Single Crystal of Lanthanum Hydroxide La（OH）3： Controlled Synthesis by High Pressure Flux Method and Its Growth Mechanism

High pressure synthesis of solid material tends to increase the density, coordination number, symmetry of material and shorten bond length. The solid synthesized at a high pressure and decompressed to ambient pressure often exhibits a meta- stable ＂stretched＂ state, within the high pressure stability field. The crystal grown at a high pressure is of great importance with the development of high pressure technology. Crystal growth is an important factor in the material synthesis. And many me- thods including gas, solid and solution methods have been used to obtain various single crystalstl]. Especially, flux method is an important method for crystal growth, where the components of the desired substance dissolved in a solvent（flux） grow in the process of deposit.

Preparation of La(OH)_3 and La_2O_3 with Rod Morphology by Simple Hydration of La_2O_3

Lanthanum hydroxide with rod-like morphology was synthesized with simple hydration processing via the hydration of its bulk oxide in normal water solution at boiling temperature. An XRD pattern shows the formation of the hexagonal phase of La（OH）3, indicating that the hydration process is very rapid. The as-prepared La（OH）3 is almost entirely with a needle- or rod-like shape with a width of 2 - 3 μm and a length of 5 - 8 μm. The mechanism of the formation of La（OH）3 with rod-like morphology was preliminarily presented. It is easier to expand the simple hydration process on a large scale than the hydrothermal process.

LaO_(x)(OH)_(y) supported platinum catalysts for CO oxidation:Deactivation by formation of lanthanum carbonate

Platinum catalyst for CO oxidation has been studied for decades,due to its high activity and good stability.In this work,we prepared three different lantha num oxide or hydroxide supports(LaO_(x)(OH)_(y)),and deposited platinum(Pt) with 0.5 at% via an impregnation approach to synthesize Pt/LaO_(x)(OH)_(y) catalysts.However,we find that these catalysts perform a poor stability for the CO oxidation reaction.The fresh and used samples were comprehensively characterized by multiple techniques including power X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),transmission electron microscopy(TEM),temperature-programmed reduction by carbon monoxide(CO-TPR) and thermogravimetric analysis(TGA),to demonstrate that the oxidized platinum atoms or clusters,without any component of Pt-Pt metallic bond,are highly dispersed on the surface of LaO_(x)(OH)_(y).Furthermore,the as-formed lanthanum carbonate(La_(2)O_(2)CO_(3)) during the exposure to ambient circumstances or in the reaction atmosphere of CO+O_(2),severely impair the reactivity of Pt/LaO_(x)(OH)_(y).On the basis of the obtained experimental results,we have drawn a conclusion that the oxidized P_(t)O_(x) atoms or PtxOy clusters are the active species for CO oxidation,while the formation of lanthanum carbonate is the origin of deactivation on reactivity.

A controllable hydrothermal method to prepare La(OH)_3 nanorods using new precursors

Using the hydrothermal method, lanthanum hydroxide nanorods were synthesized by the reaction of LaC13·7H20, ethyl- enediamine, and hydrazine. According to SEM results, ethylenediamine and hydrazine with pH management could control the parti- cle growth and played an important role in formation of lanthanum hydroxide nanorods. The morphology and microstructure of the obtained products were characterized by X-ray diffraction （XRD） spectra, energy-dispersive X-ray spectroscopy （EDX）, Fourier transformed infi＇ared （FTIR） spectrum, transmission electron microscopy （TEM）, and scanning electron microscopy （SEM）. Further- more, the effects of the molar ratio of the precursors as well as the reaction temperature and time on the morphology and particle size of the products were investigated.

Controllable synthesis of elongated hexagonal bipyramid shaped La(OH)3 nanorods and the distribution of electric property by off-axis electron holography

Rare earth oxides/hydroxides are important emerging materials owing to their unique properties. Shape-controlled synthesis of elongated hexagonal bipyramid shaped La(OH)3nanorods 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)3nanorods were found to grow along the preferred orientation [0001]. Six equivalent crystallographic facets, (Formula presented.), and (Formula presented.) 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)3nanorods 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)3nanorods exhibiting tunable microwave absorption properties is proposed based on our synthesis strategy. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.