Search results for "CERAMICS"
showing 10 items of 1599 documents
Near-coincidence lattice method for the determination of epitaxy strains during oxidation of metals
2000
Abstract A theoretical method is proposed to evaluate the strains due to epitaxy between a metal and its oxide. Based on Bollmann’s approach of two adjoining grains, it uses the quantitative texture analysis of the two materials separated by the phase boundary. Our study of the Zr/ZrO 2 and Mo/MoO 3 systems reveals strong correlations between the criterion of best fit proposed by Bollmann and the orientation distribution function obtained by a quantitative texture analysis. The results of this study are used in a thermo-mechano-chemical simulation of the oxidation process of zirconium, which leads to this observation: two different zirconia orientations induce two different oxidation kineti…
Synthesis of chloroantimonates(III) with selected organic cations. X-ray studies of phase transition in ferroelectric tris(trimethylammonium) nonachl…
2004
Abstract The dependence of molar ratio of reactants on the formula, crystal structure and physicochemical properties of chloroantimonates(III) with different organic cations was studied. It was proved, that the compounds show preferences in crystallization of one product. The changes of the molar ratio of substrates lead to the corresponding changes of these components in crystallized products. The structure of ferroelectric chloroantimonate(III), [(CH3)3NH]3[Sb2Cl9], was determined at 165 and 95 K. It crystallizes in monoclinic space group Pc: a=9.9612(11), b=9.0714(8), c=15.1807(14) A, β=90.086(8)°, R1=0.0202, wR2=0.0405 and a=9.9138(10), b=9.0783(7), c=15.1299(14) A, β=90.026(8)°, R1=0.0…
Crystal structure, phase transitions and ferroelastic properties of [(CH3)2NH2]3[Bi2Cl9]
2003
Abstract A sequence of structural phase transitions in [(CH3)2NH2]3[Bi2Cl9] (DMACB) is established on the basis of differential scanning calorimetry (DSC) and dilatometric studies. Four phase transitions are found: at 367/369, 340/341, 323/325 and 285/292 K (on cooling/heating). The crystal structure of DMACB is determined at 350 K. It crystallizes in monoclinic space group P21/n: a=8.062(2), b=21.810(4), c=14.072(3) A, β=92.63(3)°, Z=4, R1=0.0575, wR2=0.1486. The crystal is built of the double chain anions (“pleated ribbon structure”) and the dimethylammonium cations. Dielectric studies in the frequency range 75 kHz–900 MHz indicate relatively fast reorientation of the dimethylammonium cat…
In situ study of the phase transition in Bi2Ti4O11
1995
Abstract The paraelectric ⇌ antiferroelectric phase transition of the compound Bi 2 Ti 4 O 11 is studied in situ by electron diffraction and electron microscopy. The transition is reversible and clearly second order. Above T c faint streaking at the superlattice positions persists. In the low-temperature phase, antiphase boundaries with a displacement vector R = 1/2[101] are revealed; they show a finite width, suggesting a gradual displacement of the Bi atoms at the transition. A model for the domain wall configuration is proposed, based on the influence of the lone pairs of Bi 3+ ions at the transition.
Low-temperature polymorphism in tungsten trioxide powders and its dependence on mechanical treatments
1999
The polymorphism of WO3 powder samples, resulting from mild mechanical treatments and from temperature changes between 30 K and room temperature, has been investigated by using Raman spectroscopy and X-ray di⁄raction. A transition from the monoclinic (I) c-phase to the triclinic d-phase after moderate mechanical treatments has been observed for untreated powder, just what happens when the same samples are rapidly cooled to low-temperature. Evidences of the low temperature monoclinic (II) polar e-phase have been found at room temperature in samples after a stronger milling treatment. The sequence of the low-temperature phase transitions appears to be strongly dependent on the mechanical hist…
Pectin biopolymer mechanics and microstructure associated with polysaccharide phase transitions.
2019
Polysaccharide polymers like pectin can demonstrate striking and reversible changes in their physical properties depending upon relatively small changes in water content. Recent interest in using pectin polysaccharides as mesothelial sealants suggests that water content, rather than nonphysiologic changes in temperature, may be a practical approach to optimize the physical properties of the pectin biopolymers. Here, we used humidified environments to manipulate the water content of dispersed solution of pectins with a high degree of methyl esterification (high-methoxyl pectin; HMP). The gel phase transition was identified by a nonlinear increase in compression resistance at a water content …
Crystal structure transformations induced by surface stresses in BaTiO3and BaTiO3@SiO2nanoparticles and ceramics
2015
International audience; Lattice structure transformations in nanopowders of ferroelectric BaTiO3 and BaTiO3@SiO2 core-shell nanostructured ceramics were studied by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) at the temperatures 120–450 K and particle size of 300 and 500 nm. NMR spectra of all studied samples in the paraelectric phase are identical to the spectra in bulk material indicating their perfect perovskite structure without visible influence of particle surface. However, we have found that surface of particles essentially influence the ferroelectric phase transitions detected by both NMR and EPR techniques. The strongest changes as compared to bulk mat…
DIELECTRIC PROPERTIES OF LEAD-FREE [(1-x)(Na0.5Bi0.5)-xBa]Zr1−yTiyO3CERAMICS (x = 0.01, 0.06, 0.085, 0.09, 0.1 AND y = 0.96, 0.97)
2008
ABSTRACT Lead-free ceramics based on (Na0.5Bi0.5TiO3, NBT)-(Ba(Ti, Zr)O3, BTZ) were prepared by solid phase synthesis and hot pressing sintering process and their dielectric properties have been studied. The obtained results were compared with these for pure NBT. The obtained samples show pure perovskite structure. Low frequency (100 Hz-100 kHz) investigations reveal the diffuse phase transitions and relaxorlike behaviour. The obtained results are discussed in terms of inhomogeneity of ions distribution, their ferro- and antiferroactivity and internal stresses. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.
The Effect of Bias Field on Dielectric Response in Lead Ferrotantalate Ceramics
2011
Studies of dielectric properties of PbFe1/2Ta1/2O3 ceramics at low- and infra-low-frequencies under bias field over a wide range of temperatures are reported. Applied bias field is found to broaden the ϵ′(Т) maxima shifting positions Тm of the maximums to higher temperatures. Additional anomalies in the dielectric response are revealed at T<Тm. The anomalies in the vicinity of Тm are related to structural change at phase transition, while those observed at TТm – to magneto-electric interactions in PbFe1/2Ta1/2O3.
PHASE TRANSITIONS IN Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 SOLID SOLUTIONS
2009
ABSTRACT Studies of nature of polarization in ternary solid solutions of Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 were done, using measurements of dielectric properties and polarization hysteresis loops. Various stages of relaxor behavior depending on concentration of PbTiO3 were established and compared with other known ferroelectric relaxors.