Search results for "Barium"
showing 10 items of 262 documents
Long-Range and Short-Range Structure of Proton-Conducting Y:BaZrO3
2011
Yttrium-doped barium zirconate (BZY) is the most promising candidate for proton-conducting ceramics and has been extensively studied in recent years. The detailed features of the crystal structure, both short-range and long-range, as well as the crystal chemistry driving the doping process, are largely unknown. We use very high resolution X-ray diffraction (HR-XRD) to resolve the crystal structure, which is very slightly tetragonally distorted in BZY, while the local environment around Zr4+ and Y3+ is probed with extended X-ray absorption fine structure (EXAFS), and the symmetry and vibrations are investigated by using Raman spectroscopy. It is found that barium zirconate shows some degree …
Fine grain barium titanate: ferroelectric domains and X-ray diffraction diagram
2002
Through three different studies using various kinds of BaTiO/sub 3/ samples: as a powder while heating over the Curie temperature; as a green ceramic as a function of the forming pressure; as a ceramic while applying a D.C. field. It is shown how X-ray diffraction is able to give information about the evolution of the 90/spl deg/ ferroelectric domain microstructure.
Preparation and Electric Properties of Barium Zirconium Titanate Ceramic
2015
The relaxor behavior of barium zirconium titanate ceramics BaZr0.35Ti0.65O3 prepared by a conventional sintering process was investigated. The synthesized material was determined by an X-ray diffraction and scanning electron microscopy. Based on performed studies, the BaZr0.35Ti0.65O3 ceramic material has been identified as canonical relaxor, related to the Ti-rich polar regions. The freezing temperature Tf and activation energy Ea are calculated from the Vogel-Fulcher relationship.
High-pressure study of the behavior of mineral barite by x-ray diffraction
2011
In this paper, we report the angle-dispersive x-ray diffraction data of barite, BaSO 4, measured in a diamond-anvil cell up to a pressure of 48 GPa, using three different fluid pressure-transmitting media (methanol-ethanol mixture, silicone oil, and He). Our results show that BaSO 4 exhibits a phase transition at pressures that range from 15 to 27 GPa, depending on the pressure media used. This indicates that nonhydrostatic stresses have a crucial role in the high-pressure behavior of this compound. The new high-pressure (HP) phase has been solved and refined from powder data, having an orthorhombic P2 12 12 1 structure. The pressure dependence of the structural parameters of both room- and…
High-pressure transition to the post-barite phase in BaCrO4hashemite
2012
A recent high-pressure study on barium chromate BaCrO${}_{4}$ reported a phase transition but the structure of the high-pressure phase structure could not be identified. This high-pressure phase was suggested to have a monoclinic structure different from other high-pressure forms of $AB$O${}_{4}$-type compounds. In this work, we have carried out x-ray diffraction measurements up to 46 GPa using He as the quasihydrostatic pressure medium and density-functional theory calculations. Our studies allow us to identify the high-pressure phase as the $P$2${}_{1}$2${}_{1}$2${}_{1}$ post-barite-type phase, recently reported for BaSO${}_{4}$. The equations of state of both, the low- and the high-press…
Structural, microstructural and impedance spectroscopy study of functional ferroelectric ceramic materials based on barium titanate
2013
The differences between the physical properties of barium titanate BaTiO3 and newly obtained BaHfxTi1-xO3 were identified. These ceramics were prepared by solid-phase reaction from simple oxides and carbonates using the conventional method. The structure and morphology of investigated samples were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The application of impedance spectroscopy made possible to characterize of these materials in the terms of electrical properties.
Differential scanning calorimetry investigation of phase transition in $BaZr_{x}Ti_{1-x}O_{3}$
2009
ABSTRACT Lead-free BaZrxTi1-xO3 (x = 0; 0.025; 0.125) ceramics have been obtained by a conventional method. A single-phase perovskite structure of the ceramics was identified by the X-ray diffraction method. EDS analysis, performed for the individual grains of the tested sample, showed a good homogeneous distribution of all elements throughout the grains. The thermal behaviour of BaZrxTi1-xO3 (x = 0; 0.025; 0.125) ceramics was studied using the Differential Scanning Calorimetry (DSC). Measurements showed the influence of Zr addition on the character of phase transition in the BaTiO3 structure. The results were compared with these ones obtained for pure BaTiO3.
Heterobimetallic single-source precursors for MOCVD. Synthesis and characterization of volatile mixed ligand complexes of lanthanides, barium and mag…
1999
Several heterobimetallic complexes of general formula [(M 1 Q) m M 2 (dik) n ], where (M 1 Q) is Cu(salen) or Ni(salen) and M 2 (dik) n is a lanthanide tris(β-diketonate) or an alkali-earth element bis(β-diketonate) with more or less fluorinated diketonato(-) ligands, have been prepared and structurally characterized. Some of them were submitted to thermal and mass spectrometry analyses, and to isothermal vacuum sublimation tests, in view of their potential use as MOCVD single-source precursors for the deposition of heterobimetallic materials. The study stresses upon the influence of the nature of the diketone. of the M 2 cation, and of chemical modification of the salen ligand on the therm…
Crystal Structure and Local Dynamics in Tetrahedral Proton-Conducting La1-xBa1+xGaO4
2010
La1-xBa1+xGaO4-0 (LBG) compounds, based on unconnected GaO4 moieties, were recently proposed as proton conductors. Protonic defects in the lattice are inserted through self-doping with Ba2+, to create oxygen vacancies subsequently filled by hydroxyl ions. We present a combined structural analysis on self-doped LBG using X-ray diffraction (XRD) and X-ray absorption (EXAFS): these results unravel the finer structural details on the short-range and long-range scales, and they are correlated with the dynamical properties of protonic conduction coming from vibrational spectroscopy. The structure of the GaO4 groups is independent of the oxide composition. On hydration, an array of short intertetr…
The invasion history of Elodea canadensis and E. nuttallii (Hydrocharitaceae) in Italy from herbarium accessions, field records and historical litera…
2022
AbstractWe analysed the invasion history of two North American macrophytes (Elodea canadensis and E. nuttallii) in Italy, through an accurate census of all available herbarium and field records, dating between 1850 and 2019, and a rich literature collection describing the initial introduction and naturalisation phase that supports the results obtained by the occurrence records. Elodea canadensis arrived in Italy before 1866 and had two invasion phases, between the 1890s and 1920s and between the 1990s and 2000s; E. nuttallii, probably arrived in the 1970s, started invading in 2000 and the invasion is still ongoing. Botanical gardens and fish farming played a crucial role in dispersal and na…