Huarong Zeng

The synergic regulation of conductivity and Seebeck coefficient in pure polyaniline by chemically changing the ordered degree of molecular chains

Pure polyaniline (PANI) films with different molecular chain packing states were successfully prepared by simply tuning the m-cresol content in the solvent. The SEM and AFM images display that the films are dense and smooth. The Vis-UV spectrum and Raman spectrum suggested that the conformation of PANI molecules changed from a compacted coil to an expanded coil by the chemical interactions between PANI and m-cresol, which enhanced the delocalization of π-polarons along the polymer chain. The XRD analysis indicated that the PANI molecular chain with different ordered degrees formed during the solvent evaporation process. Furthermore, the measurement of temperature-dependent electrical conductivity confirmed that the ordered regions in PANI molecular structures were enhanced with increasing m-cresol content, which decreased the hopping barrier and increased the carrier mobility. Consequently, when the m-cresol content increased, the electrical conductivity increased remarkably, while the Seebeck coefficient maintained the same level or increased slightly. The experimental results clearly reveal the intrinsic effect of molecular structure on the electric transport of conducting polymers. It strongly suggests that increasing the ordered regions in the polymer molecular chain structure is an effective way to improve the thermoelectric properties of conducting polymers.

Influence of structural evolution on energy storage properties in Bi0.5Na0.5TiO3-SrTiO3-NaNbO3 lead-free ferroelectric ceramics

Lead-free (1−x)(0.8Bi0.5Na0.5TiO3-0.2SrTiO3)-xNaNbO3 (x = 0–0.1, abbreviated as BNT-ST-xNN) ceramics were fabricated by a conventional sintering route with pure perovskite phase via XRD analysis. Raman spectrum was exploited in order to give an insight into the variation of local structural evolution. All compositions exhibited an obvious evolution of dielectric relaxation behaviors. Dielectric and ferroelectric properties clarified that a crossover from nonergodic to ergodic relaxor properties was obtained with the addition of NN content. A relatively large energy storage density was obtained WRec ∼ 0.74 J/cm3 at 7 kV/mm for x = 0.05 at room temperature. Particularly, the energy storage properties exhibited temperature (25–160 °C) and frequency stability (0.1–20 Hz) with WRec around 0.6 J/cm3 at 6 kV/mm for x = 0.05 within the ergodic region. Pulsed discharging current waveforms were measured under different electric fields to detect the energy storage density and discharging speed behavior. An illustrat...

Origin of the giant electro-optic Kerr effect in La-doped 75PMN-25PT transparent ceramics

Transparent ceramics of La-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) x/75/25 are prepared, and the ferroelectric domains, dielectric, and ferroelectric properties of x/75/25 are investigated. A double hysteresis loop and small fingerprint domains with uniform distribution observed for 3/75/25 indicate an intermediate ferroelectric state. The dielectric behavior under dc bias and the evolution of the hysteresis loop with increasing electric field for 3/75/25 indicate an electric field-induced phase transition, and it is proposed that the unstable intermediate ferroelectric state which would experience obvious field-induced phase transition is the origin of the giant electro-optic Kerr effect observed in La-doped PMN-PT 3/75/25.

Type–I pseudo–first–order phase transition induced electrocaloric effect in lead–free Bi0.5Na0.5TiO3–0.06BaTiO3 ceramics

In this study, the electrocaloric effect (ECE) of Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT–0.06BT) ceramic has been directly measured using a home-made adiabatic calorimeter. The maximum adiabatic temperature change (ΔT) approaches 0.86 K under an electric field of 5 kV/mm at 110 °C, which provides experimental evidence for optimizing the ECE near the type–I pseudo–first–order phase transition (PFOPT). Most importantly, a considerable ΔT value can be maintained over a wide temperature range well above the temperature of the PFOPT under a high electric field. In addition, ΔT is closely related to the structural transition and electric field strength. This work provides a guideline to investigate the high ECE in BNT–based ferroelectric ceramics for applications in cooling technologies.

Orientation dependence on piezoelectric properties of Bi0.5Na0.5TiO3-BaTiO3-SrTiO3 epitaxial thin films

Orientation-engineered 0.755(Bi0.5Na0.5)TiO3-0.065BaTiO3-0.18SrTiO3 thin films deposited on Nb doped SrTiO3 (N:STO) single crystalline (001), (110), and (111) substrates via a sol-gel process were investigated. Highly epitaxial growth was observed in the as-deposited thin films. Excellent piezoelectric properties are exhibited by the (111) oriented thin films with the highest strain level (0.32%) and local effective piezoelectric coefficient (d33 = 210 pm/V). Strong orientation dependence of piezoelectric properties on the thin films is attributed to the relative alignment of crystallites and spontaneous polarization vector. These findings are of great significance for piezo-micro electro mechanical systems.

Simultaneously high-energy storage density and responsivity in quasi-hysteresis-free Mn-doped Bi0.5Na0.5TiO3-BaTiO3-(Sr0.7Bi0.2□0.1)TiO3 ergodic relaxor ceramics

ABSTRACT High-energy storage density, responsivity and efficiency, i.e. WR = 1.07 J/cm3, ξ = 119 J/(kV m2) and η = 92%, were simultaneously obtained in Mn-doped 0.62Bi0.5Na0.5TiO3-0.06BaTiO3-0.32(Sr0.7Bi0.2□0.1)TiO3 ergodic relaxor ceramics. Appropriate Mn doping was beneficial to enhance breakdown field strength. Moreover, temperature and different atmosphere-dependent impedance spectroscopy results indicated that oxygen vacancies were the conductivity mechanism for all samples. The valence state of Mn together with the conjugation between Mn ion and oxygen vacancies was confirmed by X-ray photoelectron spectra and electric paramagnetic resonance. The above results indicate that quasi-hysteresis-free loops with high-energy storage performances can be obtained by the induced defect complex. IMPACT STATEMENT High-energy storage density WR = 1.07 J/cm3, responsivity ξ = 119 J/(kV m2) and efficiency η = 92% were simultaneously obtained in quasi-hysteresis-free ceramics by introducing defect complex. GRAPHICAL ABSTRACT

Observation of an unusual optical switching effect in relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3-Pb(Zr0.53,Ti0.47)O3 transparent ceramics

We present an unusual optical switching effect in relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3-Pb(Zr0.53,Ti0.47)O3 transparent ceramics under strong AC electric fields, which is accompanied by a peculiar dielectric response rarely reported previously and attributed to the disruption of the ferroelectric domain structure by the strong AC field. The results provide further understanding on the domain behaviors under electric fields of the relaxor ferroelectrics and the potential for advancing electro-optic applications.

Effect of nonstoichiometric defects on antiparallel domain formation in LiNbO3

The structures of inverted nanodomains in LiNbO3 crystals were investigated using atomic force microscopy (AFM) combined with piezoresponse force microscopy and atomic force acoustic microscopy. The acoustic and AFM topographic images reflected in domain structures with polarization orientation revealed that unexpected antiparallel domains randomly exist in inverted nanodomains in congruent LiNbO3 but not in near-stoichiometric one. The Gibbs free energy change ΔG associating with the internal field Eint in congruent LiNbO3 was discussed. We propose that nonstoichiometric defects, which caused Eint during polarization reversal, play a key role in formation of antiparallel domains in congruent LiNbO3 crystals.

LOCAL ELASTICITY RESPONSE IN FERROELECTRIC CRYSTALS STUDIED BY AFM-BASED NOVEL PROBE TECHNIQUES

ABSTRACT A novel probe technique, low frequency scanning probe acoustic microscope, was firstly developed based on the commercial atomic force microscope. The excitation frequency is in the range of several kHz up to teen-kHz, which is much lower than that in the conventional acoustic microscopes. The acoustic images of nanoscale domain structures in Pb(Mg1/3Nb2/3)O3-33%PbTiO3 single crystals were successfully visualized. Different electric polarizations show the variation of the elasticity in ferroelectrics, so the contrast of the acoustic images reflects the domain structure or the subsurface elasticity. In addition, the elasticity of the sample in response to the modulation of the excitation source is also discussed.

Isolated Domain Structure and Its Polar–Surface Asymmetry of Ferroelectric BaMgF4 Single Crystals

The isolated, six-side polygonal domain structures are observed in the orthorhombic as-grown BaMgF4 single crystal by optical microscope and atomic force microscope. The domain configurations demonstrate highly domain wall anisotropy along one principal crystal axis and polar–surface inhomogeneity. The anisotropic behaviour is due to the anisotropy of domain wall energy density in the thermodynamic equilibrium process, and the asymmetric domain surface phenomena is ascribed to the combined contribution from the local electric fields and structure defects-induced mechanical stress during the domain evolution process.