Nanorods, nanowires, and nanotubes of ferroelectric perovskites have recently been studied with increasing intensity due to their potential use in non-volatile ferroelectric random access memory, nano-electromechanical systems, energy-harvesting devices, advanced sensors, and in photocatalysis. This Review summarizes the current status of these 1D nanostructures and gives a critical overview of synthesis routes with emphasis on chemical methods. The ferroelectric and piezoelectric properties of the 1D nanostructures are discussed and possible applications are highlighted. Finally, prospects for future research within this field are outlined.

Novel bur-like hierarchical nanostructures of PbTiO3 were prepared by hydrothermal synthesis. Surfactants containing phenyl-sulfonic groups resulted in self-assembly of nanocrystals. In absence of the surfactant, monodisperse PbTiO3 microspheres were formed. The microspheres were 1−5 μm in diameter, and consisted of ∼20 nm tetragonal PbTiO3 crystals. The microspheres were formed by primary nucleation of PbTiO3 nanocrystals followed by aggregation into microspheres. The hierarchical bur-like nanostructures exhibit a unique geometry consisting of a microsphere core with an outer shell of nanorods. The nanorods, which grow along the [001] direction, were ∼50−100 nm in diameter and from several hundreds of nanometers up to 2 μm in length. A mechanism for the growth of the bur-like nanostructures was proposed. First, agglomeration of PbTiO3 nanocrystals into microspheres occurs. PbTiO3 mesocrystals are formed at the surface of the microspheres by self-assembly of cube-shaped or facetted PbTiO3 nanocrystals, and the mesocrystals ripen and grow further into nanorods.

A molten salt synthesis route, previously reported to yield BaTiO3, PbTiO3, and Na2Ti6O13 nanorods, has been re-examined to elucidate the role of volatile chlorides. A precursor mixture containing barium (or lead) and titanium was annealed in the presence of NaCl at 760 or 820 degrees C. The main products were respectively isometric nanocrystalline BaTiO3 and PbTiO3. Nanorods were also detected, but electron diffraction revealed that the composition of the nanorods was respectively BaTi2O5/BaTi5O11 and Na2Ti6O13 for the two different systems, in contradiction to the previous studies. It was shown that NaCl reacted with BaO (PbO) resulting in loss of volatile BaCl2 (PbCl2) and formation and preferential growth of titanium oxide-rich nanorods instead of the target phase BaTiO3 (or PbTiO3). The molten salt synthesis route may therefore not necessarily yield nanorods of the target ternary oxide as reported previously. In addition, the importance of NaCl(g) for the growth of nanorods below the melting point of NaCl was demonstrated in a special experimental setup, where NaCl and the precursors were physically separated.

La0.58Sr0.4Co0.2Fe0.8O3-d (LSCF) cathodes have been deposited on proton-conducting BaCe0.2Zr0.7Y0.1O3-d (BCZY27) electrolyte and studied in symmetric cells to investigate the cathode microstructure and electro-chemical performance. Three different types of cathodes have been prepared: two prepared from a solution, infiltrated into a screen-printed BZCY27 porous backbone (4 and 12 infiltrations), and one prepared by spray pyrolysis onto a polished electrolyte. In all three cases, LSCF is obtained after annealing at 700°C for 2 h. Analysis of the electrochemical impedance spectra between 450°C and 600°C in air, with varying p(H2O), reveals that the charge transfer contribution is lowest for the backbone-infiltrated cathode while the oxygen dissociation/adsorption contribution is lowest for the spray-pyrolyzed cathode. The area specific resistances increase with the water vapour pressure. The area specific resistances obtained are 0.61 Ω*cm2 and 0.89 Ω*cm2 at 600°C for the spray-pyrolyzed LSCF cell in dry and humidified air, respectively; the corresponding resistances are 0.63 Ω*cm2 and 0.98 Ω*cm2 for the 12 times infiltrated LSCF cell. These resistances are the lowest reported for LSCF cathodes on Ba(Ce,Zr)O3-based electrolytes and show the promise of lowtemperature fabrication methods for these systems. Highlights Low-temperature solution routes for PCFC cathode fabrication are demonstrated  The electrochemical properties are correlated to the cathodes' microstructure

Arrays of ferroelectric lead titanate (PbTiO(3)) nanorods have been grown on a substrate by a novel template-free method. Hydrothermal treatment of an amorphous PbTiO(3) precursor in the presence of a surfactant and PbTiO(3) or SrTiO(3) substrates resulted in the growth of PbTiO(3) nanorod arrays aligned perpendicular to the substrate surface. Two steps in the growth mechanism were demonstrated: first an epitaxial layer was formed on the substrate; this was followed by self-assembly of nanocrystals forming a mesocrystal layer which matured into arrays of PbTiO(3) nanorods.