Polycrystalline sol–gel-derived SrTiO3/Na0.5Bi0.5TiO3/SrTiO3 (ST/NBT/ST) thin films were designed to achieve the electrical isolation of the NBT, and to mediate the temperature dependency of the dielectric properties. Proper thermal annealing of particulate phase enabled us to achieve compositionally graded elemental profiles between individual ST and NBT layers. The dielectric and ferroelectric properties were investigated with espect to the electrical behavior of the monophasic ST and NBT thin films. The dielectric characteristics of the multilayer thin film were marked by a temperature stable behavior (temperature coefficient of dielectric constant of 780 ppm/°C) in the measured −50°C to 200°C range, frequency independent response at room temperature and improved dielectric loss characteristics compared with the NBT; however, on the expense of decreased permittivity and a reduced ferroelectric stability.
COBISS.SI-ID: 26956839
AgNb0.5Ta0.5O3 ceramics were synthesized and analyzed, with respect to their dielectric properties, in the radio- and microwave-frequency ranges. The influences of different synthesis conditions were investigated and correlated with the difficulties in preparing single-phase ceramics, as a consequence of the inhomogeneous distribution of Nb and Ta ions and the decomposition of the matrix phase. The results revealed that with the simple mixing of all three oxides and subsequent firing in air, it is possible to prepare composite material that is attractive for microwave applications due to temperature stable resonant frequency. On the other hand, we also succeeded in fabricating single-phase ceramics with a very high density through the initial formation of a precursor and sintering in an overpressure of oxygen.
COBISS.SI-ID: 27388199
Cobalt ferrite nanoparticles (CFO NPs) were synthesized using precipitation followed by a hydrothermal treatment. The conditions for precipitation were kept constant, while the pH, the temperature and the synthesis time for the hydrothermal treatment were systematically varied. The results show that the pH plays the dominant role in the formation, growth and crystallization of the desired phase. Furthermore, by controlling the pH the magnetic properties, such as the magnetization and the coercitivity of the CFO NPs, can be tuned. An increase in the temperature induced both particle growth and a change of the morphology. The variation of the synthesis time indicated that the hydrothermal reaction proceeds for up to 8 h; however, a further prolongation of the synthesis time does not affect the structural and magnetic properties to any significant extent.
COBISS.SI-ID: 27333927
We have investigated the Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 (NBT–KBT) system, with its complex perovskite structure, as a promising material for piezoelectric applications. The NBT–KBT samples were synthesized using a solid-state reaction method and characterized with X-ray powder diffraction (XRD) and scanning electron microscopy. Room temperature XRD showed a gradual change in the crystal structure from tetragonal in the KBT to rhombohedral in the NBT, with the presence of an intermediate morphotropic region in the samples with 17 and 25% of KBT. The fitted perovskite lattice parameters confirmed an increase in the size of the crystal lattice from NBT towards KBT, which coincides with an increase in the ionic radii. Electrical measurements on the samples showed that the maximum values of the dielectric constant, the remanent polarization and the piezoelectric coefficient are reached at the morphotropic phase boundary.
COBISS.SI-ID: 23175463
The synthesis of sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) was studied using the hydrothermal treatment. The process parameters such as the alkaline conditions, the temperature, the reaction time, and the concentration of precursors, as well as the influence of the Bi/Ti ratio and microwave heating were investigated in detail. The results show that secondary sodium titanate phases formed along with the NBT phase in the initial stage of the reaction. Their stability was susceptible to the treatment conditions and the Bi/Ti ratio. Pure and well crystallized NBT nanoparticles were obtained after 48 h of reaction time at 200°C, 12MNaOH, 0.1MBi(NO3)3•5H2O and a stoichiometric amount of TiO2 relative to the Bi precursor. A chemical analysis of the powders showed a slight sodium deficiency and bismuth surplus with respect to their nominal composition.
COBISS.SI-ID: 24956455