Abstract: In the present work Iron doped Bismuth tri sulphide crystals were grown in silica gel medium at room temperature by the single diffusion method. The effects of parameters such as gel aging, gel pH, the density of gel on the growth of crystals were studied. Harvested crystals characterized by X-ray powder diffractometry (XRD). UV-Vis spectroscopy, Scan electron microscope (SEM).The UV-VIS analysis gives the energy band gap of gel grown crystal.
Crystal growth in gel is simple technique for growing single crystals.
Many investigators using gel method for growing different crystals [1-3] Bismuth sulphide is one of the most important V-VI group semiconductors and has potential application in various fields, such as thermoelectric, electronic and optoelectronic devices, etc [4-5]. With the direct gap energy ranging from 1.3 to 1.7 eV, Bi2S3 exhibits pronounced positive photoconductivity upon visible light exposure, and is a good candidate for optical switches. These materials, in which the Magnetic dopant concentration is typically a few percentage points, are known as diluted magnetic semiconductors (DMS).
The main cause of the new physical properties owned by these DMS materials is attributed to the sp-exchange interaction between the host nonmagnetic semiconductor sp-band and the partially occupied transition metal d-state [6-7]. Synthesis of several kinds of transition metal doped semiconductor nano crystals are reported in the literature, such as Mn-doped Bi2S3 [8] The Bismuth Tri-Sulphide is a quite interesting compound and hence some attempts have been made to grow. Here fe-doped Bismuth Tri-Sulphide is grown by gel technique in Silica gel medium and the grown crystals analyzed under the various Characterizations.
To grow the Bismuth Tri-Sulphide [Bi2S3] crystals, the required Silica gel medium was prepared by adding the Sodium-Metasilicate solution of specific gravity 1.04 g/cc drop by drop with constant stirring by using magnetic stirrer into the 5 ml (2N) Acetic Acid till the pH value 4.4 was set for the mixture. To the above Sodium MetaSilicate solution of pH 4.4, 15 ml the aqueous solution of H2S Gas Water solution was added as inner reagent with constant stirring. This mixture was then transferred to the test tube of length 15 and 2.5 cm diameter. To keep the solution free from dust and impurities, care was taken to cover the test tube with cotton.
The gel was usually set within 13 days. It was left for 66 to72 Hours. For gel ageing and then the outer reagent, aqueous solution of 0.5 M Bismuth Chloride (BiCl3) and 0.2 M FeCl3 was added on to the top of the gel. The outer reagent was added down the sides of the test tube using a pipette and not directly on to the gel medium. Owing to the diffusion of the outer reagent into the gel medium and its reaction with the inner reagent, crystals started growing. Nucleation was observed within 48 Hours of addition of the outer reagent. Circular shaped, opaque and brittle crystals were observed.
The experiment was carried out at an ambient temperature of about 28 0 C. The reaction between Bismuth Chloride, do pent and H2S Gas Water solution in gel medium resulted in the growth of Circular shaped Bismuth Tri-Sulphide [Bi2S3], crystals. The reaction that takes place in the gel medium.
All chemicals used were AR grade. The reaction to grow Fe doped Bi2S3 Crystal is
(2 * x) BiCl3 + x FeCl3+ 3H2S * Bi2-x FexS3+ 6HCl
Where x = 0.05, 0.1
X-ray diffraction is a technique which is used to investigate the internal arrangement of atoms. The powder sample of gel grown crystal was used to x-ray diffraction analysis. The sample was Scan between 20 0 to 800. In fig. It is found that no peak from impurities can be observed in the spectrum of the Fe-doped Bi2S3 sample, proving that none of the other different crystalline phases was formed. Grain sizes were calculated from the broadening of XRD peaks using the Scherer’s formula
D =K/cos
Where K is constant K= 0.9, is wavelength of CuK radiation (cos = 1.5409 ),
is the full width at half maxima of diffraction peaks. In the present work, the grain size of the Fe- doped Bi2S3 estimated from X-ray line broadening of the maximum intensity peak. The crystal grains mainly oriented along the (212) plane.
D is grain size (i.e. the diameter of the crystal particle in the material) the calculated average particle size is 37.66nm.
The compositional analysis of Fe- doped Bi2S3crystal is carried out by using EDAX analysis. In fig. The EDAX confirm the presence of Bismuth (Bi), Sulphur(S) and Iron (Fe) with their atomic percentage It was observed that atomic % of Bi, S and Fe are in good agreement with stoichiometrically expected atomic % 8.18, 3.73 and 88.08 respectively.
Spectrum: 10571 Date:6/7/2019 4:21:36 PM HV:20.0kV Puls th.:3.73kcps
Total: 27.55 100.00 100.00
The Scanning Electron Microscope (SEM) was used to characterize the size, shape and morphologies of formed Nano particles. The SEM images of Fe doped Bi2S3 particles shows that the as synthesized samples contain mainly the grains of doped Bi2S3 Nanoparticles with regular shape. It was also observed that the microscopic images resemble like spherical doped Bi2S3 Nanoparticles. It is observed that the face is neither dull nor very bright but it has some bright region at the left half of the fig. whole the surface is covered with figs of different shapes and size. Some of the figs are approximately seen to be triangular and pentagonal. Fig shows the random nature of particles, many of whom are identical. It shows the size distribution in the synthesized sample. The size variation is seen to be very wide.
The optical property of iron doped Bi2S3crystalwas studied by using UV-VIS spectrophotometer. The UV-Vis study of iron doped Bi2S3 crystals was taken by SHIMADZU UV-2450. UV-Vis spectrophotometer over the wavelength range 200 – 800 nm at Nano Research Laboratory, Department of Physics, Pratap College, Amalner. The graph of UV-VIS analysis is given in fig.. From the graph, it is clear that the gel grown crystal have sufficient and approximately equal transparency in the ultraviolet and visible region. The absorption coefficient is maximum at 216 nm but the variation of absorbance (A) is studied in the wavelength range of 400-800 nm for all the samples.
The high values of absorption coefficient validate their use in photovoltaic applications. Optical conductivity and thermal conductivity also show good values. The optical absorption spectrum of grown crystal shows a good absorbance in the entire visible region. This is useful for optoelectronic applications. The resulting spectrum obtained on Fe-dopedBi2S3 is shown in Figure the spectral data recorded showed the strong cut off at 600 nm; where the absorbance value is minimum. The data is corroborated in the % Reflectance mode.
Band Gap Energy (E) = h*C/ h = Planks constant = 6.626 x 10 -34 Joules sec
C = Speed of light = 3.0 x 108 meter/sec
H = Cut off wavelength = 600x 10-9 meters
E = h x C =6.626 x 10 -34x 3.0 x 108/600 nm = 6.6266 x3 x10-19 = 6.6262?1.6?10-19 x 10-19 = 2.07 eV
Where 1eV = 1.6 X 10-19Joules (conversion factor)
The iron doped Bi2S3 crystals can be successfully grown by silica gel method. The gel setting period is strongly dependent on the pH of a mixture of sodium meta silicate, acidic acid and density of sodium meta silicate.
X-ray diffraction pattern shows that the sample was crystal in nature. Gel grown crystal possesses uniform morphology and the size variation is seen to be very Wide. The UV Vis measurements indicate the band gap energy of the Fe-doped Bi2S3 crystals the variation of absorbance (A) is studied in the wavelength range of 400-800 nm Band gap energy E= 2.07 eV vi The elemental composition was determined by EDAX studies, which show that the Presence of Iron, Bismuth and sulphur.
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