Search results for "lattice [space-time]"
showing 10 items of 692 documents
Opaline Hydrogels: Polycrystalline Body-Centered-Cubic Bulk Material with an in Situ Variable Lattice Constant
2007
Opaline hydrogels were produced as a polycrystalline bulk material with a body-centered-cubic (bcc) structure by immobilization of self-ordered charged colloidal particles crystallized under equilibrium conditions in a poly(acrylamide) matrix. The final size of a polycrystalline sample is about 7 cm3; a single crystal is up to several millimeters in length. The crystal size is tunable by varying the amount of photoinitiator and the hydrogel volume change due to swelling. The resulting photonic crystals are of high quality, showing high-order reflections. These hydrogels show a reversible shift of the diffraction Bragg peak wavelength depending on external conditions due to swelling or shrin…
Ab initio molecular dynamics simulations of negative thermal expansion in ScF3: the effect of the supercell size
2020
The authors sincerely thank S. Ali, A. Kalinko, and F. Rocca for providing experimental EXAFS data, as well as M. Isupova, V. Kashcheyevs, and A. I. Popov for stimulating discussions. Financial support provided by project No. 1.1.1.2/VIAA/l/16/147 (1.1.1.2/16/I/001) under the activity “Post-doctoral research aid” realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged by D.B. A.K and J.P. would like to thank the support of the Latvian Council of Science project No. lzp-2018/2–0353.
Faceting and structural anisotropy of nanopatterned CdO(110) layers
2005
CdO(110) layers with a self-organized surface structure have been grown on (10math0) sapphire (m plane) substrates by metal-organic vapor phase epitaxy. The epitaxial relationships between layer and substrate have been determined and a crystallographic model that accounts for the CdO in-plane orientation, which results in a reduced lattice mismatch when the CdO[001] direction is perpendicular to the sapphire c axis, has been proposed. Although the measured lattice parameters indicate that the layers are almost fully relaxed, an anisotropic mosaicity is detected with symmetrical rocking curves attaining minimum values when measured along the CdO[math10] direction. The layer morphology consis…
X-ray multiple diffraction in the characterization of TiNO and TiO2 thin films grown on Si(001)
2006
Abstract TiO 2 and TiN x O y thin films grown by low pressure metal-organic chemical vapor deposition (LP-MOCVD) on top of Si(0 0 1) substrate were characterized by X-ray multiple diffraction. X-ray reflectivity analysis of TiO 2 [1 1 0] and TiNO[1 0 0] polycrystalline layers allowed to determine the growth rate (−80 A/min) of TiO 2 and (−40 A/min) of TiNO films. X-ray multiple diffraction through the Renninger scans, i.e., ϕ -scans for (0 0 2)Si substrate primary reflection is used as a non-conventional method to obtain the substrate lattice parameter distortion due to the thin film conventional deposition, from where the information on film strain type is obtained.
Hydrogen-doped cubic diamond and the crystal structure of n-diamond
2011
To understand the crystal structure of n-diamond, a hydrogen-doped (H-doped) diamond model has been investigated using first principles calculations. In particular, hydrogen concentration dependent elastic constants and lattice parameters for the H-doped diamond have been analyzed. Our results indicate that when the hydrogen concentration is less than 19 at.%, the H-doped diamond is mechanically stable. When the hydrogen concentration is about 4 at.%, the optimized lattice parameter, simulated XRD pattern and electronic properties for the H-doped diamond all agree well with the corresponding experimental values of n-diamond. The results imply that the n-diamond is likely to be an H-doped di…
Syntheses, crystal structures, and solid state NMR investigations of K4M2P6S25 and K3M2P5S18 (M=Ti, Sn)
2002
Abstract Reaction of K 2 S 5 with P 4 S 10 and Ti at 450 °C results in the formation of K 4 Ti 2 P 6 S 25 , a new titanium thiophosphate, whose crystal structure was solved by single-crystal X-ray diffraction. The title compound crystallizes in the orthorhombic space group Fdd2, with the lattice constants a =33.819(7), b =35.508(7), and c =6.251(1) A ( Z =8). The structure contains a layered arrangement of crosslinked quasi-one-dimensional Ti 2 P 6 S 4− 25 chains. The K + ions are situated between the layers. The Ti atoms within the chains are octahedrally coordinated by P 2 S 4− 7 and P 2 S 4− 9 ligands. Reaction of K 2 S with P 4 S 10 , S and Ti at 600 °C results in the formation of K 3 T…
Effect of the preparation method and grinding time of some mixed valency ferrite spinels on their cationic distribution and thermal stability toward …
1996
Abstract The reactivity in oxygen of several mixed valency ferrite spinels, namely Fe3O4, FeCr2O4, Fe3 − xTixO4 and Fe3 − xMoxO4 was investigated by derivative thermogravimetry (DTG) analysis as a function of the conditions of preparation and grinding. For all these compounds, low temperature preparation or prolonged grinding time enables small particles ( 0.5 μm), it was observed that oxidation was starting at higher temperature and that the defect spinel phases could not be retained during oxidation. This behaviour was attributed to the presence of stresses induced by the lattice parameter gradient and promoting the formation of nuclei of the α-rhombohedral phase from the superficial γ-de…
Impact of point defects on the elastic properties of BaZrO3: Comprehensive insight from experiments and ab initio calculations
2018
Abstract Acceptor doped BaZrO3 is the prototype of proton conducting perovskites which are of strong interest as electrolytes for intermediate temperature fuel cells. Elastic properties of both dry and hydrated Y-doped BaZrO3 (1.5–17 mol% Y) were determined using ultrasound time of flight (TOF) measurements, and complemented by ab initio calculations which allow for an analysis of the different contributions. The experimental and theoretical findings are consistent and reveal a strong decrease of the Young's, shear and bulk moduli upon increasing dopant concentration. This decrease is attributed to a combined effect of (i) macroscopic lattice chemical expansion mainly caused by differing io…
Isotope effects on the dynamics of a supercooled van der Waals liquid
2000
Deuteron magnetic resonance was used to study three differently isotope-labeled species of the fragile glass-forming liquid ortho-terphenyl. The calorimetric glass transition of the isotope deuterated only at the central phenyl ring is significantly lower than that of the perdeuterated one. It is shown that while the ortho-terphenyl molecule is not as rigid as previously often assumed, its overall reorientation geometry is independent of deuteration. The characteristic jump angles are found to increase with temperature, thus resolving an apparent discrepancy previously noted when comparing typical jump sizes from NMR with other data.
Impact of granularity on transport properties of mechanically stressed La0.67Ca0.33MnO3 films
2001
Abstract (La,Ca)MnO 3 is one of so called collosal magnetoresistive materials and it is of interest to correlate its transport properties to film growth in order to optimize its performance. Two-hundred nanometers thick (100)La 0.67 Ca 0.33 MnO 3 films were grown by laser ablation on (100)SrTiO 3 , (100)LaAlO 3 and (100)(LaAlO 3 ) 0.3 +(Sr 2 AlTaO 6 ) 0.7 substrates. The films were granular in structure with low angle boundaries between the grains. The volume of the unit cell was considerably smaller for films grown on a SrTiO 3 substrate than on LaAlO 3 . At temperatures higher than the one where the spins order, the strongest response of resistivity on temperature ρ ( T ) was measured for…