Indian Journal of Engineering & Materials Sciences Vol. 19, June 2012, pp. 196-198
Characterisation of BiFeO3 synthesised by microcontroller based thermogravimetric analyser P H Sureshaa*, Ramania, M C Radhakrishnaa, Basavaraj Angadia & J T Devarajb a
Department of Physics, bDepartment of Electronic Science, Bangalore University, Bangalore 560 056, India Received 31 October 2011; accepted 8 May 2012
Microcontroller based thermogravimetric analyser (MTGA) is a home built technique extensively used to study the thermal decomposition of inorganic solids and preparation of nanomaterials. This paper reports the characterization of bismuth ferrite BiFeO3 (BFO) synthesized by microcontroller based thermogravimetric analyser. The synthesized nanopowder is characterized by X-ray diffraction (XRD) method for phase confirmation, crystallite size calculations and scanning electron microscope (SEM) for morphology study. The structure and thermal properties of BFO precursor are studied by using Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The results of nano BiFeO3 synthesized by microcontroller based TGA are in good agreement with that synthesized by other techniques. Keywords: Microcontroller, Multiferroics, Peroskite, Nanoparticles, Cathetometer, Crystallites
Microcontroller based thermogravimetric analyzer1 (MTGA) is a home built synthesis technique. This can be used to study the decomposition or gassolid reaction in different gas atmospheres and the preparation of nano materials. The thermogram (graph of mass loss versus temperature) obtained from MTGA provides the valuable information about the reaction mechanism, kinetic parameters and stages of the reaction taking place in time or temperature sequence. The above synthesis technique also used to find the synthetic conditions for the material preparation and also to identify the ignition temperature of redox mixture (precursor) used in the different synthesis techniques. This paper reports the characterization of multiferroics BiFeO3 synthesized by a home built microcontroller based thermogravimetric analyser. The microcontroller based thermogravimetric analyzer1 consists of thermobalance, furnace, IR-grating assembly, microcontroller assembly and personal computer. Experimental Procedure
The nano sized bismuth ferrite oxide with a nominal formula BiFeO3 were prepared by Microcontroller based thermogravimetric analyzer using respective metal nitrates as oxidiser and glycene as fuel. The materials employed were iron nitrate-Fe (NO3)3.9H2O (Merck) bismuth nitrate-Bi(NO3)3.6H2O ———————— *Corresponding author (E-mail:
[email protected] )
(Merck) and glycene- C2H5NO2 (Merck) The compositions of metal nitrate and glycene were ground and it was taken in the sample bucket of MTGA and was heated in air at a rate of 4°C/min from room temperature to 700°C. The contraction of spiral spring of MTGA1 due to variation in mass was recorded for every 5°C rise of temperature using cathetometer (least count=0.001 cm). The voluminous foamy product was obtained and it was ground and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), diffrential thermal analysis (DTA) and scanning electron microscope (SEM). Results and discussion Thermal analysis
The variation in mass of redox (nitrates and gylcene) mixture with respect to temperature (thermogram) is as shown in the Fig. 1. The thermal studies describe the existence of two decomposition stages. The first one starts from 100-250°C being characterized by high mass loss (40%)2. This decomposition consists of initial weak endothermic effect representing water evaporation, followed by a fast intensive exothermic process consisting simultaneous evolution of NO3and glycene. The second stage decomposition (340-400°C) accompanied by a medium exothermic effect and very low mass loss represents the burning up of remaining carbaneous matter. This result
SURESHA et al.: MICROCONTROLLER BASED THEMOGRAVIMETRIC ANALYSER
indicates that the ignition temperature for the synthesis of nano size BFO is in between 100-400°C. The MTGA system has been calibrated for BFO precursors the thermogram results obtained in Fig. 1 are in good agreement with the results which are published earlier for the same sample3-5. The observed DTA curve (Fig. 2) displays two high exothermic peaks between 200-400°C. The first exothermic sharp peak at 200-250°C results from the removal of organic matter6. The effects at 370°C is assumed to be related to the Neel temperature of BFO corresponding to the magnetic phase transition of BFO4. Structural analysis
The XRD pattern (Fig. 3) of the as prepared BFO nano-powder by microcontroller based TGA reveals that, BFO obtained at low temperature belongs to rhombohedral distorted perovskite structure according to JCPDS. The pattern also shows the presence of secondary phase, as evident by a peak at 28°.
Fig. 1—Thermogram of BFO precursor
Fig. 2—Diffrential thermal analysis of BFO precursor
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The same type of graph (Fig. 4) is obtained for BFO synthesized by combustion technique at different temperatures. The intensity of secondary phase at 28° peak is highest for the samples prepared at lower combustion temperature 350°C and decreases with the increase of combustion temperature 400°C. The crystallite size were determined from FWHM of the (010) diffraction peak at 2θ=22.5° for all samples using Scherrer's equation. The crystallite size was found to be nano metric range, i.e., 20-30 nm. The average crystallite size is found to be 25 nm and it increases with the increase of combustion temperature. It can be noticed that cell parameters decreases and crystallite size increases with temperature treatments6.
Fig. 3—XRD pattern of BFO nano powder synthesized by Miccontroller based TGA
Fig. 4—X-ray diffraction pattern of BFO nano powder synthesized at 350°C and 400°C by combustion method
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nitrates while band at 1630 cm-1 corresponds to the bending vibrations of H2O7. Microstructure studies
The SEM image Fig. 6 shows particle aggregates of the BFO nano particles prepared by MTGA. The image shows high tendency of agglomeration with a non-homogeneous morphology and the powders are strongly inter connected in a kind of three-dimensional, porous skeleton structure similar to the structure of foams8.
Fig. 5—Room temperature FTIR spectrum of BFO nano powder synthesized by MTGA
Conclusions The multiferroics BFO was synthesized by a home built microcontroller based TGA. The results obtained from XRD graph of BFO synthesized by MTGA and other techniques (combustion method, sol-gel method etc) are similar. The thermal studies (TGA, DTA) reveal the ideal conditions for the preparations of nano sized bismuth ferrite. The endothermic peak at 370°C in DTA spectrum reveals the antiferromagnetic phase transformation in BFO. The formation of peroskite structure can be confirmed by the presence of metal-oxygen bond in FTIR spectrum of BFO. The microstructure shows high tendency of agglomeration, non-homogenous morphology. The results reported above are in good agreement with the that of nano BFO synthesized by other techniques. So microcontroller based thermogravimetric analyser (MTGA) is one of the sysnthesis techniques for the preparation of nano materials. References
Fig. 6—Scanning electron microscope image of BFO nano powder synthesized by MTGA
1. 2.
The FTIR spectrum of nanopowder BFO is shown in Fig. 5. The strong absorption peaks at 400-600 cm-1 are attribute to the Fe-O stretching and bending vibrations, bring the characteristics of the octahedral characterstic FeO6 group in the peroskite compounds. The formation of peroskite structure can be confirmed by the presence of metal-oxygen bond. The band at around 1380 cm-1 arose due to the presence of trapped
3. 4. 5. 6. 7. 8.
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