Tuning the crystal shape of materials by chemical potential: a combined theoretical and experimental study for NiSe2

Abstract

Understanding and controlling the shape of materials has attracted considerable attention over the past few decades. Taking a typical transition metal chalcogenide NiSe₂ as an example, we have figured out the role of chemical potential in the equilibrium shape of materials by a combined theoretical and experimental study. The theoretical equilibrium shape evolution of NiSe₂ with chemical potential has been investigated using ab initio atomistic thermodynamics and Wulff construction. Moreover, in order to confirm our theoretical results, a series of NiSe₂ crystals with different morphologies were also synthesized via a solvothermal route in mixed solvents of hydrazine hydrate, ethylenediamine and reactant. X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM) were used to analyze the products. Our results indicated that the theoretical equilibrium shapes of NiSe₂ change from pyritohedron enclosed by (210) facet, truncated octahedron to perfect octahedron occupied by (111) facet, which agrees with the experimental shapes of NiSe₂ synthesized with different volume ratios of mixed solvents. The present theory and experimental work indicates that controlling the chemical potential is a general and efficient way to tailor the shape of materials.