Accepted Manuscript Investigations on Magnetic and Electrical Properties of Zn doped Fe2O3 Nanoparticles and their correlation with local electronic structure Parmod Kumar, Vikas Sharma, Jitendra P. Singh, Ashish Kumar, Surjeet Chahal, K. Sachdev, K.H. Chae, Ashok Kumar, K. Asokan, D. Kanjilal PII: DOI: Article Number: Reference: S0304-8853(19)30898-4 https://doi.org/10.1016/j.jmmm.2019.165398 165398 MAGMA 165398 To appear in: Journal of Magnetism and Magnetic Materials Received Date: Revised Date: Accepted Date: 7 March 2019 14 May 2019 31 May 2019 Please cite this article as: P. Kumar, V. Sharma, J.P. Singh, A. Kumar, S. Chahal, K. Sachdev, K.H. Chae, A. Kumar, K. Asokan, D. Kanjilal, Investigations on Magnetic and Electrical Properties of Zn doped Fe2O3 Nanoparticles and their correlation with local electronic structure, Journal of Magnetism and Magnetic Materials (2019), doi: https:// doi.org/10.1016/j.jmmm.2019.165398 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Investigations on Magnetic and Electrical Properties of Zn doped Fe2O3 Nanoparticles and their correlation with local electronic structure Parmod Kumar1,*, Vikas Sharma2, Jitendra P. Singh3, Ashish Kumar4, Surjeet Chahal1, K. Sachdev2, K. H. Chae3, Ashok Kumar1, K. Asokan4# and D. Kanjilal4 1 Department of Physics, Deenbandhu Chhotu Ram University of Science and Technology, Murthal131039, Haryana, India 2 Department of Physics, Malaviya National Institute of Technology Jaipur – 302017, India 3 Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea 4 Materials Science Division, Inter University Accelerator Centre, New Delhi – 110067, India Abstract Present work aims at investigating the structural, magnetic and dielectric properties of zinc doped Fe2O3 nanoparticles (pure, 10%, 20% & 30%) and correlated with their local electronic structure using X-ray absorption near-edge structure (XANES) spectroscopy. Xray diffraction and Raman measurements infer that doping Zn cations and lead to the formation of secondary phases corresponding to ZnFe2O4 along with the hematite phase of Fe2O3. Magnetic measurements show that magnetization vs magnetic field curve for 10% Zn doping exhibit maximum saturation magnetization (~2.93×10-3 emu/g) as well as the coercivity (~956 Oe). Values of these parameters decrease for higher content of Zn. The temperature dependence of dielectric behaviour follows the same trend as that of the lattice parameter and magnetic measurements. The XANES spectra at Fe L-, and Fe K-edges indicates the partial reduction of Fe3+ ions into Fe2+ upon Zn doping in the Fe2O3 lattice. However, divalent state is favourable for Zn (i.e. Zn2+) within the doping range reported in this study. Corresponding author: * parmodphysics@gmail.com, # asokaniuac@gmail.com 1. Introduction Metal oxides are of scientific and technological interest for many decades because of their exceptional structural, optical, electrical, electronic and magnetic properties. Due to superior catalytic activity, superparamagnetic behaviour and large specific surface area of nanoparticles, ferric oxide (Fe2O3) nanomaterials have drawn significant attention in wide variety of applications in different areas such as in magnetic storage devices, targeted drug delivery, solar energy transformation, ferrofluids, pigments, rechargeable lithium batteries and catalysts [1-3]. Fe2O3 crystallizes in different crystalline phases viz. –Fe2O3, –Fe2O3, –Fe2O3 and –Fe2O3[4]. It has been noticed that –Fe2O3 (hematite) is most stable at low temperatures because of its high thermodynamic stability than any other form with extra advantages such as biocompatibility, non-toxicity, corrosion resistance and eco-friendliness [4,5]. It possesses hexagonal unit cell based on anion hcp packing similar to that of the corundum –Al2O3 crystal structure[6]. The structural and magnetic properties of undoped –Fe2O3 (Hematite) are well– known in recent precedent; however substitution at Fe site governs an escalating concern in the scientific community. Incorporation of metal ions at Fe site in host lattice is an effective way to alter the electrical, magnetic and many other physical properties. Various metal ions such as Ti, Cr, Ni, Zn, Al, Mg, Ga, Rh and Zr are used as dopants for substitution at Fe site in hematite lattice. It has been found that Ti doping in host –Fe2O3 enhances the donor density and reduces the rate of electron-hole recombination which in turn leads to great improvement of the photoelectrochemical (PEC) performance [7]. In a similar fashion, Zr doping also enhances the PEC performance by lowering the recombination rate of electrons and holes in –Fe2O3 nanorod arrays [8]. Furthermore, dopant like Zn not only affects various physical properties; it disturbs the crystal structure also due to the formation of cationic and anionic vacancies [9]. A report by Ingler et al. [10] have found that the presence of Zn in the form of ZnFe2O4 leads to an improvement in magnetic properties. Shen et al., reported promising photo-absorbance properties in ZnFe2O4/α-Fe2O3 hollow nanospheres [11]. It is well known that the nature of hybridization and site preference is disturbed by the concentration of dopants. As Zn stabilizes in Zn2+, it leads to the creation of hole in the oxygen (O) valence band and hence modifies the electronic properties of hematite [12]. To understand the effect of dopant on oxidation state and site occupancy, earlier reports on ferrites make use of the Mossbauer spectroscopy technique. This technique is very successful for ferrites as it provides exact information for Fe ions while the hybridization and oxidation state of dopants are very difficult to find out and are only assumed. Therefore, X-ray absorption near-edge structure (XANES) spectroscopy technique is employed to estimate the oxidation state and hybridization of all the individual elements present in the host lattice more precisely and accurately [13]. In this work, we report the effect of Zn-doping on the structural, magnetic and dielectric properties of Fe2O3 nanoparticles. The variation in physical properties after Zn doping is understood on the basis of modifications in the electronic structure in the context of changes of valence state, hybridization and crystal field parameters which have been understood using the XANES spectra at Fe L– and O K–edges. 2. Experimental Details 2.1 Synthesis and Characterization Zn doped Fe2O3 nanoparticles (Pure, 10%, 20% & 30%) were synthesized via sol-gel reaction method hereafter referred as Pure ZFO, 10 % ZFO, 20 % ZFO and 30 % ZFO respectively. The stoichiometric amounts of Zn(NO3)2.6H2O, Fe (NO3)3.9H2O were mixed in ethylene glycol. The prepared solution was stirred continuously and heated at 80 °C till it became viscous and then kept at 120 °C overnight to get precursor. Resulting powder was further sintered at 400 °C for 3 h to improve the crystallinity. The samples were characterized using x-ray diffraction (Bruker-AXS D8 Advanced diffractometer with CuKα source), Raman spectroscopy (InVia Raman microscope (Renishaw) and scanning electron microscopy (FESEM, Quanta 200F), which revealed crystallinity phase, space group and size distribution. The saturation magnetization and coercivity of samples were measured using vibrating sample magnetometer (VSM). Temperature dependent resistivity and dielectric measurements of these samples were measured using Keithley Electrometer-6517 B and Agilent E4980 LCR meter in the temperature range between 100 K and 400 K upon heating of sample with accuracy better than 0.05 K. XANES spectra at the O K-, Fe L-, and Zn Ledges were collected in total electron yield (TEY) mode at the 10D (PAL-KIST) beam line [13-15] while Fe K- and Zn K-edges were collected at the 1 D beam line of PAL. The photon energy resolution of this beam line was better than 0.6 eV (at the O K-edge). Results and Discussions 3.1. Crystal Structure Analysis Figure 1 shows the XRD pattern of pure and Zn doped Fe2O3 nanoparticles. All peaks present in hematite (Pure ZFO) sample can be perfectly indexed to rhombohedral -Fe2O3 phase (JCPDS No. 86-0550). Hematite (Fe2O3) belongs to the hexagonal crystallographic system (space group D2h16-R3c), with 30 atoms (6 Fe2O3 units) per unit cell. XRD pattern of pure ZFO exhibits major (104) peak centered at ~ 33.28°. The corresponding values of lattice parameter for pure Fe2O3 sample are found to be a–axis = 5.011 Å and c–axis = 13.16 Å. With the introduction of Zn (10 %) into the host lattice, a new peak centered at ~ 30° corresponding to (220) plane of ZnFe2O4 (JCPDS No. 22–1012) is noticed. Furthermore, there is reduction in the intensity of (104) peak while enhancement in the intensity of (110) peak of α–Fe2O3. The change in the intensity ratio of these peaks and occurrence of some additional peak infers the generation of new phase (i.e. ZnFe2O4) along with hematite (α– Fe2O3) structure. The slight enhancement in the lattice parameter values (a–axis = 5.025 Å and c–axis = 13.19 Å) are noticed for 10 % ZFO when compared with pure Fe2O3 nanoparticles. The enhancement in lattice parameter after Zn incorporation has also been reported by Deka et al. [16]. As the lattice parameters (a–axis and c–axis) are slightly enhanced with the addition of Zn, it can be assumed that some of the Zn ions replace Fe ions in –Fe2O3 and others occupy the vacant sites. These results are consistent with the observation of the enhanced lattice parameter in the case of Zn xFe3-2xO4 samples [17]. The observed changes in the lattice parameter is due to the replacement of smaller Fe3+ ions by larger Zn2+ ions in the substitutional sites. The bulk ZnFe2O4 possesses normal spinel phase in which divalent cations Zn2+, occupy the A (tetrahedral) sites only while Fe3+ cations occupy B (octahedral) sites [18]. However further increase in Zn concentration (20 % and 30 %), a shoulder peak (311) of ZnFe2O4 appears along with the (110) peak of –Fe2O3. In addition, the intensity of (110) peak dominates over (104) peak. The change in the ratio of peak intensities of –Fe2O3 and increase in the intensity of (220) of ZnFe2O4 infers that amount of ZnFe2O4 increases. For 20 % and 30 % ZFO samples, the reduction in both (a–axis and c–axis) lattice parameters are recorded and shown in Table 1. For large dopant concentrations (20 % and 30 %), Zn ions may not be incorporated into the hematite lattice due to its larger size and lower valence. It is assumed that Zn ions occupy some of interstitial sites in the lattice. Therefore, possible explanation for the reduced lattice parameters might be attributed to the presence of more oxygen, vacancies, lattice defects and formation of other phases. Furthermore, XRD measurements infer that addition of Zn in host lattice suppresses the formation of -Fe2O3 phase. The Scherer’s formula (D = 0.89/Coswhere D, are crystallite size, wavelength of X-ray (1.54 Å) and FWHM, respectively) was employed for estimating the crystallite size of samples [19]. The crystallite size for pure Fe2O3 is found to be ~ 39.54 nm. Interestingly, the average crystallite size decreases as Zn increases in host lattice (Table 1). Such behaviour has also been quoted for other ferrites and attributed to thermodynamic factors rather than nucleation features [17]. Figure 1. XRD pattern of Zn doped Fe2O3 nanoparticles. Table 1: Calculated crystallite and particle sizes, lattice parameter and other parameters for Zn doped Fe2O3 nanoparticles. Samples Pure ZFO 10 % ZFO 20 % ZFO 30 % ZFO Average crystallite size (nm) 39 39 38 37 Lattice a–axis 5.011 5.025 5.008 4.995 parameter (Å) c–axis 13.16 13.19 13.15 13.10 Particle Size (nm) 79 60 53 44 3.2 Raman Spectroscopy The synthesized nanoparticles were further investigated with the help of Raman spectroscopy to corroborate the homogeneous incorporation of the Zn2+ (mainly phase related information) in the structure. Figure 2 illustrates the room temperature Raman spectra of Zn doped Fe2O3 nanoparticles in the range of 100 – 800 cm–1. The group theory predicts the presence of seven Raman-active vibration modes (two A1g modes and five Eg ones). It is stated that certain Raman bands disappear in nanoregimes due to crystalline disorder. Apart from this, significant broadening in the peaks are observed for smaller sized materials. Figure 2. Raman spectra of Zn doped Fe2O3 nanoparticles. In the present case, Raman bands expected at ~ 245 and 412 cm1 corresponding to Eg modes are missing due to finite size effect. For pure ZFO (–phase of Fe2O3) sample, phonon modes observed at A1g (1) ≈ 214 cm1, Eg(1) ≈ 290 cm1, A1g (2) ≈ 390 cm1, Eg(2) ≈ 479 cm1, Eg(3) ≈ 590 cm1 are consistent with the reported values in literature. It is noticed that Eg modes in Raman spectrum shift toward lower wavenumber side for 10 % Zn substitution in the host lattice. However, further increase in Zn content in the matrix shifts the modes towards higher wavenumbers side. The shift in Raman modes represents the change in strain in host lattice with the addition of foreign atoms. Raman spectra for higher (20 % and 30 %) concentrations, infers the appearance of new phase peak at ~ 680 cm–1 marked as * in the figure. The appearance of new Raman band in the spectra for higher Zn doping indicates structural distortions. A number of reports have validated that the presence of peak at ~ 680 cm–1 corresponding to A1(g) is related with ZnFe2O4 structure [20]. Yogi et al. [21] have reported detection of additional peaks when Cr ions are substituted on Fe3+ site in –Fe2O3 lattice. The bands change gradually for Cr doping in –Fe2O3 that are attributed to the strong electron–phonon interaction. In a similar fashion, newly appeared band shifts systematically towards higher wavenumber side. The results from Raman are well in accordance with XRD observations where there is an enhancement in lattice parameter values for lower Zn doping while reduction takes place for higher doses due to the occupation of some interstitial sites by Zn ions and appearance of some additional peaks corresponding to newly formed phase. 3.3 FTIR Spectroscopy The chemical bonding related information of Zn doped Fe2O3 samples was examined by FTIR spectroscopy as shown in Figure 3. Two broad and strong bands in the wavenumber range 400 – 800 cm1 are evident in FTIR spectra of iron oxide. The band at ~ 460 cm−1 can be referred to bending vibration of O–Fe–O while ~ 550 cm−1 band corresponds to the stretching vibrations of Fe–O bonds in the lattice [4]. The absorption bands at ~ 1620 cm– 1 and ~ 3420 cm–1 originates due to adsorbed water and are assigned to H–O–H bending and O–H stretching vibrations [17]. Further, the peak appearing at ~ 2347 cm−1 indicates the presence of adsorbed CO2 in all samples [22]. Figure 3: FTIR spectra of Zn doped Fe2O3 nanoparticles. 3.4 Scanning Electron Microscopy (SEM) The SEM images are shown in Figure 4 and used to estimate the particle size and surface morphology. The analysis of SEM images infers that the samples consist of homogenous well–defined circular particles. The resulting average particle size estimated from these images for pure –Fe2O3 is ~ 79 nm. The reduction in the average particle size is observed with an increase in Zn content. It can also be noticed from XRD pattern that the diffraction peaks are broadening steadily with an increase in Zn content as a result of the decrease in the average particle size, in agreement with SEM data. Figure 4. SEM images of Zn doped Fe2O3 nanoparticles. 3.5. Magnetic Measurements The Magnetization (M) measurements as a function of applied field (H) have been carried out at room temperature for all samples. The effect of Zn doping on hematite nanoparticles is studied and noticed that magnetic properties are modified with changing Zn content. It is well established that magnetization of ferromagnetic materials is very much dependent on the crystal structure and morphology of grown samples. Figure 5 shows the M– H curves of pure and Zn doped Fe2O3 nanoparticles. It can be clearly seen that as prepared iron oxide (–phased Fe2O3) nanomaterials exhibit a weak ferromagnetic behaviour ~ 8.85×10-4 emu/g. The hysteresis features are gradually changed with Zn concentration as magnetic properties of host lattice are strongly affected by shape and size of dopant particles. The small remnant magnetization in present case is most probably related to fine spherical shape of hematite nanoparticles [23,24]. According to the curves, saturation magnetization and coercivity is highest for 10 % Zn doped (2.92×10-3 emu/g) among all samples. With further increase in Zn content (20 % and 30 %), reduction in both magnetization and coercivity is noticed. The enhanced saturation magnetization with Zn concentration (10 %) is likely to be due to the presence of ZnFe2O4 phase. ZnFe2O4 possess spinel structure and is denoted by the formula (ZnyFe1−y)[Zn1−yFe3−y]O4, where () and [] are referred to cations occupying tetrahedral site (A site, 8 of 64 tetrahedral interstitial sites) and octahedral site (B site, 16 of 32 octahedral interstitial sites), respectively. It is reported in literature that most of Zn cation prefer to occupy A-site and a small fraction at B-site and the ratio of Zn cations to the total cations at B site increases with further increase of Zn doping [25]. Additionally, due to substitution of Zn2+ ions in Fe3+ site, there is an increase in magnetocrystalline anisotropy contributions from Fe3+ ions. The anisotropy allows the spins to align along easy magnetic axis and prevents them in magnetizing other directions, hence leading to the enhanced remanent magnetization as well as the coercivity [21,26,27]. Figure 5. Magnetization vs. Magnetic field curves for Zn doped Fe2O3 nanoparticles. 3.6 Dielectric Measurements 3.6.1 Variation of dielectric constant (εꞋ) with temperature (at different frequencies): The dielectric measurements on Zn doped iron oxide nanoparticles were carried out due to the increasing interest in the dielectric properties of oxides. On application of ac field, the complex form of dielectric constant is given by ’+j”. Here ’ corresponds to the real permittivity or relative dielectric constant and ” denotes imaginary permittivity or dielectric loss. The room temperature dielectric measurements (not shown here) infer that the increase in frequency leads to reduction in dielectric constant [28,29]. The variation in dielectric constant as a function of frequency is well explained by the Maxwell–Wagner model [30] of interfacial polarization with the help of Koop’s phenomenological theory [31]. This is associated to lack of instantaneous polarization on the application of electric field due to inertia [32]. At low frequencies, all types of polarizations viz. ionic and orientation contribute towards polarization however; those having large relaxation times are not able to respond for higher frequencies. This delay in response of electric dipoles gives rise to loss and reduction in dielectric constant values with increase in frequencies. In other words, we can say that dielectric constant at low frequencies originates from the grain boundaries that contribute to high dielectric constant while at higher frequencies; its contribution is from grains (rather than grain boundaries) that possess small dielectric constant. Figure 6. Variation of dielectric constant with temperature at different frequencies for Zn doped Fe2O3 nanoparticles. The temperature dependent (100 K–400 K) dielectric properties for Zn doped Fe2O3 nanoparticles samples at selected frequencies (100 kHz − 500 kHz) are shown in Figure 6. The dielectric constant possesses weak frequency dispersion and small temperature dependence for all samples below ~ 220 K. All the dipoles are freezed (ceased) and do not have enough thermal energy to allow them to move freely in the lattice in low temperature regime (< 220 K). Due to this, charge carriers are incapable of orient themselves in the field direction which causes very small or almost constant dielectric constant below 220 K. On contrary, the charge carriers achieve sufficient energy to move freely inside the crystal causing polarization in higher temperature regimes (T > 220 K). The thermal energy librates more localized dipoles and the field tends to align them in its direction either by rotation or orientation. Simultaneouly, the temperature above 220 K provides sufficiently large energy to the charge carrier that increases exponentially resulting in space charge polarization. All these factors adds up and contribute towards the enhancement of ε’ in high temperature regime. Such behaviour is a generally noticed for ionic solids [17,28]. The observed value of ’ for pristine Fe2O3 samples at 380 K was 42.5 & 40.6 which increases to 48.42 & 41.48 for 10 % Zn incorporation into host lattice at 100 kHz and 500 kHz frequencies, respectively. However, further increase in the Zn content causes reduction in the dielectric constant values (Table 2). This is due to the cationic redistribution in the ZnFe2O4 phase. Initially, substitution of Zn leads to an increase of Fe2+/Fe3+pair in the B-site as discussed above which would enhance the hopping / polarization resulting in an increase in dielectric constant at this level of doping (i.e. 10 % Zn concentration). Earlier reports on ferrites have showed that inclusion of Zn, Cu, Co and Cd ions lead to an enhancement in dielectric constant due to the increase in hopping between Fe 2+ and Fe3+ ions [33-35]. It is observed through XRD and Raman analysis that for higher concentrations (20 % ZFO and 30 % ZFO), excess of Zn ions occupy some of the interstitial sites in the lattice. Due to this, the hopping between Fe2+/Fe3+ ions decreases which in turn is responsible for the reduction in dielectric constant. Table 2: Various parameters from magnetic, dielectric and XANES measurements for Zn doped Fe2O3 nanoparticles. Samples Saturation Magnetization Coercivity Hc (Oe) (emu/g) Pure ZFO 10 % ZFO 20 % ZFO 30 % ZFO 8.85×10-4 29.2×10-4 25.8×10-4 3.35×10-4 118 956 37 18 Dielectric Constant 380 K 100 kHz 500 kHz 45.02 48.42 45.92 42.04 40.63 41.48 38.16 35.91 3.7 Temperature dependent resistivity measurement: t2g/eg ratio Covalence / Extent of hybridization 0.26 0.34 0.46 0.43 0.30 0.24 0.39 0.34 The temperature dependent resistivity measurements are very important to understand electrical conduction mechanism. Figure 7 shows the temperature dependent electrical resistivities of Zn doped Fe2O3 nanoparticles in the range of 150 K – 380 K. It is well known that semiconductors follow the Arrhenius relation for resistivity, where 0 is resistivity constant, Ea is activation energy and k is Boltzmann’s constant. It can be clearly seen from the figure that resistivity decreases with the temperature. This is a typical semiconducting behaviour wherein the reduction in resistivity with temperature can be correlated with enhanced drift mobility of thermally activated charge carriers. The plot of lnρ vs 1000/T for pure Fe2O3 is plotted in the inset of figure 7. As evident there exist two different slopes depending upon temperature variation range and correspond to two different kinds of conduction mechanisms viz. nearest neighbour hopping and variable range hopping. It is suggested that nearest neighbour hopping is dominant in high temperature region while variable range hopping comes into picture for lower temperatures where decrease in temperatures freezes the nearest neighbour hopping mechanism [29,36,37].There is negligible variation in the resistivity at lower temperatures however, sudden drop in the resistivity can be seen in higher temperature regime. This is because the charge carriers donot have enough thermal energy to participate in the conduction and are affected by grain boundaries. With rise in temperature, electrons gain enough energy to participate in conduction among the grains and cross grain boundaries resulting in the reduced electrical resistivity. Figure 7. Temperature dependent resistivities of Zn doped Fe2O3 nanoparticles. Here, the inset shows the ln ρ vs 1000/T plot of pure Fe2O3 clearly indicates the presence of two different slopes. The resistivity value of pure Fe2O3 nanoparticles at 150 K is found to be ~ 2.3×109 cm. It can be clearly seen from resistivity curve that incorporation of 10 % Zn ions in Fe2O3 lattice leads to an increase in electrical resistivity (8.7×109 cm) which is quite expected. As discussed in above section that the substitution of Zn2+ ions will decrease the Fe3+ ions concentration. Due to this, the hopping rate of electron transfer will also decrease and consequently increases the electrical resistivity. The enhanced resistivity means high insulating nature and hence can be correlated with observed increase in dielectric constant in for 10 % Zn doped Fe2O3 samples. For higher doping (20 % and 30 %) levels, the resistivity decreases and found to be 6.3×109 cm and 2.8×109 cm, respectively. This behaviour is understood on the basis of non-uniform distribution of excess Zn ions which occupies some of the interstitials sites / might be segregated on the surface. The non-uniform distribution of Zn ions increases the hopping among Fe2+/Fe3+ ions and hence reduction in electrical resistivity. The enhancement in electrical resistivity for lower Zn content in Fe2O3 suggest that desired properties for high frequency applications can be achieved just by controlling the doping concentration and site occupancy of Zn ions in the host matrix. 3.8 X-ray Absorption Near-Edge Structure Study X–ray Absorption Near-Edge Structure (XANES) spectroscopy is very sensitive technique for elemental analysis, chemical states and has been used to probe the local electronic structure [38,39]. The XANES spectra at Fe L–edges were recorded for pure and Zn doped Fe2O3 samples (Figure 8) which provide the information related to Fe–3d states. Mainly, the two states Fe(2p3/2) and Fe(2p1/2) are separated by ~ 13 eV and corresponding to them two multiplets (t2g and eg) appear due to spin-orbital splitting of Fe 2p core hole[40]. The spectral features (L3 and L2 –edges) located at ~ 710 eV and ~ 723 eV have been associated with the transitions of Fe(2p3/2) and Fe(2p1/2) to an unoccupied 3d orbital respectively. For pure Fe2O3 sample, the lower energy peak in Fe(2p3/2) corresponds to the unoccupied t2g ↓ states at ~ 709.5 eV while the dominant peak ~ 711.3 eV represents unoccupied eg↓ state. In the same analogy, Fe (2p1/2) peak splits into t2g ↓ and eg↓ states and is associated to octahedral crystal ligand field. A visual inspection over XANES spectra infers that there is reduction in the peak intensity with the enhancement of Zn concentration. The reduction in spectral intensity of Fe L-edge indicates more number of occupied Fe (3d) states which clearly represent the chemical interaction among Fe2O3 and Zn. This might be probably due to charge transfer from Fe (3d) state to Zn (3d) and/or O (2p) states due to the mixing of orbitals. It is inferred that any change in Fe valence state results in the shifting of peaks and alteration of shape[40]. It can be clearly seen that peak shifts towards lower energy side indicating the presence of mixed valence state of Fe2+ and Fe3+ in Zn doped samples. The XANES spectra at Fe K-edge of pure and Zn doped Fe2O3 samples are shown in Figure 8. It is noticeable that the spectra consist of a pre-edge feature (~ 7114 eV) and the well-defined peak (~ 7133 eV). The pre-edge peak in the Fe K-edge originates due to 1s to 3d quadruple allowed transitions in a distorted centro-symmetric six fold-coordinated system [23, 24]. On the other hand, a well-defined intense peak is associated with the allowed Fe 1s → 4p transitions. Based on the existing literature, both these features are sensitive to the oxidation state of Fe. Thus, a detailed analysis of the features provides information on the oxidation state and coordination numbers. In the present case, though, the pre-edge peak position is nearly the same for all of the samples. However, there is reduction in the intensity and shifting towards lower energy side for the intense peak. The lower energy and peak shifting is possible if a fraction of Fe3+ ions converts into Fe2+ ions with Zn doping in Fe2O3 lattice. This observation is consistent to the results from Fe L-edge and strengthened Fe3+ and Fe2+ ions in the higher Zn incorporated Fe2O3 samples. Figure 8. (a) Fe L–edge and (b) Fe K–edge XANES studies of Zn doped Fe2O3 nanoparticles. The XANES spectra at Zn L–edge of Zn doped Fe2O3 nanoparticles are shown in Figure 9. According to the dipole selection rules, the Zn L3,2-edge XANES probe the unoccupied Zn s- and d driven density of states. The peaks in the energy regime (1010 – 1030 eV) are attributed to the t2g mode while (1030 – 1050 eV) energy regime corresponds to the eg orbital [41]. It is noticeable that the pure ZFO and lower Zn content doped samples have exhibited significant background in the spectra because of less Zn contents in the samples; however the spectral quality of higher Zn content doped samples is resorbable under the spectral resolution of used beam line. It is also noticeable that the FWHM of the peaks is narrowing with increasing the Zn contents in the samples. This could be due to the improved hybridization of Zn 3d orbitals with the surrounding O 2p orbitals via stabilization of certain phase within the host Fe2O3, as evidenced by the XRD results. To probe the electronic structure properties and valence state of Zn ions in the samples, systematic, Zn K-edge XANES were collected and presented in Fig 9 (b). Zn Kedge XANES spectra originate from Zn 1s → 4p transitions which are permitted by the dipole selection rules [41]. No pre-edge features (originated by the Zn 1s →3d orbital mixing) is seen in the present Zn K-edge XANES. This is because of the fact that the Zn2+ obey d10 electronic configuration and are permitting only the Zn 1s → 4p transitions in the present study. The spectral features in the Fig. 9 (b) show that the local electronic structure of lower and higher Zn doped Fe2O3 samples is approximately the same, indicating that the Zn+2 are the favorable species in all of the samples. However, it is observed that the peak intensity is slightly enhanced with increasing the Zn contents in the samples and could be due the improved strength of Zn 1s → 4p transitions with increasing the Zn concentration in the Fe2O3 host lattice. Figure 9 (a) Zn L–edge and (b) Zn K-edge XANES studies of Zn doped Fe2O3 nanoparticles. The O K-edge spectra provide information related to O 2p unoccupied density of states which are originating from core 1s excitations. Figure 10 depicts the O K–edge spectra for Zn doped Fe2O3 nanoparticles. The spectra are separated into two feature sets of interest. The first set (known as pre–edge regime) consists of the local intensity maxima in between 528 and 535 eV that corresponds to the hybridization of oxygen 2p with the transition metal 3d band. The pre-edge spectra consists a pair of well-resolved resonance peaks belonging to t2g and eg symmetry bands in effect of ligand field splitting [13,42]. The second set (known as post–edge regime) at energies greater than 535 eV describes the hybridization of O 2p state with Fe (4s, 4p) states. The O K-edge spectra are very much sensitive to the local chemical environment of the oxygen atoms. The pre edge feature provides the information related to extent of hybridization of O 2p state with 3d states of transition metal atoms. The intensity of spectral features corresponding to t2g and eg symmetry states depends on the spin states and number of 3d-orbitals [43]. Figure 10. O K–edge XANES studies of Zn doped Fe2O3 nanoparticles. On analysing the pre–edge feature in O K edge spectra, the variation in the intensity ratio of spectral t2g and eg bands is quite clear. The change in the intensity ratio of these modes infers the extent of hybridization of O (2p) orbitals with 3d orbitals of transition metal atoms. It has been found that eg orbital is very sensitive to the bonding of oxygen with neighbouring ions. A substantial decrease in the intensity of eg mode results in increase in t2g / eg ratio after Zn doping in comparison with the pure α–Fe2O3. The t2g / eg ratio for pure α– Fe2O3 sample are found to be 0.26 and it increases for Zn doped samples (Table-1). The change in value of t2g / eg peak ratio is related to the change in the symmetry of O atoms around Fe3+ ions. From XRD, it is observed that Zn doping leads to the formation of spinel phase ZnFe2O4 which affect the symmetry of O atoms and leads to the change of t2g / eg peak ratios. This indicates that pure hematite is well crystallized as observed by XRD analysis [44]. The spin states are changing with the introduction of Zn ions.The increase of t2g / eg peak ratio value with Zn doping is due to increasing inversion degree of ZnFe2O4 [45]. Further, it is speculated that the intensity ratio of O (2p) Fe (3d) feature compared with O (2p) Fe (4s, 4p) feature is used to find out the relative contribution covalent bonding in Fe2O3 nanoparticles. In the present study, the intensity ratio of these two features (O (2p) Fe (3d) and O (2p) Fe (4s, 4p)) is changing continuously with the incorporation of Zn ions in host lattice. With the introduction of Zn ions (10 %), there is sharp reduction in the intensity ratio of these features. However, this ratio is higher for 20 % and 30 % doped samples compared to 10 % Zn doped Fe2O3 nanoparticles. This behaviour depicts the changes of unoccupied O 2p projected density with Zn doping. This variation in the intensity ratio of these features are well correlated with XRD, dielectric and magnetic results, where enhanced values of magnetic and dielectric constant are noticed for 10 % doping which decreases for 20 % and 30 % Zn doped Fe2O3 nanoparticles. 4. Conclusion In conclusion, we have successfully synthesized Zn doped Fe2O3 nanoparticles through a simple approach (sol–gel reaction method) without the use of any organic surfactant. With an increase in zinc concentration to 20 % and 30 %, a migration of Zn cations are detected that lead to the formation of impurity phase (zinc ferrite) along with crystalline hematite phase. The origin of new band in the Raman spectra for these concentrations infers the formation of additional phase for higher Zn contents in supports of XRD results. The magnetic and dielectric properties analysis infer that the saturation magnetization, coercivity and the dielectric constant varies significantly with Zn content in host lattice. The values of magnetization, electrical resistivity and dielectric constant increase initially for 10 % Zn content, however reduces at the higher concentration of the Zn (for 20 % and 30 % doping) and Zn occupies interstitial sites in the host lattice. The variations in magnetic behaviour and dielectric constant are correlated with XANES spectra. Based on these results, it is concluded that transport / dielectric and magnetic properties are closely related with the site occupancy of dopant ions at substitutional or interstitial sites. The incorporation of Zn ions disturbs the Fe2+/Fe3+ ions ratio in host lattice resulting in enhanced magnetic, electrical and dielectric properties for 10 % Zn concentration and then reduction in these values. Therefore, to achieve desired properties, concentration and type of dopant ions and its site occupancy should be optimised. 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Wang, Z.H. Zhang, H.L. Tao, M. He, B. Song, Q. Li, Solid State Communications 223 (2015) 12. Highlights  Zn doped Fe2O3 nanoparticles  Study of magnetic and electrical properties  Correlation of magnetic and electrical properties with local electronic structure