Structural and optical characteristics of pre- and post-annealed sol-gel derived CoCu-oxide coatings

Abstract

Sol-gel derived CuCo-oxide coatings as solar selective surfaces, synthesized onto aluminium substrates at various annealing temperatures, are analysed by correlating their structural, chemical bonding states, and surface morphological topographies. As the annealing progressed, all the coatings displayed a Cu 0.56 Co 2.44 O 4 (ICSD 78-2175) phase with preferential orientation along (400) reflection plane. Rietveld refinement of X-ray diffraction (XRD) data indicate that residual stress and microstrains developed around the coating surfaces are reduced resulting in mechanically stable thin films. Enhancement of the crystallite size and preferred orientation of the surface were confirmed via XRD, field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM) analysis. X-ray photoelectron spectroscopy (XPS) analysis shows tetrahedral, octahedral and mixed states of Cu and Co ions with a stable atomic ratio of Co/Cu, and an increase of O and C contents but no metal-carbon bonding on the surface of materials. Optical reflectance investigations indicated that solar selectivity of the coatings increased from 3.81 to 24 as the annealing temperature reached up to 500 °C.

Investigation of the post-annealing electromagnetic response of Cu–Co oxide coatings via optical measurement and computational modelling

“…These parameters are consistent with that obtained from our previous X-ray diffraction study: a ¼ 8.09Å. 27 In the current cluster model of Cu 0.5 Co 2.5 O 4 , there are 4 Cu, 20 Co and 32 O atoms. The crystal structure was optimized and is shown in Fig.…”

“…First-principles calculation is one of the most promising approaches to predict the ground state properties of a material. The XRD results from Miran et al 27 revealed that the adopted phase for this coating material, as annealing temperature progress within the same range of temperatures is, Cu 0.56 Co 2.44 O 4 . The Cu 0.5 Co 2.5 O 4 system was dealt with the level of density functional theory (DFT+U) proposed by Dudarev et al 28 as implemented in the Cambridge Serial Total Energy Package (CASTEP) 29,30 of Material Studio.…”

“…Structural and morphological analyses of these coatings carried out via XRD, XPS, FESEM and AFM spectroscopic methods, before annealing and aer annealing, were reported in our most recent studies. 27 Before annealing the CuCo-oxide coatings, FESEM showed mould-like structures. However aer thermal treatment homogeneously distributed particles with compact and smooth morphologies were observed.…”

“…Annealing results in the occurrence of major grain growth around the coating surface. 27 XRD studies attributed that the Cu-Co oxide coatings possesses the cubic symmetry consisting of Cu Fig. 1 shows the spinel structure of Cu-Co oxide system drawn using GaussView 5.0.8 soware.…”

A holistic analysis of surface, chemical bonding states and mechanical properties of sol-gel synthesized CoZn-oxide coatings complemented by finite element modeling

“…The three key parameters namely, the mean surface roughness, R a , rms value of surface roughness, R q , and z scale were estimated from the AFM micrographs. The mean surface roughness, R a of a thin film materials can be calculated using [50],…”