Studying Effect of Fe Doping on the Structural Properties and Infrared Spectroscopy of Tin Oxide powders by Solid State Reaction Method

Fe doped tin oxide transparent conducting powder were prepared by solid state reaction method. Structural properties of the samples were investigated as a function of various Fe-doping levels (x=0.00-0.01-0.03-0.05-0.06). The results of x-ray diffraction have shown that the samples are polycrystalline structure in tetragonal phase with preferential orientations along the (110) for all samples The relative intensities, distance between crystalline planes (d), crystallite size (D), dislocation density (ẟ) and lattice parameters (a), (c) were determined. Infrared Spectroscopy have been studied by Infrared Spectrometer Device. Keywords : powder, Iron doped Tin Oxide, solid state reaction, Structural properties, Infrared Spectroscopy. DOI : 10.7176/CMR/11-4-01 Publication date : April 30 th 2019


Introduction
Transparent conducting oxides (TCOs) are semiconductors that are produced from a combination of metal and oxygen such as: ZnO, In2O3, SnO2. The studying of TCOs is very important because of their special properties that is used in technology applications [1].
Tin oxide (SnO2) is considered as one of the most important member of the TCOs for its unique electrical and optical properties because it has low electrical resistivity, high optical transparency in visible region, high optical reflectance in infrared region and chemical inertness. So, SnO2 is used in solar cells, sensor gas, display devices and in other important applications [2].
SnO2 is an n-type semiconductor with wide band gap energy (Eg = 3.5-4 eV) [3]. SnO2 has tetragonal structure belonging to the P42/mnm space group. The lattice parameters are a = b = 4.7382 and c = 3.1871 A [4]. Its unit cell contains two tin and four oxygen atoms as is shown in figure 1. The tin atom is at the center of six oxygen atoms placed at the corners of a regular octahedron. Every oxygen atom is surrounded by three tin atoms at the corners of an equilateral triangle [5,6].

.Experimental Method
Sn1-xFexO2 powders (x = 0.00.0.01,0.03, 0.05, 0.06) were prepared by a solid state reaction method. were accurately weighed in required proportions and were mixed and ground thoroughly using an Agate mortar and pestle to convert to very fine powders. The grinding of the mixtures was carried out for 3 hours for all the powder samples. The ground powder samples were firing at 700°C for 3 hours.  2d.sinθ = nλ (1) Where d is distance between crystalline planes (A), θ is the Bragg angle, λ is the wavelength of X-rays (λ=1.54056 A). The crystallite size is calculated from Scherrer's equation [7]: (2) Where, D is the crystallite size, λ is the wavelength of X-ray, ẞ is full width at half maximum (FWHM) intensity in radians and θ is Braggs's angle.
The dislocation density is defined as the length of dislocation lines per unit volume and calculated by following equation [2]: (3) The lattice constants a and c for tetragonal phase structure are determined by the relation [8]: (4) Where d and (hkl) are distance between crystalline planes and Miller indices, respectively. The calculated lattice constants a, c values are given in table 1,2,3. It was seen that a, c and c/a match well with JCPDS data ( a=b= 4.737 A and c= 3.185 A). The change in peak intensities is basically due to the replacement of Sn 4+ ions with Fe 3+ ions in the lattice of the SnO2. This process leads to the movement of Sn 4+ ions in interstitial sites. Figure 3 represents variation of the average grain size with different concentrations of Fe doped SnO2 powdres. We observed from tables 1,2,3 that 6 wt% Fe doped SnO2 is the closest value to undoped sample. , (e) 6 wt% Fe doped SnO2 FTIR is a technique used to obtain information regarding chemical bonding and functional groups in a material. In the transmission mode, it is quite useful to predict the presence of certain functional groups which are adsorbed at certain frequencies; thus, it reveals the structure of the material. The band positions and numbers of absorption peaks depend on the crystalline structure, chemical composition, and also on morphology [9]. To investigate chemical groups on the surface of sintered samples, an FTIR analysis was carried out at room temperature over the wave number range of 400-4000 cm -1 . There are several bands appearing in the wave number range 400-4000 cm -1 . The broad absorption band at 3423 cm -1 , the peaks at 2977 cm -1 , and 1630 cm -1 are assigned to the vibration of hydroxyl group due to the absorbed/adsorbed water and show a stretching vibrational mode of O-H group [10]. Absorption peaks observed around 2380 cm -1 belong to the stretching vibrations of C-H bonds that could be due to the adsorption and interaction of atmospheric carbon dioxide with water during the firing process [11]. The bands observed in the range of 970-700 cm -1 are due to the vibration of Sn=O and Sn-O surface cation oxygen bonds [10]. The very strong absorption bands observed in the range of 420-700 cm -1 are attributed to the Sn-O antisymmetric vibrations. In that region, the peak at 686 cm -1 are assigned to Sn-O-Sn vibrations, respectively [34]. The bands exhibited in the low wave number region 430-620 cm -1 are attributed to the Sn-O stretching vibrations [13]. The Fe doping shifts the positions of the absorption bands. It has been previously reported that changes observed in the shape, width, and positions of FTIR peaks are attributed to the variation in the local defects, grain size and shape of the samples [14]. In all samples, the vibrations associated to C-H and O-H bonds are seen. This implies that the surface is highly active and adsorbed these molecules.

Conclusion
This paper presents a study of structural properties of Fe doped SnO2 powders prepared by solid state reaction method. X-ray diffraction patterns confirm that the samples have polycrystalline nature with tetragonal structure and show presence (110)