We report the structural investigations of β-HgS and HgSe quantum dots as a function of temperature between 300 and 600 K using x-ray diffraction. For both the chalcogenides, the zinc-blende structure remains stable up to 600 K without undergoing any phase transformation. The crystallite size increases as a function of temperature. However, for nanocrystallite ～5.0 nm, lattice parameters show reduction in comparison to their bulk values. With increase in temperature, the lattice parameter increases and approaches the equilibrium value as the crystallite sizes grow to more than 10.0 nm. We attribute the temperature induced increase in crystallite size primarily to normal grain growth, a phenomenon observed in crystalline solids when the crystallite size undergoes gradual increase as function of time at elevated temperatures with accompanying recrystallization of new crystallite nuclei, and we rule out the possibility of size-dependent melting.
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