Search results for "barium"
showing 10 items of 262 documents
High frequency dielectric relaxation in BaTio3derived materials
1992
Abstract A systematic study of the dielectric relaxation phenomenon has been carried out for ceramics with compositions derived from barium titanate in the frequency and temperature ranges 1 MHz–1 GHz and 250–500 K, respectively. Whatever the composition may be, a minimum of the relaxation frequency and a maximum of the dielectric dispersion appears at each phase transition temperature. The dipole-type relaxation is correlated to coherent displacements of the ions in the octahedron sites ordered either along chains or in 3D-lattice.
Elastic and piezoelectric properties of BaTiO3 at room temperature
1999
Abstract We have calculated the phonon dispersion curves of barium titanate (BaTiO 3 ) at room temperature. A lattice dynamical formalism using the shell model is used. This microscopic model includes the short-range interactions of axially symmetric type and the long-range Coulomb interactions and taking into account the electronic polarizability of constituent ions. Zone center phonon and a few phonons in the first Brillouin zone are used for fitting. The values of relevant parameters are critically analyzed. A calculation of the elastic and piezoelectric properties is presented and compared with the available experimental data.
Photorefractive detection of antiparallel ferroelectric domains in BaTiO 3 and BaTiO 3 :Co crystals
1998
An all-optical method involving one coherent beam of light and based on photorefractive wave mixing is used to reveal antiparallel ferroelectric domains in one pure, and two cobalt-doped, barium titanate crystals (BaTiO 3 ). Rod-shaped domains with square cross sections are revealed.
The Ba2LnFeNb4O15 “tetragonal tungsten bronze”: Towards RT composite multiferroics
2009
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 300 K 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 mat…
Indium Doping in Barium Cerate: the Relation between Local Symmetry and the Formation and Mobility of Protonic Defects
2007
The solid solution series Ba(In,Ce)O3-ä has been investigated with respect to structure, formation, and mobility of protonic defects. Compared to the limited solubility of Y2O3 in BaCeO3 and BaZrO3, the complete solubility of In2O3 is suggested to reflect a relation between absolute hardness of the dopant and the ease of insertion into the hosting lattices. Extended X-ray absorption fine structure (EXAFS) was used to probe the local environment of In3+ in barium cerate: in the surroundings of the dopant, the orthorhombic structure is strongly modified, resulting in an increase of local symmetry. The InO6 octahedra are very regular, and there is no indication for any defect clustering. This …
Study of the Dielectric Properties of Europium Doped Barium Titanate Ceramics by an Impedance Spectroscopy
2015
The barium titanate (BaTiO3) and the BaTiO3 + 0.1wt.% Eu2O3 ceramics were prepared by a conventional ceramic method. The structural studies were carried out by means of an X-ray diffraction technique. The influence of the grains and the grain boundaries on the electrical properties was investigated using a impedance spectroscopy. This technique enables us to determine the values of grain and grain boundary resistance. The results show that the Eu doping leads to a significant reduction in the resistance value of the grains (˜105Ω) with respect to the pure BT ceramics (˜107Ω). The conductivity processes were determined from the Arrhenius behaviour of grain and grain boundary resistances.
Local environment of Barium, Cerium and Yttrium in BaCe1−xYxO3−δ ceramic protonic conductors
2007
Abstract Y-doped barium cerate protonic conductors with composition BaCe 1 − x Y x O 3 − δ ( x = 0.02, 0.1, 0.2, 0.3) have been synthesized by sol–gel route, giving by X-ray diffraction tests a homogeneous crystalline phase. A commercial sample BaCe 0.8 Y 0.2 O 3 − δ produced by combustion spray pyrolysis was also provided for comparison aim. The local structure around the cations was studied by X-ray absorption spectroscopy at the K-edges of Ba, Ce and Y. It is demonstrated that the insertion of yttrium in the site of cerium produces a remarkable local distortion of the dopant first-shell octahedral environment that affects also the next coordination shells by a static disorder increas…
Energy leaks through the optical barrier created by H+ implantation in BaTiO3 and LiNbO3 planar waveguides
1998
Abstract The energy leaks through the index barrier created by the proton implantation process are put in evidence in planar optical waveguides made in BaTiO 3 and LiNbO 3 substrates. The selective detection of the light emerging from the guiding region permits to measure the optical attenuation of the guided wave. The results obtained on mono or twice implanted LiNbO 3 and BaTiO 3 waveguides are presented and discussed. It is shown that the light confinement is better in BaTiO 3 than in LiNbO 3 .
Two-wave mixing at 854 nm in BaTiO3:Rh planar waveguide implanted with He+
2001
Abstract Guided waves at 854 nm are observed in a BaTiO 3 :Rh waveguide fabricated by the technique of ion-beam implantation. The photorefractive interaction between two guided modes is demonstrated and characterized. The experiments reveal that the gain direction is reversed in the guiding layer in comparison with that in the bulk. A maximum gain of 24 cm −1 is achieved.
Continuous hydrothermal synthesis of nanometric BaZrO3 in supercritical water
2007
Abstract Nanocrystalline barium zirconate (BaZrO 3 ) was synthesized using a hydrothermal synthesis process working in supercritical conditions and in a continuous way. By this method, we succeeded in the continuous and rapid production of nanopowders. As a preliminary work three barium precursors have been investigated: barium hydroxide (Ba(OH) 2 ), barium acetate (Ba(CH 3 COO) 2 ) and barium nitrate (Ba(NO 3 ) 2 ). Two of them (Ba(CH 3 COO) 2 and Ba(NO 3 ) 2 ) led to the pure perovskite phase. Then an experimental design has been conducted in order to determine the influence of the experimental parameters on the crystallinity and the grain size of the final product.