Shanming Ke

Relaxor behavior in CaCu3Ti4O12 ceramics

The dielectric properties of CaCu3Ti4O12 (CCTO) ceramics have been investigated in a temperature range of 143–573K and a frequency range of 1Hz–10MHz. A dielectric anomaly has been observed between 350 and 600K. The broad dielectric peaks in e′(T) can be well fitted by a modified Curie-Weiss law and a Vogel-Fulcher relationship, which is indicative of a relaxor ferroelectric behavior. A slim I-V loop as well as the P-E hysteresis loop and broad maxima in e″(f) also suggest the existence of a relaxor ferroelectric behavior in CCTO ceramics.

Large Energy Storage Density and High Thermal Stability in a Highly Textured (111)-Oriented Pb0.8Ba0.2ZrO3 Relaxor Thin Film with the Coexistence of Antiferroelectric and Ferroelectric Phases.

A highly textured (111)-oriented Pb0.8Ba0.2ZrO3 (PBZ) relaxor thin film with the coexistence of antiferroelectric (AFE) and ferroelectric (FE) phases was prepared on a Pt/TiOx/SiO2/Si(100) substrate by using a sol-gel method. A large recoverable energy storage density of 40.18 J/cm(3) along with an efficiency of 64.1% was achieved at room temperature. Over a wide temperature range of 250 K (from room temperature to 523 K), the variation of the energy density is within 5%, indicating a high thermal stability. The high energy storage performance was endowed by a large dielectric breakdown strength, great relaxor dispersion, highly textured orientation, and the coexistence of FE and AFE phases. The PBZ thin film is believed to be an attractive material for applications in energy storage systems over a wide temperature range.

Lorentz-type relationship of the temperature dependent dielectric permittivity in ferroelectrics with diffuse phase transition

The temperature dependence of the dielectric permittivity of perovskite Ba(ZrxTi1−x)O3 solid solutions, PbMg1/3Nb2/3O3 relaxor, and BaTiO3 ferroelectric ceramics was measured. It is found that a Lorentz-type law can be used to describe the dielectric permittivity of either the normal ferroelectrics with or without diffuse phase transitions (DPT) or the typical ferroelectric relaxors. The ferroelectric DPT can be well described by just one fitting process using the Lorentz-type law, while the relaxor ferroelectric transition needs two independent fitting processes. The Lorentz-type law fails at the low temperature side of the dielectric maximum of a first-order ferroelectric phase transition. Above the transition temperature, the dielectric curves of all the studied materials can be well described by a Lorentz-type law.

Giant Electric Energy Density in Epitaxial Lead‐Free Thin Films with Coexistence of Ferroelectrics and Antiferroelectrics

Ferroelectrics/antiferroelectrics with high dielectric breakdown strength have the potential to store a great amount of electrical energy, attractive for many modern applications in electronic devices and systems. Here, it is demonstrated that a giant electric energy density (154 J cm−3, three times the highest value of lead-based systems and five times the value of the best dielectric/ferroelectric polymer), together with the excellent fatigue-free property, good thermal stability, and high efficiency, is realized in pulsed laser deposited (Bi1/2Na1/2)0.9118La0.02Ba0.0582(Ti0.97Zr0.03)O3 (BNLBTZ) epitaxial lead-free relaxor thin films with the coexistence of ferroelectric (FE) and antiferroelectric (AFE) phases. This is endowed by high epitaxial quality, great relaxor dispersion, and the coexistence of the FE/AFE phases near the morphotropic phase boundary. The giant energy storage effect of the BNLBTZ lead-free relaxor thin films may make a great impact on the modern energy storage technology.

Antiferroelectric-like properties and enhanced polarization of Cu-doped K0.5Na0.5NbO3 piezoelectric ceramics

Abnormal evolution of ferroelectric hysteresis (P-E) loops was observed in Cu-doped K0.5Na0.5NbO3 (KNN) ceramics. The 1 mol. % Cu-doped fresh sample exhibited double-loop-like characteristics, while the 1.5 and 2 mol. % Cu-doped KNN ceramics showed normal single loops. Electron paramagnetic resonance spectra verified the formation of non-switchable (CuNb‴−VO••) ′ (DC1) and non-polar (VO••−CuNb‴−VO••)• (DC2) defect complexes in these ceramics. According to the experimental results, it is suggested that DC1 would provide the driving force for domain back-switching, leading to the double P-E loops, while DC2 would contribute to the space charges. Dielectric aging behaviors of the samples also supported this mechanism. It is the competition between the DC1 and DC2 defect complexes that induced the observed compositional evolution of P-E loops in the Cu-doped KNN ceramics.

Dielectric dispersion behavior of Ba(ZrxTi1-x)O3 solid solutions with a quasiferroelectric state

The temperature dependence of dielectric permittivity was investigated for the barium zirconium titanate solid solution system [BZT, Ba(ZrxTi1−x)O3 0.25≤x≤0.5]. The dielectric relaxation behavior was observed in these ferroelectrics with diffused phase transition. In contrast to the canonical relaxors such as Pb(Mg1/3Nb2/3)O3, the diffused phase transition of BZT could not be well described by the popular modified Curie–Weiss law. Quasiferroelectric state theory was introduced to explain the dielectric results of the BZT relaxors.

Electrical modulus analysis on the Ni/CCTO/PVDF system near the percolation threshold

A type of Ni/CCTO/PVDF three-phase percolative composite was prepared, in which the filler content (volume fraction) of Ni and CCTO was set at 60?vol%. The dependence of permittivity, electrical modulus and ac conductivity on the concentration of Ni and CCTO fillers near the percolation threshold was investigated in detail. The permittivity of the composites dramatically increased as the Ni content approached 24?vol%. This unique physical mechanism was realized as the formation of conductive channels near the percolation threshold. Analysis on the electrical modulus showed that the conductive channels are governed by three relaxation processes induced by the fillers (Ni, CCTO) and PVDF matrix, which are the interfacial polarization derived from the interfaces between fillers (Ni, CCTO) and PVDF matrix, and the polarization of CCTO ceramic filler and PVDF matrix. The conductivity behaviour with various Ni loadings and temperature suggested that the transition from an insulating to a conducting state should be induced by charge tunnelling between Ni?Ni particles, Ni?CCTO fillers and Ni?PVDF matrix. These findings demonstrated that the tunnelling conduction in the composite can be attributed to the unique physical mechanism near the percolation threshold.

Ferroelectric-Enhanced Polysulfide Trapping for Lithium–Sulfur Battery Improvement

A brand new polysulfide entrapping strategy based on the ferroelectric effect has been demonstrated for the first time. By simply adding the nano-ferroelectrics (BaTiO3 nanoparticles) into the cathode, the heteropolar polysulfides can be anchored within the cathode due to the internal electric field originated from the spontaneous polarization BaTiO3 nanoparticles, and thus significantly improving the cycle stability of Li-S batteries.

Dielectric, ferroelectric properties, and grain growth of CaxBa1−xNb2O6 ceramics with tungsten-bronzes structure

Dielectric properties, microstructures, and phase transition behaviors of α and β phases of CaxBa1−xNb2O6 (x=0.22, 0.30, and 0.38) ceramics were investigated. All the three compositions had partially filled tungsten-bronze structure (TTB) and relatively high Curie temperatures (up to 345°C) compared with Sr1−xBaxNb2O6. The α phase exhibits unambiguously a diffused phase transition, while the β phase is associated with an incommensurate phase and needs to be further studied. The dielectric and ferroelectric properties of CaxBa1−xNb2O6 ceramics were strongly processing-dependent. A mechanism was proposed to explain the grain growth behavior of TTB ceramic niobates.

Revisit of the Vögel-Fulcher freezing in lead magnesium niobate relaxors

The Vogel–Fulcher (VF) equation ω=ω0 exp[−Ea/kB(Tm−Tf)] was frequently used to describe the dielectric relaxation of relaxor ferroelectrics where ω is the probe frequency at the peak temperature Tm of either the real or imaginary parts of the dielectric constant. We revisited this relation in a typical relaxor lead magnesium niobate and found that the parameters obtained were not physically meaningful. Meaningful results can only be obtained by fitting the VF relation on the characteristic relaxation time τc, whose temperature dependence can be obtained from the Cole–Cole model. The freezing temperature we obtained is 230 K, below which τc becomes temperature independent.