Grain oriented lead-free piezoelectric 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 (NBT-7BT) were fabricated by templated grain growth (TGG) method using single-crystalline NBT-7BT platelets with a morphotropical phase boundary (MPB) as templates. The NBT-7BT templates were synthesized by the topochemical technique, using Na0.5Bi4.5Ti4O15 (NBIT) platelets as precursors. The grain oriented NBT-7BT ceramics were textured with 10 wt% of NBT-7BT templates and sintered at 1175 °C for 5–50 h. The microstructure, strain behavior and temperature-dependent permittivity of lead-free NBT-7BT ceramics were systematically investigated. The strain responses of the grain oriented NBT-7BT ceramics were found to increase monotonously with the increase of the grain orientation degree. The NBT-7BT ceramic with 89% degree of grain orientation had an excellent actuating performance with up to 0.7% free strain at 7 kV/mm at room temperature, corresponding to a field-induced Smax/Emax of as high as 1000 pm/V.

In this study, a relaxor ferroelectric ceramic, 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMN–PT), was synthesized by a molten-salt growth method with lower remnant polarization and slimmer hysteresis loops than traditional ferroelectric ceramics. The PMN–PT particles remained homogeneously dispersed in the composite and adhered tightly to a poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix due to the modification of the particles with dopamine. The composites had a maximum dielectric constant of 65.1 and a low dielectric loss of less than 0.037 at 1 kHz. Due to the low remnant polarization of the relaxor ferroelectric ceramic of PMN–PT, the energy density of the composites significantly increased. The discharged energy density of the sample with 50 vol% PMN–PT was 4 times that of P(VDF-HFP) at 80 kV mm−1. It was demonstrated that the dopamine functionalized PMN–PT/P(VDF-HFP) composite was a potential dielectric material with potential future applications in energy storage.

Cost-effective electrocatalysts based on nonprecious metals for efficient water splitting are crucial for various technological applications represented by fuel cell. Here, 3d transition metal layered double hydroxides (LDHs) with varied contents of Ni and Fe were successfully synthesized through a homogeneous precipitation. The exfoliated Ni–Fe LDH nanosheets were heteroassembled with graphene oxide (GO) as well as reduced graphene oxide (rGO) into superlattice-like hybrids, in which two kinds of oppositely charged nanosheets are stacked face-to-face in alternating sequence. Heterostructured composites of Ni2/3Fe1/3 LDH nanosheets and GO (Ni2/3Fe1/3-GO) exhibited an excellent oxygen evolution reaction (OER) efficiency with a small overpotential of about 0.23 V and Tafel slope of 42 mV/decade. The activity was further improved via the combination of Ni2/3Fe1/3 LDH nanosheets with more conductive rGO (Ni2/3Fe1/3-rGO) to achieve an overpotential as low as 0.21 V and Tafel plot of 40 mV/decade. The catalytic activity was enhanced with an increased Fe content in the bimetallic Ni–Fe system. Moreover, the composite catalysts were found to be effective for hydrogen evolution reaction. An electrolyzer cell powered by a single AA battery of 1.5 V was demonstrated by using the bifunctional catalysts.Keywords: graphene; heteroassembly; layered double hydroxide; nonprecious metal catalyst; water splitting;

Titanium dioxide sols were synthesized by hydrothermal reactions with addition of poly (ethylene glycol) (Mw = 20,000). Using techniques of X-ray diffraction, transmission electron microscopy, dynamic light scattering, and scanning electron microscopy, effect of PEG on the crystallographic properties, particle size, aggregating behavior, and the morphological properties of nanoparticles in the sols were studied. It was found that growth of anatase nanocrystallites was retarded by PEG. Average crystallite size of anatase nanocrystallites first decreased from 20.7 nm to 10.5 nm as the polymer concentration increased from 1 g/L to 3 g/L, and then changed little. Meanwhile, small amount of rutile phases like rutile nanowires, twin crystallites, and the “flowers” appeared continuously when the concentration increased from 3 g/L to 5 g/L. Mono-dispersion was obtained with relatively lower PEG concentration. The observed evolvement was discussed based on the interaction between the polymers and the nanocrystallites with assistance of FTIR. The coverage of polymer chains on surface of nanocrystallites leads to isolated reactors, which benefits the uniform coarsening rate of the nanocrystallites. The synthesized TiO2 sols were utilized in dye sensitized solar cells. Performance parameters of the solar cells were discussed with assistance of dye desorption experiments. The improved dispersion in sols was found to benefit the photovoltaic performance of the cells.Graphical abstractHighlights► We examine the effect of PEG on particle growth dynamics of TiO2 sols. ► Growth of anatase particles is retarded, while that of rutile is favored. ► The synthesized TiO2 sols are utilized in dye sensitized solar cells. ► Low concentration of PEG benefits the performance parameters of the solar cells.