Fe-doped Samples Research Articles

Observation of n-type behavior in Fe-doped tetrahedrite at low temperature

Tetrahedrite exhibits favorable thermoelectric properties, while also being composed of non-toxic and earth-abundant elements. Although tetrahedrite has been studied extensively as a p-type thermoelectric, n-type behavior in this material has not yet been observed. We report the first findings of n-type conductivity in tetrahedrite observed over a temperature range of 80 to 310 K, with typical p-type conductivity found at higher temperatures. Herein, we characterize electrical and thermal transport properties on these samples from 80 to 673 K. Mechanical alloying and modified polyol synthesis methods were used to synthesize Fe-doped samples (Cu12-xFexSb4S13 with x = 1, 1.3, and 1.5) by solid-state and solution-phase approaches, respectively. Elemental analysis by energy-dispersive X-ray spectroscopy was conducted to investigate the relationship between thermoelectric properties and chemical composition. A maximum ZT = 0.67 at 673 K was obtained for Cu10.5Fe1.5Sb4S13 synthesized by the modified polyol process. Our observation of negative Seebeck coefficient values in the low-temperature regime should serve as a foundation for further study of n-type behavior in tetrahedrite materials.

The functionalization of morphological, structural and optical properties of Fe doped SnO2 nanocrystals synthesized by the sol–gel method

In this study, undoped SnO2 nanocrystals and SnO2 nanocrystals with Fe dopant at different atomic ratios (0, 5, 10, 15 and 20%) were synthesized by using the sol–gel method. SnO2 based nanoceramic materials, which can be used in several scientific researches and high technology applications, are easily synthesized, and have superior properties, were produced by using this method. The changes in the structural, morphological and optical properties of the Fe-doped samples were investigated through the X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier Transform IR (FT-IR), and UV–Vis–NIR spectroscopy. XRD spectra obtained from the samples showed that the samples had a tetragonal crystal structure and the cassiterite phase. The crystal size of the samples decreased from 30.28 to 24.84 nm along with the rate of the Fe dopant. SEM images revealed that the grain size of SnO2 distinctly decreased since it prevented the grain growth of Fe. In compliance with the results of XRD and EDX, FTIR spectra displayed the peaks confirming that the doped Fe was added in the structure of SnO2. The optical band gaps of the samples were calculated from the diffuse reflectance curves using the Kubelka–Munk function. It was observed that Eg values of the samples increased from 3.58 to 3.61 eV depending on Fe dopant.

Enhanced gas-phase photocatalytic oxidation of n-pentane using high visible-light-driven Fe-doped WO3 nanostructures

The main aim of this study was to investigate the photocatalytic potential of pure and Fe-doped WO3 nanoparticles for conversion of volatile organic compounds (VOCs). N-pentane, one of the n-alkanes VOCs, was selected as the pollutant model in gaseous phase. The used photocatalysts were synthesized by a facile method and characterized to determine the structural and optical properties. Results showed that the synthesized nanoparticles had small grain size with high crystallinity. The analyses of XRD, FTIR, and Raman exhibited that all doped and un-doped WO3 samples were in monoclinic form. The UV–vis and PL spectroscopies revealed that introducing Fe into WO3 led to narrowing band gap energy from 2.83 to 2.56 eV and decreasing the recombination rate of photo-generated electron-holes due to implanted defects and impurities in the host matrix. The photocatalytic experiments of n-pentane degradation were conducted in a self-design batch photo-reactor in the presence of O2 as oxidizing agent. The Fe-doped samples obviously exhibited the photocatalytic activity higher than the bare WO3. An almost full conversion of n-pentane, 99.91%, was provided without any catalyst deactivation by visible-light-irradiated 4.65 at.% Fe-doped WO3 which was 14.77% greater than that of the un-doped sample. Finally, a mechanism study was done based on the main intermediates detected using mass spectroscopy.

Optical and magnetic properties of Cd(1−x)FexTiO3 (x = 1%)

Sol–gel route was used to prepare Fe-doped CdTiO3 sample with 1 wt% and its optical and magnetic properties investigated. In particular, photoluminescence study revealed the existence of defects, such as oxygen vacancies, and of transitions from electronic states of Cd2+, Ti4+ and Fe2+ to those of O2−. Magnetic investigations showed the existence of two oxidation states of iron, 2+ and 3+, and of an antiferromagnetic order at temperatures inferior to 20 K with a slight canting of spin moments of the magnetic species leading to spontaneous magnetization which values decrease with the temperature. Above 20 K, a ferromagnetic behaviour is dominant and, at room temperature, a diamagnetic behaviour prevails. The latter has been interpreted as due to the presence of CdO impurities as revealed by XRD and photoluminescence results.

Conductivity Characterizationof Iron Oxide Doped 8 mol% Yttria Stabilized Zirconia

A facile strategy was proposed to incorporate the dopant Fe into 8YSZ-based material, which can be potentially applied as solid electrode materials for Solid Oxide Fuel Cells (SOFC). In this study, 8YSZ powder was investigated in terms of densification, conductivity and thecrystal structure as a solid electrolytes. Therefore, varying mol% of Fe included 1, 2, and 3 were prepared for investigation. The crystalline structure of the pristine and Fe doped samples were characterized by X-ray diffraction (XRD) and the phase contents were evaluated by using the Rietveld method. Rietveld quantitative phase analysis demonstrates that the monoclinic-ZrO2phase increases (12.8 wt% to 39.7 wt%) as the concentration of Fe increases, while the amount of tetragonal-ZrO2 phase drop (40.4 wt% to 11.9 wt%) dramatically. Sintering activity was applied to improve incorporation of the 8YSZ powder and the dopant Fe where the relative density increases from 77% to 92%. Sample YSZ-2Fe has been fitted with CPE equivalent circuit and achieved 6.251 x 10-6S/cm at 300 °C in air. However, it was found that conductivity levels decreased as the mol% of Fe increased. In short, sample YSZ-2Fe ceramic demonstrated good results in terms of densification (92.09%), cubic ZrO2 phase (22 wt%) and conductivity 6.251 x 10-6 S/cm.

Effect of B-site dopants on the electrical properties of BaMn1−xAxO3 ceramics via low temperature impedance spectroscopy

Single phase polycrystalline BaMn1−xAxO3 (x = 0.01, A = Ru, Fe and Nb) ceramics samples with a rhombohedral (15R) symmetry were prepared via a conventional solid-state sintering route. The microstructure of all the samples was porous, and the substitutions at B-site did not affect the microstructure of these ceramics. Undoped BaMnO3 ceramics exhibited relatively lower impedance values at low temperatures. The observed capacitance and resistance values suggested that the grain region (activation energy = 0.138 eV ± 0.0275) was slightly more conductive than the grain boundary (activation energy = 0.1430 eV ± 0.0246). No electrode effect was observed for the BaMnO3 ceramics at 10–320 K; however, all the B-site doped BaMn1−xAxO3 ceramics showed a decrease in resistivity with an increase in temperature, suggesting a semiconductor-like behaviour. For Ru–doped ceramics, the observed activation energies for the grain, grain boundary and electrode regions were 0.151 eV ± 0.0313, 0.172 eV ± 0.0022 and 0.170 eV ± 0.0511, respectively. Impedance spectroscopy of Fe-doped samples at 300–320 K revealed bulk only response with an activation energy of 0.165 eV ± 0.0029. For the Nb-doped samples, the grain effect was dominant at 40–80 K, the electrode effect was dominant near room temperature, and at intermediate temperatures, the grain boundary effect appeared more active. The calculated activation energies for the grain, grain boundary and electrode were 0.018 ± 0.0196 eV, 0.092 ± 0.0106 eV and 0.092 ± 0.0062 eV, respectively. For the Nb-doped ceramics, impedance spectroscopy was performed at room temperature using In/Ga alloy electrodes and the extrinsic effect (i.e. electrode effect) was confirmed by applying a dc bias.

High electron mobility transistors with Fe-doped semi-insulating GaN buffers on (1 1 0) Si substrates grown by ammonia molecular beam epitaxy

The electrical properties of AlGaN/GaN high electron mobility transistor structures with composite Fe-doped GaN/undoped GaN buffers grown on (1 1 0) Si substrates by ammonia molecular beam epitaxy were reported. Fe concentration in the range of 1017 cm−3 is sufficient to compensate the residual donors (<1016 cm−3) of undoped GaN and demonstrated a highly resistive GaN on (1 1 0) Si substrates. For buffers with Fe concentration of 1 × 1017 ∼ 1 × 1018 cm−3, the buffer was semi-insulating, with the Fermi level pinned near 0.5–0.7 eV which is determined by temperature-dependent I-T measurements. From the PICTS measurements, the Fe-related peaks of 0.69 eV (B) and 0.86 eV (C) are observed. The peak B is most likely due to the center pinning the Fermi level which is close to the activation energy observed in the temperature-dependent current measurement of Fe-doped sample, tentatively attributed to complexes between substitutional Fe ions and native defects such as nitrogen vacancies. The peak C is similar to the hole trap of 0.85 eV previously reported. In spite of similar transfer device characteristics, the Fe-doped buffer shows a noticeable difference in the off-state leakage behaviors. The sample grown with the optimized Fe concentration of 1 × 1017 cm−3 had a buffer resistivity of approximately 3.84 × 1011 Ω cm, increased by almost four orders of magnitude with respect to that (4.5 × 107 Ω cm) of the reference sample with undoped GaN buffer.

Flame retardant and visible light-activated Fe-doped TiO2 thin films anchored to wood surfaces for the photocatalytic degradation of gaseous formaldehyde

Flame retardant and visible light-activated Fe-doped TiO2 thin films were anchored to wood surfaces by a facile precipitation method for the photocatalytic degradation of gaseous formaldehyde. All of the as-prepared TiO2 thin films exhibited the anatase crystal structure and grew on the wood surfaces by the aggregation of nanoparticles with diameters ranging from 11 to 16 nm. The UV–vis diffuse reflectance spectroscopy (UV–vis DRS) results showed that the presence of a small amount of iron ions in the TiO2 matrix could significantly extend the optical responses in the UV to visible region. Compared to the pure TiO2/wood samples, the Fe-doped TiO2/wood samples exhibited higher photocatalytic activities under visible light irradiation. The optimum nFe/nTi molar ratio was 2.0 at. %. The electron spin resonance (ESR) tests further confirmed that the active oxygen species of OH and O2– that were generated on the Fe-doped TiO2/wood samples under visible light irradiation are responsible for the degradation of formaldehyde. The Fe-doped TiO2 samples also exhibited high stability and reusability after 6 cycles. Additionally, the limiting oxygen index of the original wood increased from 24.8% to 33.9% after it was coated with Fe-doped TiO2 thin films, indicating a significant improvement in its flame resistance.

Electron Trapping in Extended Defects in Microwave AlGaN/GaN HEMTs With Carbon-Doped Buffers

This paper investigates AlGaN/GaN high-electron mobility transistors (HEMTs) fabricated on epistructures with carbon (C)-doped buffers. Metalorganic chemical vapor deposition is used to grow two C-doped structures with different doping profiles, using growth parameters to change the C incorporation. The C concentration is low enough to result in n-type GaN. Reference devices are also fabricated on a structure using iron (Fe) as dopant, to exclude any process related variations and provide a relevant benchmark. All devices exhibit similar dc performance. However, pulsed ${I}$ – ${V}$ measurements show extensive dispersion in the C-doped devices, with values of dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}~3$ –4 times larger than in the dc case. Due to the extensive trapping, the devices with C-doped buffers can only supply about half the output power of the Fe-doped sample, 2.5 W/mm compared to 4.8 W/mm at 10 GHz. In drain current transient measurements, the trap filling time is varied, finding large prevalence of trapping at dislocations for the C-doped samples. Clusters of C around the dislocations are suggested to be the main cause for the increased dispersion.

Changes in structural, optical and magnetic properties of nano-CuS upon doping with Mn and Fe: a comparative study

Nano-CuS doped with Mn or Fe (Cu1–x(Mn or Fe) x S; 0 ≤ x ≤ 0.2) was prepared by a thermolysis method. The structural, optical and magnetic properties were investigated using XRD synchrotron radiation, scanning electron microscope (SEM), ultraviolet spectroscopy (UV–Vis), photoluminescence (PL) and vibrating sample magnetometer (VSM). Diffraction patterns manifested a single phase of CuS hexagonal structure with a minor phase Cu2S in case of Fe doped and only a single phase in case of Mn-doped CuS samples. Analysis indicated a necessity of good diffraction patterns and Rietveld analysis for phase’s determination. The changes in bond lengths, lattice parameters, and microstrain were determined by Rietveld method and correlated with the measured physical properties. Energy gaps showed an irregular change with increased amount of Mn doped while they exhibited a regular decrease as the amount of Fe increased in CuS matrix. The PL emissions revealed three sub-violet, (two violet, one blue) and (two violet, one blue, one green) emitted peaks for pure, Mn- and Fe-doped CuS, respectively. The PL intensity was enhanced for x = 0.1 doped Mn or Fe then it quenched by further doped. Bare CuS showed diamagnetic properties; while Mn- and Fe-doped samples had paramagnetic properties.

Structural, optical and magnetic properties of Fe-doped CeO2 samples probed using X-ray photoelectron spectroscopy

The present study reports the effect of Fe-doping on the structural, optical, magnetic and electronic properties of polycrystalline CeO2 (for 5 and 10% doping concentration of Fe-cation) samples synthesized by low-temperature solid-state reaction method. Rietveld refinement of the X-ray diffraction patterns establishes fluorite-type face-centred cubic structure of the Fe-doped CeO2 samples and also confirms successful incorporation of Fe ions in the CeO2 lattice. The UV–Vis–NIR absorption spectra displays reduce band gap energy with rising fluency of Fe-ions, which confirm red shifts in the Fe-doped CeO2 samples. The electronic structure of the pure CeO2 and Fe-doped CeO2 polycrystalline samples have been investigated by X-ray photoemission spectroscopy (XPS). The XPS spectra of Ce 3d reveals the reduction of Ce4+ to Ce3+ states Fe-doped CeO2 samples, which are well supported by the Fe 2p and O 1s spectra. Pure polycrystalline CeO2 displays diamagnetic behaviour at room temperature. Interestingly, 5% Fe-doped CeO2 sample displays S-shape hysteresis loop and establishes room temperature ferromagnetism, whereas, 10% Fe-doped CeO2 sample shows weak ferromagnetic behaviour. A decrement is observed in the magnetization on increasing the doping concentration. The possible reason for ferromagnetism in the Fe-doped CeO2 samples may be incorporation of oxygen vacancies, which are further discussed using F-centre exchange mechanism and double exchange interaction. These experimental findings offer potential opportunities for spintronics and optoelectronics applications by integrating them into device structures and evaluating their performance as a function of their material properties.

Structural, optical and electrical properties of pure and Fe doped V2O5 nanoparticles for junction diode fabrications

Structural, optical and electrical studies of V2O5 and FexV2O5 (x = 5%) nanostructures synthesized by a wet chemical method have been reported. The synthesized nanostructures were characterized by XRD, SEM–EDX, HRTEM, XPS, UV(DRS), FT-IR, PL, TG–DTA, AC and DC conductivity study’s. The anorthic phase was observed in the XRD patterns of undoped and Fe doped samples which are prepared at low temperature. This anorthic phase was reduced with the heat treatment and gradually transformed into orthorhombic phase in the samples annealed at 600 °C for 1 h. The change in the surface morphology in the present samples from micro-rod to nanorods network seems to be dependent on the substitution of Fe. As observed from the PL analysis that the ultraviolet (UV) emission intensity was found to be decreased and exhibited a blue shift with the increase of Fe concentration. The analysis of AC and DC conductivity measurements recorded at room temperature in the temperature range of 303–403 K, revealed that the activation energy is high for Fe doped V2O5 compared to undoped V2O5. The junction diodes of n-V2O5/p-Si and V2O5:Fe/p-Si was successfully prepared by the nebulizer spray pyrolysis method. The (I–V) characteristics of nonlinear and asymmetric nature revealed the Schottky diode based behavior for pure and doped samples.

Enhanced dielectric constant and structural transformation in Fe-doped hydroxyapatite synthesized by wet chemical method

We report the synthesis of single-phase Fe-doped hydroxyapatite (HAp) [Ca10−xFe x (PO4)6(OH)2 (0.0 ≤ x ≤ 0.3)] and enhanced dielectric constant of HAp with Fe doping. Rietveld analysis shows the change in x-axis-oriented lattice constant a in Fe-doped x = 0.1 and 0.3 compositions in comparison with parent HAp, while z-axis-oriented lattice constant c does not show any considerable change. Analysis of absorbance data shows two new symmetric stretching peaks for Fe-doped x = 0.1 and x = 0.3 compositions, which are not present in parent HAp. Magnetic measurements show paramagnetic behaviour of all Fe-doped samples at 300 K. Fe-doped Ca9.9Fe0.1(PO4)6(OH)2 composition shows increase in impedance in the presence of 500 Oersted (Oe) applied magnetic field in comparison with impedance in the absence of magnetic field. Ca9.9Fe0.1(PO4)6(OH)2 composition shows increase in dielectric constant in comparison with parent HAp in frequency range 5–35 MHz. Fe-doped Ca9.9Fe0.1(PO4)6(OH)2 composition shows ~ 970% colossal magnetoimpedance at 100 Hz and ~ 200% at 20 MHz frequency.

Influence of Ba substitution, Fe doping and annealing effect on magnetic and optical properties of Sr0.9Ba0.1Ti1−xFexO3 nanoparticles prepared by the hydrothermal method

Sr0.9Ba0.1Ti1−xFexO3 (x = 0, 0.05, 0.10 and 0.15) nanoparticles were synthesized by the hydrothermal method. Influence of Ba substitution, Fe doping and annealing effect on magnetic and optical properties of these samples was studied. X-ray diffraction (XRD) results indicated a cubic perovskite structure with the increase of lattice parameter and crystallite sizes of all samples owing to the substitution with a larger ionic radius of Ba and Fe ions at Sr and Ti sites in the crystal structure, respectively. Ba substitution could result in a pure phase of annealed samples. Magnetization of as-prepared samples measured at room temperature by vibrating sample magnetometer (VSM) revealed a diamagnetic and paramagnetic behavior of undoped and Fe-doped samples, respectively. Interestingly, annealing could significantly affect the magnetic behavior of all samples i.e. undoped sample showed paramagnetic behavior, whereas all Fe-doped samples exhibited ferromagnetic behavior with the enhancement of saturation magnetization (Ms) from 0.28 to 0.78 emu/g owing to the increase of Fe content. Ferromagnetic behavior was suggested to originate from Fe3+−VO−Fe3+ coupling in the crystal structure due to the promotion of oxygen vacancy (VO) as confirmed by the X-ray photoelectron spectroscopy (XPS) results. Moreover, coercivity (Hc) and remanent magnetization (Mr) also increased from 110–442 Oe to 0.01–0.15 emu/g, respectively. The determined optical band gaps of annealed samples determined by ultraviolet–visible (UV–vis) spectroscopy were found to decrease from 3.3907 to 3.3469 eV with increasing Fe content.

Magnetic properties of M0.3Fe2.7O4 (M = Fe, Zn and Mn) ferrites nanoparticles

In the present article a comparative study on the structural and magnetic properties of nano-sized M0.3Fe0.7Fe2O4 (M = Fe, Zn and Mn) ferrites have been reported. The X-ray diffraction (XRD) patterns show that the crystallite size depends on the cation distribution. The Rietveld refinement of XRD patterns using MAUD software determines the distribution of cations and unit cell dimensions. The magnetic measurements show that the maximum and minimum value of saturation magnetization is obtained for Zn and Mn doped samples, respectively. The peak temperature of AC magnetic susceptibility of Zn and Fe doped samples below 300 K shows the superparamagnetic behavior in these samples at room temperature. the AC susceptibility results confirm the presence of strong interactions between the nanoparticles which leads to a superspin glass state in the samples at low temperatures.

Effect of Blocking and Superconducting Layer Doping on the Superconductivity and Magnetic Properties of Polycrystalline Sr2CaCu2O6

The possible difference in the properties upon doping the Sr2CaCu2O6 superconducting or blocking layers with Fe and Eu respectively was investigated in this work. The homogeneous Sr2−yEu y CaCu2O6+δ and Sr2CaCu2−xFe x O6+δ (y = 0, 0.1, 0.5, x = 0, 0.05) compounds were produced by a high-pressure synthesis route. Judging by the magnetic susceptibility measurements, all samples exhibit a superconductivity transition and the Eu/Fe concentration dependencies on the diamagnetic moment and average Tc have been constructed using the experimental data. As a result, an unusual behavior of the Tc value was observed for the samples with doped Eu: a fivefold reduction in the europium concentration in the sample does not give a noticeable effect on the transition temperature value while the diamagnetic signal becomes more stronger. Complex superconducting dome was found for Eu-doped material: 0.1 ≤ y ≤ 0.5 region Tc vs. concentration data were approximated by inverted parabola-like curve with a maximum at y = 0.3. Difference in properties of the Eu and Fe-doped samples was also found in the behavior of the hysteresis loops showed the opposite orientations.

Structural and Electrochemical Characterization of Zn1-xFexO-Effect of Aliovalent Doping on the Li⁺ Storage Mechanism.

In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs), new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with varying dopant concentrations, potentially serving as anode for LIBs (Rechargeable lithium-ion batteries). The wurtzite structure of the Zn1−xFexO samples (with x ranging from 0 to 0.12) has been refined via the Rietveld method. Cell parameters change only slightly with the Fe content, whereas the crystallinity is strongly affected, presumably due to the presence of defects induced by the Fe3+ substitution for Zn2+. XANES (X-ray absorption near edge structure) data recorded ex situ for Zn0.9Fe0.1O electrodes at different states of charge indicated that Fe, dominantly trivalent in the pristine anode, partially reduces to Fe2+ upon discharge. This finding was supported by a detailed galvanostatic and potentiodynamic investigation of Zn1−xFexO-based electrodes, confirming such an initial reduction of Fe3+ to Fe2+ at potentials higher than 1.2 V (vs. Li+/Li) upon the initial lithiation, i.e., discharge. Both structural and electrochemical data strongly suggest the presence of cationic vacancies at the tetrahedral sites, induced by the presence of Fe3+ (i.e., one cationic vacancy for every two Fe3+ present in the sample), allowing for the initial Li+ insertion into the ZnO lattice prior to the subsequent conversion and alloying reaction.

Drastic improvement in magnetization of CdO nanoparticles by Fe doping

Hydrothermal route was used in the preparation of Fe-doped CdO nanoparticles with 3, 5, 7 and 10 wt% and their structural and magnetic properties were investigated. Structural characterization using powder X-ray diffraction confirmed the single phase cubic symmetry of these nanoparticles. Particle size decreased monotonically with increasing the dopant ion concentration. The microstructure of the synthesized samples was studied by a high-resolution transmission electron microscopy (HRTEM) which confirmed the nanocrystalline nature of the samples. A vibrating sample magnetometer provided the hysteresis curves of all samples. Pure CdO reveals ferromagnetic behavior while antiferromagnetization is observed for all Fe-doped samples. Large coercivity as well as large area for the sample x = 0.05 is achieved.

Magnetic anomalies in Fe-doped NiO nanoparticle

Undoped and iron-doped NiO nanoparticle were synthesized by standard hydrothermal method. A detailed study is carried out on the effect of dopant concentration on morphology, structural, resonance and magnetic properties of NiO nanoparticle by varying the Fe concentration from 0.01 to 0.10 M. The synchrotron-x-ray diffraction confirmed that no secondary phase was observed other than NiO. The x-ray photoelectron spectroscopy studies revealed that, Fe was primarily in the trivalent state, replacing the Ni2+ ion inside the octahedral crystal site of NiO. The Electron paramagnetic studies revealed the ferromagnetic cluster formation at high doping concentration (5 and 10%). The ZFC–FC curves displayed an average blocking temperature around 180 K due to particle size distribution. The anomalous behaviour of spontaneous exchange bias (HSEB) and magnetic remanence (Mr) for all Fe-doped samples observed at 5 K showed an increase (0.1316–0.1384 emu g−1) in the moment of frozen spin (Mp) as the dopant concentration increased. The role of frozen spin moment in spontaneous exchange bias behaviour was discussed.

Magnetic and dielectric study of Fe-doped CdSe nanoparticles

Nanoparticles of cadmium selenide (CdSe) and Fe (5% and 10%) doped CdSe have been synthesized by soft chemical route and found to have cubic structure. The magnetic field dependent magnetization measurement of the doped samples indicates the presence of anti-ferromagnetic order. The temperature dependent magnetization (M-T) measurement under zero field cooled and field cooled conditions has also ruled out the presence of ferromagnetic component in the samples at room temperature as well as low temperature. In order to estimate the anti-ferromagnetic coupling among the doped Fe atoms, an M-T measurement at 500 Oe has been carried out, and the Curie-Weiss temperature θ of the samples has been estimated from the inverse of susceptibility versus temperature plots. The dielectric relaxation peaks are observed in the spectra of imaginary part of dielectric constant. The temperature dependent relaxation time is found to obey the Arrhenius law having activation energy ~ 0.4 eV for Fe doped samples. The frequency dependent conductivity spectra are found to obey the power law.