Phase transitions in cadmium sulfide nanoparticles

CdS nanoparticles were synthesized by the microwave assisted chemical precipitation method and solvothermal method. X-ray power diffraction, scanning electron microscopy, and transmission electron microscopy were employed to characterize the crystalline structure, morphology, and size of the synthesized samples. X-ray diffraction studies reveal that the synthesized samples are of two different forms, cubic and hexagonal. The DC electrical resistance of the two samples was measured in the temperature range 300-500 K. Near room temperature cubic nanoparticles behave as a semiconductor, and hexagonal nanoparticles show the behavior of an insulator. The temperature resistance curves of the cubic sample show a transition from the cubic to hexagonal phase above 340 K. The temperature resistance curve of the hexagonal sample also shows a discontinuity at 463 K due to the transition from the hexagonal to cubic phase. The thermogravimetric analysis of the two samples also confirms the two transitions. UV, PL, and Raman spectra of the two forms are compared.