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Register a new userEffect of gamma irradiation on the structure and valence state of Nd in phosphate glass
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Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectra (XPS) of Nd doped phosphate glasses have been studied before and after gamma irradiation in order to find the behavior of chemical bonds, which decide the structural changes in the glass samples. IR absorption spectra of these glasses are found dominated mainly by the characteristics phosphate groups, water (OH) present in the glass network as well as on the composition of glass matrix. The effects of gamma irradiation are observed in the form of bond breaking and possible re-arrangement of the bonding in the glass. Energy dispersive X-ray spectroscopy (EDX) and XPS measurements show changes in the relative concentration of elements; particularly decrease in the concentration of oxygen in the glass samples after gamma irradiation, a possible source of oxygen vacancies. The decrease in the asymmetry in O 1s spectra after gamma irradiation indicates towards decrease in the concentration of bridging oxygen as a result of P-O-P bond breaking. Asymmetric profile of Nd 3d5/2peak after gamma irradiation is found to be due to conversion of Nd3+ to Nd2+ in the glass matrix.
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Nd doped phosphate glasses have been studied before and after gamma irradiation in order to understand the effect of glass composition and radiation induced defects on the optical properties of glasses. UV, Vis absorption and photoluminescence spectra of these glasses are found strongly dependent on the composition of glass matrix, particularly on the ratio of oxygen (O) and neodymium (Nd) concentration obtained from energy dispersive X-ray spectroscopic (EDX) measurement. Gamma irradiation of glass modifies the transmission below 700 nm due to generation of some new absorption bands corresponding to different types of defects. Observations indicate toward possibility of change in the valence state of Nd3+ to Nd2+ and generation of oxygen vacancies in glass matrix. EDX and X-ray photoelectron spectroscopic (XPS) measurements indicate change in the composition of glasses particularly decrease in the relative concentration of oxygen in glass samples after gamma irradiation.
The effects of high pressure on the crystal structure of orthorhombic (Pnma) perovskite type cerium scandate have been studied in situ under high pressure by means of synchrotron x-ray powder diffraction, using a diamond anvil cell. We have found that the perovskite type crystal structure remains stable up to 40 GPa, the highest pressure reached in the experiments. The evolution of unit-cell parameters with pressure has indicated an anisotropic compression. The room-temperature pressure-volume equation of state is obtained from the experiments. From the evolution of microscopic structural parameters like bond distances and coordination polyhedra of cerium and scandium, the macroscopic behavior of CeScO3 under compression has been explained and reasoned for its large pressure stability. The reported results are discussed in comparison with high-pressure results from other perovskites.
Adsorption of organic molecules on well-oriented single crystal coinage metal surfaces fundamentally affects the energy distribution curve of ultra-violet photoelectron spectroscopy spectra. New features not present in the spectrum of the pristine metal can be assigned as interface states having some degree of molecule-substrate hybridization. Here it is shown that interface states having molecular orbital character can easily be identified at low binding energy as isolated features above the featureless substrate sp-plateau. On the other hand much care must be taken in assigning adsorbate-induced features when these lie within the d-band spectral region of the substrate. In fact, features often interpreted as characteristic of the molecule-substrate interaction may actually arise from substrate photoelectrons scattered by the adsorbates. This phenomenon is illustrated through a series of examples of noble-metal single-crystal surfaces covered by monolayers of large pi-conjugated organic molecules.
We report a numerical study of the equation of state of crystalline body-centered-cubic (BCC) hydrogen, tackled with a variety of complementary many-body wave function methods. These include continuum stochastic techniques of fixed-node diffusion and variational quantum Monte Carlo, and the Hilbert space stochastic method of full configuration-interaction quantum Monte Carlo. In addition, periodic coupled-cluster methods were also employed. Each of these methods is underpinned with different strengths and approximations, but their combination in order to perform reliable extrapolation to complete basis set and supercell size limits gives confidence in the final results. The methods were found to be in good agreement for equilibrium cell volumes for the system in the BCC phase, with a lattice parameter of 3.307 Bohr.
The magnetic susceptibilities and specific heats of the crystalline garnet and glass forms of Mn3Al2Si3O12 are reported. This allows a direct comparison of the degree of magnetic frustration of the triangle-based garnet lattice and the structurally disordered solid at the same composition for isotropic spin 5/2 Mn^2+ (3d^5). The results show that the glass phase shows more pronounced signs of magnetic frustration than the crystalline phase. Through comparison of the specific heats of Ca3Al2Si3O12 (grossular) and Mn3Al2Si3O12 (spessartine) garnets, information is provided concerning the anomalous extra specific heat in the latter material.
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