Journal of Advanced Dielectrics
Co-Editors-in-Chief
Xi Yao
Javier E. Camargo, Leandro A. Ramajo, and Miriam S. Castro

Ni0.5Co0.5Fe2O4 (NCF) powders were obtained employing two alternative synthesis routes: solid-state reaction and Pechini’s methods. The ceramic powders were pressed and sintered in the temperature range of 1100∘C to 1250∘C. Microstructural and structural properties were evaluated by SEM, XRD, and Raman spectroscopy. Magnetic hysteresis loops of sintered samples were also recorded. A secondary phase was observed in samples synthesized by Pechini’s method, whereas samples obtained by the solid-state reaction method, with the mechanochemical activation of the reagents, only produced the spinel structure. Magnetic properties of samples obtained by the solid-state method displayed higher magnetic saturations and lower coercive fields than those obtained from the Pechini’s method.Ni0.5Co0.5Fe2O4 (NCF) powders were obtained employing two alternative synthesis routes: solid-state reaction and Pechini’s methods. The ceramic powders were pressed and sintered in the temperature range of 1100∘C to 1250∘C. Microstructural and structural properties were evaluated by SEM, XRD, and Raman spectroscopy. Magnetic hysteresis loops of sintered samples were also recorded. A secondary phase was observed in samples synthesized by Pechini’s method, whereas samples obtained by the solid-state reaction method, with the mechanochemical activation of the reagents, only produced the spinel structure. Magnetic properties of samples obtained by the solid-state method displayed higher magnetic saturations and lower coercive fields than those obtained from the Pechini’s method.

Jan. 01, 1900
  • Vol. 11 Issue 3 2140001 (2021)
  • J. A. Cortés, J. Camargo, M. F. Rachia, F. Rubio-Marcos, L. Ramajo, M. Castro, and M. A. Ramírez

    The effect of sintering condition on structure, microstructure, and ferroelectric properties of (K0.44Na0.52Li0.04) (Nb0.86Ta0.10Sb0.04)- O3 (KNL–NTS) has been investigated. Ceramic powders have been synthesized by the solid-state reaction method and sintered at different temperatures (1115∘C, 1125∘C, and 1140∘C). Then, samples were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. Through XRD results, the perovskite structure and small peaks corresponding to a secondary phase were detected. Ceramics processed at the highest temperatures showed higher densities and good piezoelectric properties (d33, Kp, and Kt), particularly specimens sintered at 1125∘C presented the highest piezoelectric performance.The effect of sintering condition on structure, microstructure, and ferroelectric properties of (K0.44Na0.52Li0.04) (Nb0.86Ta0.10Sb0.04)- O3 (KNL–NTS) has been investigated. Ceramic powders have been synthesized by the solid-state reaction method and sintered at different temperatures (1115∘C, 1125∘C, and 1140∘C). Then, samples were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. Through XRD results, the perovskite structure and small peaks corresponding to a secondary phase were detected. Ceramics processed at the highest temperatures showed higher densities and good piezoelectric properties (d33, Kp, and Kt), particularly specimens sintered at 1125∘C presented the highest piezoelectric performance.

    Jan. 01, 1900
  • Vol. 11 Issue 3 2140002 (2021)
  • J. A. Jaramillo Palacio, K. A. Muñoz Pulido, J. Arbey Rodríguez, D. A. Landínez Téllez, and J. Roa-Rojas

    In the search for new materials with applicable magnetic properties in spintronic devices, the aim of this work is to report the synthesis of the lanthanide ferrocobaltite La2CoFeO6 using the modified Pechini route; the experimental study of structural, morphological and magnetic properties, and the analysis of the electronic structure and bands are obtained in the framework of the Density Functional Theory. Rietveld refinement of experimental X-ray diffraction patterns revealed the crystallization of this oxide material in a perovskite-like monoclinic structure, space group P21/n (# 14). Scanning electron microscopy and atomic force microscopy images revealed that the surface morphology is essentially polycrystalline, with mean grain sizes between 177 and 188 nm. The dispersive X-ray spectroscopy suggests that the material obtained contains La, Fe, Co and O in the stoichiometric proportions expected by up to 98%. The magnetic susceptibility curves as a function of temperature indicated that the material is ordered ferromagnetically, showing strong irreversibility effects due to the disorder of the Fe and Co cations in the three crystallographic directions of the structure and to the strong distortions in the FeO6 and CoO6 octahedra. Magnetic hysteresis curves confirmed the ferromagnetic character of the material for all temperatures evaluated, up to room temperature. I–V response curves revealed a semiconductor-like behavior with a figure of merit exponent 1.53 of the varistor type. The ferromagnetic semiconductor behavior suggests the potential applicability of the material in spintronic technological devices.In the search for new materials with applicable magnetic properties in spintronic devices, the aim of this work is to report the synthesis of the lanthanide ferrocobaltite La2CoFeO6 using the modified Pechini route; the experimental study of structural, morphological and magnetic properties, and the analysis of the electronic structure and bands are obtained in the framework of the Density Functional Theory. Rietveld refinement of experimental X-ray diffraction patterns revealed the crystallization of this oxide material in a perovskite-like monoclinic structure, space group P21/n (# 14). Scanning electron microscopy and atomic force microscopy images revealed that the surface morphology is essentially polycrystalline, with mean grain sizes between 177 and 188 nm. The dispersive X-ray spectroscopy suggests that the material obtained contains La, Fe, Co and O in the stoichiometric proportions expected by up to 98%. The magnetic susceptibility curves as a function of temperature indicated that the material is ordered ferromagnetically, showing strong irreversibility effects due to the disorder of the Fe and Co cations in the three crystallographic directions of the structure and to the strong distortions in the FeO6 and CoO6 octahedra. Magnetic hysteresis curves confirmed the ferromagnetic character of the material for all temperatures evaluated, up to room temperature. I–V response curves revealed a semiconductor-like behavior with a figure of merit exponent 1.53 of the varistor type. The ferromagnetic semiconductor behavior suggests the potential applicability of the material in spintronic technological devices.

    Jan. 01, 1900
  • Vol. 11 Issue 3 2140003 (2021)
  • M. Difeo, L. Ramajo, and M. Castro

    Doping effects of CuO on the sintering behavior and electrical properties of 0.94(Bi0.5Na0.5)TiO3–0.06(BaTiO3)–xCuO (BNT–BT6–xCu) lead-free piezoceramic obtained by the conventional solid-state reaction method were investigated. Regarding the undoped system, it is already known that it presents the best densification values when it is sintered at 1150∘C, however, the doped system was sintered at 1150∘C, 1100∘C, 1050∘C, 1025∘C, and 975∘C to determine the effect of Cu on the densification process. Therefore, it was obtained that the CuO-doped samples sintered at 1050∘C presented the highest density values and therefore were the ones chosen to perform the characterization tests together with the undoped system. The samples were characterized using X-ray diffraction (XRD), Raman microspectroscopy, and scanning electron microscopy (SEM) analysis, whereas the ferroelectric and dielectric properties were evaluated by means of ferroelectric hysteresis loops and impedance spectroscopy studies. As a result, the addition of CuO allowed an improvement in sinterability and densification, with the subsequent grain growth, and the improvement of the piezoelectric coefficient (d33).Doping effects of CuO on the sintering behavior and electrical properties of 0.94(Bi0.5Na0.5)TiO3–0.06(BaTiO3)–xCuO (BNT–BT6–xCu) lead-free piezoceramic obtained by the conventional solid-state reaction method were investigated. Regarding the undoped system, it is already known that it presents the best densification values when it is sintered at 1150∘C, however, the doped system was sintered at 1150∘C, 1100∘C, 1050∘C, 1025∘C, and 975∘C to determine the effect of Cu on the densification process. Therefore, it was obtained that the CuO-doped samples sintered at 1050∘C presented the highest density values and therefore were the ones chosen to perform the characterization tests together with the undoped system. The samples were characterized using X-ray diffraction (XRD), Raman microspectroscopy, and scanning electron microscopy (SEM) analysis, whereas the ferroelectric and dielectric properties were evaluated by means of ferroelectric hysteresis loops and impedance spectroscopy studies. As a result, the addition of CuO allowed an improvement in sinterability and densification, with the subsequent grain growth, and the improvement of the piezoelectric coefficient (d33).

    Jan. 01, 1900
  • Vol. 11 Issue 3 2140004 (2021)
  • J. D. S. Guerra, C. A. Guarany, E. C. Lima, E. B. Araújo, and J. E. Garcia

    Electromechanical and dielectric properties of PMN–PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, 𝜀(E), which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90∘ and 180∘ domains walls.Electromechanical and dielectric properties of PMN–PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, 𝜀(E), which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90∘ and 180∘ domains walls.

    Jan. 01, 1900
  • Vol. 11 Issue 3 2140005 (2021)
  • B. R. Moya, A. C. Silva, A. Peláiz-Barranco, and J. D. S. Guerra

    (1–x)Bi0.5Na0.5TiO3–xBaTiO3lead-free ceramics have been obtained from the conventional solid-state reaction sintering method. The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques. Results revealed well-crystallized ceramic samples with perovskite structure. Microstructural properties, obtained from scanning electron microscopy measurements, have shown high density with very low porosity level. The dielectric response, analyzed as a function of the temperature and several frequencies, showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system. Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties.(1–x)Bi0.5Na0.5TiO3–xBaTiO3lead-free ceramics have been obtained from the conventional solid-state reaction sintering method. The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques. Results revealed well-crystallized ceramic samples with perovskite structure. Microstructural properties, obtained from scanning electron microscopy measurements, have shown high density with very low porosity level. The dielectric response, analyzed as a function of the temperature and several frequencies, showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system. Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties.

    Jan. 01, 1900
  • Vol. 11 Issue 3 2140006 (2021)
  • Y. González-Abreu, S. P. Reis, F. E. Freitas, J. A. Eiras, and E. B. Araújo

    BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.

    Jan. 01, 1900
  • Vol. 11 Issue 3 2140007 (2021)
  • C. Carreras-Casas, O. García-Zaldívar, A. Peláiz-Barranco, Y. González-Abreu, F. Calderón-Piñar, and J. D. S. Guerra

    The relaxor behavior of PLZT ferroelectric ceramics has been analyzed in a wide frequency and temperature ranges, below and above the temperature for the formation of the so-called polar nano-regions (PNRs). An approximation to the dynamical behavior of the PNRs has been discussed using Cole–Cole’s relaxation model and Jonscher’s Universal Relaxation Law. The analysis considers both the dipolar contribution and those ones associated with DC and AC electric conductivities, this latter not being previously reported in the literature for relaxor materials. The effectiveness of the developed model has been verified from the agreement between the experimental data and the theoretical calculations. This study also offers an indirect method to predict the DC component of the electrical conductivity.The relaxor behavior of PLZT ferroelectric ceramics has been analyzed in a wide frequency and temperature ranges, below and above the temperature for the formation of the so-called polar nano-regions (PNRs). An approximation to the dynamical behavior of the PNRs has been discussed using Cole–Cole’s relaxation model and Jonscher’s Universal Relaxation Law. The analysis considers both the dipolar contribution and those ones associated with DC and AC electric conductivities, this latter not being previously reported in the literature for relaxor materials. The effectiveness of the developed model has been verified from the agreement between the experimental data and the theoretical calculations. This study also offers an indirect method to predict the DC component of the electrical conductivity.

    Jan. 01, 1900
  • Vol. 11 Issue 3 2140008 (2021)
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