polarization reversal processes. Such diagrams are useful tools for identifying the best operational temperature regimes for a given composition in actuator applications.

A comparative study of Ba0.95Ca0.05Zr0.25Ti0.75O3 relaxor ceramics prepared by conventional and microwave sintering techniques

Abstract A comparative study on the dielectric properties of (Ba0.95Ca0.05Zr0.25Ti0.75O3 (BCZT) ) bulk ceramics prepared by conventional and microwave sintering (MWS) has been done. High-density ceramic materials were obtained in 4 h of cycle time for microwave sintered sample whereas it took 22 h for conventional method. Samples prepared by both sintering techniques showed single-phase formation in XRD with cubic structure. The dielectric properties of the samples were measured as a function of temperature in the frequency range of 100 Hz–100 kHz. Relaxor behaviour was observed in both types of samples. It was observed that the peak value of dielectric constant was higher for microwave sintered sample compared to conventional one and also the dielectric loss was lower. The value of activation energy was found to be ∼0.53 eV and 0.29 eV for microwave sintered and conventional sintered samples, respectively.

Influence of long-range structural order on electrostriction in the as-sintered and annealed (0.4)Pb(In1/2Nb1/2)O3 : (0.6) Pb(Mg1/3Nb2/3)O3 relaxor ceramics

Longitudinal electrostrictive strains in an as-sintered and two annealed (0.4)Pb(In1/2Nb1/2)O3 : (0.6)Pb(Mg1/3Nb2/3)O3 relaxor ceramics were measured by laser-interferometry. The field-related electrostriction coefficients (M33) of the ceramics were then determined. The electrostrictive coefficients progressively decreased with annealing and the strain responses became nonlinear. The ferroelectric hysteresis loops of the as-sintered and annealed ceramics showed progressive decrease in coercive fields and maximum polarizations with increasing annealing time. Transmission electron microscopy studies revealed enlargement of 1 : 1 B-site ordered domains with annealing. The changes in the high-field responses of the annealed ceramics are interpreted as arising from a higher degree of long-range order caused by annealing. A field-induced mechanism is proposed to explain the correlation between the B-site cation long-range order and the electrostrictive behaviour in this relaxor.

Dielectric properties of cobalt and chromium doped lead iron tungstate relaxor ceramics

The effect of Co and Cr doping on the dielectric properties of Pb(Fe2/3 W1/3)O3 relaxor ceramics is analysed in this work. No second phases were detected for Co doped PFW for Co < 7.5 at%. On the other hand, a Pb2WO5 second phase was identified in Cr doped PFW. Both Co and Cr decrease the permittivity maximum and shift transition temperature to high temperatures. Relaxor aging behaviour was observed for both doped compositions, being more pronounced for Cr doped PFW. Oxygen annealing post-sintering treatment increases εrmax and the sharpening of temperature dielectric response of Cr doped PFW. The observed dielectric modifications are discussed in relation to the probable defects present in the ceramics

The characteristics of the diffuse phase transition in Mn doped Pb(Fe2/3W1/3)O3 relaxor ceramics

The characteristics of the diffuse phase transition of Pb(Fe2/3W1/3)O3 relaxor ceramics doped with different amounts of Mn are investigated. The freezing temperature Tf, obtained by fitting the ω,Tmax to the Vogel–Fulcher relationship, clearly changes with the Mn content. It increases as the Mn content increases, approaching the Tmax(1 MHz) value of the relaxor curve. A concomitant decrease in the frequency dispersion of Tmax is also observed. The freezing temperature also increases as the 1:1 order of Fe3+ and W6+on B sites increases by air annealing but decreases by oxygen annealing. It is suggested that the Mn ions, which are predominantly compensated by oxygen vacancies, form with them defect pairs and that these pairs can couple to the spontaneous polarization vectors, increasing the correlation between the dipole moments and originating the increase of the freezing temperature. It is further suggested that filling up the oxygen vacancies by oxygen annealing will decrease the defect pairs and cause the opposite effect.

Preparation and dielectric properties of Pb[(Mg1/3Ta2/3), (Zn1/3Nb2/3)]O3 relaxor ceramics

Powders of Pb(Mg1/3Ta2/3)O3-Pb(Zn1/3Nb2/3)O3 ceramic system were prepared by a B-site precursor method. Perovskite phase contents and lattice parameters of the system are reported. Weak-field radio-frequency dielectric constants and losses of sintered samples were investigated as functions of composition, temperature, and frequency. Dielectric relaxation and diffuse phase transition behaviors were characterized. Microstructures were examined and correlated with dielectric characteristics.