Graphical traits about VHTM in the light
of FTIR Studies on Zn & Sb substituted Cu
ferrites
R.Dhana Raju†
Department of physics, Andhra University, Visakhapatnam, Andhra Pradesh, India-530003 [email protected]
M.K.Raju†
V.Brahmajirao
Dept. Of Nano science and Technology, School of Biotechnology, MGNIRSA , D.Swaminathan Research Foundation,[DSRF] , Gaganmahal,HYDERABAD-500029., Andhra Pradesh. INDIA
Abstract
This paper presents the FTIR studies and their comparison with our already reported previous studies on Zn & Sb substituted Cu ferrites, carried out at Material Science Research Laboratories, Department of Physics, Andhra University, and Visakhapatnam, INDIA, applied to analyze VHTM, in a different perspective. The FTIR spectra are recorded on twelve samples of doped ferrites with substituent concentration ‘x’ varying in steps of 0.1, and the corresponding morphological micrograms, taken on a SEM are also presented. Our results are compared with very recent similar ones of literature. Clear evidences of missing aspects about studies in VHTM are pointed out from the Wave number Transmittance plots .The findings provide a coherent tuned explanation with those given by a host of other authors pursuing studies in the similar lines cited along with .
Keywords
FTIR studies, substituted (doped) ferrites, Verwey’s Hopping Transition Mechanism, SEMand XRDstudies, Ceramic method, wavenumberof IR, Transmittance
Introduction
Infrared spectroscopy has been a workhorse technique for materials analysis in the laboratory. The resulting spectrum of the IR Radiation emerging from the sample represents the molecular absorption and transmission, creating a molecular fingerprint of the sample. Chemical bonds vary widely in their sensitivity [1], to probing by infrared techniques. For example carbon-sulfur bonds often give no infrared signal, and so cannot be detected at any concentration,while silicon-oxygen bonds can produce signals intense enough to be detected when probing sub monolayer quantities, or in the order of 1013 bond/cc.
The infrared spectrum reported is presented as a plot of wavenumber versus Transmittance ‘T’ where ; Where Tw, is the transmittance of the sample (at wavenumber ‘υ’, the reciprocal of wavelength) , which is a measure of the intensity of the transmitted light.
Photograph of FTIR SPECTROMETER at Research Labs, Pharmacy Dept., A.U. Visakhapatnam, INDIA
Experimental:
The conventional ceramic method [6, 7 & 8] is used for the preparation of the sample. Suitable temperature is required to perform solid state reaction among constituent oxides of the mixed ferrite to be formed. Since the mechanical grinding cannot give particles of uniform size and shape the homogeneity, morphology and microstructure of the material are affected.
First series, of samples are having general formula
Zn Cu Fe 0
1-x x 2 4 (with x=0, x=0.2, x=0.4, x=0.6, x=0.8) , Second series of copper zinc & copper antimony ferrites with basic compositions:[Cu (1-x) Zn x Fe2 04 ], &[Cu(1-x)SbxFe204], in which, x varies from x = [0.0 to 1.0] in steps of 0.2., have been synthesized by the above method.
Highly pure (analytical reagent grade) CuO, Fe2 03 and Sb2 05 and ZnO chemicals were used. The details of the method of synthesis were shown in the flowchart given below.
The oxides, taken in correct proportions, were crushed , mixed and ground to fine particles in a power operated agate mortar and pestle, ensuring uniformity of mixing thoroughly for 5 hours in methanol . The mixture was calcinated for 6 hours at 9000C in muffle furnace and then it was allowed to cool in the furnace. Poly Vinyl Alcohol was used as Binder compound formed after crushing it for 2 hours. The material was granulated through sieves and the granules were palletized. The pellets and toroids were finally sintered at 11500C in Nabertherm Furnace with Eurotherm controller. Material was heated to 300 0 C in an hour following heating rate with 3000C/hr. until 1150 0 C and kept for 4 hours. Then it was cooled at the rate of 3000C /hr. and later the furnace was allowed to normal cooling in air atmosphere. These samples were used to systematically to obtain the data in Morphological studies using SEM, of JEOL, make model JSM-840 & Structural studies using XRD Philips Diffract meter (model PW-3710) Setup,
TYPICAL FLOW CHART FOR THE SYNTHESIS OF FERRITE SPECIMENS
.
Results and discussion
Zinc oxide due to specific electrical, optical and acoustic properties is the important semiconductor material, which has a variety of applications [10]. ZnO is a high-temperature wide band gap semiconductor (band gap Eg = 3.37 еВ) & its properties are very close to those of widely recognized semiconductor for optical devices of a blue and ultraviolet range GaN (Eg = 3.39 еВ). Hence ZnO is very useful for optical devices of UV interval of wavelengths. Highly transparent electro conductive ZnO films were used by G. Lashkarev et.al.,(2004), and XRD analysis and AFM study were carried out for characterization of crystal lattice perfectness and surface morphology respectively by them . The typical grain size was reported to be 40-60 nm. UV photoluminescence studies using nitrogen laser were reported by them. Zn Fe 2 0 4, is a widely used catalyst, being a nonmagnetic normal spinel and is an ideal template to test the Hypothesis of cation redistribution, if any, in the Nano regime. Herein Our studies about the finite size effects on the electrical and structural properties reported elsewhere [8,9] are used for comparison sake. All our findings are supported by those of S.D. Shenoy [27]. A.A.Fursina [11] observed recently a new effect with Fe3 O4 while performing experiments at the Nano scale; He reported strong evidences of this effect which is a novel mechanism called Electric Field Driven transition (EFD) in magnetite below Tv , from high- to low-resistance states driven by application of high bias. The EFD transition is detected both in Fe3O4 nanoparticles and thin films, and is hysteretic in voltage under continuous biasing, and is not caused by self-heating. Verwey‘s Hopping Transition Mechanism (detected in the year 1913 ) as per Waltz [12] is due to the intricate multi-particle system Fe3O4 with its various magneto-electronic interactions that are not completely understood as yet - although considerable progress has been achieved, especially during the last two decades. A series of uncertainties and erroneous statements [12] concerning the reaction order (is it one or two?) and type of the transition (multi-stage or single stage), characterizes the period of the last several years after its detection. A most inspiring conference organized in 1979 by Sir Nevill Mott in Cambridge , has brought out several anomalies that require both the quality control in the method of synthesis ,as well as the details and variety of the characterization techniques in the study of the Mechanism .
RAW MATERIALS: CuO,Fe
2O3,ZnO & Sb2O5
MIXED in methanol and ground for 5 hours usig agate mortar and pestel. After words it is dried.
Pre sintering (calcination) 6 hours in a muffle furnace at 9000c in glazed silica crucible with lid.
Cooled at the rate of 50c/minute in the furnace to almost room temperature for nearly 175 minutes before Quenching with the binder
Crushed ,ground& mixed with binder(PVA-5%) Sintering at11500c in a Noberthem furnace
with Eurotherm controller for 4 hours Samples are collected polythene containers.
Further analysis with these samples
Plot 1.Zn ferrite plot for sample CuFe2O4
Plot2. Zn ferrite plot for sample Cu 0.8 Zn 0.2 Fe2O4
Plot 3. Zn ferrite plot for sample Cu0.6Zn0.4Fe2O4 Plot 4. Zn ferrite plot for sample Cu0.4Zn0.6Fe2O4
Plot 5. Zn ferrite plot for sample Cu0.2Zn0.8Fe2o4 Plot 6. Zn ferrite plot for sample ZnFe2O4
Plot 7. Wavenumber VS T plot for CuFe
2
O
4
Plot 8. Wavenumber VS T plot for Cu
0.8
Sb
0.2
Fe
2
O
4
Plot 9. Wavenumber VS T plot for Cu
0.6
Sb
0.4
Fe
2
O
4
Plot 10. Wavenumber VS T plot for Cu
0.4
Sb
0.6
Fe
2
O
4
Plot 11. Wavenumber VS T plot for Cu
0.2
Sb
0.8
Fe
2
o
4
Plot 12. WavenumberVS T plot for Zn Fe
2
O
4
et.al.,[19] intheir studies on Polycrystalline Li (0.5+x ) Nb x Fe (2.5 -2x) O4 samples (x= 0.00, 0.05, 0.10, 0.15 and 0.2) prepared using the standard ceramic method found that, the substitution of Nb up to x = 0.1 improves the magnetization and initial permeability, while these properties are decreased for x > 0.1.
They explained this by assuming that, for x < 0.1 Nb ions occupy the tetrahedral sites. However for higher Nb concentration, the Nb ions reside at the grain boundaries. IR absorption spectrum supports the proposed Nb cation distribution. Talaat. M. Meaza et.al., [20] synthesized two series of polycrystalline substituted M-type hexagonal ferrite, for X-ray diffraction ( established single phase M-type hexagonal structure ) and Mössbauer spectroscopy studies at room temperature . Mössbauer spectra obtained at room temperature were found to be substitution dependent. With increasing substitution the Mössbauer spectra change from magnetically ordered (x=0) towards magnetically ordered with strong line broadening (X= 0.4 to 1.6) to nonmagnetic (x=2.0), due to decreasing of Curie temperatures. XRD, TEM, SEM, ESR and magnetic susceptibility measurements on Fe 2 O 3 Nanoparticles Dispersed in a Silica Matrix Prepared by sol-ge1 Technique, reported by H. H. Fifty et.al, [21] showed at low temperatures an amorphous phase and anti- ferromagnetic properties. A further increase of the temperature results in the γ to α- Fe2O3 transformation. They found that the variation of iron oxide content affected the abundance of γ- Fe2O3 formation, and recorded the maximum percent values in the more dilute samples. Besides, the latter methods characterize only the surface, while the bulk might behave in an entirely different manner. J. P. Attfield et al., used Magnetic After-Effect (MAE) spectroscopy which is a sensitive probe for quality control and investigation of low-temperature (4 K<T<Tv) charge transport mechanisms [22]. Our results on the Cu (1-x ) Zn x Fe2O4 and Cu (1-x) Sb x Fe204 on FTIR Spectrometer are reported in this paper. In the region 200cm -1 to 500cm -1, of the IR conspicuous peaks are observed in the transmittance plots . These observations were repeated several times to confirm the finding . Three of the maxima of transmittance in this wave number range were found to confine to the same fixed positions almost of the abscissae, but the transmittance recorded gradual decrease with the increase in the concentration of the Zn (increase of value of ‘x’ in the molecular formula of the ferrite).This indicates the usage of the electromagnetic energy by the
Fe 2 + and Fe 3+ for the hopping transition. Details of energy calculations in this regard will be published shortly. With Sb substitution transmittance maxima appear in the higher wavenumber region and they are fairly packed .Further the transmittance maxima are less sharper and few in number, possibly due to larger absorbance of the EM-energy of the IR radiation. This is in consonance with our SEM and XRD studies [8]. R. Iyer et.al. [23] In his studies with [Mn (1-x) Zn xFe 2 O 4 ] ferrites prepared them by using the co-precipitation technique by doping the Zn 2+ ion impurities. They found that the Zn 2+ ion’s presence is not restricted to A-site alone for some of the Mn –Zn ferrite series. Also D.Ihle and B Lorenz [28], calculated the electrical small-polaron (SP) conductivity of Fe 3 O 4 above the Verwey transition taking into account the polaronic short-range order. It is shown that the conductivity results from the superposition of SP band and SP hopping conduction. Concerning the DC conductivity below room temperature, the SP band conduction is the dominant mechanism. The observed maximum in the optical conductivity near 0.2 eV is explained as an SP hopping effect. A vivid and clear support to our findings is found in the work of, Kozo Iwauchi et.al. [29, 30], who showed that dielectric relaxation is caused by the hopping of electron between Fe2+ and Fe 3+ ions. Hsing-I Hsiang et.al.,[24]studied Hexagonal Ferrite powders that are used in magnetic recording media. Because of its large coercive force, which results from the large magnetic anisotropy [25] these materials are utilized in his studies to isolate the Carbonate group. The absorption bands at 1384, 1454 and 1749 cm−1 & 3400 cm−1 observed by him are attributed to the COO and the OH groups, respectively. No attempt for the analysis otherwise is evident. Yin Hong [26] in his FTIR Studies , gave a summary of the precursor composition , bulk composition, & surface composition, and corresponding x, y values in Ni xFe yO4 .
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