Structural, electric modulus and complex impedance analysis of zno at low temperatures

Received: 19 February 2016 | Accepted: December 2016 DOI: 10.1111/jace.14725 ORIGINAL ARTICLE Structural, electric modulus and complex impedance analysis of ZnO/TiO2 composite ceramics Raoudha Ben Belgacem1 | Mariem Chaari1 | Alejandro F Bra~ na2 | Basilio Javier Garcia2 | Adel Matoussi1 Laboratory of Composite Ceramic and Polymer Materials (LaMaCoP), Sfax Faculty of Science, Sfax, Tunisia Grupo de Electronica y Semiconductores, Departamento de Fısica Aplicada, Universidad Autonoma de Madrid, Madrid, Spain Correspondence Raoudha Ben Belgacem, Laboratory of Composite Ceramic and Polymer Materials (LaMaCoP), Sfax Faculty of Science, Sfax, Tunisia Email: rawdabelgacem@gmail.com Abstract ZnO/TiO2 composite ceramics have been prepared by solid-state reaction technique at 900°C The X-ray diffraction results revealed the formation of secondary phases referred to as spinel Zn2TiO4 and hexagonal ZnTiO3 The structural analysis showed that all the composites that have been prepared have a polycrystalline nature and a hexagonal wurtzite structure The complex modulus (M) and electric impedance of the samples have been investigated by broadband dielectric spectroscopy in a wide range of temperature (40°C-110°C) and frequency (0.1 Hz to 10 MHz) The modulus plots (M00 , M0 ) illustrate the presence of non-Debye type of relaxations attributed to the effects of interfacial and dipolar polarizations The real and the imaginary parts of the impedance are well fitted to equivalent circuit models At high temperatures, Z″max varies from 0.03 106 to 4.9 106 Ω when the TiO2 doping concentration increases from to wt% From the obtained results, the secondary phase ZnTiO3 plays an important role in the electrical properties KEYWORDS dielectric spectroscopy, impedance, modulus, zinc oxide | INTRODUCTION In recent years, several theoretical and experimental studies have been based on zinc oxide (ZnO) due to its remarkable electric, dielectric, and optical properties ZnO is a wide band gap n-type semi conductor (3.3 eV at room temperature) with a high exciton binding energy (60 meV) which can be used in various applications such as transparent conducting electrodes, display materials, gas sensors, solar cells, and systems varistors.1–4 Numerous ZnO nanoparticles are prepared with a variety of deposition techniques such as: sol-gel,5,6 RF sputtering,7 chemical vapor deposition,8 pulsed laser deposition,9 and spray pyrolysis.10 Furthermore, ZnO may contain different types of defects and behaves as an n-type semi-conductor due to oxygen vacancies,11 oxygen interstitial,12 zinc vacancies,13 zinc interstitial,14 and more complex defects.15 This can be modified J Am Ceram Soc 2017;1–14 thoroughly by appropriate substitution dopants Many researchers have reported that small concentrations of dopant material such as Al, Ga, Mg, Cu, In, and Y can significantly affect the electrical, dielectric, and optical properties of ZnO.16–20 Among these dopants, titanium dioxide (TiO2) is one of the best candidates because of its excellent stability, non-toxicity, low cost, and ease of availability.21,22 Recently, Dulin and Rase23 reported that three compounds exist in the ZnO/TiO2 system: zinc orthotitanate Zn2TiO4 with a cubic spinel crystal structure, zinc metatitanate ZnTiO3 with a hexagonal structure, and Zn2Ti3O8 with a cubic defect spinel structure Zinc titanates are promising candidates in many fields such as dielectric materials for microwave devices and for preferably lowtemperature co-fired ceramics,24–26 gas sensors for the detection of NO, CO,27 paint pigments,28 and catalytic sorbents for desulfurization of hot coal gases.29 Synthesis and wileyonlinelibrary.com/journal/jace © 2017 The American Ceramic Society | | BEN BELGACEM characterization of ZnO/TiO2 composites have been previously reported by many groups.30,31 E Garcia-Ramirez et al.30 synthesized ZnO/TiO2 thin films by the r f sputtering technique on glass substrates They obtained a mixture of ZnO, TiO2 (anatase and rutile), ZnTiO3, and Zn2TiO4 phases which coexist They also reported that the average grain size was about 31 nm for ZnO phase P K Jain et al.31 prepared zinc titanates (ZnTiO3) ceramics by conventional solid-state reaction method using ZnO and TiO2 in a molar ratio 1:1 They reported that the crystallite size increased and FWHM decreased with the increase in the substrate temperature They also showed that the dielectric constant of ZnTiO3 increased as the substrate temperature increased due to the enhancement in crystallinity and improved morphology The purpose of this study was to investigate the effect of the TiO2 doping content on the structural, morphological, and electric properties of the ZnO material | EXPERIMENTAL DETAILS The ZnO/TiO2 ceramics was prepared by solid-state reaction method between reagent graded precursors of ZnO (purity >99%) and TiO2 Different powder blends of ZnO containing 1, 3, 5, and wt% of TiO2 were milled in an agate mortar and heated in air at an annealing temperature of 300°C for hours to remove humidity and to improve the solid solubility of the composites Next, the powder was pressed into pellets of mm in diameter and mm thickness These pellets were sintered at 900°C in an air furnace for 12 hours After that, the furnace was cooled slowly to room temperature The structural properties were investigated by BRUKER AXS D8 Advance X-ray diffractometer using the Cu-Ka radiations wavelength of F I G U R E XRD patterns of ZnO/TiO2 pellets ET AL 1.54059 Å at room temperature (Sfax, Tunisia) The scanning angle 2h was varied in the range of 15°-70° in steps of 2° minÀ1 for the pellets The scanning electron microscope (SEM, HITACHI S-800, Madrid, Spain) was used to study the morphology of the prepared composites Then, we used the Novocontrol BDS system (Novocontrol Technologies GmbH & Co KG, Sfax, Tunisia) to measure the complex modulus and electrical impedance in the frequency range from 0.1 Hz to 10 MHz at different temperatures (40°C-110°C) The flow of nitrogen was used for temperature adjustment at the pellet which was inserted between two gold parallel plate electrodes (diameter of 24 mm) A sinusoidal voltage was applied (Ỉ1 V), creating an alternating electrical field which was measured perpendicularly to the disks This produces polarization in the sample, which oscillates at a similar frequency as the electric field, but with a phase angle shift between the voltage and the current signals 3.1 | RESULTS AND DISCUSSIONS | Structural analysis Figure shows the X-ray diffraction diffractogram of the prepared ZnO/TiO2 composite ceramics in the 2h range of 15°-70° From the patterns, it is clear that the composites have a polycrystalline nature and a hexagonal structure The major peaks observed are identified to (10.0), (00.2), (10.1), (10.2), (11.0), and (10.3) planes for the wurtzite phase of ZnO (JCPDS Card No 36-1451) This reveals that the hexagonal structure of the pellets has not been affected by the TiO2 doping content We note also the appearance of two secondary phases of ilmenite-type hexagonal ZnTiO3 (JCPDS Card No 26-1500) and spinel Zn2TiO4 F I G U R E The enlarged part of XRD patterns in the range of 32°-40° BEN BELGACEM | ET AL (JCPDS Card No 19-1485), but no additional phases corresponding to TiO2 are observed Figure shows an enlarged part of XRD patterns in the selected interval of 2h values (31°-37°) A slight shift of these peaks to higher angles is seen as the content of TiO2 is increased from to wt%; above that, they shift toward lower angles By increasing the TiO2 concentration, the intensities of ZnTiO3 peaks increase until wt% and decrease after that without affecting the ZnO phases This is probably related to strain and stress effects caused by the substitution of Ti4+ ions in ZnO matrix, which may be due to the difference in the ion radii of zinc and titanium (rTi4+=0.6 Å and rZn2+=0.7 Å).32 Indeed, the values of the texture coefficient TC (hkl) attributed to the diffraction plane (100) of the ZnO structure wurtzite are higher than the two major orientations (101) and (002) Hence, the plane (100) is considered as the preferred orientation (Table 1) Moreover, the ZnO crystallinity decreases from 84% to 46% with the increase of the TiO2 doping content from to wt%, whereas, the ZnTiO3 crystallinity increases from 12% to 42% as can be seen in Table These observations indicate a strong segregation of TiO2 in the ZnO wurtzite structure The lattice constants were determined from X-ray patterns (Table 1), which are in good agreement with those obtained in the JCPDS standard (a0=3.25 and c0=5.2  A).33 34 Similar results were found by El Mir et al and K T A B L E The XRD data results of ZnO/TiO2 composite ceramics Crystallinity (%) D (nm) c (nm) a (nm) ZnO ZnTiO3 ZnO/TiO2:1% 39.2 5.205 3.25 84 12 ZnO/TiO2:3% 46.4 5.197 3.245 66 ZnO/TiO2:5% 40.3 5.192 3.243 39 ZnO/TiO2:7% 25.7 5.216 3.26 46 (A) (B) (C) (D) TC(hkl) Zn2TiO4 (10.0) (00.2) (10.1) 2.2 1.5 1.3 25 1.8 0.9 1.1 40 20 0.6 0.7 42 12 0.9 0.5 0.5 F I G U R E SEM photograph of the ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt% TiO2 | BEN BELGACEM Omri.35 A slight decrease of the c is clearly observed with the increase of the TiO2 parameter doping content until wt% This can be explained by the shifting of (002) peak to higher diffraction angles However, for the samples doped with wt% of TiO2, the parameter c increases, which is related to the shift to lower angles The grain size D for the most intense peak (101) was estimated from Scherrer’s formula:36 D¼ Kk b cos h (1) where K=0.9, k (=1.5  A) is the wavelength of the X-ray used, and h is Bragg’s angle for the most intense peak (101), b is the full width at half maximum (FWHM) (in radians) The crystallite size is seen to increase as the TiO2 content is equal to wt% and then a small fall is noticed above this level This result confirms that the doping modifies the microstructure and the crystalline quality of the ZnO/TiO2 composites The results are summarized in Table Similar ET AL results have been reported in the literature.37,38 M Chaari37 has observed the increase of the mean crystallite size along (101) plane when the Sn2O3 content increased to wt% and decreased after that from 112 to 93 nm This may be due to the effect of the crystallization process with doping.38 A D Bachvarova-Nedelcheva et al.39 have fabricated the ZnO/ TiO2 powders via the combustion gel method During the combustion process, they obtained various phases (ZnO, TiO2-anatase and rutile, ZnTiO3) and the average crystallite size of all the powders is below 20 nm Figure exhibits the surface morphologies of the prepared samples As seen in these images, the surface is rough for all the nanoparticles and the nano-grains change shape with the different TiO2 doping concentration Indeed, it is shown that these crystallites are irregularly disoriented The grain size decreases with an increase in the TiO2 doping content from to wt%, which is in good agreement with the XRD results Hence, the doping content has a strong effect on the morphological properties of the ZnO material F I G U R E Frequency-temperature dependence of M0 of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt % TiO2 BEN BELGACEM 3.2 | Complex modulus analysis The complex electric modulus representation M* (x), which was developed by Provenzano et al.,40 is one of the methods to understand the electrical process of hopping charge carriers in conducting materials where the low-frequency electrode polarization effects are suppressed.41 The electric modulus M* is given by the following equation: Mà ¼ | ET AL 1 e0 e00 ẳ M ỵ iM 00 ẳ ẳ 02 ỵ i 02 00 00 e e ỵ ie e ỵe e ỵ e002 (2) where M0 , M″, e0 , and e00 are the real and the imaginary parts of the electric modulus M* and the dielectric constants e*, respectively Figure shows the spectrum of the real part M0 of the ZnO/TiO2 pellets with frequencies at different temperatures For frequencies below 103 Hz, it can be observed that the value of M0 is found to be almost zero for all temperatures, which suggests the suppression of the electrode polarization.42 However, at higher frequencies, M0 reaches a maximum value corresponding to M∞=(ɛ∞)À1 due to the relaxation process.42 Additionally, it exhibits a decrease in M0 with temperatures for the compositions studied in the considered range (40°C-110°C), which reveals a temperature-dependent relaxation process in the materials Similar results have been reported in the literature.43,44 These observations are in good agreement with the results obtained by R Ranjan et al.44 for Sm-modified Pb (Zr0.05Ti0.45)1Àx/4O3 ceramics They have shown an increase in M0 with increasing frequency, which may be attributed to the conduction phenomena due to the shortrange mobility of charge carriers Macedo45 explained this continuous dispersion with increasing frequency as being related to the lack of motion of the charge carriers under the applied electric field Besides, it reveals significant shifts of curves towards higher frequencies In addition, it shows clearly that the time relaxation decreases up to wt F I G U R E Frequency-temperature dependence of M″ of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt% TiO2 | % of TiO2 content, and above that level it increases Such behavior suggests the long-range mobility of charge carriers (electrons or holes).44 The frequency-temperature dependence of the imaginary part of the electric modulus M″ for all ZnO/TiO2 composites is shown in Figure It exhibits two relaxation peaks (clearly seen at low temperatures) that shift toward the higher frequency side with the increase in temperature It indicates a thermally activated behavior of the relaxation time These two peaks indicate the transition from longrange to short-range mobility with increasing frequency.46 The high peak observed at lower frequencies is commonly attributed to the interfacial polarization effects known as Maxwell-Wagner-Sillars (MWS).47,48 However, the second peak observed at high frequencies is associated with the dipolar polarization of the ZnO grains This latter peak is usually related to oxygen interstitial Oi, oxygen vacancy VO, and zinc interstitial Zni ions.49 Similar trends were BEN BELGACEM ET AL observed by M Chaari and J Othman.49,50 Y Ben Taher and N Moutia51 synthesized RbAlP2O7 by the conventional solid-state technique They observed that M″ exhibited a single relaxation peak centered in the dispersion region of M0 and associated with the grain effect They showed also that as the temperature is increased, the movement of the charge carriers becomes faster, leading to a decreased relaxation time, with a consequent shift of the peak value in M″ toward higher frequencies Figure shows the variation of log(Wmax) vs 1000/T, where Wmax is the angular frequency of M″ peaks The experimental data are suitably fitted according to the Arrhenius law: Ea Wmax ẳ W0 exp ị (3) KB T where W0 is the relaxation pulsation at infinite temperature, kB is the Boltzmann constant, T is the absolute temperature, F I G U R E Arrhenius’ plots of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt% TiO2 BEN BELGACEM | ET AL and Ea is the activation energy of the considered relaxation process, which is determined from the slopes of the curves log(Wmax)=f(1000/T) The values of activation energies are found to depend on temperature and TiO2 concentration (see Figure 6) At low temperature, the activation energy ranges from 0.09 to 0.50 eV For the doping content wt %, Ea value is equal to 0.5 eV that is very near to 0.54 eV, which emanates from the state charge of interstitial oxygen 52,53 OÀ1 For the TiO2 content of wt%, the value i =Oi Ea=0.19 eV corresponds to the states of electron traps generated by oxygen chemisorptions at grain boundaries.54 In addition, the doped ZnO with wt% TiO2 has an activation energy very near to 0.1 eV, which is assigned to neutral (Oi+) positively charged oxygen interstitial (Oi1+).53 However, for the wt% TiO2 content, Ea value is about 0.36 eV, which is related to the oxygen vacancy.55,56 With respect to the higher temperatures, the activation energies are found to be between 0.70 and 1.09 eV, which may be related to the MWS polarization occurring at the grain interfaces.57 Moreover, the rise of the TiO2 doping content makes activation energies increase, which may be due to the increase of secondary phases ZnTiO3 and Zn2TiO4 in the ZnO matrix Thus, the ZnTiO3 and Zn2TiO4 observed in the XRD spectra may be explained by the increase in the activation energy Figure shows the cole-cole plots (complex modulus spectra M″ vs M0 ) of the ZnO/TiO2 samples at some selected temperatures (40°C-110°C) It exhibits two deformed semicircles for all doped ZnO samples, where the centers lie below the real axis M0 This confirms the presence of a non-Debye type of relaxation in these pellets The first semicircle is attributed to the grain contribution, whereas the second one is related to the grain boundary effects Similar results were obtained by Ranjiv.44 The intercept of the first semicircle on the real M0 axis indicates the total capacitance contributed by the grain and the intercept of the second semicircle indicates the total capacitance contributed by the grain boundary It shows a marked F I G U R E Plots of imaginary modulus M″ vs real modulus M0 of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt% TiO2 | BEN BELGACEM change in shape upon an increase in temperature, which suggests a change in the value of capacitance of the material with temperature Indeed, it can be seen that the value of capacitance decreases when the TiO2 doping content increases from to wt%, and then, it increases This result is probably related to the secondary phases, which are in good agreement with those obtained in the XRD patterns 3.3 | Impedance analysis Figure shows the variation of the imaginary part of the impedance (Z″) of the ZnO/TiO2 pellets with frequency at different temperatures It can be seen that the peak position shifts towards higher frequencies with increasing temperature, whereas Z″max values decrease This indicates a thermally activated dielectric relaxation process This type of temperature dependence is attributed to the presence of a space charge in the material.20 At low frequency ET AL (≤100 Hz), the curve appears almost flat with zero values for doped pellets The same observation was seen in Figure In addition, the maximum value (Z″max) is found to be dependent on the TiO2 content It exhibits a small fall when the content of TiO2≤5 wt%, nevertheless it shows a rise as the TiO2 content equals wt% At high temperatures, Z″max varies from 0.03 106 to 4.9 106Ω when the TiO2 doping concentration increases from to wt% This is probably related to the increase of ZnTiO3 phases in the ZnO matrix, which may be due to the rise of the secondary phases ZnTiO3 in the ZnO hexagonal structure, which is in good agreement with the XRD The temperature dependence of the complex impedance spectrum (Z00 vs Z0 ) of ZnO/TiO2 pellets is shown in Figure At each temperature, the figure exhibits two semicircles that are deformed and depressed with their centers below the real axis, which indicates the existence of two relaxation phenomena with different relaxation times (s=RC), where R is the resistance and C is the capacitance F I G U R E Frequency-temperature dependence of Z″ of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt % TiO2 BEN BELGACEM | ET AL F I G U R E Variation of Z″ vs Z0 at different temperatures of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt% TiO2 T A B L E Value parameters of equivalent circuits of ZnO/TiO2 composites at 40°C Rg(KO) Cg(F) n1 À11 1 wt% TiO2 16.3 2.5 10 wt% TiO2 87.4 3.3 10À11 0.2 10 À11 1.9 10 À10 wt% TiO2 wt% TiO2 420 0.89 Rjg(KO) CPEjg(F) n2 R1(KO) À10 0.89 2220 2.2 10À11 0.96 345 5.2 10 À11 0.92 916 1.3 10 À11 0.98 – 33.8 10 3.3 10 associated with that phase.58 This is in good agreement with the two relaxation processes confirmed in the modulus plots The appearance of a complete or partial semicircle depends upon the strength of the relaxation and the available frequency.59–61 Such overlapped semicircles confirm the dispersal nature of the relaxation and the presence of a strong heterogeneity in the materials Here, the intercept of the arcs on the real axis gives the resistance values which shifted toward the original plots This behavior suggests a 1404 C1(F) n3 C2(F) 2.5 4.5 10À12 10À11 0.3 10À10 15.8 345 7.1 10 3.6 R2(KO) À12 À11 2.3 10 0.95 – – – – decrease of the resistivity of the samples assisted by the grain and the grain boundary conduction when the temperature is increased.62 Moreover, the high values of resistance for the sample doped with wt% in comparison with the other samples may be due to the rise of the secondary phases in the ZnO hexagonal structure, which is shown in the XRD results One can notice that the presence of free carrier charges and impurities at the grain boundaries can influence the electrical conductivity.20,49 At high frequency, 10 | BEN BELGACEM ET AL the second semicircle is very weak, which indicates the dominance of the grain boundary contributions in conductivity To explain the non-ideal Debye type behavior in the ZnO/TiO2 pellets, we have introduced in our model a constant phase element (CPE) associated with resistors and capacitors The CPE component was proposed for the first time by Abram.63 Its impedance is expressed by: ZCPE ẳ ẵA0 jxịn (4) pffiffiffiffiffiffi where A0 ¼ cosðAnpÞ; j ¼ À1: A and n are the frequency2 independent parameters of Jonscher’s power law.64,65 ZCPE is usually considered to be a dispersive capacitance: if n = 1, the element is an ideal capacitor; if n = 0, it behaves as a frequency-independent ohmic resistor Figure shows the fitted impedance curves with adequate equivalent circuits Using Scribner’s ZView software, the fitted equivalent circuit parameters at 40°C are given in Table The proposed circuits are similar to those obtained for bulk ZnO varistors.66,67 For the doped ZnO with 1-5 wt% content of TiO2, the insets illustrate three cells corresponding to the electrodes, grains, and grain boundary contributions However, for the ZnO/TiO2:7 wt% pellet, the electrode effect is not observed In the other work, the resistivity of the polycrystalline material decreases with the increase in grain size.68,69 Therefore, we have found that the sample doped with wt% of TiO2 content has the lowest value of resistivity, thus, less grain boundary M Chaari et al.70 have fabricated zinc oxide ceramics sintered at various temperatures (700°C-1000°C) by solid-state route They found that the pellet sintered at 900°C has the lowest value of resistivity, hence, less grain boundary Indeed, when the temperature increases, it shows a significant decrease of the resistance values of the grain (Rg) and the grain boundary (Rjg) (Figure 9) This result suggests the increase of conductivity which can cause a negative temperature coefficient of resistance behavior as observed in semi-conductor materials.44 It is also shown that the magnitude of the capacitance CPE is about 10À11 F to10À12 F, which suggests that the semicircle was due to double-layer effect of grain boundaries.63 Using the impedance spectroscopy, the activation energy for the trap levels could be determined from the slopes of the activation plots Ln(s) vs 1000/T (see Figures 10, 11 and 12) The activation energy levels are calculated from sg=Rg Cg sjg=(Rjg CPEjg)1/p and s1=(R1 CPE1)1/p The linear behavior of relaxation time is in good agreement a with Arrhenius’ law:s ¼ s0 expðÀE kBT Þ where Ea is the activation energy, kB is the Boltzmann constant, and T is the absolute temperature F I G U R E Arrhenius’ plots of relaxation time s1of the carriers at electrodes of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 From Figure 10, for the composites added with wt% TiO2 and w% TiO2, the activation energy values are equal to 0.75 and 0.17 eV, respectively This might be attributed BEN BELGACEM ET AL | 11 F I G U R E 1 Arrhenius’ plots of relaxation time sg of the carriers at grains of ZnO pellets doped with (A) wt% TiO2 (B) wt% TiO2 (C) wt% TiO2 (D) wt% TiO2 either to electron traps in shallow potential wells or to chemical trap states due to the chemisorptions of oxygen at the grain boundaries.71 For the same composites, the activation energy values are equal to 0.7 and 0.75 eV, respectively (see Figure 11) It seems that this relaxation is an interfacial process MWS type Gambino et al.72 have obtained an activation energy between 0.6 and 0.7 eV for interfacial states below the conduction band of the ZnO Other researchers reported that the interfacial states are lower than eV below the conduction band, but somewhat higher for the above energy value.49,73–75 According to Gavryushin et al.,76 the obtained value of 0.43 eV for the content of wt% is induced by Zn interstitials On the other hand, the activation energy which is close to 0.2 eV is associated with the second ionization energy of zinc ion.77,78 The ZnO pellet doped with wt% TiO2 has an activation energy equal to 0.6 eV, which is far from the origins as superficial or deep electron traps (Figure 12).57 In addition, the existence of 0.08 eV is connected to neutral (O0i ) positively charged oxygen interstitial 79,80 (Figure 12) The difference in activation states (O1ỵ i ) energy calculated from impedance spectra and modulus spectra suggests that both localized and nonlocalized conduction processes may be attributed to the same type of charge carriers.81 By comparing the Nyquist plots at the same temperature, it was noted that the resistance value increased significantly with the TiO2 content This behavior was correlated with the electrical conductivity, which the lowest value of rdc obtained for the wt% of TiO2 content.54 Moreover, the electrical circuit equivalent obtained from the pellet to which wt% of TiO2 content was added presented fewer components of resistance and capacities than the other pellets This result indicated the reduction of carriers when the TiO2 content attains wt% and confirmed the fast increase in the resistance value with the TiO2 content Also, it is shown, from Table 1, that the crystallinity of the formed ZnTiO3 is higher than that of ZnO; hence, ZnTiO3 plays an important role in the electrical properties 12 | BEN BELGACEM ET AL F I G U R E Arrhenius’ plots of relaxation time sjg of the carriers at grain boundaries of ZnO pellets doped with (A) wt% TiO2 (B) wt % TiO2 (C) wt% TiO2 (D) wt% TiO2 | CONCLUSION In this study, ZnO/TiO2 ceramics were prepared by conventional ceramic processing method The XRD patterns indicated that the prepared composites had a wurtzite structure and revealed the presence of three crystalline 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(purity >99%) and TiO2 Different powder blends of ZnO containing 1, 3, 5, and wt% of TiO2 were milled in an agate mortar and heated in air at an annealing temperature of 300°C... relaxation peaks (clearly seen at low temperatures) that shift toward the higher frequency side with the increase in temperature It indicates a thermally activated behavior of the relaxation... decrease This indicates a thermally activated dielectric relaxation process This type of temperature dependence is attributed to the presence of a space charge in the material.20 At low frequency