ABSTRACT
In the present paper, composite thin films of barium strontium titanate (BaxSr1-xTiO3) with an acceptor modifier (magnesium oxide-MgO) were deposited on metal substrates (stainless steel type) using the sol-gel method. The composite thin films feature BaxSr1-xTiO3 ferroelectric solid solution as the matrix and MgO linear dielectric as the reinforcement, with MgO concentrations ranging from 1 to 5 mol%. Following thermal treatment at 650 °C, the films were analyzed for their impedance response. Experimental impedance spectra were modeled using the Kohlrausch-Williams-Watts function, revealing stretching parameters (ß) in the range of approximately 0.78 to 0.89 and 0.56 to 0.90 for impedance and electric modulus formalisms, respectively. Notably, films modified with 3 mol% MgO exhibited the least stretched relaxation function. Employing the electric equivalent circuit method for data analysis, the "circle fit" analysis demonstrated an increase in capacitance from 2.97 × 10-12 F to 5.78 × 10-10 F with the incorporation of 3 mol% MgO into BST-based thin films. Further analysis based on Voigt, Maxwell, and ladder circuits revealed trends in resistance and capacitance components with varying MgO contents, suggesting non-Debye-type relaxation phenomena across all tested samples.
ABSTRACT
In the present paper, results of X-ray photoelectron studies of electroceramic thin films of barium strontium titanate, Ba1-xSrxTiO3 (BST), composition deposited on stainless-steel substrates are presented. The thin films were prepared by the sol-gel method. A spin-coating deposition of BST layers with different chemical compositions was utilized so the layer-type structure of (0-2) connectivity was formed. After the deposition, the thin-film samples were heated in air atmosphere at temperature T = 700 °C for 1 h. The surfaces of BST thin films subjected to thermal treatment were studied by X-ray diffraction. X-ray diffraction measurements confirmed the perovskite-type phase for all grown thin-film samples. The oxidation states of the elements were examined by the X-ray photoelectron spectroscopy method. X-ray photoelectron spectroscopy survey spectra as well as high-resolution spectra (photo-peaks) of the main metallic elements, such as Ti, Ba, and Sr, were compared for the layer-type structures, differing in the deposition sequence of the barium strontium titanate layers constituting the BST thin film.
ABSTRACT
In this study, ceramic CaCu3Ti4O12 (CCTO) and CaCu3-xMgxTi4O12 solid solutions in which 0.1 ≤ x ≤ 0.5 were prepared by the mechanochemical method, realized by a high-energy ball milling technique. The effects of the Mg2+ ion concentration and sintering time on the dielectric response in the prepared ceramics were investigated and discussed. It was demonstrated that, by the use of a sufficiently high energy of mechanochemical treatment, it is possible to produce a crystalline product after only 2 h of milling the mixture of the oxide substrates. Both the addition of magnesium ions and the longer sintering time of the mechanochemically-produced ceramics cause excessive grain growth and significantly affect the dielectric properties of the materials. The X-ray diffraction (XRD) analysis showed that all of the as-prepared solid solutions, CaCu3-xMgxTi4O12 (0.0 ≤ x ≤ 0.5), regardless of the sintering time, exhibit a cubic perovskite single phase. The dielectric study showed two major contributions associated with the grains and the grain boundaries. The analysis of the electric modules of these ceramics confirmed the occurrence of Maxwell-Wagner type relaxation, which is dependent on the temperature.
ABSTRACT
Results of studies focusing on the electric behavior of Bi6Fe2Ti3O18 (BFTO) ceramics are reported. BFTO ceramics were fabricated by solid state reaction methods. The simple oxides Bi2O3, TiO2, and Fe2O3 were used as starting materials. Immittance spectroscopy was chosen as a method to characterize electric and dielectric properties of polycrystalline ceramics. The experimental data were measured in the frequency range Δν = (10-1-107) Hz and the temperature range ΔT = (-120-200) °C. Analysis of immittance data was performed in terms of complex impedance, electric modulus function, and conductivity. The activation energy corresponding to a non-Debye type of relaxation was found to be EA = 0.573 eV, whereas the activation energy of conductivity relaxation frequency was found to be EA = 0.570 eV. An assumption of a hopping conductivity mechanism for BFTO ceramics was studied by 'universal' Jonscher's law. A value of the exponents was found to be within the "Jonscher's range" (0.54 ≤ n ≤ 0.72). The dc-conductivity was extracted from the measurements. Activation energy for dc-conductivity was calculated to be EDC = 0.78 eV, whereas the dc hopping activation energy was found to be EH = 0.63 eV. The obtained results were discussed in terms of the jump relaxation model.
ABSTRACT
Solid-state sintering method was used to prepare ceramic materials based on bismuth ferrite, i.e., (BiFeO3)1 - x -(BaTiO3) x and Bi1 - x Nd x FeO3 solid solutions and the Aurivillius Bi5Ti3FeO15 compound. The structure of the materials was examined using X-ray diffraction, and the Rietveld method was applied to phase analysis and structure refinement. Magnetoelectric coupling was registered in all the materials using dynamic lock-in technique. The highest value of magnetoelectric coupling coefficient α ME was obtained for the Bi5Ti3FeO15 compound (α ME ~ 10 mVcm(-1) Oe(-1)). In the case of (BiFeO3)1 - x -(BaTiO3) x and Bi1 - x Nd x FeO3 solid solutions, the maximum α ME is of the order of 1 and 2.7 mVcm(-1) Oe(-1), respectively. The magnitude of magnetoelectric coupling is accompanied with structural transformation in the studied solid solutions. The relatively high magnetoelectric effect in the Aurivillius Bi5Ti3FeO15 compound is surprising, especially since the material is paramagnetic at room temperature. When the materials were subjected to a preliminary electrical poling, the magnitude of the magnetoelectric coupling increased 2-3 times.