Anisotropic Broadening of Diffraction Peaks of Metallic Cobalt: Determining Parameters of a Nanoheterogeneous Domain Structure

Abstract

The disordered structure of metallic cobalt nanoparticles prepared by the in situ Co₃O₄ and Co_2.95Al_0.05O₄ reduction at different temperatures is characterized. According to the transmission electron microscopy data, individual particles have a stripe contrast indicating that they consist of plate-like domains with different structures. The main feature of the recorded XRD patterns is the anisotropic peak broadening. The Rietveld analysis shows that the model represented by homogeneous particles with hcp and/or fcc structures does not agree well with the experiment. The XRD patterns calculated using statistical models of 1D disordered crystals show that metallic cobalt particles are heterogeneous and consist of plate-like domains with hcp and fcc structures. The dependences of diffraction peak parameters on the thickness of two types of domains are determined; the corresponding calibration graphs are constructed. The phase composition and domain structure parameters are determined as functions of temperature for two series of metallic particles.