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All issues Volume 98 (2023) Eur. Phys. J. Appl. Phys., 98 (2023) 5 Full HTML
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Eur. Phys. J. Appl. Phys.
Volume 98, 2023
Article Number 5
Number of page(s) 6
Section Semiconductors and Devices
DOI https://doi.org/10.1051/epjap/2022220228
Published online 13 January 2023

© EDP Sciences, 2023

1 Introduction

TiO2 ceramic is used to fabricate different optoelectronic devices for solar cells, photocatalysis, gas sensor applications, etc [1–6]. Usually, TiO2 crystallizes into the following phases: (1) tetragonal anatase [A]-phase, (2) tetragonal rutile [R]-phase, and (3) orthorhombic brookite [B]-phase [7–10]. TiO2 has semiconducting transparent properties of a wide bandgap ∼3.2 eV for [A] phase and ∼3.0 eV for [R] phase [11]. Consequently, pristine TiO2 was classified within the group of the transparent-conducing-oxides (TCOs). Therefore, its optoelectronic properties could be controlled by doping with different ions, which can control its natural point defects (interstitials and vacancies) and, consequently controls its optoelectronic properties [12,13]. In addition, it was found that doping of TCO with some metal ions can generate some appropriate exotic physical properties, like magnetic. In the current work, anatase TiO2 nanoparticles (NPs) were synthesized co-doped with Co and Sb ions [referred to as (Sb/Co):TiO2]. The physical (structural/optical/electrical) properties of the co-doped TiO2 were studied. Furthermore, the influences of the moderate-temperature hydrogenation reduction on the physical properties were also studied.

The Sb-doped TiO2 [14,] and co-doped TiO2 [15] were previously investigated, where observed that they crystallized with [A] phase only (JCPDS card no. 73-1764). In the current study, it was planned to co-doped TiO2 NPs with Sb and Co ions by using the known facial hydrothermal synthesis technique.

The VI-coordination crystal radius of Ti4+ in TiO2 structure is 74 pm and the most reliable dopant ionic radius of Sb5+ is 60 pm and of Co2+ is 74.5 pm [16]. Thus, the ionic radius of Co2+ ion is almost identical to the crystalline radius of Ti4+ ions while that of Sb5+ ion is less than that of Ti4+ ion by ∼23%. Therefore, according to the empirical Hume-Rothery (H-R) rules, both ions Co2+ and Sb5+ can incorporate into the TiO2 lattice occupying interstitial crystalline positions (ICPs) and substitute for Ti ions (SbTi), which should cause a measurable lattice distortion in the host TiO2 lattice. In general, such co-doping can partially create a substitutional solid solution (SSS) with a high density of itinerant electrons. In addition, some tinny amount of dopants ions might expect to participate in mounting up distinct crystallite boundaries (CBs) forming feeble shells of clusters [17] through some bonding. Such feeble core/shell structural changes should have sensible and measurable influences on the physical properties.

Nanoparticles (Nps) TiO2 doped with some suitable ions can be utilized as a ceramic material in the field of dielectrics. Moreover, the hydrogenation of a doped ceramic can develop or destroys its distinct feeble crystallite boundaries (CBs), which are responsible for its weak core/shell constructions that have a control on its dielectric properties. In the present work, it was concluded that the hydrogenation of the synthesized (Sb/Co):TiO2 NPs ceramic partially destroys its feeble CBs or partially destroy its core/shell construction through the H2 dissociation, which creates H species that could remove structural oxygen creating a O-vacancies (VOs), especially on CBs. Such a process weakens the dielectric performance of feeble CBs or increases the conductivity and reduces the dielectric permittivity. The present work is aimed to clear this experimental model.

2 Experimental procedure

Ceramic (Sb/Co:TiO2) NPs were synthesized by a hydrothermal decomposition method. The antimony(III) chloride (SbCl3 · H2O)−the source of Sb ions, Co-acetylacetonate (Co (C5H7O2)3) − the source of Co ions, and titanium (III) chloride (TiCl3) (of Anlar grade from Sigma-Aldrich) are the starting materials used for the following synthesis. The molar ratios of Sb/Ti and Co/Ti were ∼3%. The synthesis process started with the precursor, which was prepared from a mixture of ∼3 ml TiCl3, ∼30 ml ethanol, ∼120 ml distilled deionized water, ∼3 ml acetone, and appropriate amounts of Sb- and Co-compounds. Those materials were dissolved together in a glass beaker. The mixture was kept under magnetic stirring for 24 h at room temperature, followed by rising the temperature to ∼70 to 80 °C for the next ∼10 h until a precipitate fine powder was obtained. The obtained precipitate powder in the beaker was inserted in a closed oven at ∼500 °C for sintering for 1 h, followed by a natural slow cool with the closed oven to room temperature. Finally, the precipitate powder was pelletized into a disc for characterization: X-ray fluorescence (XRF), X-ray diffraction (XRD), optical spectral diffuse reflectance (DRS), and dielectric measurements. The reference pristine, TiO2 NPs were also synthesized by the same technique, for comparison. A portion of the synthesized (Sb/Co):TiO2 fine powder was annealed in pure H2 gas atmospheric at 550 °C for 30 min. and, then cooled with the gas outside the oven to room temperature, to obtain the hydrogenated (Sb/Co:TiO2-H) ceramic. The synthesized samples: TiO2, Sb/Co:TiO2, and Sb/Co:TiO2-H discs were characterized by traditional techniques. The energy dispersive X-ray fluorescence (ED-XRF) spectroscopy was used to test the elemental purity of the samples. A Philips PW1710 X-ray source was used to excite the sample contents. The XRF spectra of E > 1.5 keV were detected by an Amptek XR-100CR (USA) detector. The crystalline structures of the synthesized samples were studied by Cu Kα-X-ray diffraction (XRD) method of a Rigaku Ultima-VI diffractometer controlled by built-in programs. The optical diffuse reflectance (DRS) spectra of the samples in the range of 200–830 nm, were measured by a Shimadzu UV-3600 spectrophotometer. The dielectric properties of the synthesized ceramic NPs pressed in form of cylindrical samples were measured by a Keithley 3330 LCZ instrument. The cylindrical NPs samples of ∼1 mm thickness and ∼12 mm diameter were made by pressing the synthesized NPs under ∼600 MPa for ∼10 min. The silver paste used for good electrical lead contacts was heat-treated at ∼200 °C for ∼10 min.

2.1 Structural analysis

Figure 1 shows the obtained XRF spectra of the synthesized pristine and Sb/Co-codoped TiO2. The spectra show intense Ti signals: Ti-Kα (4.51 keV) and Ti-Kβ (4.93 keV) in addition to weal signals from the dopants Sb-Lα (3.60 keV) and Co-Kα (6.93 keV). Therefore, the spectra confirm the purity of the samples.

Figure 2 shows the XRD of the synthesized TiO2, Sb/Co:TiO2, and Sb/Co:TiO2-H NPs, and the results of the structural analysis are given in Table 1. The absence of any XR reflection due to the pure or any compounds of Sb (3 at.%) and Co (3 at.%) confirms the dissolution of the dopants into TiO2 ceramic lattice. The (Sb/Co) codoping of TiO2 resulted in a single [A] phase, as shown in Figure 2, although there were tiny amounts of [B] and [R] phases crystallized together with the main [A] phase during the synthesis of pristine TiO2. Thus, the 3 at.% Sb/Co dopant ions did not agglomerate separately outside the lattice of the host TiO2, but they mainly doped into the lattice of TiO2 crystallites, in addition to residing on the CBs, without creating any additional phase.

The previous XPS study [18] has proved that the Co ions doped in host TiO2 were in the divalent oxidation state only. Thus the Co2+ dopant substitution: CoTi forming SSS should create oxygen vacancies (VOs) to balance the charge neutrality as the ionic charges of Ti4+ and Co2+ are different [19]. The slight shift of the XR(101) peak to a lower angle (Tab. 1), was mainly caused by the creation of VOs and partially by the replacement of the Ti4+ ions (74 pm) by slightly larger Co2+ ions (74.5 pm). The slight increase of d(101) value confirms the increase of the unit-cell parameters and volume, Vcell due to doping and vacancies formation.

The smaller ionic radius of Sb5+ ions than that of Ti4+ by ∼23% supports the interionic a substitution of Ti4+ by Sb2+ [14]. In a summary, the Sb/Co ions could partially form substitutional solid solution (SSS) in addition to the possibility to occupy interstitial crystalline positions (ICPs). However, a slight accumulation of dopant Sb/Co ions on the crystallite boundaries (CBs) is also possible, which could build a feeble core-shell structure that might generate weak colossal permittivity (wCP) properties [6].

In general, the incorporation of Sb/Co ions has noticeable effects on the structural parameters presented in Table 1. The average nano-crystallite size (CS) was estimated by the known Debye-Scherrer equation. Thus, the CS was increased by ionic inclusion into the lattice as well as by the hydrogenation. Moreover, any inclusion of ions creates some corresponding microstructural strain (ϵs) in the host lattice, which could be estimated byϵs  =  − Δ (2θ(101))  cot θ(101), where Δ (2θ101) is the angular shift (in rad.) of the intensive (101) refection, as compared to the same reflection in the pristine TiO2 NPs prepared by the same method. Thus, the created structural strain (ϵs) refers to the real inclusion of (Sb/Co) ions into the lattice of the host TiO2 crystallites. The considerable increase of ϵs by the hydrogenation of the sample demonstrates the creation of oxygen-vacancies VOs-defects, which increases the unit-cell volume.

More analysis, the experimental data in Table 1 confirm that the hydrogenation caused an increase in the average CS, which “increases the compact” of the crystallites together in the grains. Such a compress causes a reduction in the CB barriers that increase the electrical conductivity (Sect. 3.3). These variations reduce the dielectric permittivity of the hydrogenated sample: (Sb/Co): TiO2-H in comparison to the as-synthesized (Sb/Co):TiO2 sample.

thumbnail Fig. 1

XRF of the synthesised pristine TiO2(reference) and Sb/Co:TiO2 ceramics.
thumbnail Fig. 2

XRD patterns of the synthesized ceramics NPs.
Table 1

(101)-reflection angle, structural microstrain (εs (%)), crystallite size (CS (nm)), lattice parameters (a = b and c), unit-cell volume (Vcell), and the optical bandgap (Eg) of the synthesized NPs samples.

2.2 Optical properties

The spectral diffuse reflectance, R(λ) of the synthesized ceramic NPs samples was investigated in the range 200–800 nm. After that, the Kubelka-Munk (K-M) equation [F(λ)  = (1 −  R(λ)) 2 / 2R(λ)] was applied to calculate the spectral absorption functions, F(λ), which are shown in Figure 3. The graphs depicted in Figure 4 are the Tauc plots, (F. E)2 vs. E, where E is the photon energy for the direct electronic transitions, which are used to estimate the bandgap of the present samples. The bandgap of the pristine synthesized anatase TiO2 (∼3.26 eV) agrees well with the published value [11]. In general, the optical absorption spectra, F(λ) show great modifications, due to the codoping and hydrogenation. Figure 4 shows the formation of two edges (2.56 eV and 1.85 eV) with Sb/Co codoping, which can be explained by the creation of an isolated intermediate band (or interband) deep in the bandgap of host TiO2, a similar interpretation was theoretically calculated by the density functional theory (DFT) for Cu/N codoping of TiO2 in reference [20]. This interband is responsible for high visible-light absorption (HVA in Fig. 3) by two optical transition steps, between valence and conduction bands of host TiO2 via the interband. Comparing with the pristine TiO2, the high-energy bandgap edge of (Sb/Co):TiO2 ceramic was reduced by ∼27%, due to the formation of O-vacancy (VOs) defects, which energetically occupied the bottom of the host TiO2 conduction band. The hydrogenation that effectively creates VOs, redshifted the two edges to (1.32 eV and 0.78 eV), as shown in Figure 4 and Table 1. These hefty changes were caused by the substitutional and interstitial doping of both types of ions into the lattice of TiO2, in addition to the creation of O-vacancies (VOs) and itinerant electrons. These effects were enhanced by the hydrogenation, especially the great creation of oxygen vacancies which, in turn, induce more weak-binding itinerant electrons in the host TiO2 crystals, according to the following mechanism: The dopant transition metal ions (Co) act as catalysts for dissociation of adsorbed H2 [21,22]. The dissociated hydrogen H+ species can remove structural O from TiO2 lattice creating O-vacancies (VOs defects) and itinerant electrons, which strongly affect the absorption spectrum observed experimentally in Figure 3 [23,24] in addition to the high red band shift down to less than 1 eV, as shown in Figure 4, according to the Urbach effect [14]. The creation of O-vacancies could also liberate Sb ions, which accumulated together into tinny crystallites, as observed in Figure 2.

thumbnail Fig. 3

Spectral absorption function F(λ) of the synthesised ceramics NPs.
thumbnail Fig. 4

Tauc plots for the synthesized ceramics NPs.

2.3 Dielectric properties

The dielectric permittivity, ε∗ of the synthesized ceramics, (Sb/Co):TiO2 and (Sb/Co):TiO2-H were investigated as a function of signal frequency, f (1–100 kHz): ε∗(ω) = ε'(ω) − iε”(ω) where ε'(ω) and ε”(ω) are the real (dielectric constant) and the imaginary (loss), respectively, aiming to investigate the influence of the hydrogenation on the dielectric properties of the investigated samples. The frequency dependence of the dielectric constant, ε'(f) is shown in Figure 5. It was found that the permittivity of (Sb/Co):TiO2 ceramic sample show weak colossal permittivity (it was ∼385.4 at 1 kHz) with slow variation with frequency. However, the permittivity was lowered by ∼50% to (193 at 1 kHz) with the hydrogenation, due to the increase in the conductivity and liberation of Sb ions. Moreover, the increase of VOs in the crystallites by the hydrogenation is usually accompanied by an increase in itinerant electrons concentration, which causes an increase in in the conductance (Gac) and imaginary part of the permittivity ϵ ”(ω) of the insulator, as shown by the inset of Figure 5.

The ac-conductance of insulators (Gac) is described by Gac = Gdc + Gac (ω), where Gdc is the dc-component and Gac is the ac-component. The Gac depends on the signal frequency following Jonscher power relation [25]: Gac(ω) = C σωs, where C σ is a coefficient, s = 1–6kBT/WM < 1 [25–27], and WM is the maximum barrier height, which depends on the microstructure of the sample like phase content, texture orientation, defect distribution, average grain size, etc. Figure 6 shows the f-dependence of ac-conductanceG(ω). The fitting of the power-law gives the following values of (s, WM) = (0.26, 0.2 eV) for (Sb/Co):TiO2 ceramic and (0.7, 0.5 eV) for hydrogenated ceramic (Sb/Co):TiO2-H.

thumbnail Fig. 5

f-dependence of the dielectric permittivity (ε') and the insert shows the f-dependence of the dielectric loss-factor (ε”) of the synthesized ceramics NPs.
thumbnail Fig. 6

f-dependence of AC-conductance (Gac) of the synthesised ceramics NPs.

3 Conclusions

TiO2 NPs ceramic co-doped with Sb/Co ions were synthesized by a moderate-temperature hydrothermal decomposition method. The XRD showed crystallization of anatase [A] phase only. The XR analysis indicates that both dopant ions (Sb and Co) did not accumulate separately in form of crystallites or nanograins outside the TiO2 crystallites, and they might partially create a feeble core/shell structure, which enhances the permittivity to a nearly colossal scale and behavior. Moreover, the Vcell of the host TiO2 was increased by the hydrogenation, due to the great creation of O-vacancies (VOs).

The optical absorption F(λ) function of Sb/Co:TiO2 and Sb/Co:TiO2-H samples show a great modification, which was attributed to the creation of an isolated interband deep in the bandgap of host TiO2 with two edges (Tab. 1). However, the incredibly higher modification was generated due to the hydrogenation in Sb/Co:TiO2-H sample, which was attributed to the hefty creation of VOs- defects by the catalysts effect of doped Co2+ ions to the adsorbed H2-dissociation mechanism. Therefore, the hydrogenation strongly reduced the permittivity due to the huge increase of itinerant electrons, electrical conductivity, the concentration of itinerant electrons, and liberation of Sn ions. The obtained experimental results are important from a theoretical and experimental points of view and should find many applications.

No data used to support the finding of the present study are included within the article.

I wish to confirm that there are no conflicts of interest associated with this publication. There is no significant financial support, which could have influenced its outcome.

References

  1. W. Tuichai, S. Danwittayakul, P. Srepusharawoot, P. Thongbai, S. Maensiri, Giant dielectric permittivity and electronic structure in (A3+, Nb5+) codoped TiO2 (A = Al, Ga and In), Ceram. Int. 43, S265 (2017) [CrossRef] [Google Scholar]
  2. J. Fan, S. Leng, Zh. Cao, W. He, Y. Gao, J. Liu, G. Li, Colossal permittivity of Sb and Ga co-doped rutile TiO2 ceramics, Ceram. Int. 45, 1001 (2019) [CrossRef] [Google Scholar]
  3. C. Yang, X. Wei, J. Hao, Disappearance and recovery of colossal permittivity in (Nb+Mn) co-doped TiO2, Ceram. Int. 44, 12395 (2018) [CrossRef] [Google Scholar]
  4. A. Balhamri, A. Deraoui, Y. Bahou, M. Rattal, Az. Mouhsen, M. Harmouchi, A. Tabyaoui, E.M. Oualim, Surface and optical properties of zinc oxide doped with fluor synthesized by magnetron sputtering: applications in transparent conductive oxides (TCO), Int. J. Thin. Films Sci. Technol. 4, 205 (2015) [Google Scholar]
  5. N. Thongyong, W. Tuichai, N. Chanlek, P. Thongbai, Effect of Zn2+ and Nb5+ co-doping ions on giant dielectric properties of rutile-TiO2 ceramics, Ceram. Int. 43, 15466 (2017) [CrossRef] [Google Scholar]
  6. W. Tuichai, P. Srepusharawoot, E. Swatsitang, S. Danwittayakul, P. Thongbai, Giant dielectric permittivity and electronic structure in (Al + Sb)co-doped TiO2 ceramics, Microelectron. Eng. 146, 32 (2015) [Google Scholar]
  7. Y. Masuda, K. Kato, Synthesis and phase transformation of TiO2 nano-crystals in aqueous solution, J. Ceram. Soc. Jpn. 117, 373 (2009) [CrossRef] [Google Scholar]
  8. S.M. Gupta, M. Tripathi, A review of TiO2 nanoparticles, Chin. Sci. Bull. 56, 1639 (2011) [CrossRef] [Google Scholar]
  9. W. Hu, Y. Liu, R.L. Withers, T.J. Frankcombe, L. Norén, A. Snashall, M. Kitchin, P. Smith, B. Gong, H. Chen, J. Schiemer, F. Brink, J. Wong-Leung, Electron-pinned defect-dipoles for high-performance colossal permittivity materials, Nat. Mater. 12, 821 (2013) [Google Scholar]
  10. I.S. Elfimov, S. Yunoki, G.A. Sawatzky, Possible path to a new class of ferromagnetic and half-metallic ferromagnetic materials, Phys. Rev. Lett. 89, 216403 (2002) [Google Scholar]
  11. R. Lance, Optical analysis of Titania: Band gaps of Brookite, Rutile and Anatase, A B. Sc. thesis, Oregon State University (2018) [Google Scholar]
  12. Y.H. Lin, M. Li, C.W. Nan, J. Li, J. Wu, J. He, Grain and grain boundary effects in high-permittivity dielectric NiO-based ceramics, Appl. Phys. Lett. 89, 032907 (2006) [CrossRef] [Google Scholar]
  13. T. Nachaithong, W. Tuichai, P. Moontragoon, N. Chanlek, P. Thongbai, Giant dielectric permittivity and dielectric relaxation behaviour in Fe1/2Nb1/2)Ti1-xO2 ceramics, Ceram Int. 44, S186 (2018) [CrossRef] [Google Scholar]
  14. M. Wang, S. Bai, A. Chen, Y. Duan, Q. Liu, D. Li, Y. Lin, Improved photovoltaic performance of dye-sensitized solar cells by Sb-doped TiO2 photo anode, Electrochim. Acta 77, 54 (2012) [CrossRef] [Google Scholar]
  15. L.C.J. Pereira, M.R. Nunes, O.C. Monteiro, A.J. Silvestre, Magnetic properties of Co-doped TiO2 anatase nanopowders, Appl. Phys. Lett. 93, 222502 (2008) [CrossRef] [Google Scholar]
  16. R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr, Sect. A 32, 751 (1976) [CrossRef] [Google Scholar]
  17. L. Jing, X. Sun, B. Xin, B. Wang, W. Cai, H. Fu, The preparation and characterization of La doped TiO2 nanoparticles and their photocatalytic activity, J. Solid State Chem. 177, 3375 (2004) [Google Scholar]
  18. K. Prakash Misra, A. Kumawat, A. Bandopadhyay, B. Modak, S.K. Mukherjee, P.D. Babu, S. Kabi, S. Chattopadhyay, R.D.K. Misra, Structural analysis and magnetic properties of cobalt-doped nanotitania, Mater. Sci. Eng., B 282, 115761 (2022) [Google Scholar]
  19. B. Choudhury, A. Choudhury, Luminescence characteristics of cobalt doped TiO2 nanoparticles, J. Lumin. 132, 178 (2012) [Google Scholar]
  20. A. Dashora, N. Patel, D.C. Kothari, B.L. Ahuja, A. Miotello, Formation of an intermediate band in the energy gap of TiO2 by Cu-N-codoping: First principles study and experimental evidence, Sol. Energy Mater. Sol. Cells 125, 120 (2014) [Google Scholar]
  21. M. Bououdina, A.A. Dakhel, Creation of RT-FM in CdO nanocrystalline powder by codoping with Cu and Gd: Effect of annealing in hydrogen atmosphere, J. Alloys Compd. 601, 162 (2014) [CrossRef] [Google Scholar]
  22. M. Pozzo, D. Alfe, Hydrogen dissociation and diffusion on transition metal (=Ti, Zr, V, Fe, Ru, Co, Rh, Ni, Pd, Cu, Ag)-doped Mg(0001) surfaces, Int. J. Hydrogen Energy 34, 1922 (2009) [CrossRef] [Google Scholar]
  23. A.A. Dakhel, Influence of hydrogen and cerium dopant on structural, optical, and magnetic properties of anatase nanoparticles, J. Electroceram. 45, 22 (2020) [CrossRef] [Google Scholar]
  24. D. Fernández-Torre, J. Carrasco, M.V. Ganduglia-Pirovano, R. Pérez, Hydrogen activation, diffusion, and clustering on CeO2(111): a DFT+U study, J. Chem. Phys. 141, 014703 (2014) [CrossRef] [PubMed] [Google Scholar]
  25. R.M. Hill, A.K. Jonscher, DC and AC conductivity in hopping electronic systems, J. Non-Cryst. Solids 32, 53 (1979) [Google Scholar]
  26. W.Z. Yang, M.S. Fu, X.Q. Liu, H.Y. Zhu, X.M. Chen, Giant dielectric response and mixed-valent structure in the layered-ordered double perovskite ceramics, Ceram. Int. 37, 2747 (2011) [Google Scholar]
  27. F. Yakuphanoglu, Y. Aydogdu, U. Schatzschneider, E. Rentschler, Electrical conductivity, dielectric permittivity and thermal properties of the compound aqua[bis(2-dimethylaminomethyl-4-NIT-phenolato)] copper(II) including NaCl impurity, Physica B 334, 4 (2003) [Google Scholar]

Cite this article as: Aqeel A. Dakhel, Hydrogenation shrinks the colossal permittivity of Sb/Co co-doped TiO2 nanoparticles-structural and optical investigations, Eur. Phys. J. Appl. Phys. 98, 5 (2023)

All Tables

Table 1

(101)-reflection angle, structural microstrain (εs (%)), crystallite size (CS (nm)), lattice parameters (a = b and c), unit-cell volume (Vcell), and the optical bandgap (Eg) of the synthesized NPs samples.

In the text

All Figures

thumbnail Fig. 1

XRF of the synthesised pristine TiO2(reference) and Sb/Co:TiO2 ceramics.
In the text
thumbnail Fig. 2

XRD patterns of the synthesized ceramics NPs.
In the text
thumbnail Fig. 3

Spectral absorption function F(λ) of the synthesised ceramics NPs.
In the text
thumbnail Fig. 4

Tauc plots for the synthesized ceramics NPs.
In the text
thumbnail Fig. 5

f-dependence of the dielectric permittivity (ε') and the insert shows the f-dependence of the dielectric loss-factor (ε”) of the synthesized ceramics NPs.
In the text
thumbnail Fig. 6

f-dependence of AC-conductance (Gac) of the synthesised ceramics NPs.
In the text

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