Effect of aluminum oxide codoping on copper-lead-germanate glasses.

Glasses from xCuO⋅(100-x)[7GeO(2)⋅3PbO(2)⋅0.05Al(2)O(3)] system where x=0, 1, 5, 10, 20 and 30 mol% CuO were studied by FT-IR, UV-VIS and ESR spectroscopy in order to obtain information about the structural correlations and the relationship between structure and optical properties in these materials. The analyses of these IR spectra reveal that the accommodation of the network with the excess of oxygen ions is possible by the depolymerization of the germanate network in shorter chains, especially ortho- and/or pyrogermanate structural units. UV-VIS absorption spectrum of the sample with x=1% CuO begins with a rising absorption band situated at about 250 nm. This band can be assigned to the GeOGe wrong bonds such as the Ge(+2) centers. Optical study is performed to calculate the refractive index and optical band gap using UV-VIS spectra in the wavelength range 250-1,000 nm. The increase in optical band is explained on the basis of the average bond energy of the system and the number of non-bridging oxygen ions. ESR spectra of CuO substituted samples are characterized by broad peaks probably because of the formation of Cu(+2)-Ge(+2) exchange pairs which are weakly coupled though the oxygen atom.

Structural study of ternary iron-lead-germanate glass ceramics.

Glass ceramics with the composition xFe(2)O(3)·(100-x)[7GeO(2)·3PbO(2)] where 0≤x≤60 mol% were obtained and studied using XRD, FTIR and UV-vis spectroscopy investigations. Heat treatment of glass samples at 400°C for 8 h led to the formation of α, γ-PbGe(4)O(9), Pb(3)Fe(2)Ge(4)O(14) and PbO(1.44) crystalline phases. The content of these crystalline phases depends of Fe(2)O(3) concentration. FTIR spectroscopy data suggest that the lead ions have a pronounced affinity towards [GeO(5)] structural units containing non-bridging oxygens and [FeO(4)] anions producing formation of the Pb(3)Fe(2)Ge(4)O(14) crystalline phase. The introduction of low concentrations of Fe(2)O(3) into the host matrix results in the formation of new absorption UV bands between 320 and 450 nm. These bands arise from to the d-d transitions of the Fe(+3) ions. The light absorption in the range from 250 to 600 nm increases with increasing iron oxide content in matrix network, accompanied with the changes on color from white to brown yellow and darker brown.

Distributions of transverse relaxation times for soft-solids measured in strongly inhomogeneous magnetic fields.

The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG (1)H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/T(2,short) and 1/T(2,long) were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T(1)/T(2) ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T(2)/T(2,eff) is derived as a function of the T(1)/T(2) ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T(1)-T(2) correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T(1)-T(2) experimental correlations maps were corrected for the T(1)/T(2) effect using the derived T(2)/T(2,eff) correction factor.