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Solvothermal Synthesis of Lanthanum Hydroxide Nanobelts

In this contribution, we report on the solvothermal synthesis of polycrystalline lanthanum hydroxide nanobelts. The applied synthesis route involved a nonaqueous sol-gel method [1, 2] involving the reaction of lanthanum(III) isopropoxide with a mixture of benzyl alcohol and 2-butanone. The final product of this synthesis approach was La(OH)3 in the form of fine long nanobelts. The Rietveld refinement of XRD powder patterns, transmission electron microscopy (TEM), combined high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analysis were employed for structural characterization of La(OH)3. TEM measurement was performed on a Zeiss EM 912
instrument at an acceleration voltage of 120 kV, while HRTEM characterization was done using a Philips CM200-FEG microscope (200 kV, Cs=1.35 mm) equipped with a field emission gun. A representative TEM image of La(OH)3 is shown in FIG. 1a), where one can clearly see fine long nanobelts, approximately with the lengths of 0.5-10 m and width in the range of 10-80 nm. HRTEM analysis revealed that La(OH)3 nanobelts are highly crystalline. The characteristic HRTEM image of one isolated nanobelt is displayed in FIG. 1b). The width of selected nanobelt is around 24 nm. The (101) and (002) lattice planes are resolved from the Fourier transform (FT) of selected La(OH)3 crystal, which is shown in FIG. 1c). By analyzing the FT image, we concluded that the investigated crystal is oriented in [010] zone axes. The XRD powder pattern of La(OH)3 is shown in FIG. 1d), where the strong Bragg reflections are denoted with corresponding Miller indices. The Rietveld refinement of XRD pattern gave us structural information of as-synthesized La(OH)3. The crystal structure was refined in the space group P63/m (176), hexagonal crystal system with refined values of unit-cell parameters: a=0.6528 nm, and c=0.3852 nm. The strong preferred orientation was observed in [201] direction. From EDX spectrum shown in FIG. 1e), the presence of constitutive elements, La and O was corroborated at investigated spots of La(OH)3 nanobelts. The lines corresponding to Cu originated from an inelastic electron scattering onto copper grid.

Nanobelts; Solvothermal synthesis; Electron microscopy

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