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RSC Advances This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. This Accepted Manuscript will be replaced by the edited, formatted and paginated article as soon as this is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/advances Page 1 of 6 RSC Advances RSC Advances Dynamic Article Links ► Cite this: DOI: 10.1039/c0xx00000x www.rsc.org/xxxxxx ARTICLE TYPE Tuning optical and dielectric properties of calcium copper titanate Ca xCu 3-xTi 4O12 nanopowders Ali Omar Turky *a,c , Mohamed Mohamed Rashad a, Zaki Ismail Zaki a,b , Ibrahim Ahmed Ibrahim a, Mikhael Bechelany c 5 Received (in XXX, XXX) XthXXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x Calcium copper titanate Ca xCu 3-xTi 4O12 (CCTO) nanopowders have been synthesized using organic acid precursor method based on commercially available materials. The results revealed that cubic CCTO phase was accomplished for the formed citrate precursors annealed at 1000 oC for 2h. The crystallite size of the 2+ 10 formed powders was found to increase from 44.2 to 64.8 nm with increasing the Ca ion content from 1.0 to 2.0, respectively. Meanwhile, a slightly increase in the lattice parameter “ a” and unit cell volume were observed whereas a slightly decrease in the porosity; % was evinced as the result of increasing of Ca 2+ ion concentration. FE-SEM observations of these powders confirmed their homogeneous regular cubic like Manuscript structure. Of note, the transmittance of the sample was around 85 % with Ca 2+ ratio 1.0. Furthermore, the 4 15 band gap energy was increased from 3.8 to 4.2 eV while the DC resistivity was increased from 6.4 x10 to 6.8 x10 4cmΩ with calcium content. We demonstrate that without any dopant, only by controlling the chemistry and engineering, the interfacial regions at the grain boundaries, the dielectric loss was suppressed remarkably while retaining the giant dielectric constant. These investigations allow the applications of these materials in transparency, microelectronics and memory devices. solid-state reaction method, stoichiometric mixtures of CaCO 3, 20 A. Introduction TiO 2 and CuO are usually heated up to a high temperature (1000– 1150 oC) for long duration (4–50h) 22 . The procedures of the solid- Accepted Dielectric materials with high permittivity, low loss, light weight state synthesis are straightforward. However, the reaction and good process ability are highly desirable for a broad range of 50 products are usually not structurally and compositionally applications including electromechanical actuators, gate homogeneous. The solid-state reacted products often not only dielectrics, and energy storage devices. 1-5 Although dielectric contain CCTO phase but also impurities such as CaTiO 3 and CuO 25 behaviour mechanism is still open to debate, a commonly were observed. Besides, it is difficult to obtain nanosized CCTO accepted theory based on the internal barrier layer capacitor powders imputed to high annealing temperature used. The high (IBLC) model, 6 suggested that semiconducting grains, insulating 55 impurity and poor powder characteristics, represented by a coarse grain or domain boundaries form parallel capacitors, lead to an particle size, wide particle size distribution, irregular particle exceptionally high dielectric permittivity (ε'). Therefore, fine morphology, and a high degree of inhomogeneity made this 30 calcium copper titanate (CCTO) nanoparticles smaller than 100 23 24 process unsuitable . In this regard, Manik and Pradhan employ Advances nm is eagerly desired. Indeed, CCTO complex perovskite the ball milling technique for synthesis of pure CCTO (18 nm) structure is very flexible, i.e. its dielectric constant (ε) and 60 after milling for 8h. Otherwise, researchers and scientists are dielectric loss (tan δ) is highly dependent on the various cationic working for the development of high purity CaCu 3Ti 4O12 phase substitutions, such as La and Pr at Ca site or Ta, Cr, and Hf at the 7-12 with improved powder morphology, which will provide enhanced 35 Ti site. In spite of, the cationic substitution at the Cu site and dielectric constant with low loss. Hence, wet chemistry methods RSC its concentration in CCTO ceramic affect the dielectric properties, are used to synthesize CCTO nanopowders including because Cu ion is one of the most effective inter-granular dopants 25 26 27 13 65 polymerized complex, microwave heating, sol–gel, and co- for barrier layer capacitors and it can act as an acceptor ion. 28 precipitation methods . Thereby, the presence of Cu 1+ /Cu 2+ ratios and their correlation Among these techniques, combustion route seems to be 40 with oxygen vacancies has great influence on the dielectric promising one as an attractive technique for the excellent properties of polycrystalline CCTO via the internal barrier layer chemical homogeneity, high purity and nano-sized powders. capacitance (IBLC) mechanism 14 . 70 Moreover, this method has been adopted due to its many To date, CCTO materials are generally synthesized via two advantages compared with other methods such as energy major routes, i.e. the conventional high-temperature solid-state 15-16 17-21 efficiency, short reaction rate, the reagents are simple 45 reaction method and the wet chemical methods . In the i.e. compounds, easy operable, dopants can be easily introduced into This journal is © The Royal Society of Chemistry [year] [journal] , [year], [vol] , 00–00 |1 RSC Advances Page 2 of 6 the final product, low annealing temperature, better particle size 55 (JCPDS card no.75-2188). Peaks belonging to (200), (211), distribution, high probability of formation of single domain and (220), (013), (222), (321), (400), (422), (440), (433), and (620) 29 planes of cubic CCTO phase were indexed. No extra secondary agglomeration of powders remains limited . As far as we know 2+ the synthesis of CCTO powders by citrate precursor (CP) method impurity phases were detected with increasing Ca ions content 30-32 . Weak diffraction peaks observed on Figure 1 are not 5 has not been reported yet. Therefore, in this study, we 2+ 60 corresponding to secondary phases but it is noise due to the investigated the details pertaining to the effect of Ca ion granular morphologies of CCTO sample. It is clear that the variation on the crystal structure, microstructure, optical, samples with large Ca +2 ion concentrations exhibited a small shift electrical and dielectric properties of CCTO nanopowders in the XRD peaks towards larger 2 θ (Figure SI1). The shift was fabricated using the citrate precursor route based on low cost increased with increasing Ca +2 ion content corresponding to a 10 effective materials. Herein, the starting materials used were citric 65 decrease of the distances between the crystalline planes. acid, calcium carbonate, copper chloride and titanium dioxide. B Materials and Methods 1. Materials Anhydrous chemically grade calcium carbonate CaCO 3 (98.5 % 15 Sigma Aldrich), copper chloride CuCl 2 (98.6%, BDH Chemical Ltd), titanium dioxide TiO 2 (99.8%, Fluka), and citric acid C6H8O7 (98 % ADWIC) were used as starting materials. Moreover, deionized water was used in the whole work. 20 2. Procedure Manuscript Calcium copper titanate (CCTO) nanopowders were prepared via the citrate precursor route by mixing aqueous solutions of calcium carbonate CaCO 3, copper chloride CuCl 2 and titanium 2+ 2+ Fig. 1 XRD patterns of CCTO nanopowders with different Ca dioxide TiO 2 with Ca: Cu : Ti ratios of x:3-x:4 with different Ca ion content 1.0, 1.5, and 2.0 prepared by citrate precursor method 25 ion molar ratios ( x=1.0, 1.5, and 2.0) using certain amount of o citric acid. The molar ratio of metals precursor to citric acid was 70 and annealed at 1000 C for 2h 1:5. The solutions were slowly heated on a hot plate with a magnetic stirring at 80°C to form viscous gel. Then, the swelled gel was dried at that temperature for 6h resulted in the dried gel 30 citrate precursors. After that, the precursors were annealed in pure Accepted alumina crucibles at 1000 °C for 2 h in a muffle furnace (in air) with 10°C/min heating rate in order to achieve the corresponding perovskite structure in the samples. 35 3. Physical Characterization X-ray powder diffraction (XRD) was carried out on a model Bruker AXS diffractometer (D8-ADVANCE Germany) with Cu Kα (λ = 1.54056 Å) radiation, operating at 40 kV and 40 mA. The diffraction data were recorded for 2θ values between 10 o and 80 o. Fig. 2 Lattice constant of CCTO nanopowders as a function of 2+ 40 Scanning electron microscopy was performed by a FE-SEM Ca concentrations (JEOL-JSM-5410 Japan). The UV-Vis absorption spectrum was Advances The lattice parameter ( a) and the unit cell volume (V ) for the measured by UV-VIS-NIR-scanning spectrophotometer (JASCO cell 75 cubic perovskite structure were calculated using the following V-570 spectrophotometer, Japan). An electrometer and DC power equations: 18 supply (Agilent-4339B, USA) were used for the electrical dhkl = (Equation 1 ) 45 resistivity measurement.