Structural and Optical Studies on Strontium-Filled CoSb₃ Nanoparticles Via a Solvo-/Hydrothermal Method

In the present work, strontium-filled CoSb₃ nanoparticles (Sr_yCoSb₃, y = 0, 0.025, 0.05, 0.075 and 0.1) were synthesized by a solvo-/hydrothermal method. Powder x-ray diffraction (pXRD) analysis reveals a cubic phase of CoSb₃ with space group Im \( \bar{3} \). The Sr-filled samples show a slight peak shift and broadening of the high-intensity peak at 31.2491° corresponding to the (013) plane which can be attributed to the interaction of Sr atoms filled into voids of the CoSb₃ cage-like structure with some of the lattice vibrations in the structure. Field emission scanning electron microscopy (FESEM) images show as-synthesized nanoparticles in the range of 50–160 nm, and energy-dispersive x-ray spectroscopy (EDX) analysis reveals the chemical composition of Sr-filled CoSb₃. Fourier transform infrared spectroscopy (FTIR) studies confirm vibrational modes below 1000 cm⁻¹ corresponding to Co-Sb and cobalt complexes in both filled and unfilled CoSb₃ nanoparticles. UV–Vis absorption analysis indicates a peak shift towards the longer-wavelength region (redshift) and a decrease in the optical band gap as a function of the increase in Sr filling concentration. This can be considered strong evidence for successful filling of voids in the cage-like structure of CoSb₃ by strontium.