Publications Internationales
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Item Tuning the dielectric properties of CaCu3Ti4O12 ceramic by Cu2O addition and microstructural modifications(Elsevier, 2023) Djafar, Rabah; Boumchedda, K.; Fasquelle, D.; Chaouchi, A.; Sedda, K.; Bououdina, M.; Bellucci, S.Cuprous (I) oxide (Cu2O) was used instead of Cupric (II) oxide (CuO) for the synthesis of CCTO ceramic by solid-state reaction. The impact of sintering time on the structure stability, grain size, and dielectric performance of Cu2O-based CCTO ceramics was discussed. XRD analysis indicates that the CaCu3Ti4O12 cubic phase was successfully synthetized. The studied samples manifested high permittivity and quite low dielectric loss values in the frequency range (20–106 Hz); with optimum values of 15,423 and 0.083 respectively achieved after sintering at 1050 °C for 14 h while for longer sintering times of 19 h and 24 h resulted in higher values of permittivity of 19,943 and 21,392 respectively were obtained and associated with an improved loss tangent of ∼0.114 and 0.127, respectively. It was found that a longer sintering time of Cu2O-based CCTO ceramics resulted in an important improvement of the dielectric propertiesItem Dielectric properties of nanocrystalline CaCu3Ti4O12 (CCTO) ceramics fabricated from Algerian limestone raw material(Elsevier, 2023) Djafar, Rabah; Boumchedda, K.; Fasquelle, D.; Chaouchi, A.; Sedda, K.; Bououdina, M.; Bellucci, S.; Bánhegyi, G.Algerian natural limestone was used to fabricate the perovskite CaCu3Ti4O12 phase (CCTO) to replace commercial calcium carbonate (CaCO3) powder by a solid-state method. X-ray diffraction analysis of CCTO ceramics sintered at 1010 °C manifested the formation of well-crystallized pure (CCTO) phase with narrow crystallite size (43–99 nm) without any additional phases after sintering beyond 4 h. Thermal analysis by DSC indicated that CCTO phase is stable up to 1151 °C, afterwards it decomposes into CaTiO3 and TiO2 and accompanied by the segregation of the CuO/Cu2O phase. Scanning electron microscopy observations of the ceramics sintered at 1010 °C showed that most of the grains have an average particle size in the narrow range of 1–2 μm. The sintered pellet at 1010 C° for 14 h showed the optimum density (>94%). This study highlights the importance of using natural calcium carbonates (extracted from Guelma limestone in Algeria) as potential replacement to commercial counterpart for the fabrication of dense well-crystallized perovskite-type ceramics with controlled particle size distribution as promising candidates for electronic applicationsItem Impedance spectroscopy studies on steatite with B 2 O ceramics materials from Algerian palygorskite(International Institute for the Science of Sintering (IISS), 2021) Khalfaoui, K.; Boumchedda, K.; Chaouchi, A.; Saidi, M.; Lamrani, N.B2O3 was used to reduce the sintering temperature of steatite (named MSB) dielectric ceramics. Electrical properties of this composition have been studied using impedance spectroscopic method to get better understanding of the electrical conduction, dielectric relaxation mechanism, and microstructure –electrical properties relationship of the materials as a function of temperature and frequency. These samples were prepared by a solid-state reaction technique and their single phase formation was confirmed by the X-ray diffraction technique. Dielectric and complex impedance spectroscopic studies were carried out in a wide frequency (102-106 Hz) and temperature (30-500oC) range. The dielectric constants decrease with increasing frequency for each sample, and then stabilize at frequencies lower than 100 kHz. The dielectric constant increases with the addition of B2O3. The nature of frequency dependence of ac conductivity of MSB follows the Jonscher power law and calculated DC conductivity follows Arrhinius behavior. The Nyquist plot (Z″ vs Zʹ) revealed the presence only of the grain boundary effect from 350oC onwards. The occurrence of single arc in the complex modulus spectrum of MSB compositions confirms the single-phase characteristics, and also confirms the presence of non-Debye type of multiple relaxations in the materialItem Cu2O addition and sintering temperature dependence of structural, microstructural and dielectric properties of CaCu3Ti4O12 ceramics(Elsevier, 2020) Djafar, Rabah; Boumchedda, K.; Chaouchi, A.; Fasquelle, D.; Sedda, K.; Brahimi, S.; Khalfaoui, K.; Bououdina, M.This study is aimed in the replacement of commonly used (CuO) by Cu2O in the synthesis of perovskite CaCu3Ti4O12 (CCTO) phase by the solid-state reaction method. The XRD analysis of powder calcined at 1100 °C and ceramics sintered at different temperatures show that the CCTO phase was well crystallized with the presence of small quantities of additional phases. The SEM/EDS analysis of prepared pellets show that the formation of Cu2O/CuO phase occurs above 950 °C, resulting in enhanced densification at 1050 °C (>96%). However, it is found that the Cu2O-based CCTO begins to degrade around 1090 °C. The densification after sintering at 1050 °C reaches 96%, meanwhile dielectric constant and loss tangent values are optimum in the low frequency range (<103 Hz); i.e. 13378 and 0.177, respectively. This favors the use of Cu2O instead of CuO in CCTO ceramics for applications at low frequencies