S. Rada

Toward modeling phosphate tellurate glasses: the devitrification and addition of gadolinium ions behavior.

Glasses in the xGd2O3 x (100 - x)[7TeO2 x 3P2O5] system with 0 < or = x < or = 20 mol % have been prepared using the melt quenching method. The influence of gadolinium ions on structural behavior of the phosphate tellurate glass has been investigated using infrared spectroscopy and density functional theory (DFT) calculations. The addition of gadolinium ions into the host glass matrix leads to an increase of the glass network polymerization due to the replacement of P-O-P bonds by the more resistant P-O-Te bonds having as result the improvement of the chemical durability of the glass. The structural evolution of the studied glasses with the gradual increase of the gadolinium oxide content up to 20 mol % could be explained by considering that the excess of oxygen may be accommodated by the conversion of some orthophosphate structural units into metaphosphate or/and pyrophosphate units. X-ray diffraction and IR spectra revealed that heat treatment of the samples also causes an increase of the glass network polymerization for heat treatment times, t, up to 36 h, while for 36 h > t > or = 48 h showed a drastic structural modification which lead to the apparition of the Te4P2O13 crystalline phase. DFT calculations show that tellurium atoms occupy two different sites in the proposed model. In the first case the tellurium atom is coordinated with four oxygen atoms giving a trigonal bipyramide arrangement, while in the second case the tellurium atom is coordinated with three O atoms. The calculated IR absorption spectrum of the proposed model for phosphotellurite glasses is in good agreement with the experimental absorption data.

Structural properties of molybdenum-lead-borate glasses.

Glasses and glass ceramics in the system xMoO₃·(100 - x)[3B₂O₃·PbO] with 0 ≤ x ≤ 30 mol% have been prepared from melt quenching method and characterized by means of X-ray diffraction, FTIR, UV-VIS and EPR spectroscopy. We have examined and analyzed the effects of systematic molybdenum ions intercalation on lead-borate glasses and glass ceramics with interesting results. The observations present in these mechanisms show the lead ions bonded ionic have a strong affinity towards [BO₃] units containing non-bridging oxygens and [MoO₄]²⁻ molybdate units. The pronounced affinity towards molybdate anions yields the formation of the PbMoO₄ crystalline phase. Then, the excess of oxygen can be supported into the glass network by the formation of [MoO₆] and [Mo₂O₇] structural units. Pb²(+) ions with 6s² configuration show strong absorption in the ultraviolet due to parity allowed s²-sp transition and yield an absorption band centered at about 310 nm. The changes in the features of the absorption bands centered at about 310 nm can be explained as a consequence of the appearance of additional absorption shoulder due to photoinduced color centers in the glass such as the formation of borate-molybdate and lead-molybdate paramagnetic defect centers in the glasses. The concentration of molybdenum ions influences the shape and width of the EPR signals located at g ∼ 1.86, 1.91 and 5.19. The microenvironment of molybdenum ions in glasses is expected to have mainly sixfold coordination. However, there is a possibility of reduction of a part of molybdenum ions from the Mo⁶(+) to the Mo⁵(+) and Mo⁴(+) to the Mo³(+) states.

Dual role of the six-coordinated molybdenum and lead ions in novel of photochromic properties of the molybdenum-lead-borate glasses

Transparent glasses were prepared by conventional melting-quenching method in the xMoO(3).(100-x)[3B(2)O(3).PbO] system where 0<or=x<or=15 mol%. By increasing the MoO(3) content up to 20 mol% the PbMoO(4) crystalline phase appears. These systems exhibit a photochromic effect which can be induced through laser exposures (lambda=633 nm) directly on the bulk sample. Structural investigations by FTIR spectroscopy show that the photosensitive effect is due to a reduction of Mo(6+) to Mo(4+) and/or Mo(5+) promoted by the oxidation of Pb(2+) and some structural changes of the borate network.

The network modifier and former role of the bismuth ions in the bismuth-lead-germanate glasses.

The present work is focused on the enhancement of network former environment in lead-germanate glasses by bismuth ions doping. A series of bismuth-lead-germanate glasses with the xBi2O3·(100-x)[7GeO2·3PbO] composition glass where 0≤x≤30 mol% Bi2O3 were synthesized by melt-quenching method. The FTIR, UV-VIS spectroscopy and cyclic voltammetry were conducted on these samples to evaluate the doping effect of structure of the host matrix network. Our results indicate that direct incorporation of Bi2O3 into the lead-germanate network modifies the lead-germanate network and the internal structure of glass network is rearranged. The structural flexibility of the lead-germanate network is possible due to its incapacity to accommodate with the excess of oxygen atoms and the creation of bridging oxygen ions. Optical gap energy and refractive index were obtained as a function of Bi2O3 content. Gap energy values decrease as Bi2O3 content increased from 0 to 10 mol%. Further increase of Bi2O3 concentration beyond 10 mol% increased the gap energy values. These behaviors of the glass system can be explained by two mechanisms: (i) for x≤10 mol% Bi2O3--increase of degree of disorder of the host matrix because Bi2O3 is network modifier and (ii) for x>10 mol%--Bi2O3 acts as a network former. Cyclic voltammetry measurements using the glass system with 10Bi2O3·90[7GeO2·3PbO] composition as working electrode show the mobility of the lead ions, in agreement with UV-VIS data.

Infrared spectroscopic and DFT investigations of the vanadate–tellurate glasses structures

Vanadate-tellurate vitreous systems with composition (1-x)TeO(2).xV(2)O(5) where x=0.3 and 0.4 have been prepared by the conventional melt-quench method. The structural aspects have been investigated using FTIR spectroscopy and the density functional theory (DFT) calculations. The present study provides the interesting information concerning devitrification behavior of the vanadate-tellurate vitreous system which occur Te(2)V(2)O(9) crystalline phase. The structure of the heat-treated glasses was found to consist mainly of rings containing [TeO(3)], [TeO(4)], [VO(4)] and some [VO(5)] structural units.

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.

Experimental and theoretical studies of the structure of tellurate-borate glasses network

The structural properties of the xTeO2·(1-x)B2O3 glasses (x = 0.6; 0.7) were investigated by FT-IR spectroscopy. From the analysis of the FTIR spectra, it is reasonable to assume that by the increasing of boron ions content, the tetrahedral [BO4] units are gradually replaced by the trigonal [BO3] units. The increase in the number of non-bridging oxygen atoms would decrease the connectivity of the glass network and will yield the depolymerization of the borate chains. The molecular structure and vibrational frequencies of the proposed structural models have been studied by exploring the density functional theory (DFT) calculations. The FTIR spectra of the xTeO2·(1-x)B2O3 vitreous systems were compared with the calculated spectrum. This procedure allowed us to assign most of the observed IR bands.

Preparation and structural characterization of some Fe2O3-B2O3-ZnO glasses and glass ceramics

X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy have been employed to investigate the (Fe2O3)x?(B2O3)(60-x)?(ZnO)40 samples, with 0 ? x ? 20 mol%. The samples have been prepared by melting at 1100 ?C for 10 minutes followed by rapid cooling at room temperature. The structure of samples was analyzed by means of XRD. XRD pattern show that the sample without iron ions and the samples contained 3 and 5 mol% were glasses. For samples contain 10, 15 and 20 mol% Fe2O3 it obtains glass ceramics. These glass ceramics contains a unique crystalline phase, zinc ferrite (ZnFe2O4), embedded in an amorphous matrix. FTIR spectroscopy data suggest that for the glass samples the iron ions play the network modifier role. These data show that the glass network consists of BO3 and BO4 structural units. For glass ceramics samples FTIR spectra show characteristic bands of ZnFe2O4.

FTIR spectroscopic study of some lead germanate glasses

The structures of two lead germante glasses – yGeO2(100-y)PbO and xNd2O3(100-x)[GeO2PbO] – are investigated by the Fourier transform infrared (FTIR) spectroscopy. The structural role of germanium, lead and neodymium ions is discussed. The presence of GeO4, GeO6 and PbO4 structural units was evidenced in the studied glass networks. In the case of the xNd2O3(100-x)[GeO2PbO] glasses it was shown that the ratio of the mentioned structural units depends on the Nd2O3 content of the samples. Therefore Nd2O3 play the network modifier role in studied glasses.

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.