Vibrational spectroscopic studies on crystallisation of sol–gel derived thin films of calcia–alumina binary compound

Abstract

Abstract:An optimized sol-gel process has now been developed to produce homogeneous thin films of calcium aluminate binary 12CaO.7Al2O3 compound, 12CaO.7Al2O3, on magnesium oxide substrates via spin coating. Fourier transform infrared (FTIR) and Raman spectroscopies have been employed to investigate the effect of annealing temperature and duration on the phase transformations in the films. Heat treatment at 13000C under air atmosphere for 2 hours produced single-phase 12CaO.7Al2O3 films. However, annealing at a lower temperature of 11000C in air for a period of 4 hours in total resulted in the crystallization of 5CaO.3Al2O3 rather than 12CaO.7Al2O3. The Xray photoelectron spectrum of the thin film annealed at 13000C corresponds to the binding energies of C12A7 compound. The annealing temperature of 13000C for 2 hours is found to be sufficient for formulating single phase calcia-alumina binary films in correct stoichiometric ratio of 12:7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 While the fabrication of C12A7 single crystal and polycrystalline bulk has been studied extensively during the last few years, studies on the fabrication of C12A7 thin films are rather limited. The thin film fabrication techniques include pulsed laser deposition and sol-gel method, and magnesium oxide (MgO) single crystal is used as the substrate. A heat treatment temperature of 1100 o C in air atmosphere has been suggested for the crystallization of amorphous thin films prepared via pulsed laser deposition [7,8], while this temperature is mentioned to be too low for the crystallization of the sol-gel derived films [9]. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems CorporationThe fabrication of C12A7 thin films via sol-gel technique has been previously reported employing ethyl acetoacetate (EAA) and aluminium sec-butoxide (ASB) as a chelating agent and the main precursor of aluminium oxide, respectively in the molar ratio of 1:1 in an ethanol solvent.Hydrochloric acid (HCl) was used as the pH regulator [10,11]. However, our initial attempt in the deposition of C12A7 thin films on the MgO substrates using this recipe resulted in the formation of discontinuous films with dendritic growth behaviour. Therefore, the solution recipe was modified in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 order to increase the homogeneity and continuity of the films. Highly stable spreading solutions for spin coating were obtained using the modified recipe without the need for the addition of acid. This article presents the Fourier transform infrared (FTIR) and Raman spectroscopy investigations into the effect of heat treatm...

High temperature optical absorption investigation into the electronic transitions in sol–gel derived C12A7 thin films

“…Thin films were prepared via spin coating on magnesium oxide (MgO) single crystal substrates and subsequent isothermal annealing at 1300°C was performed for 2 h under air atmosphere in order to obtain a singlephase crystalline structure. The details of the sample preparation are given in our previous publication [21]. The thickness of the films on MgO substrates were measured by means of a Dektak 150 surface profiler.…”

“…Using EAA as a chelating agent with aluminium secbutoxide (ASB) in the spreading solution, we have successfully deposited high quality 5-6 lm thick C12A7 thin films on magnesium oxide (MgO) single crystal substrates by spin coating method. Vibrational spectroscopic measurements showed the formation of a single-phase C12A7 film when as-deposited film was annealed at 1300°C and the heat treatment duration had no significant effect on the formation of calcium aluminate phases [21]. The present article reports the optical absorption properties of sol-gel derived C12A7 thin films and the effect of temperature on optical parameters, such as band gap energy, Urbach energy and steepness parameter have been examined in terms of relevant physical models.…”

Extraction of the optical parameters of sol–gel processed 12CaO·7Al2O3 thin film for optoelectronic applications

“…The films were applied on magnesium oxide single crystal (100) via spin coating. The details of solution preparation and sol-gel method are explained elsewhere [12]. A post-deposition annealing treatment of 1300°C for 2 h was performed to produce crystalline C12A7 films.…”

“…We have previously reported the successful production of C12A7 thin films with main focus on the production of high quality continuous films via sol-gel method [12]. This film processing technique is known to be simple and cost effective.…”

Applicability of Time-Gated Raman Spectroscopy in the Characterisation of Calcium-Aluminate Inclusions

“…[20][21][22][23][24] Furthermore, steel is not Raman active, which means that the Raman spectra measured from steel samples originate from the inclusions in the steel. Previous studies have used Raman spectroscopy to distinguish different calcium aluminate phases [25][26][27][28][29] and for specific inclusions characterisations. [30][31][32] The previous works have mainly focused on the characterisation of individual phases, but binary calcium aluminate phases have not been quantified.…”