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Abstract

Morphology and exposed facets control are a hot and challenging topic in the design and synthesis of small-sized materials. Starting by studying the surface structure and surface energy of nanostructures is an important way to achieve this goal. In our experimental work, tetragonal phase LaVO⁴ (t-LaVO⁴) nanocrystals are prepared via the hydrothermal method by tuning the pH of the growth solution. The products are characterized by X-ray diffractometry, transmission electron microscopy, and high-resolution transmission electron microscopy, and the results show that the aspect ratios and exposed facets of the nanocrystals changed with the variation of pH values. By combining the experimental findings, first-principles calculations are used to investigate the effect of surface chemistry on the morphology transformation of t-LaVO⁴ nanocrystals. Equilibrium geometries, surface energies, and surface tensions are calculated for selected low-index surfaces of t-LaVO⁴ under the different surface passivated conditions. The surface energies of (100) and (101) surfaces increase first and then decrease, while the (001) surface decreases monotonously with the fraction of hydrogen in the adsorbates decreased. The equilibrium shapes of t-LaVO⁴ nanocrystals can be obtained according to the Wulff law. Our results indicate that surface energy has an important role to control the morphology and exposed facets of the nanocrystals; the effect of surface chemistry on the morphology of t-LaVO⁴ nanocrystals is obvious, which is consistent with our experimental findings. Besides, a modified Wulff construction model that considers the effect of surface tension is used and draws the same conclusions. Our investigations provide a useful approach to predict and evaluate the effect of surface chemistry on the shape of the nanocrystals, which is for better understanding the shape-controlled nanocrystal growth.