Rare earth oxides/hydroxides are important emerging materials owing to their unique properties. Shape-controlled synthesis of elongated hexagonal bipyramid shaped La(OH)₃ nanorods with different aspect ratios and trigram-shaped LaCO₃OH nanosheets was systematically carried out by controlling the reaction conditions. Hydrazine and polyvinylpyrrolidone (PVP) surfactants used in synthesis are assumed to play a key "dual-template" role in determining the aspect ratio and shape of the resulting nanostructures. Elongated hexagonal bipyramid shaped La(OH)₃ nanorods were found to grow along the preferred orientation [0001]. Six equivalent crystallographic facets, $(20\overline{2}0),(02\overline{2}0),(2\overline{2}00),$ $(0\overline{2}20),(\overline{2}200),\text{and}(\overline{2}020)$ lattice planes, were found to be exposed on the side surfaces on each nanorod as confirmed by combined transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) analyses. A double-polarization phenomenon was found to occur at the nanorod surfaces by employing off-axis electron holography, implying that the material could be used as an effective dielectric microwave absorber. La(OH)₃ nanorods with larger aspect ratios exhibit better absorption properties with respect to the maximum reflection loss and effective absorbing bandwidth. Thus, a novel method towards the reasonable design of bipyramid shaped La(OH)₃ nanorods exhibiting tunable microwave absorption properties is proposed based on our synthesis strategy.

FullText for HTML:https://doi.org/10.1007/s12274-016-1142-6