Papers by Keyword: Perovskite Structure

Abstract: The influence of LiSbO₃ on the structure, microstructure, dielectric, ferroelectric and local piezoelectric properties of (K_0.5Na_0.5)NbO₃ ceramics has been studied. Changes in unit cell parameters correlated with ionic radii changes and high effective local d₃₃ piezoelectric coefficient values were observed depending on solid solutions compositions.

Abstract: In the present paper (1-x)Pb (Zr_1-yTi_y)O₃ – xPb (Mn_1/3Sb_2/3)O₃ – z at%E system, with E = Pr³⁺, Nd⁵⁺ and Gd³⁺ where x = 0.12; y = 0.48; z = 0 and 0.02 ceramic synthesized by solid state reaction technique is analysed. The investigation aims studying of the effect of dopants on the dielectric and piezoelectric properties of such piezoelectric ceramic. The prepared powders have been uniaxially pressed into discs with diameter of 10 – 12 mm and thickness of 1.2 mm. Sintering has been carried out in air atmosphere at temperatures of 1150^°C and 1200^°C, respectively, for 2 hours each, followed by a controlled cooling at a rate of 200^°C /h. The piezoelectric properties have been investigated after a suitable preparation, including polishing, metallization. The structure of the samples has been determined by X-ray diffractometry (XRD), while the morphology and grains size have been investigated by the scanning electron microscopy (SEM). The piezoelectric properties have been studied by the resonance - antiresonance method. XRD analysis reveals a perovskite tetragonal structure and, as expected for ceramic materials, SEM analysis indicates that the average grain size increases as sintering temperature increases. The dielectric and piezoelectric properties have been determined measuring the ceramic discs, and properties, as dielectric permittivity (ε_r), dielectric loss (tg δ), and the electromechanical coupling factor (k_p) have been obtained. The acquired results indicate a significant effect of the dopants on the dielectric and piezoelectric properties of such materials.

Abstract: Effects of cation nonstoichiomtry on crystal structure parameters, microstructure, and dielectric properties of ceramics (Na_0.5+xBi_0.5)TiO₃ and (Na_0.5-xBi_0.5)TiO₃ with Bi/Na<1 and of solid solutions [(Na_0.5Bi_0.5)_1-xK_x]TiO₃ and (Na_0.5Bi_0.5)(Ti_1-xMg_x)O₃ with x = 0 – 0.1 have been studied. Changes in the unit cell parameters and microstructure of the samples observed in ceramics prepared correlate well with both preparation conditions and radii of substituting cations. Ferroelectric phase transitions near ~ 400 K and ~ 600 K were confirmed ib the systems studied. Phase transitions near ~ 400 K demonstrate a pronounced relaxor behavior determined by the presence of polar regions in a nonpolar matrix. Besides, additional anomalies related to presence of relaxing dipoles formed by oxygen vacancies were observed on temperature dependences of dielectric permittivity at temperatures higher than 700 K. The results obtained confirmed that increase in nonstoichiometry lead to increase in ionic conductivity of the samples.

Abstract: Nowadays, Hybrid Perovskite materials perform a major role in solar cell industry due to their superior power conversion ability. CH₃NH₃PbI₃ is the prominent material in hybrid perovskite, where they comprised with advanced photovoltaic properties. But considering the toxicity, it’s more important to observe the role of metal atom in hybrid perovskite. Therefore, this research is basically focused on the objective of figuring out the fundamental properties of CH₃NH₃PbI₃ and CH₃NH₃SnI₃ with the idea of replacing Pb to Sn in future. Ab-Initio Simulation has been used throughout this research along with basic density function theories (DFT) like Exchange correlation functional, Local-density approximation of Kohn-Sham theory. Moreover, the research was also focused upon the Energy band gap variation, crystallographic orientations, density of states in P, S orbitals of cubic and tetragonal phases in CH₃NH₃PbI₃ and CH₃NH₃SnI₃.

Abstract: In this work, lead-free Ba_0.4Sr_0.4Ca_0.2Zr_0.05Ti_0.95O₃ ceramics were prepared by the seed induced method using (0.5Ba_0.6Sr_0.4TiO₃–0.5BaZr_0.05Ti_0.95O₃) (BST-BZT) seed. Seed crystals with concentrations of 0, 2.5, 5, 7.5, 10 mol% were mixed with BSCZT powder for 24 h and sintered at 1400 °C for 4 h. The phase formation and microstructure of BSCZT ceramic were characterized by X-ray diffraction technique (XRD) and the scanning electron microscopy (SEM). All samples showed a single phase perovskite structure without impurities and exhibited the existence of the tetragonal phase. The density values of the ceramics decreased from 4.90 to 4.75 g/cm³ with increasing seed crystal concentrations. The grain size of the sample without seed was 3.71 μm, whereas a grain size of 8.99 μm was observed for the sample with 10 mol% seed crystal. The dielectric constant at room temperature at 1 kHz was 1831 for the sample with 10 mol% seed crystal while the dielectric constant of the sample without seed was 1484. From the results in this work, BST-BZT seed can increase grain size and improve the dielectric constant at room temperature.

Abstract: In this paper, (K_0.5Na_0.53)_0.932Nb_0.932O₃-0.008BF-0.06LS (abbreviated as KNN-BF-LS) piezoelectric ceramic was prepared by sol-gel method. Structure and properties of ceramics were analyzed.Through analysis of the results, when sintering temperature is 1080°C, ceramic has good perovskite structure. At this temperature, grain size is more uniform, and structure is the most dense. Piezoelectric constant d₃₃, electromechanical coupling coefficient Kp, dielectric constant ε_r reached the maximum value, respectively, 113pC/N, 0.33, 591. Dielectric loss tanδ reached the minimum 0.11.

Abstract: NaMgH₃ perovskite hydride and graphitic carbon nitride (g-C₃N₄) powder with multi-layer structure have been synthesized by high-energy ball-milling and heating-decomposition method respectively. In comparison with pristine NaMgH₃ hydride, the as–milled NaMgH₃+5wt.% g-C₃N₄ (NMH-5CN) composite presents better dehydriding kinetic properties and lower onset decomposition temperature. The onset decomposition temperature of NMH-5CN composite can be decreased about 87K, the hydrogen-desorbed amount is about 3.2 wt. % within 40min, and 1.4 wt. % within 10min at 638K, and the Kissinger analysis demonstrated that the activation energy (ΔE) of the first and second dehydrogenation step for NMH-5CN can be reduced about 40 kJ mol^-1 and 22.4 kJ mol^-1, respectively. The results suggest that g-C₃N₄ is an effective catalyst for the improvement of dehydriding properties of NaMgH₃ perovskite hydride.

Abstract: Barium cerate (BaCeO₃) ceramics were synthesized via a solid-state reaction technique. Pure phase perovskite powders were obtained at a calcination temperature of 1200 °C. BaCeO₃ ceramics were fabricated from the calcined powder and their properties were investigated. XRD data of the ceramics was consistent with an orthorhombic symmetry. However, the pure phase perovskite of the BaCeO₃ ceramics was only observed for sintering temperatures less than 1500°C. The microstructural analysis indicated that grain sizes of the ceramics increased with increasing sintering temperature. The dielectric constant of the samples had a constant value over a very wide range of temperature. All ceramics showed very good dielectric performance where the ceramics sintered at 1450 °C showed the highest dielectric constant.

Abstract: In this work, ceramics of Sr(Fe_0.5Nb_0.5O₃) doped with Ba(Zr_0.25Ti_0.75)O₃ (10 mol%), were synthesized by a solid-state reaction technique. The powders were calcined at 1300 °C for 12 hr and then sintered at 1400-1500 °C for 4 hr. Effects of sintering temperature on the properties of the ceramic were studied. Phase formation, microstructure, and dielectric properties were investigated. The ceramics exhibited a perovskite structure with cubic symmetry. Grain size of the ceramics increased with increasing the sintering temperature. The ceramics exhibited a dielectric relaxation like behavior with high dielectric constants over a wide temperature range

Abstract: The possibility of functional nanostructured materials for electronic devices synthesis by sol-gel method have been discussed such as ferroelectrics (SrBi₂(Ta_xNb_1-x)₂O₉) , ferromagnetics (Fe_xCo_yO_z) and semiconductors (ZnO). The structural features of the surface (AFM), crystallization behavior (XRD) during the heating and properties of synthesized films are discussed. Achieved parameters suggest the possibility of using synthesized SBTN sol-gel films in non-volatile memory devices, semiconductors active ZnO layers in solar sells, ferromagnetics Fe_xCo_yO_z films in radioabsorbing covers.