Search results for "Solid"
showing 10 items of 3575 documents
Automated Stress Separation Along Stress Trajectories
2007
A procedure for the separation of principal stresses in automated photoelasticity is presented. It is based on the integration of indefinite equations of equilibrium along stress trajectories, also known as Lame-Maxwell equations. A new algorithm for precise and reliable stress trajectory calculation, which is an essential feature of the procedure, has also been developed. Automated stress separation is carried out along stress trajectories starting from free boundaries. Experimental tests were performed on a disc in diametral compression and on a ring with internally applied pressure. Full-field principal stress values were obtained and results were compared with those from the theory of e…
Chemical surface ageing in ambient conditions of an Al–Fe–Cr approximant phase.
2007
International audience; The γ -Al65Cr27Fe8 phase is a complex metallic alloy with interesting electrochemical properties. Here we present a detailed study of the surface ageing of this alloy when exposed to ambient conditions for a long time. A combination of x-ray reflectivity, photoemission spectroscopy and secondary neutral mass spectroscopy measurements is used to provide a model of the modification of the surface structure and its composition as functions of ageing time. The near surface structure is described by the stacking of three layers. The first layer on top of the substrate corresponds to a mixed metal oxide and is amorphous. The intermediate layer consists of pure aluminum oxy…
Oxygen-excess amorphous SiO2 with 18O-labeled interstitial oxygen molecules
2011
Abstract Exchange between oxygen molecules embedded in amorphous SiO 2 (interstitial O 2 ) and oxygen atoms in the a -SiO 2 network is found to be remarkably slow at 500 °C. Thermal loading of 18 O 2 at this temperature yields a -SiO 2 containing 18 O-labeled interstitial O 2 whose 18 O fraction is as high as ~ 90%. The 18 O fraction of interstitial O 2 in this sample is quickly decreased by thermal annealing at or above 700 °C because of the oxygen exchange accompanied by the release of 16 O from the a -SiO 2 network. This finding indicates that the oxygen exchange starts at much lower temperatures than indicated by previous works, based on monitoring of the isotopic composition of oxygen …
Excitation and emission spectra of LaInO3-based solid solutions doped with Sm3+, Sb3+
2017
Abstract X-ray analysis showed that all the ceramic samples of La 1- x Sm x InO 3 (0.010≤ x ≤0.025) solid solutions were single-phased but the samples of nominal composition of LaIn 0.98 Sb 0.02 O 3 , La 0.98 Sm 0.02 In 0.98 Sb 0.02 O 3 contained a small amount of impurity phase of LaSbO 3 -based solid solutions. It was established that La 0.98 Sm 0.02 InO 3 solid solution under the excitation of 275 nm and 320 nm exhibits the strongest photoluminescence among La 1- x Sm x InO 3 solid solutions with 0.010≤ x ≤0.025. Photoluminescence bands located in wavelength ranges of 550–580 nm, 585–625 nm and 630–680 nm exhibit 2–3 clear maxima each. According to the locations of these maxima we calcul…
Structural inhomogeneity of Ge-doped amorphous SiO2 probed by photoluminescence lifetime measurements under synchrotron radiation.
2007
We report a study of the photoluminescence (PL) time decay of the B-type center, characterized by an optical absorption band peaked at similar to 5.2 eV and two related PL bands peaked at similar to 3.2 eV and similar to 4.3 eV, in sol-gel Ge-doped a- SiO2 under excitation by synchrotron radiation. Measurements were carried out by excitation in UV and in vacuum-UV (VUV), and were performed in the temperature range from 8 K up to 300 K in order to isolate the effects of the intersystem-crossing process, proposed to link the two emission bands of the center. Repeating the time decay measurement at several emission energies falling inside the 4.3 eV band, we have observed a variation of the PL…
Short-lived luminescence of mixed silver halides
1993
Abstract Two kinds of excitonic luminescence were investigated for the entire series of solid solutions, AgBr1−xClx, (0 ⪕ x ⪕ 1). The time-resolved spectra observed around 2.5 eV after both pulsed high-power electron beam and N2-laser irradiations are analyzed in terms of the diffusion-controlled recombination of Frenkel defects Ag0i and Ag2+V-c. It is shown that the effective activation energy of Ag0i migration is a linear function of the composition x; and predominantly two kinds of nearest neighbours contribute to this process. The position of maximum of the excitonic molecule luminescence found in mixed monocrystals and fibers reveals a distinctive dependence on the composition x. Its a…
Luminescence and Raman Detection of Molecular Cl2 and ClClO Molecules in Amorphous SiO2 Matrix
2017
The support from the Latvian Research Program project IMIS 2 (L.S., K.S.) and Latvian Science Council Grant 302/2012 (A.S.) is acknowledged. K.K. was partially supported by the Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology. H.H. was supported by the MEXT Element Strategy Initiative to form research cores.
Diffusive equilibrium properties of O2 in amorphous SiO2 nanoparticles probed via dependence of concentration on size and pressure
2014
An experimental study on the diffusive equilibrium value of interstitial O2 in silica nanoparticles was carried out on samples with average particles diameter 40, 14, and 7 nm. The investigation was performed by measuring the concentration of interstitial O2 by Raman and photoluminescence techniques. The dependence of diffusive equilibrium concentration on pressure and temperature was investigated in the pressure range from 0.2 to 76 bar and in the temperature range from 98 to 244 °C. The equilibrium concentration of interstitial O2 follows Henry’s law at pressures below 13 bar whereas a departure from this model is observed at higher pressures. In particular, O2 concentration saturates abo…
High pressure and high magnetic field behaviour of free and donor-bound-exciton photoluminescence in InSe
2009
We report here first magneto-photoluminescence investigations under high pressure up to 6 GPa on III-VI layered semiconductor InSe. Both diamagnetism and magnetic field induced gap opening driven by Landau quantization became observable by using a 60 T pulsed magnet. The pressure-induced enhancement of the diamagnetic coefficient is consistent with the increase of the dielectric constant under pressure while the evolution of the linear coefficient is consistent with a slight increase of the electron effective mass up to 4 GPa and a direct-to-indirect conduction-band crossover around that pressure.
Isotope Effect on the Infrared Photoluminescence Decay of Interstitial Oxygen Molecules in Amorphous SiO2
2009
The decay constants of the a1Δg(v=0)→X3Σg-(v=0) infrared photoluminescence (PL) of isotopically-labeled oxygen molecules 16O18O and 18O2 dissolved in the interstitial voids of a-SiO2 are ~1.7 and ~2.5 times larger than that of 16O2. This difference originates from the isotope shift in the energy of the nonradiative transitions from the a state to the vibronic levels of the X ground state. Calibration of the PL quantum yield using the measured decay constants is essential to measure the correct concentration of isotopically-labeled interstitial O2.