Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping

JMRTEC-1158; No. of Pages 10

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

Available online at www.sciencedirect.com

www.jmrt.com.br

Original Article

Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping Imen Raies b , Sharah A.A. Aldulmani a , Lamia Ben Farhat a,b , Mongi Amami a,b,∗ a

Departement of Chemistry, Faculty of Sciences for Girls, King Khalid University, Abha, Saudi Arabia Laboratoire des Matériaux et de l’Environnement pour le Développement Durable, LR18ES10.9, Avenue Dr. Zoheir SAFI, 1006 Tunis, Tunisia

b

a r t i c l e

i n f o

a b s t r a c t

Article history:

Mossbauer spectroscopy, magnetic measurements, X-ray diffraction (XRD), as well as

Received 4 November 2019

impedance analyzer are some of the techniques that have been employed in this study to

Accepted 2 December 2019

evaluate how the dielectric, magnetic and structural properties of GaFeO3 (GFO) ceramics are

Available online xxx

affected by Ti and Zn doping. polycrystalline Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1) were prepared by solid state reaction. They showed an orthorhombic crystal structure with Pc21 n space

Keywords:

group. The magnetic transition temperature decrease due to the dilution of the magnetic

Multiferroic material

interaction. A noteworthy effect of substitution of multiple elements at the Ga and Fe sites

Mossbauer analysis

on dielectric constant and tangent loss of GaFeO3 has been observed. Complete studies of

Magnetism

temperature and frequency dependence of dielectric constant and impedance have provided

Site disorder

the effect of grains and grain boundaries on the conduction mechanism and dielectric relax-

Dielectric study

ation of the material. Impedance spectroscopy results have revealed a distinct conduction process at grain and grain boundaries. © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.

Introduction

Materials comprising both ferroelectric and ferromagnetic properties, known as multiferroic materials. The electric and magnetic properties in the materials causes coupling which in turn brings about magnetoelectric effects of interest. As a result of these effects, electric field application would control magnetization and vice-versa [1–5]. Naturally, simultaneous exhibition of ferromagnetic and ferroelectric properties is only present in very few single phase materials. The ear-

∗

lier reports showed that GaFeO3 (GFO) is a piezoelectric [6]. Studies conducted later on proved its state as a multiferroicmagnetoelectric coupled material [7–12]. This material has a magnetic transition temperature of approximately 250 K which is a hindrance to its application. However, when the Fe/Ga ratio is increased [7] or the reaction temperature reduced [13], it is possible to successfully elevate the transition temperature to higher than room temperature. This temperature can also be successfully improved with anneal [14]. The structure of GaFeO3 (GFO) is non-centrosymmetric orthorhombic of space group Pc21n [15]. The crystal constants are a = 8.751 Å, b = 9.399 Å and c = 5.081 Å, while the cationic sites are Ga1, Ga2, Fe1 and Fe2. Oxygen ions tetrahedrally coordinate with Ga1 while on the other side, oxygen ions

Corresponding author. E-mail: [email protected] (M. Amami). https://doi.org/10.1016/j.jmrt.2019.12.002 2238-7854/© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

2

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

octahedrally coordinate with Fe1, Fe2, and Ga2 [16]. Although GaFeO3 is antiferromagnetic in ground state [17], below its Curie temperature Tc, it exhibits ferrimagnetism with substantial magnetic moment. This is because both Ga and Fe have similar sizes and thus causing Ga2 and Fe2 sites to have a cationic site disorder. The magnetic transition temperature tuning is facilitated by the mixed occupancy which changes the composition. The changes also affect interaction exchanges between Fe3+ ions since Fe O Fe bond parameters are modified [18–20]. Studies on doping have revealed that dielectric and related properties are significantly affected by the disorder of cation as well as the nature of A-cations [21–23]. It has been reported that divalent ion substitution at the A site enhances magnetization [24]. Moreover, a comparison between pristine samples of GFO and Zn-doped samples revealed that Zn has enhanced electric polarization and magnetization [25]. At room temperature, it is possible to obtain phase transition as well as ferroelectricity signature by Tidoping GaFeO3 . Recently, the GFO related research activities are focused on thin films rather than bulk materials due to the large leakage current density and low polarization associated with bulk ceramics, which prohibit the applications of GFO-based materials in devices. It has been confirmed that the high leakage current density is the result of valence fluctuation of Fe ions, such as Fe 2+, Fe3+ and Fe 4+, and oxygen vacancies. There has been a continuous effort to resolve these issues by adopting following approaches: utilization of suitable processing techniques and effective substitution of desirable cation at Ga-site, or Fe-site or both A and B-site. Recently, Zu et al. have reported that the leakage current in BFO bulk can be decreased by codoping. The impacts of GaFeO3 magnetic and electrical properties co-doping with 2% Zn and Ti had been reported in previous work with prominent results being obtained [26]. Based on the results, further optimization of GFO could be possibly achieved by studying the impacts of Zn-Ti co-doping in GFO ceramics. With a key aim of ensuring a similar average valence state between dopants and Fe3+ , similar amounts of Zn2+ and Ti4+ co-doped GaFeO3 were used. As such, this work employs the solid state reaction method for synthesizing Zn2+ and Ti4+ co-substituted Ga1-x Znx Fe1-x Tix O3 multiferroics. Additionally, their magnetic, dielectric as well as structural properties are also investigated.

2.

Experimental procedures

The solid state reaction method was used to prepare polycrystalline GaFeO3 (GFO) and Ga0.98 Zn0.02 Fe0.98 Ti0.02 O3 (GZFTO2) samples. Through amount approximation, Ga2 O3 (99.99%), Fe2 O3 (99.9%), ZnO (99.9%) and TiO2 (99.9%) were scooped and mixed. An agate mortar was used to grind them till formation of a homogenous mixture. At varying durations and different temperatures, the resulting mixture was then pre-calcinated. Further on, thorough regrinding, pelletizing, and sintering of the powders was done at 1350 ◦ C (10 h). The purity of samples was proved by X-ray diffraction with the use of MoK␣ with ␭ = 0.709 703 Å wavelength. FULLPROF program package was then used to refine the samples’ lattice constants. At a

temperature ranging from 2 to 320 K, a SQUID magnetometer was used to evaluate magnetization at a magnetic field of 1000 Oe. A constant acceleration mode (triangular wave) in transmission geometry-operated Mossbauer spectrometer was used to record the room temperature Mossbauer spectra (MS). The operation was conducted at Co-57 in Rh, 50 mCi-strength matrix. An enriched ␣-57 Fe metal foil was used for velocity scale calibration maintaining a 0.23 mm/s calibration spectrum in the inner line width. Ti achieves a thinner absorber of 0.114 mg 57 Fe per cm2 , a WinNormos site fit program was used to fit the recorded MS. To achieve the fitting, the line widths were kept fixed while the rest parameters were left free. The isomer shift (␦) values are relative to (␦ = 0.0 mm/s) ␣57 Fe metal foil. A Weber presser KIP100E Isostatic press-wet bag pressing technique was used to cold press the uniaxially pressed powder to get the dielectric measurements. After a uniform distribution was achieved throughout the pellet, sintering was then done at 1400 ◦ C (10 h). Following preparation of silver electrode samples, a programmable electrometer (KEITHLEY 617) was used to take the dielectric measurements. A Novocontrol Alpha-A analyzer (f = 10–107 Hz) was employed in the exploration of complex dielectric permittivity with ZGS active sample cell at temperature range of 180−400 K.

3.

Result and discussion

3.1.

Structural analysis

Fig. 1a is an illustration of obtained diffraction patterns of the system Ga1−x Znx Fe1-x Tix O3 . As indicated by Phase analysis, it is clear that all patterns resemble the single phase of orthorhombic structure with space group Pc21 n (no. 33). From the least square fit of all four nominal compositions’ XRD nominal data, refined lattice parameters are obtained. A shift of the (221) diffraction peaks of GaFeO3 towards lower diffraction angle upon substitution with Zn, and Ti was remarkably observed from the XRD data. This is a clear indicator that doping increases the unit cell volume as well as lattice parameters. A revelation emerges upon close examination of cell evolution, a higher pronunciation is present in lattice constant c variation with Zn and Ti substitution than that of constants a’ and b’ as illustrated in Fig. 1b. When GaFeO3 was Sc-doped, a comparable behavior was reported [27]. Cation distribution was the major problem encountered when conducting Rietveld refinement. Ga/Zn and Fe/Ti cations have six oxygen sites and four different crystallographic sites which are Ga1, Ga2, Fe1 and Fe2. With Octahedral coordination manifesting itself in Ga2, Fe1, and Fe2 sites while tetrahedral coordination manifests in Ga1, majority of them have no special position but rather x, y, z general coordinates to be refined. In addition to poor differentiation between X-ray scattering factors of close neighboring atoms, the aforementioned position poses as extra challenges in Rietveld analysis. It should be noted that in octahedral coordination, the ionic radius of Ti4+ ion is 60.5 pm while that of Fe3+ in the high spin state is 64.5. In an octahedral oxygen environment, Fe3+ has an ionic radius of 55.0 in the low spin state. The ionic radius of Ga3+ is 62.0 pm and 47.0 pm in octahedral coordination and tetrahedral coordination respectively. On the other side, the ionic radius of

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

ARTICLE IN PRESS 3

j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

Fig. 1 – XRD pattern (a) and cell parameters evolution (b) with (Zn,Ti) content.

Zn2+ in tetrahedral coordination and octahedral coordination is 60.0 pm and 74.0 pm respectively. Though tetrahedral coordination is the highest preference of Zn2+ , the large ionic radii difference between Ga3+ and Zn2+ make it relatively difficult for Zn2+ to be inserted in Ga1 site. Ti at G2 site displays the smallest ionic radii difference than when in Fe1 or Fe2 sites. Upon substitution of Ti at the Fe2 sites, compressive stress on the crystal is anticipated to occur and subsequently causing unit cell volume to reduce. This is contrary to the results of this study where unit cell volume is realized. In X-ray absorption near edge structure (XANES) study by Walker et al. [28], and a combined theoretical and experimental study by Zein et al. [29] and Saha et al. [30], similar results were derived. Generally, Fe1 and Fe2 site octahedron shows a high distortion while that on Ga2 site shows relatively lower distortion. On the other hand, the Ga1 site tetrahedron show the possibility of no distortion at all [28]. It is also expected that an increase in the distortion for the three octahedrons will be moderately recorded with (Ti, Zn) content x.

3.2.

Magnetic properties

Fig. 2 is an illustration of the Ga1-x Znx Fe1-x Tix O3 (x = 0, 0.02, 0.05 and 0.10) samples magnetic properties. It come out clearly that, other than in GZFTO10 where a magnetization increase is recorded, (Zn,Ti) doping decreases magnetization. Using the minimum position of the dM/dT versus temperature curve, the magnetic transition temperatures for GFO, GZFTO2, GZFTO5, and GZFTO10 are calculated and recorded as 205 K, 177, 170 and 168 K respectively. From this, bifurcation of FC and ZFC magnetization curves at the irreversibility temperature can be noted. According to Wang et al. [31], disorder of Fe ions at the Fe1, Fe2, Ga1, and Ga2 non-equivalent cationic sites is the leading cause of this feature. Additionally, uncompensated ordering of two sub-lattices gives rise to GFO magnetization. One sub-lattice constitutes G1 and Fe1 while the other one constitutes Ga2 and Fe2. Their structure is MFe2 + MGa2 − MFe1 -MGa1 , with M being each site’s sublattice magnetization while A is cation site. Distribution of cation on the four sites largely determines the magnetization. As such, MFe1 and MGa1 increase and/or MFe2 and MGa2 occurs whenever M is decreased through (Zn,Ti) substitution. It is a

Table 1 – Mossbauer parameters (isomer shift ‘␦’, quadripole splitting ‘QS’, line width ‘L.W.’ and relative area ‘R.A.’) extracted from Mossbauer spectra recorded at RT of for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1). Samples

FeFe (%)

FeGa (%)

GFO GZFTO2 GZFTO5 GZFTO10

76 73 71 64

24 27 29 36

Ga 1.00 0.98 0.95 0.90

FeFe /FeGa 3.17 2.70 2.45 1.78

general expectation that MFe2 and MGa2 decrease will be realized when Ti4+ substitution causes a decrease in the amount of the Fe ions at Fe1, Fe2 and Ga2 sites. Katayama et al. [32] also reported the possibility of Fe3+ ions increase at Ga1 site as a result of inserting Zn2+ in Ga2 site. As such, increase of the Fe3+ ions at Ga1 site could be one of the leading causes of decrease of M after Ti4+ substitution. The overall unit cell volume could be enlarged by Ti and Zn co-substitution without the symmetry of the unit cell being changed. When a smaller radical Ti ion is used to substitute Fe, a shorter Fe O Fe bond arises while a contractive FeO6 octahedron is achieved. Ferromagnetism in GZFTO samples could be reduced as a result of these actions. Furthermore, in GFO ceramics with Zn2+ and Ti4+ molar ratio as 1:1, it is possible for the charge defects to be reduced without changing the iron valence when co-substitution of Zn and Ti is conducted. Replacing Fe3+ and Ga3+ with Ti4+ and Zn2+ respectively bring around a high possibility of charge compensation. This may result to charge defects suppression and consequently lower the magnetism [31]. For all the four samples, Mossbauer spectra have been recorded at room temperature to facilitate magnetic environment investigation around the Fe sites as well as determination of Fe oxidation state in the GZFTO matrix as illustrated in Fig. 3. Other than a tinny broadening at the peaks, no observations are made indicating significant changes in spectra. The interpretation of the pattern was made as a composition of two quadripole pairs shifted with regards to each other. Table 1 is an illustration of the analyzed area ratio (RS) as well as the quadripole splitting (QS). From the two doublets, one has a relatively high QS value that has been allocated to Ga sites (QS1) while the other one has a low QS value that is displaying more asymmetry around Fe ions and has been

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

4

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

Fig. 2 – Temperature dependence of the magnetism with (Zn,Ti) content.

Fig. 3 – Room temperature Mossbauer spectra and variation in (a) quadripole splitting, isomer shift and relative area for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1).

assigned to Fe sites (QS2). Fig. 3 (b), (c), and (d) shows isomer shift () relative area, and quadripole splitting with (Zn,Ti) doping variations respectively. It is notable that a decrease in QS2 for Fe-assigned quadripole in Ga sites occurs when doping is conducted. On the other hand, an increase ofQS1 up to 5% is recorded before a decrease commences. The most logical explanation for this is that structural distortion increase with substitution. Other than the GZFTO5 which displayed higher ranges of isomer shift (␦) compared to the other values, which are in a similar ranges (0.327–0.325 for GFO and 0.348–0.353 mm/s). The coordination number, and oxidation state, of iron is confirmed without ambiguity by the values. For all the two doublets, the presence of Fe ions present in high spin +3 oxidation states is indicated by the ␦ values. Fe3+ has a lower ␦ than Fe2+ at ranges between 0.8 and 1.2 mm/s. addition-

ally, the tetrahedral coordination ␦ value is smaller than that of octahedral coordination [33]. An increase of the of Fe occupation at Ga site due to doping is due to doping. Consequently, a decrease in the difference of sum of Fe2, Ga2 sites to that of Fe1 and Ga1 sites, which id the resultant moment, is noted. Conducting In-field Mossbauer measurements on the samples could reveal any Fe population at Ga1 site.

3.3.

Dielectric properties

In a 10 Hz to 10 MHz frequency range, dielectric constant temperature dependence was conducted. Fig. 4 (a), and (b) shows the relative dielectric constant (’) and dielectric loss (tan) at 1 KHZ respectively. The dielectric constant for GZFTO10 displays approximately 350 K relaxation that then broadens at

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

5

Fig. 4 – Real part of the dielectric constant and loss tangent as a function of temperature variation measured at 1KHz for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1).

Fig. 5 – Room temperature variation of dielectric constant and dielectric loss with frequency for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1).

5% before its intensity decreases when the Ti, Zn content is increased. At low frequency (100 Hz) in GZFTO5, a small anomaly of approximately 230 K emanates from permittivity. This is close to the magnetic transition temperature. For GZFTO5, additionally, around 250 K relaxation was realized to exist from dielectric loss. As illustrated in Fig. 5 (b) which represents temperature T (240 K), an initial decrease in tan ␦ is noted followed by a Debye-like relaxation. The loss related to conductivity is attributed as the main cause of the initial tan ␦ decrease. Dc conductivity and Debye-type dipolar relaxation are the two mechanisms contributing to tangent loss. At higher temperatures and lower frequencies, cd conductivity is the more dominant of the two. Various types of polarization contribute to the observed low dielectric constant at higher frequencies as well as high dielectric constant at lower frequencies. All four polarizations contribute at low frequencies, whereby, a one by one freezing of contribution polarization occurs as frequencies increases. On the other hand, only electronic polarization’s contribution persists at high frequencies. Through doping, a 5% enhancement of dielectric permittivity is realized with a 10% decrease below GFO value being noted later on. At low frequencies, a small anomaly of around 230 K is shown by GZFTO5 permittivity. This is relatively close to the magnetic transition temperature. Additionally, it was noted that increase in Ti con-

tent resulted to increase in Dielectric permittivity in Ti-doped GFO [34]. This is as a result of dielectric values increment due to ferroelectric donor doping. On the other hand, an increase in Zn content resulted to dielectric reduction in Zn-doped GFO [35]. It can therefore be stated that Ti effect is pronounced in GZFT5 and GZFTO2. Zn effect is however dominant in cases of higher content. Increased distortion of the crystal lattice is credited for enhanced polarization. This distortion occurs when Ga3+ -cations are substituted with Zn2+ -cations in the doped samples. For all samples, at room temperature, their dielectric permittivity which are also frequency dependent are shown in Fig. 5(a), and (b). A behaviour similar to the one exhibited by high-dielectric-constant materials is shown in a dielectric constant samples’ frequency dependent plot [29,30]. For GZFTO2 and GZFTO5, a high dielectric constant is exhibited in the studied materials. On frequency increase, the constant shows a step-like decrease, with the frequency dependent plot being accompanied by a loss peak. Additionally, ␧’ is significantly enhanced reaching a maximum in GZFTO5 by Ti and Zn doping in low frequency section. Thus, a distinctive space charge relaxation characteristic is revealed [29,30], an indicator of potential presence of good ferroelectric properties in GZFTO. It is revealed that Ti- or Zn-doping GaFeO3 results to enhanced dielectric constant [22,23].

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

6

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

Fig. 6 – Variation of imaginary part of the modulus (M”) with frequency for selected temperature for (a) GZFTO2, (b) GZFTO5 (c) GZFTO10 at low temperature region (d) high temperature region.

In this study, a larger dielectric enhancement is achieved when compared to that reported by Ti or others bivalent doping ions [20]. Smaller size of the particles could be another cause of this high dielectric constant values [30]. There are two permittivity mechanisms as shown in Fig. 5 (a). They have different slopes with the first one having a steep slope at high frequency while the second one has a shallow slope at low frequency. The Grain Boundary (GB) effect is the reason behind the high permittivity and low frequency curve. On the other hand, intrinsic bulk effect is the reason behind the low permittivity and high slope. Extremely high values of around 1000–8.105 are observed for GaFeO3 low-frequency constant upon a 0–5% increase of Zn, Ti content. The Maxwell-Wagner mechanism is responsible for this giant dielectric behaviour as it causes space charge polarization. As such, low activation energy and resistance manifest in the grain while on the other side, higher activation energy and high resistance manifest in the grain boundary. The gigantic dielectric constant in the samples is attributed to a conducting grain that produces an internal layer capacitor as well as a surface from its insulating grain boundary [31–34]. Doping up to 5% content triggers a relaxation phenomenon in frequency dependence of dielectric loss spectrum (tan ␦) than it vanishes in GZFTO10. This is an indicator that since a loss peak is an essential feature of charge carrier hopping transport, the hopping of charge carriers therefore have significant role in GZFTO5 and GZFTO2 transport procedures [28]. As temperature rises, a shift of loss peaks towards higher frequencies is realized. This is an indicator that the material

could be having thermally activated Debye-like dipolar relaxation. Fig. 6 presents the spectroscopic plots of M”(f) measured at the temperatures ranging from 160 to 400 K with an interval of 20 K. Though the modulus spectra show a set of pronounced relaxation peaks, a careful examination reveals that the M¨(f) curves are asymmetric. This could be confirmed ¨ max)plot. ¨ by the normalized electric modulus peak (M/M When the temperature is increased, a shift to the higher frequency side is sighted for all relaxation peaks. In turn, this is an indicator of fall in relaxation which could be as a result of reduced resistance with temperature increase. Additionally, temperature increase also leads to M” (max) increase. In view of charge recompense, substitution of Zn2+ at Ga/Fe-site produces oxygen vacancy to maintain charge neutrality. However, the metastable Fe2+ ions if produced, is easy to be oxidized to create oxygen vacancy in the structure and will be distorting the FeO6 octahedron which leads to change of bond angles and bond lengths of Fe-O plane. Frequencies dependent behavior at low temperature arises due to oxygen vacancy from the preparation process, this facilitates the short range ordered dipole, observed in low temperature. Further, an increase in temperature shows a transition from short range to long range ordering. Ferroelectric materials are commonly known for showing T-dependent capacitance in above transition temperature. T-independent capacitor is however expected to prevail when below transition and in materials that are non-ferroelectric. Clearly, a second contri-

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

7

Fig. 7 – Room temperature nyquist plots for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1).

Fig. 8 – Room Temperature combined plots of M” and Z” with frequency for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1).

bution develops at the high frequency end of the spectra in GZFTO10. The capacitance of this second contribution is similar or smaller than the first contribution, which excludes the possibility of an electrode interface effect. Interface contribu-

tions commonly exhibit larger capacitance and would occur at the low frequency end. The second contribution could potentially represent a secondary phase, surface layer or another unwanted contribution.

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

8

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

Fig. 9 – Variation of log ac conductivity with inverse of the absolute temperature for selected frequency for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1).

Moreover, a study of room temperature impedance plots is conducted to bring out clearly the contributions of grain and grain boundary. Only one depressed semi-circular arc was entailed in the GFO impedance plot at room temperature as shown in Fig. 7. This is an indicator that a parallel RQC circuit can be used to represent the shown gain contribution. Nevertheless, high frequency and low frequency semi-circular arcs are observed for systems with Zn, Ti doping, and thus indicating grain relaxations and grain boundary. Increasing the doping percentage results to a diminishing high-frequency semi-circular arc, therefore, showing that increase in doping

causes deterioration of grain relaxation. As such, an observation of lowly dominant grain relaxations as well as highly dominant grain boundary relaxations is made. When T is increased, a decrease in the radii of the semicircles is recorded, while at the same time, a semiconducting nature is indicated by decrease in electrical resistance. The grain boundary is dominated by the grain effect at low doping, while at high doping, a grain boundary effect dominance is observed following diminishing of grain effect. As such, the low and high frequencies regions exhibited relaxation conduction behaviour. In Zn doped LaFeO3 , a similar behaviour is visible [35,36], with con-

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

ARTICLE IN PRESS

JMRTEC-1158; No. of Pages 10

j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

Table 2 – Variation of the grain and grain boundary electrical parameters at the room temperature for Ga1-x Znx Fe1-x Tix O3 (0 ≤ × ≤ 0.1). (RGB, RG: grain and grain boundaries resistance respectively, CGB and CG: capacitance of grain and grain boundaries resistance respectively).

GFO GZnFTiO2 GZnFTiO5 GZnFTiO10

Rg (105 )

Cg (nF)

Rgb (105 )

Cgb (nF)

20.4 0.44 0.002 4.30

37.9 9.17 842 0.857

– 0.107 0.1516 –

– 618 859 –

duction mechanism possibly due to 2+ or 3+ valence Fe ions. These ions emanate from lattice distortion with the potential of successfully inducing polarization into the system. A series connection of two parallel RQC circuits could be used to represent the gain and grain boundary contribution. As listed in Table 2, it is possible to have an evaluation of grain capacitance (Cg), grain resistance (Rg), grain boundary capacitance (Cgb) and grain boundary resistance (Rgb) values’ from the fitted curve. A simple examination of the Nyquist plot can be used to directly infer the large GB resistance value, whereby, the bulk effect semicircle is smaller than the semicircle corresponding to the GB effect. A relatively conducting grain with its surrounding being an insulating grain boundary is vividly indicated by the activation and resistance energy values’. It is from this situation that the internal barrier layer capacitors (IBLCs) and the surface are formed resulting to enormous dielectric constants. ¨ Fig. 8 is an outline of imaginary components’ Mand ¨ Zfrequency dependences. The presence of non-Debye-type relaxation in the compounds is indicated by lack of concur¨ rence for peaks of all Mand Z¨samples. Determining whether short-range or long-range charge carrier movements are the causes of a particular relaxation process in a material is ¨ ¨ achieved by combined Zversus Mfrequency plots. As such, from the plots, lack of coincidence between the curves indicates that short range carrier movements are the causes of the relaxation. Fig. 9 (a)–(d) shows ac conductivity temperature dependence for GFO, GZFTO2, GZFTO5 and GZFTO10 at varying frequencies. Increase in temperature and frequency results to a remarkable conductivity increase for all compositions which then stabilizes at high temperature. It can be generally stated that conductivity increase emanates from charge hopping which is a thermally initiated process. A straight line that is broken and having a transition temperature is well satisfied by GZFTO2 and GZFTO5 conductivity. As previously mentioned, there is a consistency between dielectric constant behaviour and changes in the slope. ln ␴-1/T curves of pure as well as Zn,Ti doped GaFeO3 samples at 1KHz are exhibited in Fig. 9 (e). Whereas two different slopes in the high temperature range and low temperature range, respectively are exhibited by fitting Zn,Ti doped GaFeO3 lines, pure GaFeO3 curve can be fitting into an almost straight line.

4.

9

Conclusion

We have carried out detailed experiments on magnetic dielectric and transport properties of Zn, Ti doped GaFeO3 . For all the compositions and at room temperature, Fe ions are in high spin 3+ oxidation state as confirmed by the isomer shift value. The temperature dependent dielectric properties pointed forward a relaxor behavior of the system. Impedance measurement reveals an electrically inhomogeneous system with different transport properties at grain and grain boundary. The Contribution of conductivity at high temperature and low frequency has been analyzed. This situation leads to the formation of surface and internal barrier layer capacitors and results in very large dielectric constants. Grain and grain boundary effects were explained and correlated in the dielectric, impedance and conductivity spectra.

Conflict of interest statement Hier with we, authors of the submitted paper confirm that no conflict of interest exist.

Acknowledgment The authors extend their appreciation to the Deanship of Scientific Research (DSR), King Khalid University, Abha, Saudi Arabia for funding this work through General Research Project, under grant no. G.R.P-300-39.

references

[1] Kimura T, Goto T, Shintani H, Ishizaka K, Arima T, Tokura Y. Magnetic control of ferroelectric polarization. Nature 2003;426:55. [2] Masrour R, Bahmad L, Hlil EK, Hamedoun M, Benyoussef A. Superparamagnetic Behavior in La0.7Ca0.3MnO3 Perovskite: Monte Carlo Simulations. J Supercon Nov Magn 2015:165–8. [3] Masrour R, Hlil EK, Hamedoun M, Benyoussef A, Mounkachi O, El Moussaoui H. Electronic Structure and Magnetic Properties of La0.7Ca0.3MnO3 Perovskite. J Supercon Nov Magn 2015;28::2115–9. [4] Masrour R, Jabar A, Hlil EK, Hamedoun M, Benyoussef A, Hourmatallah A, et al. Ab Initio and Monte Carlo Approaches for the Magnetocaloric Effect in BaMnO3 Oxide Perovskite. J Supercon Nov Magn 2018;31:1083–8. [5] Erchidi Elyacoubi AS, Masrour R, Jabar A. Coexistence of blocked, metamagnetic and canted ferrimagntic phases at high temperature in Co–Nd ferrite nanorods. Appl Surf Sci 2018;459:537–43. [6] Remeika JP. GaFeO3 : A Ferromagnetic-Piezoelectric Compound. J Appl Phys 1960;31:S263–4. [7] Arima T, Higashiyama D, Kaneko Y, He JP, Goto T, Miyasaka S, et al. Structural and magnetoelectric properties of Ga2−xFexO3 single crystals grown by a floating-zone method. Phys Rev B 2004;70:064426. [8] Kan E, Xiang H, Lee C, Wu F, Yang J, Whangbo MH. Ferroelectricity in Perovskites with s0 A-Site Cations: Toward Near-Room-Temperature Multiferroics. Angew Chem 2010;49:1603.

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002

JMRTEC-1158; No. of Pages 10

10

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 1 9;x x x(x x):xxx–xxx

[9] Erchidi Elyacoubi AS, Masrour R, Jabar A, Ellouze M, Hlil EK. Magnetic properties and magnetocaloric effect in double Sr2FeMoO6 perovskites. Mat Res Bull 2018;99:132–5. [10] Erchidi Elyacoubi AS, Masrour R, Jabar A. Magnetocaloric effect and magnetic properties in SmFe1-xMnxO3 perovskite: Monte Carlo simulations. Solid State Comm 2018;271:39–43. [11] Masrour R, Jabar A, Benyoussef A, Hamedoun M, Hlil EK. Monte Carlo simulation study of magnetocaloric effect in NdMnO3 perovskite. J Magn Magn Mat 2016;401:91–5. [12] Masrour R, Jabar A, Khlif H, Ben Jemaa F, Ellouze M, Hlil EK. Experiment, mean field theory and Monte Carlo simulations of the magnetocaloric effect in La0.67Ba0.22Sr0.11MnO3 compound. Solid State Comm 2017;268:64–9. [13] Mohamed MB, Senyshyn A, Ehrenberg H, Fuess H. Structural, magnetic, dielectric properties of multiferroic GaFeO3 prepared by solid state reaction and sol–gel methods. J Alloys Compd 2010;492:L20–7. [14] Uk Kang K, Baek Kim S, An SY, Cheong SW, Sung Kim C. Magnetic properties of GaFeO3 prepared by slow cooling and quenched heat treatment method. J Magn Magn Mat 2006;304:e769–71. [15] KanekoY, Arima T, PHe J, Kumai R, Tokura Y. Magnetic and crystal structures of polar ferrimagnet Ga2−x Fex O3 . J Magn Magn Mat 2004, 272-276: 555-556. [16] Abrahams SC, Reddy JM. Magnetic, Electric, and Crystallographic Properties of Gallium Iron Oxide. Phys Rev Lett 1964;13:688. [17] Roy A, Prasad R, Auluck S, Garg A. Effect of site-disorder on magnetism and magneto-structural coupling in gallium ferrite: A first-principles study. J Appl Phys 2012;111:043915. [18] Han MJ, Ozaki T, Yu J. Magnetic ordering and exchange interactions in multiferroic GaFeO3. Phys Rev B 2007;75:60404. [19] Frankel RB, Blum NA, Foner S, Freeman AJ, Schieber M. Ferrimagnetic Structure of Magnetoelectric Ga2−xFexO3. Phys Rev Lett 1965;15:958. [20] Roy A, Mukherjee S, Gupta R, Auluck S, Prasad R, Garg A. Electronic structure, Born effective charges and spontaneous polarization in magnetoelectric gallium ferrite. J Phys: Condens Matter 2011;23:325902. [21] Srimathy B, Bhaumik I, Ganesamoorthy S, Bhatt R, Karnal AK, Kumar J. On the Neel temperature and magnetic domain wall movements of Ga2−x Fex O3 single crystals grown by floating-zone technique. J Alloys Compd 2014;590:459–64. [22] Mukherjee S, Roy A, Auluck S, Prasad R, Gupta R, Garg A. Room Temperature Nanoscale Ferroelectricity in Magnetoelectric GaFeO3 Epitaxial Thin Films. Phys Rev Lett 2013;111:087601.

[23] Atanelov J, Mohn P. Electronic and magnetic properties of GaFeO3: Ab initio calculations for varying Fe/Ga ratio, inner cationic site disorder, and epitaxial strain. Phys Rev B 2015;92:104408. [24] Han TC, Chung YD, Lee YC. Enhancement of multiferroic and magnetocapacitive properties in nanocrystalline Mg-doped GaFeO3 . J Alloy Comp 2017;692:569–72. [25] Mukhopadhyay K, Mahapatra AS, Chakrabarti PK. Enhanced magneto-electric property of GaFeO3 in Ga(1−x) Znx FeO3 (x=0, 0.05, 0.10). Physica B 2014;448:214–8. [26] Raies I, Aldulmani SA, Amami M. Dielectric relaxation and magnetic properties of Ti and Zn co-doped GaFeO3 . Physica B: Cond Matter 2018;538:1–7. [27] Chakraborty Keka R, Deshpande SK, Meena Sher Singh, Grover Vinita, Tyagi AK, Yusuf SM, et al. Revealing structural distortion and dielectric relaxation in Ga1−x Scx FeO3 (0≤x≤0.3). J Magn Magn Mater 2016;417:165–74. [28] Walker JDS, Grosvenor AP. An X-ray absorption spectroscopic study of the metal site preference in Al1−x Gax FeO3 . J Solid State Chem 2013;197:147–53. [29] Heiba Zein K, Mohamed MB, Imem NG. Structural Magnetic, and Optical Performance of Al and Mo Doped GaFeO3 . J Supercond Nov Magn 2016;29:1647–55. [30] Kalashnikova A, Pisarev R, Bezmaternykh L, Temerov V, Kirilyuk A, Rasing T. Optical and magneto-optical studies of a multiferroic GaFeO3 with a high Curie temperature. JETP Lett 2005;81:452. [31] Cheng CF, Ruan YJ, Liu W, Wu XS. Effect of local structural distortion on magnetic and dielectric properties in BiFeO3 with Ba Ti co-doping. Physica B 2015, 468-469:81-84. [32] Katayama T, Yasui S, Osakabe T, Hamasaki Y, Itoh M. Ferrimagnetism and Ferroelectricity in Cr-Substituted GaFeO3 Epitaxial Films. chem Mett 2018;30:1436–41. [33] Sharma K, Meena SS, Saxena S, Yusuf SM, Srinivasan A, Kothiyal GP. Structural and magnetic properties of glass-ceramics containing silver and iron oxide. Mater Chem Phys 2012;133:144. [34] Sen S, Chakraborty N, Tripathy S, Pradhan DK, Rana P, Sen A, et al. Effect of Ti doping on the structural, electrical and magnetic properties of GaFeO3 . J Mater Sci: Mater Electron 2016;27:4647–52. [35] Katayama T, Yasui S, Hamasaki Y, Itoh M. Electric Transport Characteristics of Gallium Iron Oxide Epitaxial Thin Film. MRS Advances 2017;2:3459–64. [36] Lakshmana Rao T, Pradhan MK, Dash S. Structural, microstructure and impedance spectroscopy analysis of Zn2+ doped LaFeO3 nanoparticles. AIP Conference Proceedings 2019;2115:030089.

Please cite this article in press as: Raies I, et al. Effect of restricted structural deformation on magnetic and electrical properties in GaFeO3 with Zn, Ti co-doping. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.002