Per Martin Rørvik

One‐Dimensional Nanostructures of Ferroelectric Perovskites

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.

Influence of Volatile Chlorides on the Molten Salt Synthesis of Ternary Oxide Nanorods and Nanoparticles

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.

PbTiO3 nanorod arrays grown by self-assembly of nanocrystals

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.

Coated wooden claddings and the influence of nanoparticles on the weathering performance

Accelerated climate aging experiments and cup measurements have been performed to investigate the effect of adding TiO2 nanoparticles and nanoclay to acrylic stain coatings against the influence of weathering. The coated specimens resistance toward solar radiation and water spray was evaluated by the discoloration rate from visual assessment and color analysis and by the chemical changes observed by Fourier transform infrared spectroscopy. Furthermore water vapor resistance was examined by the cup measurements. The nanomaterial containing coatings provided in general better protection against the artificial aging than the unmodified coating, showing the nanomaterials may have a natural place in coatings for protection of wood.

Polarization control in ferroelectric PbTiO3 nanorods

In this work we demonstrate by transmission electron microscopy and piezoresponse force spectroscopy that the polarization direction in hydrothermally synthesized lead titanate (PbTiO3) nanorods can be changed from parallel to the nanorod axis to perpendicular to it by a simple heat treatment above the Curie temperature. The heat treatment also introduced 90° domains, caused a rearrangement of the surface and a reduction in the amounts of defects. The polarization of the heat-treated nanorods could be successively switched in the direction perpendicular to the nanorod axis. This control of the polarization in PbTiO3 nanorods opens up possibilities of tailoring the ferroelectric properties and is therefore highly relevant for the use of ferroelectric nanorods in devices.

Impregnated wooden claddings and the influence of nanoparticles on the weathering performance

Abstract This work was an investigation of the effect of nanoparticles on the durability of wood specimens exposed to artificial weathering. TiO2 and clay nanoparticles were mixed with preservative (Wolmanit CX-8) for improving the durability of Norway spruce (Picea abies). Impregnated and untreated specimens were subjected to Atlas Solar Simulator accelerated ageing test chamber for solar radiation and water spray exposure. The effectiveness of the treatment against colour and chemical changes was investigated using CIEL*a*b* colour measurements system and Fourier transform infrared analysis. The present study showed that the wood specimens that had been treated with preservatives containing nanoparticles were slightly more stable against artificial ageing than both untreated specimens and specimens treated with preservative alone.

Detailed TEM characterization of PbTiO3 nanorods

1D functional oxides at nm-scale are interesting for fundamental reasons and promising for future applications. Here, ferroelectric PbTiO3 nanorods, produced through a hydrothermal process, have been studied in detail by transmission electron microscopy. The length (up to one μm) and the diameter (30–100 nm) as well as the growth direction ([001]) of the nanorods could easily be determined using conventional imaging and electron diffraction techniques. However, variations along the length of the rods were clearly visible in the bright field images. Steps on the outer surfaces of the rods could be identified using energy filtered transmission electron microscopy and spectrum imaging thickness maps. The thickness variation parallel to the electron beam affected the bright field contrast and energy dispersive spectroscopy of the nanorods. From cross-sectional specimens, it was determined that the outer surfaces of the rods were dominantly {110} type, leading to a rectangular cross-section. The cross section diameter of the rods was reduced by the introduction of {100} surfaces. In addition, the cross-sectioned specimen revealed the presence of internal channels in the growth direction, especially in the bottom part of the rods. Such a detailed structural description of the nanorods was necessary to study the possible ferroelectric domain structure and to reveal the growth mechanism of the rods.