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Dive into the research topics where M. Rada is active.

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Featured researches published by M. Rada.


Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2010

Structural properties of molybdenum-lead-borate glasses.

M. Rada; S. Rada; Petru Pascuta; E. Culea

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.


Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2010

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

M. Rada; Vistrian Maties; Monica Culea; S. Rada; E. Culea

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.


Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2014

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

M. Rada; L. Rus; S. Rada; E. Culea; T. Rusu

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.


Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2010

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

S. Rada; M. Rada; E. Culea

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.


Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2011

Structural study of ternary iron-lead-germanate glass ceramics

R. Chelcea; S. Rada; E. Culea; M. Rada

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.


Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2013

Effect of aluminum oxide codoping on copper–lead–germanate glasses

M. Rada; R. Chelcea; S. Rada; L. Rus; N. Dura; Tania Ristoiu; T. Rusu; E. Culea

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.


Journal of Physics: Conference Series | 2009

Immobilization of gadolinium in borate-tellurate glasses

S. Rada; E. Culea; M. Rada; Vistrian Maties; Maria Bosca; Lidia Pop; Radu Fechete; R. Chelcea; Dumitriţa Moldovan

Glasses in the xGd2O3?(100-x)[6TeO2?4B2O3] system, where x = 0, 5, 10, 15, 25 and 30 mol%, have been prepared from melt quenching method. The structural changes were studied by FTIR spectroscopy and DFT calculations. The FTIR spectroscopy data for these systems show that the gadolinium ions have a strong affinity towards the structural units containing non-bridging oxygens, which are negative-charged, because they are readily available for charge compensation. So that, it seems that the content of [BO4] structural units cannot become higher, because the modified [BO3] units containing one or more B-O-Gd bonds are unable to accept a fourth oxygen atom. On the other hand, the gadolinium ions have also an affinity pronounced towards [TeO3] structural units yielding the deformation of the Te-O-Te linkages. The compositional evolution of the network was accommodated with excess of oxygen by the formation of orthoborate structural units, disintegration of some boroxol rings and radical rearrangement of the network formed by the [TeO6] octahedral units.


Journal of Physics: Conference Series | 2009

The local structure of gadolinium-borate-tellurate vitroceramics investigated by FTIR and EPR spectroscopy

M. Rada; E. Culea; S. Rada; Petru Pascuta; M Culea; Viorel Dan; T. Rusu; Vistrian Maties; I Bratu

The present study provides interesting information concerning devitrification behavior of xGd2O3(100-x)[6TeO24B2O3] vitreous system with 0 ≤ x ≤ 30 mol%. The structural changes have been analyzed with increasing rare earth concentration. Two halos characteristic of the amorphous compounds can be observed in XRD diffraction pattern for sample with x ≥ 20 mol% Gd2O3. These changes can be explained only if we admit that the adding of gadolinium oxide now participate in the network as [GdOn] structural units yielding a change from the continuous borate-tellurate network to the continuous gadolinium-borate-tellurate network with interconnected through Gd-O-B and Gd-O-Te bridges. The EPR spectra of the studied glass ceramics reveal an increase of the content of Gd+3 ions in network former and modifier positions. Therefore, Gd+3 ions will coordinate more with non-bridging oxygens leading the decreased of the number of individual Gd+3 ions.


Analytical Letters | 2018

Spectroscopic Characterization of Dental Ceramics Composed of Yttrium-Stabilized Zirconium

M. Rada; Jing Zhang; Wu Zhongua; Mioara Zagrai; Lidia Magerusan; S. Rada

ABSTRACT Yttria–zirconia ceramics in various compositions of Y2O3 and SiO2 were synthesized by a high temperature solid state reaction process in alumina crucibles at 1400°C for 2 h. The obtained samples were characterized by X-ray diffraction, infrared spectroscopy and X-ray absorption near edge structure analysis. Combining all of the structural characterizations, we conclude that the addition of lower Y2O3 and SiO2 contents induces structural changes in the host matrix without partially or/and fully stabilizing the lattice of the zirconia crystalline phase.


Analytical Letters | 2018

Spectroscopic Characterization of a Lead–Lead Dioxide Automobile Battery

Sergiu Macavei; M. Rada; Mioara Zagrai; S. Rada; V. I. Bodnarchuk; Radu Balan; Raul Erhan

ABSTRACT Here we combine small angle neutron scattering measurements (SANS) with X-ray diffraction analysis (XRD) and infrared spectroscopy (IR) measurements to obtain information about nanoparticles formed in a series of lead-lead dioxide samples mixed with various CuO concentrations. New vitreous systems with the xCuO • (100−x)[4PbO2 • Pb] composition where x = 0, 30, and 70 mol% CuO were prepared by the melt-quenching method using CuO mixed in suitable proportion with the active electrodes of a disassembled car battery as the starting materials. The X-ray diffraction patterns permit the identification of the metallic Pb phase and the presence of oxidic nanoparticles of the lead and copper ions. By doping with higher CuO contents, the SANS curves have a concave shape indicating inhomogeneities and tendency of phase separation due to formation of nanoparticles of the lead and copper ions in recycled host matrix. The studied samples can be considered as polydispersed systems. The matrix is the solvent and the soluble phase is formed from the oxidic lead and/or copper particles with sizes smaller than 69 Å dispersed either inside the host matrix grains or between the host matrix grains. The formation of the nanoparticles in the host matrix and the knowledge of the type of nanoparticles have a decisive role in applications for the construction of essential components of the automobile batteries.

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S. Rada

Technical University of Cluj-Napoca

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E. Culea

Technical University of Cluj-Napoca

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Vistrian Maties

Technical University of Cluj-Napoca

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Petru Pascuta

Technical University of Cluj-Napoca

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T. Rusu

Technical University of Cluj-Napoca

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L. Rus

Technical University of Cluj-Napoca

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Monica Culea

University of Agricultural Sciences

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M. Zagrai

Technical University of Cluj-Napoca

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R. Chelcea

Technical University of Cluj-Napoca

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Tania Ristoiu

Technical University of Cluj-Napoca

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