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Pure and well-crystallized Barium Strontium Titanate (BST) nanoparticles with controlled Ba/Sr ratio have been successfully synthesized under supercritical conditions using a continuous-flow reactor in the temperature range of 150-380 degrees C at 26 MPa. To synthesize the Ba0.6Sr0.4TiO3 composition, alkoxides, ethanol and water were used. The resulting nanopowder consists of fine particles with an average particle size of 23 nm. The results show that the Ba/Sr ratio of this powder can be accurately controlled from the composition of precursor. The characterization of the as-synthesized Ba0.6Sr0.4TiO3 solid-solution and the dielectric properties of the sintered ceramics are here reported.

Abstract: Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln=La, Pr, Nd, Sm, Eu, Gd) with the “tetragonal tungsten bronze” (TTB) structure have been synthesised by conventional solid state methods. The neodymium, samarium and europium compounds are ferroelectric with Curie temperature ranging from 320 to 440K. The praseodymium and gadolinium compounds behave as relaxors below 170 and 300K respectively. The praseodymium, neodymium, samarium, europium and gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these materials as composites multiferroic. Based on crystal-chemical analysis we propose some relationships between the introduction of Ln3+ ions in the TTB framework and the chemical, structural and physical properties of these materials. [Copyright &y& Elsevier]

Polycrystalline samples of Ba 1−x Pb x (Ti 1−y Zr y )O 3 (BPTZ) with x = 0.025 & 0.1 and 0.10 ≤ y ≤ 0.50 have been synthesized by high-temperature solid-state reaction technique. X-ray diffraction reveals the formation of single phase with tetragonal or cubic structure. Dielectric investigations were carried out in the temperature range from 80 to 445 K with frequencies range from 10 2 to 10 6 Hz. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates either a diffuse phase transition or relaxor behavior in some of these ceramics. Whatever lead content, when zirconium is substituted by titanium, T C and ε’r max decreases while ΔT m(f) = [T m (10 6 Hz)−T m (10 2 Hz)] and tgδ increase. The diffuse phase transition parameters were estimated from a linear fit of the modified Curie–Weiss law. A good fit to the Vogel–Fülcher relation further corroborates such a relaxor nature. [ABSTRACT FROM AUTHOR]

Abstract: The BaTi0.4(Fe0.5Nb0.5)0.6O3 ceramic is synthesized by a solid-state reaction technique. The X-ray diffraction of the sample at room temperature shows a cubic phase. The dielectric properties are investigated as a function of frequency (20–106 Hz) at different temperatures (80–417K). A giant low frequency dielectric permittivity () was obtained. Two dielectric relaxation peaks were observed on the curve of dielectric loss vs. temperature. The intrinsic dielectric permittivity calculated by impedance spectroscopy from the values of the obtained bulk capacitances were remarkably high 230<<330. The extrinsic factors play an important role on their dielectric response giving rise to a giant dielectric permittivity at T>150K. The heterogeneities conduction in the grains, grain boundaries and interfacial layers are related to a Maxwell–Wagner relaxation. [Copyright &y& Elsevier]