Search results for "Solid"
showing 10 items of 3575 documents
Detection of morphotropic phase boundary in A-site/Ca-substituted Na0.5Bi0.5TiO3 complex oxides ferroelectric system
2020
Abstract Vibrational and structural properties of lead-free piezoelectric (1-x)Na0.5Bi0.5TiO3–xCaTiO3 (0 ≤ x ≤ 1.00) solid solutions have been investigated using Raman spectroscopy and X-ray diffraction. Different anomalies were detected and analyzed taking into consideration the phase transition from rhombohedral to orthorhombic phase at room temperature. All Raman bands were interpreted through the variation in the peak positions (frequency) and the corresponding half-widths at half maximum (HWHM) as a function of x. XRD used as a complementary technique to Raman spectroscopy, showed that the rhombohedral – orthorhombic phase transition went gradually through an intermediate phase consist…
Experimentally constrained density-functional calculations of the amorphous structure of the prototypical phase-change materialGe2Sb2Te5
2009
Phase change materials involve the rapid and reversible transition between nanoscale amorphous $(a\text{\ensuremath{-}})$ and crystalline $(c\text{\ensuremath{-}})$ spots in a polycrystalline film and play major roles in the multimedia world, including nonvolatile computer memory. The materials of choice are alloys of Ge, Sb, and Te, e.g., ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$ (GST) in digital versatile disk--random access memory. There has been much speculation about the structure of $a\text{\ensuremath{-}}$ GST, but no model has yet received general acceptance. Here we optimize the structure by combining the results of density-functional calculations with high-energy x-ray diffr…
Synthesis and structural study of sodium titanium phosphate-sodium tin phosphate solid solutions. II. Thermal expansion
1993
Abstract The structure of NaTi 2 (PO 4 ) 3 shows the space group R3c, whereas that of NaSn 2 (PO 4 ) 3 presents the space group R3 at room temperature and it undergoes a second order phase transition at 575°C from this structure to another with the space group R3c. Evolution of the structure of NaTi 2 (PO 4 ) 3 NaSn 2 (PO 4 ) 3 solid solutions with temperature has been studied and temperature phase transition established for the compositions studied. Lattice thermal expansion of NaTi 2−x Sn x (PO 4 ) 3 solid solutions with x = 1, 1.2, 1.5 has been determined from x-ray diffraction data at temperatures ranging from 26 to 1000°C. DSC and dilatometric measurements have been also carried out o…
Structure and Dielectric Properties of Na1/2Bi1/2TiO3-BaTiO3Solid Solutions
2013
Dielectric properties, polarization and x-ray diffraction are studied for (1-x)Na1/2Bi1/2TiO3-xBaTiO3 solid solutions in a concentration range above the morphotropic phase boundary. It is showed that all the studied compositions have tetragonal structure with maximal tetragonality slightly above the morphotropic phase boundary. Ferroelectric relaxor behavior is observed in a wide concentration range of BaTiO3. Stability of the relaxor state decreases with increasing BaTiO3 concentration, but only for compositions with low Na1/2Bi1/2TiO3 content the normal ferroelectric-paraelectric phase transition, which is characteristic to pure BaTiO3, occurs. Mechanisms, which influence the change of th…
First principles simulation of amorphous InSb
2013
Ab initio molecular dynamics simulations based on density functional theory have been performed to generate a model of amorphous InSb by quenching from the melt. The resulting network is mostly tetrahedral with a minor fraction ($10%$) of atoms in a fivefold coordination. The structural properties are in good agreement with available x-ray diffraction and extended x-ray-absorption fine structure data and confirm the proposed presence of a sizable fraction of homopolar In-In and Sb-Sb bonds whose concentration in our model amounts to about $20%$ of the total number of bonds.
Isomerism in [MCl2(ERR‘)2] (M = Pd, Pt; E = S, Se; R, R‘ = Me, Ph)
2006
A series of thioether and selenoether complexes [MCl2(EPh2)2] and [MCl2(SMePh)2] (M = Pt, Pd; E = S, Se) have been prepared and characterized to explore the isomerism of the complexes in solution and in the solid state. The NMR spectroscopic information indicates that only one isomer is present in solution in case of the palladium complexes, while two isomers are formed in the case of most platinum complexes. Single-crystal X-ray structures of trans-[PdCl2(SPh2)2] (1t), trans-[PdCl2(SePh2)2] (2t), cis-[PtCl2(SePh2)2] (4c), trans-[PdCl2(SMePh)2] (5t), and trans-[PtCl2(SMePh)2] (7t) are reported and have been used as starting points for the X-ray powder diffraction structure determinations us…
<title>Relaxation processes in amorphous As-S and As-Se films</title>
1997
The relaxation of optical, mechanical and chemical properties of as-evaporated amorphous As-S and As-Se films while storing them at room temperature is investigated. The AsxS1-x films with arsenic content 0.3 less than x less than 0.4 are found to undergo maximal changes. It is shown that the phenomenon of dark self-enhancement of holograms (an increase of diffraction efficiency over time without any special treatment) can be used as an efficient method for investigation of relaxation processes in the amorphous chalcogenide films. The changes of diffraction efficiency in amorphous As2S3 films have been measured as a function of aging time and recording light intensity. The relaxation proces…
Disorder in molecular crystals justified with the help of statistical mechanics: a case of two enantiomer solid solutions
2019
An elegant statistical mechanics approach has been exploited in combination with accurate quantum chemical calculations to justify the disorder in two previously reported racemic solids. Generated canonical ensembles and performed lattice energy calculations show that the disorder in the studied systems of small organic enantiomer molecules can be modelled with great accuracy. Ensemble averages fully correspond to the disordered structure models repeatedly obtained in X-ray diffraction studies. The present work not only demonstrates that disorder and its extent in molecular crystals can be theoretically calculated, but also explains from a thermodynamic point of view the origins of the rare…
Perfluoro-1,1′-biphenyl and perfluoronaphthalene and their derivatives as π-acceptors for anions
2015
Addition of anions to perfluorinated 1,1′-biphenyl 1 or naphthalene 2 results in a shift of the 19F NMR signals. However, any specific interaction cannot be assigned to this effect. In order to study the interaction in more detail, the salt derivatives 3 and 4 were prepared and studied by single crystal X-ray diffraction revealing weak anion–π interactions in the solid state.
Stability of non-stoichiometric laof phases: x-ray diffraction investigation
1998
Summary The X-ray diffraction patterns of the polycrystalline LaO 1−x F 1+2x (0.05≤x≤0.3) phases were measured at room temperature and analyzed by the Rietveld profile refinement method. All compounds crystallize in the tetragonal PbFCl-type structure with P4/nmm as the space group. No distortion to lower orthorhombic symmetry was observed. The tetragonal lattice parameters a and c increase with increasing excess of fluoride. The La-oxygen (La-fluorine) distances first decrease (increase) but then these trends are reversed. The Global Instability Index calculated from the bond valence model increases towards the higher fluoride content of the compounds indicating decreasing stability