Search results for "tetragonal crystal"
showing 10 items of 216 documents
Crystal structure of lactitol (4-O-beta-D-galactopyranosyl-D-glucitol) dihydrate.
1992
Abstract Lactitol dihydrate, C 12 H 24 O 11 ·2H 2 O, is tetragonal, space group P 4 3 2 1 2 with cell dimensions a and b = 8.762(1), c = 45.500(3) A, and V = 3493.2(3) A 3 ; Z = 8, D x = 1.45 Mg.m −3 , λ(Cu- K α ) = 1.54056 A, μ = 1.108 mm −1 , F (000) = 1632, and T = 23°. The structure was solved by direct methods and refined by least-squares calculations to R = 0.054 for 2037 unique observed reflections. There are three intra- and twelve inter-molecular hydrogen bonds in the structure. Bond lengths and angles accord quite well with the mean values of related structures. The galactopyranosyl ring has a chair of conformation.
The influence of the raw material and production method on the morphology, microstructure, chemical and phase composition of tetrabasic lead sulfate …
1992
Abstract Tetrabasic lead sulfate (4BS) produced by two different methods (solution and paste) and from two different raw materials (tetragonal PbO and leady oxide) were charaterized by different analytical techniques. The techniques applied were wet-chemical methods, scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The preparation method was observed to be the most decisive factor influencing the structure and the morphology of the 4BS pastes in this study.
Raman study of the phase transitions sequence in pure WO3 at high temperature and in HxWO3 with variable hydrogen content
1999
Abstract An extensive investigation of the temperature dependence of Raman spectra has been carried out on WO 3 powders from room temperature to 800°C. In particular the orthorhombic-to-tetragonal phase transition occurring at about 740°C has been studied for the first time. The Raman active mode at 710 cm −1 of the orthorhombic phase disappears from the spectrum at temperature below the phase transition point and the Raman activity in the tetragonal phase results very low. A comparative study of hydrogenated tungsten bronzes H x WO 3 ( x ≤0.23), where the same transition sequence is driven by an increase of the proton concentration from x =0 to 0.23, reveals similar behaviour of the high f…
In situ XRD analysis of the oxide layers formed by oxidation at 743 K on Zircaloy 4 and Zr–1NbO
2000
Abstract Two alloys, having different oxidation behaviour (Zy4 and Zr–1NbO), have been investigated during oxidation at high temperature (743 K) and low oxygen pressure (10 kPa) by in situ X-ray diffraction (XRD). Tetragonal phase content and ‘pseudo-stresses’ on the monoclinic phase have been measured as a function of the oxide layer thickness. The tetragonal phase contents are similar for both alloys and decreased with the oxide layer thickness. Pseudo-stresses were much more compressive on Zr–1NbO alloy, with limited changes at the corrosion kinetics transition. On cooling, the tetragonal fractions do not change, while ‘pseudo-stresses’ decreased in different ways for the two alloys. Wit…
Micro-Raman analysis of the fuel-cladding interface in a high burnup PWR fuel rod
2017
International audience; New insights on the fuel-cladding bonding layer in high burnup nuclear fuel were obtained using micro-Raman spectroscopy. A specimen was specifically prepared from a fuel rod which had been irradiated to an average burnup of 56 GWd.tU-1 in a pressurized water reactor (PWR). Both inner and outer corrosion scale regions were investigated. A 10-15 et956;m thick zirconia bonding layer between fuel and cladding materials which consisted of three distinct regions was observed. Close to the fuel, tetragonal, then monoclinic zirconia was identified as the main phases. Close to the bonding layer-cladding interface, peculiar Raman signals were observed. Similar signals were ob…
Electric hyperfine interaction in199Hg fluorides
1985
With the current integration technique, the Mossbauer effect on the 158 keV, 5/2−→1/2− transition in199Hg was studied using the cubic HgF2 and the tetragonal Hg2F2 as absorbers; in the latter, a quadrupole splittingeQVzz=}- 9.0(2) mm/s was observed. Electron densities were calculated with the self-consistent-charge-extended-Hueckel-molecular-orbital method and δ〈r2〉=(3.26±0.11) fm2 derived. From the quadrupole splitting and the calculation, an effective antishielding factor almost twice that of the neutral Hg atom is derived.
Complexes of Ni(II) and Cu(II) with ofloxacin. Crystal structure of a new Cu(II) ofloxacin complex.
2001
Several coordination compounds formed between Ni(II) or Cu(II) with ofloxacin have been synthesised and characterised. According to elemental chemical analysis and FT-IR spectroscopy data, direct reaction of Ni(II) and Cu(II) salts with ofloxacin leads to formation of precipitates for which mass spectrometry demonstrates their polymeric nature. However, crystalline [Cu(oflo)2(H2O)].2H2O is formed if the reaction is carried out in the presence of ammonia. This complex crystallises in the triclinic system, space group P-1 with a=9.2887(12), b=11.2376(14), c=17.874(2) A, alpha=92.12(3), beta=95.39(3), gamma=91.71(3) degrees and Z=2. The local geometry around the Cu(II) ion is a slightly distor…
Interlocking inorganic screw helices: synthesis, structure, and magnetism of the novel framework uranium orthothiophoshates A11U7(PS4)13 (A = K, Rb).
2002
The novel quaternary uranium thiophosphate K11U7(PS4)13 has been synthesized by reacting uranium metal, K2S, S, and P2S5 at 700 degrees C in an evacuated silica tube. The crystal structure was determined by single crystal X-ray diffraction techniques. K11U7(PS4)13 crystallizes in the tetragonal space group I42d (a = 32.048(2) A, c = 17.321(1) A, Z = 8). The structure contains a tunnel framework composed of eight interlocking uranium U7(PS4)13 screw helices, with alkali metal cations residing inside the framework channels. The uranium atoms are coordinated in a bi- or tricapped trigonal prismatic fashion. The screw helices are built up from uranium atoms interconnected by PS4 tetrahedral uni…
OH/OD-IR absorption bands in SrxBa1−xNb2O6
1995
Single crystals of Sr x Ba 1−x Nb 2 O 6 (SBN) with congruent composition (x = 0.61) and Sr 0.61 Ba 0.39 Nb 2 O 6 crystals doped with various concentrations of cerium are grown with the Czochralski method. A subsequent doping of the crystals with protons and deuterons is performed either by hydrothermal high temperature treatment or by field supported hydrogen diffusion at elevated temperatures in humid atmosphere. The presence of the protons is revealed by the infrared absorption of the OH stretching vibration. This broad OH absorption band is essentially the same for Sr 0.61 Ba 0.39 Nb 2 O 6 and Sr 0.61 Ba 0.39 Nb 2 O 6 :Ce (0.025 wt% CeO 2 ). It shows a polarization dependence with respec…
Tuning the dielectric properties of hafnium silicate films
2007
The influence of Si concentration in hafnium silicate dielectrics on thermal stability and dielectric permittivity was analyzed. A phase diagram was developed using GIXRD and FTIR measurement. The stabilization of the ''higher-k'' cubic/tetragonal phase for annealing temperatures up to 1000^oC with a steady increase in capacitance was demonstrated for Hf"0"."9"4Si"0"."0"6O"2 films. It was also shown that the stabilization of nano-crystalline Hf"0"."8"0Si"0"."2"0O"2 films can be realized for annealing temperatures up to 900^oC. The influence of TiN electrodes on the dielectric constant and the leakage current characteristic was also investigated. A permittivity increase for annealing tempera…