Effect of Sb doping on the electrical and dielectric properties of ZnO nanocrystals

Author’s Accepted Manuscript Effect of Sb doping on the electrical and dielectric properties of ZnO nanocrystals Ramzi Nasser, Walid Ben Haj Othmen, Habib Elhouichet www.elsevier.com/locate/ceri

PII: DOI: Reference:

S0272-8842(18)33472-2 https://doi.org/10.1016/j.ceramint.2018.12.089 CERI20315

To appear in: Ceramics International Received date: 14 October 2018 Revised date: 11 December 2018 Accepted date: 11 December 2018 Cite this article as: Ramzi Nasser, Walid Ben Haj Othmen and Habib Elhouichet, Effect of Sb doping on the electrical and dielectric properties of ZnO n a n o c r y s t a l s , Ceramics International, https://doi.org/10.1016/j.ceramint.2018.12.089 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 galley proof before it is published in its final citable 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.

Effect of Sb doping on the electrical and dielectric properties of ZnO nanocrystals

Ramzi Nasser1, Walid Ben Haj Othmen1, Habib Elhouichet2,1,* 1

Laboratoire de Caractérisations, Applications et Modélisation des Materiaux LR18ES08, Sciences Faculty of Tunis, University of Tunis El Manar 2092, Tunisia.

2

*

Physics department, Sciences faculty, University of Bisha, Kingdom of Saudi Arabia. Corresponding author: [email protected]

Keywords: ZnO nanocrystals; Sb doping; Impedance spectroscopy; P-type conductivity; Dielectric constants.

Abstract The effect of antimony doping on electrical and dielectric behaviors of ZnO nanocrystals was investigated using impedance spectroscopy. The XRD diffractograms suggest that the ZnO lattice parameters are closely affected by Sb doping. The electrical conductivity of the ZnO nanocrystals depends obviously on the Sb amount. The variations of the resistivity and the dc conductivity with varied Sb content were correlated to lattice parameters variations and are consistent with the compensation phenomenon between electrons and holes which eventually induced by the appearance of p-type conductivity in the Sb-doped ZnO. The dielectric constants and the loss tangent were found to decrease with Sb amounts. Low values of dielectric loss with Sb doping suggest that Sb-doped ZnO is suitable way for low frequency devices applications. The study of the electrical modulus provided some evidence that the dielectric relaxation is thermally activated and reveals a spread in relaxation time for low Sb concentrations.

1

Introduction In the last decade, ZnO has been extensively studied due to its wide band gap of about 3.4 eV and large exciton binding energy of 60 meV at room temperature [1,2], which promises its applicability in optoelectronics devices [1,2]. The undoped ZnO typically exhibits n-type conductivity, which has been ascribed usually to the presence of native defects such as oxygen vacancies and interstitial zinc [3,4]. Over the past several years, the successful realization of p-type ZnO is still difficult due to the asymmetric ability of such oxides to be doped n-type or p-type [5,6], which in turn brakes the development of ZnO based optoelectronic devices. Nevertheless, p-type ZnO was successfully obtained once doped with group-V elements such as N, P, As and Sb. Recently, the antimony was theoretically proposed as a dopant for p-type ZnO [7], and the experimental results [6, 8,9] seems to be promising and well in accordance with the theoretical predictions [7]. Furthermore, Limpijumnong et al. [7], pointed out that the substitution of Zn by Sb ions could simultaneously induce two Zn vacancies. They reported that such a defect complex possesses a low formation energy and it is considered to be stable. On the other hand, the high exciton binding energy is a particular property of ZnO that can be closely related to the dielectric constant of the material [10]. In fact, an eventual reduction of the dielectric constant increases coulomb interaction energy between electron and hole may causes an enhancement in excitonic binding energy [10], which is benefic for optoelectronic applications. However, the number of research devoted to the study of electrical and dielectric properties of doped ZnO is still limited. To the best of our knowledge, there is no published work have paid attention to the electrical and dielectric properties of ZnO NCs doped with antimony. Hence, in this work, we are motivated to study the electrical and dielectric properties of Sb-doped ZnO using impedance spectroscopy known as a useful method to study the behavior of charge transport in grain interior (Bulk), interfaces (grains boundaries) [11] and dielectric dispersion [12,13]. Herein, Sb doped ZnO nanocrystals are elaborated by economical sol gel method. Zinc acetate (Zn(O2CCH3)2(H2O)2), antimony trichloride (SbCl3) and citric acid (C6H8O7) are used as zinc source, antimony doping source and stabilizer, respectively. The solutions were dissolved in 200 ml of bi-distilled water and stirred magnetically for 3h and evaporated at 120°C. The powders are heated at 300°C in order to eliminate the organic products, then, they are submitted to calcination at 500°C to obtain the pure phase of ZnO nanocrystals. 2

The elaborated Sb doped ZnO NCs are followed by a rigorous and deep structural, electrical and dielectric properties characterizations. The behavior of dc conductivity is correlated to the lattice parameters variations and is found in accordance with the compensation between electrons and holes resulted from the appearance of the p-type conductivity in Sb doped ZnO NCs. On the other hand, we have shown that dielectric properties are modified by doping with antimony. In this respect, the low dielectric loss of Sb doped ZnO NCs make the NCs suitable for way for low frequency devices applications.

1. Preparation of samples All chemicals are purchased from Sigma–Aldrich Company and are of a high purification quality. The preparation precursors are: zinc acetate (Zn(O2CCH3)2(H2O)2), antimony trichloride (SbCl3) and citric acid (C6H8O7), used as zinc source, antimony source and stabilizer, respectively. All the prepared samples ZnO, ZnO:Sb (1%), ZnO:Sb (2%),ZnO:Sb (3%) and ZnO:Sb (5%) will be indexed by ZnO, ZSb1, ZSb2, ZSb3 and ZSb5, respectively. The detailed description of the Sb-doped ZnO nanocrystals elaboration was reported in a previous study [14].

2. Experimental of characterization X-ray diffraction (XRD) patterns were obtained at room temperature with a Philips X’Pert system, using CuK radiation ( = 1.54056 Ǻ), operating at 40 kV and 100 mA. The diffractometer settled in the 2 range 25° -70° by changing the 2 with a step of 0.01°. Impedance measurements has been performed using an impedance analyzer (Model: Agilent4294A) in the frequency range 40 Hz - 8MHz at various temperature range (200°C - 330°C). The prepared ZnO nanopowders were consolidated into disk pellets with 1 cm diameter and 1 to 1.5 mm in thickness by using uniaxial pressing of 10 tones/cm2. The pellets were sintered at 500°C for 3H. The two adjacent faces of the pellets were coated with silver paste to form parallel plate capacitor. Further, the coated pellets were putted between two platinum plates to assure good ohmic electrodes.

3. Results and discussion 3.1

X-ray diffraction analysis

3

Figure 1 shows the XRD patterns of the prepared Sb doped ZnO samples, annealed at 500 °C. All the diffraction peaks clearly correspond to the Würtzite hexagonal structure of the Sbdoped ZnO and are in a good accordance with the standard PDF database (JCPDS file No. 361451).The (100), (002) and (101) peaks are detected at 31.8◦, 34.5◦and 36.4◦, respectively. No additional reflections related to antimony metal or antimony oxide phase were observed, indicating the purity of the obtained ZnO phase. The diffractograms peaks are found to be broadened and shifted upon modification with the Sb as shown in figure 1.a and 1.b, reflecting the successful substitution of the antimony. In addition, this shift of the XRD peaks is attributed to the variation of the lattice parameters following this substitution [14, 15], which can alter the electrical properties of the Sb-doped ZnO. It is to note that the same samples are reported in our previous report [14] showed the successful substitution of antimony in ZnO lattice basing on XPS measurement. The obtained diffraction peaks can also be used to estimate the strain undergone by the ZnO nanocrystals through the Williamson–Hall (W–H) equation [16]: (1) where ε is the strain,

is the full width at half maximum (FWHM). The W–H crystallite size

D is determined from the reciprocal of the intercept of the straight line plot of cos(versus 4sin(and the strain from its slope. The variation of the crystallite size and the strain with the Sb concentration is illustrated in Table 1. As shown in table 1, the deduced grain size decreases continuously with the Sb concentration. It is suggested that the introduction of Sb dopant induces certainly point defects in ZnO, which probably limits the grain growth. When increasing the antimony amount, it is believed that the grain size variation is rather correlated to the variation in the lattice parameters. Similar results are reported for both Na and Fe doping in ZnO [17,18].

3.1

Electrical study 3.1.1 Nyquist diagram Fig.2 shows the Nyquist plot for undoped ZnO and ZSb3 samples obtained by plotting

the imaginary part of the complex impedance versus the real part measured at different temperature. The obtained plots are semi-circles slightly depressed to the Z’ axis. The size of the semicircles is reduced when increasing temperature reflecting the semiconductor nature of the material [19]. The plot of the real part of the impedance versus frequency (Fig. 3) reveals that Z’ gives an increasing dip prior to merger at high frequency that may be associated to the 4

charge carrier hopping [13]. In the same figure, it is observed that the complex component of the impedance Z” a maxima peak Z”max that shifts to higher frequencies with antimony amounts, which indicates that the relaxation phenomenon, i.e., the relaxation time is affected by Sb doping [20]. The obtained Nyquist plots were theoretically fitted using the software ORIGIN8.0 (Microcal Software, Inc., Northampton, Ma USA).The theoretical adjustment is ensured by the modelisation of the sample through an equivalent circuit formed by a resistance representing the bulk resistance and a capacitor in parallel. Due to the depression of the semicircles, the capacitor can be replaced by a constant phase element (CPE) that has an impedance given by:

(

the angular frequency (

,

[21, 22] where is the imaginary unit (

)

is the frequency),

in F.cm-2.sn-1 [23,24], and the

is an independent frequency constant

is a dimension less parameter.

tendency toward a perfect semi-circle. When

) and

reflects the

, the CPE acts as a capacitance

.

The total impedance of the circuit is given by: = +

= (1/

)-1

1/

(

( (

) (

( (

where

) (

(2)

)) )

) )

(3)

(4)

is the bulk resistance.

The obtained parameters values are illustrated in Table 2. The magnitude of the A0 parameter is found to be around 10-9, informing that the grain boundary response is included in the total response of the system [25]. The resistivity Rb is found to increase with the antimony concentration. A similar behavior of the resistivity was found for Sb-doped ZnO thin films [26]. Furthermore, a similar comportment was found in Na-doped ZnO. In fact, A. Tabib et al. [12] reported that the resistance of ZnO increases with the addition of Na, and they proposed that Na+ substitutes Zn2+ sites and results in the appearance of acceptor level in the band gap. Therefore, the observed increase in the Rb values with Sb amount can reflects the successful substitution of Zn2+ by Sb3+ ions in the ZnO matrix as reported in our previous report [14], due to the small difference in the ionic radii values between Sb3+(0.076 nm [7, 9]) and Zn2+ (0.074 nm [7, 9]). 5

It is important to note that this substitution is accompanied by the formation of the complex acceptor level (SbZn-2VZn) substantial in the appearance of the p-type conductivity in ZnO [7, 9]. 3.1.2 Dc conductivity study The dc conductivity is determined using the expression [12]: (5) Where Z0 is the interception of the Nyquist plot with the real axis in the low frequency region, S is the surface area of the sample and e is the sample thickness. The variation of

with Sb content at T = 300°C is illustrated in table 3. We note that

until 3% of Sb, the ZnO conductivity decreases with antimony amount. Probably, this decrease is related to the influence of the Sb doping on the nature and density of defects in ZnO. Actually, we estimate that the formation of the complex acceptor (SbZn-2VZn), the most probable formed defect following the Sb-doping [6-9,14], affects closely the conductivity comportment of ZnO and can induces such a decrease in

. Similar behavior of

is

reported in Na-doped ZnO [12] and Fe-doped ZnO [27]. Other way, this decrease in the material conductivity can be strongly related to the variation in the unit cell volume, which presents the same tendency as

(figure 5). This

correlation between the variation of lattice parameters and conductivity with Sb concentrations is also confirmed through the variation of Rb values extracted from Nyquist plots, as clearly shown in fig.5. Actually, an increase in lattice parameters, as deduced from the XRD shift (Fig.5), affects closely the carrier hopping between sites and then the mobility of the charge carriers [9]. Thus, the increase noted by

gets to be justified, especially that

the particularity in the unit cell volume variation observed for ZSb5 sample is also observed in the resistivity behavior (Fig.5). For relatively high Sb doping, it is suggested that the antimony occupied interstitial sites as reported in our previous work [14], an increase in the Sbi sites, may leads to an enhancement in the conductivity as observed for the ZSb5 sample [14]. Furthermore, this particularity for the ZSb5 sample was also observed with the photocatalytic efficiency and PL measurements of the same sample [14], and it is attributed to the formation of the complex (SbZn-2VZn). In fact, this complex is energetically traduced by the appearance of an acceptor level above the valence band [7], usually accompanied with the appearance of the p-type conductivity for a given Sb concentration [14].

6

This feature results in a compensation phenomenon between holes and intrinsic electrons responsible for n-type conductivity in ZnO, reducing then the charge carrier density and consequently the conductivity of Sb-doped ZnO. In light of the above results, the conductivity of ZnO material may be switched to p-type especially for ZSb3 sample. The variation of the σdc as function of temperature for the different Sb-doped samples was depicted in Figure 6. It is found that the dc conductivity obeys to the Arrhenius law and consequently it can be expressed as follow [12]: (

)

(6)

Where σ0 is a prefactor, Ea is activation energy and KB is the Boltzmann constant. The different values of the activation energy Ea can be obtained from the slope of the

versus

1000/T curve. The existence of a single slope suggests the presence of a sole conduction mechanism for both undoped and Sb-doped ZnO samples. Table 3 illustrates the values of obtained activation energies. The Ea value for the undoped ZnO is found to be equal to 0.59 eV, which is in the same range than reported by other similar studies [12,21]. This conductivity type was essentially explained by the presence of important density of defects such as Zn vacancies, oxygen vacancies and Zn interstitial [12]. It is found that the activation energy decreases for ZSb1 sample. It can be due to the filling of defect sites present in the ZnO surface by Sb dopant [9], leading to a small enhancing in the crystallinity of the ZnO surface, which in turn minimizes the potential barriers between the grain boundaries reducing then the activation energy. Above 1% doping, Sb3+ ions start substituting Zn sites [14], which decreases the electron density due the difference in the valence state between the triply charged Sb3+ ions and Zn2+ ions, that in addition to the effect of the variation in lattice parameter, contributes to the decrease in the conductivity through the material. As shown in table 3, this decay in

is

accompanied by an increase in the Ea value. Actually, the activation energy is strongly correlated to the Fermi level position [12, 23]. Then, this increase in the activation energy of the ZSb2 sample compared to the ZSb1, can be attributed to the shift of the Fermi level toward the valence band due to the tendency for a p-type conductivity as suggested previously. The subsequent decrease in the activation energy for the ZSb3 and ZSb5 samples can be attributed to the establishment and stabilization of the p-type conductivity following the formation of the complex (SbZn-2VZn) level. In fact, for ZSb3 sample the Sb content seems to be sufficient to form a stable complex level that acts as acceptor to ensure a stable p-type conductivity in ZnO [9]. The influence of the complex acceptor (SbZn-2VZn) level on the 7

charge separation ability, band gap variation and photoluminescence of the Sb-doped ZnO was actually noted and discussed in our previous report [14], which further confirm its formation at such level of Sb doping.

3.1.3 AC conductivity study Fig. 7 represents the variation of the ac conductivity as a function of frequency for the ZSb2 sample, measured at different temperatures. It is clear that the conductivity has a constant value at low frequencies. At high frequencies, the frequency dependence of the conductivity start to be evident when σac increases sharply from a certain frequency range called the hopping frequency [12]. It is observed that this frequency shifts to lower values with increasing temperature. The obtained curves can be adjusted using the Jonscher power law generally adopted to fit the ac conductivity in oxides [28]: ( ) Where

( )

( ) (7)

( ) is the conductivity with a direct current.

are the characteristic parameter verifying generally and

and and

are constant and

and

. The exponents

represent the degree of interaction between mobile ions with the surrounding lattice

around them while the prefactor exponents A1 and A2 represent the strength of polarizability [28]. It is to note that the variation of ac conductivity with Sb doping, also, shows the same behavior as observed in dc conductivity at fixed temperature. The theoretical fit of the above equation was in a good agreement to the experimental data in figure 7. In this case, the variation of

suggests that the power law is obeyed [12].

At low frequencies, the low conductivity values can be attributed to the accumulation of charge carriers due to the low applied electric field. In this frequency range, the electrodes polarization effects seems to be dominant and are suggested to be absent in high frequencies region [29]. At high frequencies, the observed change in the slope of AC conductivity with frequency is related to the domination of bulk grain resistance over grain boundary resistance. Herein, the cumulated charge carriers at the grain boundaries have sufficient energy to overcome this localized potential barrier [30]. In general, this comportment confirms the presence of hopping mechanism between the localized states. Consequently, the mechanism of small polaron hopping [29] is the more probable process of conduction in ZnSb2 sample.

3.2

Dielectric study

3.2.1 Permittivity and Loss studies 8

Dielectric study gives an important insight on the ac capacitance of the system that can be determinate through the relaxation behavior of the charge carriers. Generally, the different dielectric parameters can be extracted from the impedance measurements. Actually, the complex permittivity ( ) is expressed according to the following equations: ( )

( )

( )

(

( ) Where

( ) and

( )

(

(

(8)

)

(9)

)

(10)

)

( ) are respectively the real part, known as dielectric constant, and

imaginary part, known as dielectric loss of the complex permittivity. capacitance of the empty cell ( flat surface of the pellet and

,

is the

is the cross-sectional area of the

is the thickness), for our experiments

.

Actually, the dielectric constant ( ) describes the ability of a given material to be polarized by an electric field [31], while the dielectric loss

( ) defines the efficiency with which the

electromagnetic energy is converted into heat [31,32]. As shown in Fig.8 (a), the real and imaginary parts of the dielectric constant increase with temperature and decrease with frequency. This behavior indicates the Debye-type dielectric dispersion [12]. Figure 8 (a) represents the variation of

with temperature for the ZSb3 sample. At low

frequency range, the dielectric constant increases with temperature, which indicates that the present dipoles require an enough thermal energy to be polarized following the application of the electric field reflecting then their limited contribution to the global polarization. Similar dependence of the dielectric constant on temperature is also observed in ZnO related works [12, 22]. The decrease of

with frequencies may be related to the decrease in number of

dipoles contributing to the polarization mechanism [33]. At high frequencies,

tends to

constant value, which is probably due to the rapid polarization phenomenon in the ZnO material [34]. On the other hand, the variation of the imaginary part the SZb3 sample is depicted in Fig.8 (b). It is clear that

with frequencies and temperature for undergone a rapid decrease at low

frequencies. At high frequencies, the dielectric loss became zero indicating the absence of energy loss at this frequency range. This result is rather expected due the decrease of the 9

dielectric constant i.e. the polarization ability at this frequency range. Actually, the dielectric dispersion process in ZnO nanocrystals can be explained by Maxwell-Wagner Effect [35]. In this model, the dielectric medium is assumed to high conducting grains separated by resistive grains boundaries. Consequently, after the application of an electric field, the charge carriers can easily move within the grains before being accumulated at grains boundaries. This behavior leads to high dielectric constant at low frequencies that can be explained on the basis of interfacial/space charge polarization due to inhomogeneous dielectric structure [35], and which may be attributed to the porosity or induced defects following the Sb doping. (11) As shown in figure 8(c), the dielectric loss factor takes relatively high values at low frequencies similarly to

and

behaviors. It is important to note that the dielectric loss

factor decreases with Sb contents as obviously observed in figure 8(c).The non-doped ZnO presents the higher

value, which indicates that the dissipation of the electromagnetic

energy decreases with Sb concentrations. The decrement of the dielectric loss with Sb content can be attributed to the small dielectric polarizability of Sb ions compared to Zn ions [36]. Therefore, as the Sb doping concentration increases, more antimony ions substitute zinc ions and thereby decreasing the dielectric polarization, which in turn may decreases the dielectric constant. Thus, in addition to the applicability of ZnO for high frequencies devices [37], the Sb doping allows the effective use of ZnO at low frequencies range for which the dielectric loss presents a large reduction as demonstrated previously. 3.2.2

Modulus studies

The electric modulus constant

is defined in terms of the reciprocal of the complex dielectric

( ) as follows [12]: ( )

Where respectively.

and

( )

( )

(12)

are the real and imaginary parts of complex modulus,

Fig.9 presents the real part of the modulus

. The tendency of

to zero in the low-

frequency region confirms the negligible effect of the electrode polarization phenomenon [38]. As depicted in Fig.9, It is clearly shown that maximum value

increases with frequency and reaches a

then decreases for high frequencies. The observed peak is slightly

asymmetric, which indicates that the relaxation in the Sb-doped ZnO material is of a nonDebye behavior type [39]. 10

The observed peak helps to evaluate the relaxation time through the relation = 1/τ where observed that

and

is the frequency of

[40]. Actually, it is

shifts to higher frequencies when increasing temperature, which then

indicates that the dielectric relaxation time

increases with temperature. This behavior makes

evidence that the dielectric relaxation, in which hopping mechanism of charge carrier dominates intrinsically, is thermally activated [41]. As shown in Fig.10, the variation of as a function of inverse of the absolute temperature appears to be linear and can be described using the relation: ( where

is the pre-exponential factor,

)

(13)

can be considered as the energy of dipolar

relaxation, kB is the Boltzmann constant and T is the absolute temperature. The obtained values of

and those of the relaxation time τ at fixed T=300°C are shown in table 2. The

values are found to be slightly different from those found using the plot ln(σdc.T) versus 1000/T, which can suggest a non-statistic distribution of the Sb3+ cations in the lattice inducing then a random conductivity, thus similarly the relaxation of dipoles is occurring randomly [13]. In this respect, the response of Sb3+ cations as elastic and electric dipole to the elastic and electric fields is not exactly the same in the samples. For example, 180° rotation of an elastic dipole does not lead to a relaxation, while that of an electric dipole does [42]. Furthermore, B. Kang et al. [43] reported that a relationship between the dielectric relaxation and the mode of electrical conductivity following the relaxation species in the range of high temperatures. On the other hand, the relaxation time τ shows an obvious increase for all the doped samples. Such behaviour suggests a spread in relaxation time for low Sb concentrations [13]. It is also important to note that the relaxation time has a similar tendency with Sb amounts compared to those of the activation energy and the unit cell volume with Sb concentration, which insight that the structural effects of the Sb doping affects also the relaxation behavior of the Sb-doped ZnO. Fig.11 illustrates the plot of

/

versus f/fmax for the ZSb2 sample under

different temperatures. The broadening feature of observed peak can be attributed to the summation of relaxations occurring in ZnO NCs bulk [12]. The overlap of the modulus curves for all temperatures indicates that the dynamical processes occurring at different frequencies are independent of temperature [44].

11

Conclusion Electrical and dielectric behaviors of both undoped and Sb doped ZnO nanocrystals prepared by sol-gel method, were investigated using impedance spectroscopy. The obtained Nyquist plots were theoretically fitted using a constant phase element CPE. The ZnO conductivity as well as the activation energy are found to be closely affected by Sb doping. The variation of resistivity and lattice parameters with Sb doping is related to dc conductivity which may induced the appearance of p-type conductivity especially for ZSb3 sample. Such change of the conductivity type is interesting for optoelectronic application of ZnO. Small polaron mechanism is suggested to be the dominant conduction mechanism. AC conductivity plots were analyzed by using Jonscher power law and its dependence of conduction mechanism can be inspired from small polaron model. Dielectric study of the as prepared samples reveals that the dielectric constant was also affected by antimony doping. The relatively low values of dielectric constant at low frequencies makes of Sb-doped ZnO NCs suitable for device applications. The investigation of the electrical modulus shows a spread in the relaxation time following the Sb doping. The change of conductivity type from n to p make of ZnO useful material in a broad range of device applications, among them as UV-Blue LED.

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[26] S.K. Pandey, S. K. Pandey, V. Awasthi, A. Kumar, U. P. Deshpande, M. Gupta, S. Mukherjee, p-type conduction from Sb-doped ZnO thin films grown by dual ion beam sputtering in the absence of oxygen ambient, J. App. Phys. 114 (2013) 163107. [27] M. Arshad, A. S. Ahmed, A. Azam, A.H. Naqvi, Exploring the dielectric behavior of Co doped ZnO nanoparticles synthesized by wet chemical route using impedance spectroscopy, J. Alloy. Compd. 577 (2013) 469–474. [28] B. Sundarakannan, K. Kakimoto, H. Ohsato, Frequency and temperature dependent dielectric and conductivity behavior of KNbO3 ceramics, J. Appl. Phys. 94 (2003) 5182. [29] R. Mimouni, O. Kamoun, A. Yumak, A. Mhamdi, K. Boubaker, P. Petkova, M. Amlouk, Effect of Mn content on structural, optical, opto-thermal and electrical properties of ZnO: Mn sprayed thin films compounds, J. Alloy. Compd. 645 (2015) 100–111. [30] R. O. Ndong, G. Ferblantier, F. P. Delannoy, A. Boyer, A. Foucaran, Electrical properties of zinc oxide sputtered thin films, Microelectron. J. 34 (2003) 1087–1092. [31] Idalia Bilecka and Markus Niederberger, Microwave chemistry for inorganic nanomaterials synthesis, Nanoscale, 2 (8) (2010)1269-1528. [32] D. M. P. Mingos and D. R. Baghurst, Tilden Lecture. Applications of microwave dielectric heating effects to synthetic problems in chemistry, Chem. Soc. Rev., 20 (1991) 1-47 [33] A. Awadhia, S. K. Patel, S.L. Agrawal, Dielectric investigations in PVA based gel electrolytes, J. Prog. Cryst. Growth Charact. Mater. 52 (2006) 61–68. [34] K. Srilatha, K. Sambasiva Rao, Y. Gandhi, V. Ravikumar, N. Veeraiah, Fe concentration dependent transport properties of LiI–AgI–B2O3 glass system, J. Alloys Comp. 507 (2010) 391–398. [35] K.W. Wagner, Zur theorie der unvollkommenen dielektrika, Annalen der Physik 345 (5) (1913) 817–855. [36] Mohd Arshad, Arham S. Ahmed, Ameer Azam, A.H. Naqvi, Exploring the dielectric behavior of Co doped ZnO nanoparticles synthesized by wet chemical route using impedance spectroscopy, J. Alloy. Comp. 577 (2013) 469–474 [37] J.B. Charles, F.D. Ganam, Dielectric studies on sodium fluoroantimonate single crystals, Cryst. Res. Technol. 29 (1994) 707–712. [38] F.S. Howell, R.A. Bose, P.B. Macedo, C.T. Moynihan, Electrical relaxation in a glassforming molten salt, Phys. Chem. 78 (1974) 639-648. [39] K. Praveen, B. Banarji, V. Srinivas, R.N.P. Choudhary, Complex Impedance Spectroscopic Properties of Ba𝟑V O𝟖 Ceramics, Res. Lett. 10 (2008) 1-5. 15

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Figures captions

Figure 1: a) X-ray diffraction pattern of Sb doped ZnO NCs. b) Zooming of the 3 principals peaks. Figure 2: Nyquist plots (Z″ vs Z’) at different temperatures for undoped ZnO and ZSb3. Figure 3: Variation of imaginary Z’’and real Z’ part of Sb doped ZnO NCs at fixed T=300°C, with frequency for different Sb concentrations. Figure 4: Experimental and theoretical impedance diagrams of ZnO:Sb NCs at T = 300 °C. Figure 5: Unit cell volume and Rb Nyquist vs. Sb concentration. Figure 6: Arrhenius relation of Ln(σdc.T) versus 1000/T for undoped and Sb doped samples. Inset: Variation of dc with Sb content at T=300°C. Figure 7: Theoretical fit and experimental data of σac for the sample ZSb2. Figure 8: Frequency dependence of (a) the real dielectric constant ɛ’, (b) ε” imaginary part and (c) tan(atC for all samples.

16

Figure 9: The frequency dependence of (a) M’ and (b) M” at different temperatures for the sample ZSb2.

200 112 201

103

110

10000

102

100 002

(a)

101

Figure 10: Variation of relaxation time Ln( with inverse of temperature 103/T.

ZSb3 5000

ZSb2 ZSb1 0

ZnO

30

40

50

60

70

2Theta (degree)

(b)

002

100

101

ZSb5

ZSb3

Intensity (a.u.)

Intensity (a.u.)

ZSb5

ZSb2

ZSb1

ZnO 31.2

31.8

32.4

34.0

34.5

35.0

2Theta (degree)

Figure 1

17

36.0

36.5

37.0

4

6.0x10

240°C

ZnO

250°C 260°C 270°C

4

4.0x10

280°C

Z"()

290°C 300°C 310°C 320°C 4

2.0x10

0.0 0.0

4

2.0x10

4

4.0x10

4

6.0x10

4

5

8.0x10

5

1.0x10

1.2x10

Z'()

5

7x10

210°C 220°C 230°C 240°C 250°C 260°C 270°C 280°C 290°C 300°C 310°C

ZSb3

5

6x10

5

Z"( )

5x10

5

4x10

5

3x10

5

2x10

5

1x10

0 0.0

5

2.0x10

5

4.0x10

5

6.0x10

5

8.0x10

Z'( )

Figure 2

18

6

1.0x10

6

1.2x10

6

1.4x10

T=300°C

5

8x10

ZnO ZSb1 ZSb2 ZSb3 ZSb5 ZnO ZSb1 ZSb2 ZSb3 ZSb5

Z'

5

7x10

5

6x10

Z', Z"

5

5x10

5

4x10

Z''

5

3x10

5

2x10

5

1x10

0 2

3

10

4

10

5

10

6

10

7

10

10

ln(f(Hz)

Figure 3

5

1.8x10

T= 300°C

ZnO

R

ZSb1 ZSb2 ZSb3 ZSb5

CPE

Fit

5

Z"

1.2x10

4

6.0x10

0.0 0

5

1x10

5

5

2x10

3x10

Z'

Figure 4

19

5

4x10

5

5x10

Unit Cell Volume Rb Nyquist

51

5

4.0x10

5

3.5x10

50 °3

5

2.5x10 48

5

2.0x10

5

1.5x10

47

5

1.0x10 46

4

5.0x10 45 0

1

2

3

4

5

Sb(% at.)

Figure 5 -7

-8

ZnO ZSb1 ZSb2 ZSb3 ZSb5 Linear Fit

-6

1.2x10

T=300°C

-6

1.0x10

-7

8.0x10 dc (sm -1 )

Ln(dc.T)

-9

-10

-7

6.0x10

-7

4.0x10

-7

2.0x10

-11

0.0 0

1

2

3

4

%Sb

-12 1.6

1.7

1.8

1.9

1000/T

Figure 6

20

2.0

2.1

2.2

2.3

5

Rb Nyquist

Unit Cell volume(A )

5

3.0x10 49

230°C 240°C 250°C 260°C 270°C 280°C 290°C 300°C 310°C 320°C Fit

ZSb2

-6

1.6x10

-6

-1

s m )

1.2x10

-7

8.0x10

-7

4.0x10

0.0 1

10

2

10

3

10

4

5

10

6

10

7

10

8

10

10

ln( f (Hz))

Figure 7

(a)

210°C 220°C 230°C 240°C 250°C 260°C 270°C 290°C 300°C 310°C

3000

ZSb3 2500

'

2000

1500

1000

500

0 2

10

3

10

4

10

Ln(f(Hz))

21

5

10

6

10

7

10

(b)

55000 50000

210°C 220°C 230°C 240°C 250°C 260°C 270°C 280°C 290°C 300°C

ZSb3

45000 40000

"

35000 30000 25000 20000 15000 10000 5000 0 -5000 2

10

3

10

4

5

10

10

6

10

7

10

Ln(f(Hz))

(c) 250

T=300°C

tan(

200

ZnO ZSb1 ZSb2 ZSb3 ZSb5

150

100

50

0 10

2

10

3

10

4

10

ln(f(Hz))

Figure 8

22

5

10

6

10

7

(a)

0.30

230°C 240°C 250°C 260°C 270°C 280°C 290°C 300°C 310°C 320°C

ZSb2 0.25

M'

0.20

0.15

0.10

0.05

0.00 1

10

2

10

3

10

4

10

5

6

10

7

10

8

10

10

Ln(f (Hz))

ZSb2

(b)1.04 0.96

230°C 240°C 250°C 260°C 270°C 280°C 290°C 300°C 310°C 320°C

0.88 0.80 0.72

M"

0.64 0.56 0.48 0.40 0.32 0.24 0.16 0.08 0.00 -0.08 1

10

2

10

3

10

4

10

Ln(f (Hz))

Figure 9

23

5

10

6

10

7

10

8

10

-12.0

ZSb2 Linear fit

-12.5

ln((s))

-13.0

-13.5

-14.0

-14.5

-15.0 1.65

1.70

1.75

1.80

1.85

1.90

1.95

2.00

1000/T(K)

Figure 10

230°C 240°C 250°C 260°C 270°C 280°C 290°C 300°C 310°C 320°C

1,0

M"/M"max

0,8

0,6

0,4

0,2

0,0 1E-5

1E-4

1E-3

0,01

0,1

f/fmax

24

1

10

100

1000

Figure 11: Plots of

/

versus f/fmax, for the ZSb2 sample, at different temperatures.

Tables Captions

Table 1: Structural parameters of ZnO:Sb NCs. Table 2: Fitting values of equivalent circuit elements for different samples at T = 300 °C. Table 3: Calculated values of σdc, activation energy Ea and relaxation time  at T=300°C.

Table 1 samples

a(Å)

c(Å)

Unit Cell Volume(Å3)

size

Strain

W-H (nm)

(10-4)

ZnO

3.21

5.24

46.43

53.2

1.2

ZSb1

3.19

5.21

45.57

49.3

3.3

ZSb2

3.27

5.28

48.55

47.1

4.12

ZSb3

3.30

5.31

49.73

46.5

4.83

ZSb5

3.22

5.23

46.48

51.1

0.8

25

Table 2 Sample

Rb (KΩ)

A0 (10-8 F.cm2sn-1)

n

ZnO

23.212

2.18

0.63

ZSb1

95.156

41.9

0.69

ZSb2

363.814

45.5

0.72

ZSb3

389.897

67.4

0.73

ZSb5

128.456

12.74

0.64

Table 3 μs

Samples

σdc (10-7Sm-1)

Ea (eV)

ZnO

11.4

0.59

0.61

6.4

ZSb1

5.85

0.35

0.34

193.6

ZSb2

1.9

0.69

0.72

53.4

ZSb3

1.7

0.42

0.45

78.5

ZSb5

4.83

0.48

0.49

3.3

26

(eV)