Marinela Culea - Academia.edu (original) (raw)

Papers by Marinela Culea

Research paper thumbnail of Diagnosis and Control by Using Biomarkers

IFMBE Proceedings, 2009

Non-invasive and semi-invasive methods were developed for diagnosis of some diseases by using sel... more Non-invasive and semi-invasive methods were developed for diagnosis of some diseases by using selected ion monitoring (SIM)-GC-MS. A method for PKU and MSUD diagnosis in neonatal blood samples, a method for liver dysfunction test and one for quantitative measuring of biomarkers in asthma were developed. GC-MS was used for the diagnosis by metabolite profiling and fingerprint or quantitative analyses of

Research paper thumbnail of Toward Modeling Phosphate Tellurate Glasses: The Devitrification and Addition of Gadolinium Ions Behavior

The Journal of Physical Chemistry A, 2008

Glasses in the xGd2O3 x (100 - x)[7TeO2 x 3P2O5] system with 0 < or = x < or = 20 m... more 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.

Research paper thumbnail of Structural and Optical Behavior of Vanadate-Tellurate Glasses Containing PbO or Sm2O3

Infrared Spectroscopy - Materials Science, Engineering and Technology, 2012

Research paper thumbnail of Dinuclear manganese centers in the manganese–lead–tellurate glasses

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011

a b s t r a c t FTIR, UV-VIS and EPR spectra of manganese doped lead-tellurate glasses with compo... more a b s t r a c t FTIR, UV-VIS and EPR spectra of manganese doped lead-tellurate glasses with composition xMnO·(100 − x)[4TeO 2 ·PbO 2 ] where x = 0, 1, 5, 10, 20, 30, 40 mol% have been studied. The FTIR spectra show the formation of the Mn-O-Pb and Mn-O-Te bridging bonds by increasing of MnO concentration. The UV-VIS spectra show the Mn +3 species exhibit pronounced absorption, which masks the Mn +2 spin-forbidden absorption bands when Mn +2 ions are in high concentrations in these glasses. The EPR spectra exhibit resonance signals characteristic of Mn +2 ions. The resonance signal located at g ≈ 2 is due to Mn +2 ions in an environment close to octahedral symmetry, whereas the resonance at g ≈ 4.3 and 3.3 are attributed to the rhombic surroundings of the Mn +2 ions. The increase in the MnO content gives rise to absorption at g ≈ 2.4 and the paramagnetic ions are involved in dinuclear manganese centers.

Research paper thumbnail of Amino Acids Profiles in Biological Media

An accurate analytical method was developed to determine amino acids in some biological specimens... more An accurate analytical method was developed to determine amino acids in some biological specimens by GC/MS technique. Stable isotopes provide useful tools for a variety of studies, offering ideal internal standards in quantitative information. Isotopic dilution gas chromatography-mass spectrometry (ID-GC/MS) is the techniques used for quantitative analysis of compounds labeled with stable isotopes. A Trace DSQ Thermo Finnigan quadrupole mass spectrometer coupled with a Trace GC was used. Amino acids were separated on a Rtx-5 MS capillary column, 30 m×0.25 mm, 0.25 mum film thickness, using a temperature program from 50 °C, 1 min, 6 °C/min at 100 °C, 4 °C/min at 200 °C, 20 °C/min at 300 °C, (3 min). The transfer line temperature was 250 °C, the injector temperature 200 °C and ion source temperature 250 °C splitter: 10:1. Electron energy was 70 eV and emission current, 100 muA. The amino acids were purified on a Dowex 50W-W8 exchange resin and were derivatized in a procedure following two steps to obtain trifluoroacetyl butyl esters. The identification of amino acids was obtained by using NIST library but also by using amino acid standards.

Research paper thumbnail of Structural properties of the boro-bismuthate glasses containing gadolinium ions

Vibrational Spectroscopy, 2008

The structural properties of the xGd 2 O 3 (100Àx)[4Bi 2 O 3 ÁB 2 O 3 ] vitreous system, with 0 x... more The structural properties of the xGd 2 O 3 (100Àx)[4Bi 2 O 3 ÁB 2 O 3 ] vitreous system, with 0 x 30 mol% were investigated by FT-IR spectroscopy, density measurements and ab initio calculations.

Research paper thumbnail of EPR AND MAGNETIC SUSCEPTIBILITY STUDIES OF Gd 3+ IONS-DOPED BISMUTH–GERMANATE GLASS MATRIX

Modern Physics Letters B, 2008

Glasses of the xGd2O3 · (100-x)[4Bi2O3 · GeO2] system, with 1 &am... more Glasses of the xGd2O3 · (100-x)[4Bi2O3 · GeO2] system, with 1 <= x <= 30 mol% were obtained and investigated by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The EPR spectra of the studied glasses reveal resonance sites with an unexpected high crystalline field in addition to the "U" spectrum, typical for Gd3+ ions in glasses. This absorption line

Research paper thumbnail of LOW-TEMPERATURE STUDY OF MAGNETIC BEHAVIOR OF EUROPIUM IN LEAD-BISMUTHATE GLASSES

Modern Physics Letters B, 2006

Glasses of the xEu2O3(1-x)[3Bi2O3PbO] system with x=0-0.25 were prepared and studied using low-te... more Glasses of the xEu2O3(1-x)[3Bi2O3PbO] system with x=0-0.25 were prepared and studied using low-temperature magnetization measurements. The obtained data suggest the presence of both Eu3+ and Eu2+ ions in the host glass matrix. The determined fraction of the Eu2+ ions/total number of europium ions was very small (2.1-3.4%). Magnetization data show that the europium ions exert superexchange interactions and show an

Research paper thumbnail of Semi conducting properties amd microstructure of x%V2O5·(100−x)% (As2O3·B203) glasses

Materials Chemistry and Physics, 1985

Research paper thumbnail of Structure of TeO2·B2O3 glasses inferred from infrared spectroscopy and DFT calculations

Journal of Non-Crystalline Solids, 2008

a b s t r a c t Glasses in the system (1 À x)TeO 2 Á xB 2 O 3 glasses (with x = 0.3 and 0.4) have... more a b s t r a c t Glasses in the system (1 À x)TeO 2 Á xB 2 O 3 glasses (with x = 0.3 and 0.4) have been prepared from melt quenching method. The structural changes were studied by FTIR spectroscopy and DFT calculations. From the analysis of the FTIR spectra it is reasonable to assume that when increasing boron ions content the tetrahedral [BO 4 ] units are gradually replaced by trigonal [BO 3 ] units. The increase in the number of non-bridging oxygen atoms would decrease the connectivity of the glass network, would depolymerize of borate chains and would necessite quite a radical rearrangement of the network formed by the [TeO 6 ] octahedral. This is possible considering that tellurium dioxide brings stoichiometrically two oxygen atoms in [TeO 4 ] and needs an additional oxygen atom for the formation of [TeO 6 ] octahedra. This additional oxygen atom is evidently taken off from the boron co-ordination and thus boron atoms transfer their [BO 4 ] co-ordination into [BO 3 ] co-ordination. We used the FTIR spectroscopic data in order to compute two possible models of the glasses matrix. We propose two possible structural models of building blocks for the formation of continuous random network glasses used by density functional theory (DFT) calculations.

Research paper thumbnail of Experimental and theoretical investigations of the copper–lead–germanate glasses

Journal of Molecular Structure, 2010

Research paper thumbnail of The local structure of europium–lead-borate glass ceramics

Journal of Molecular Structure, 2009

Glass ceramics in the xEu 2 O 3 (100 À x)[3B 2 O 3 ÁPbO] system with 0 6 x 6 50 mol% have been pr... more Glass ceramics in the xEu 2 O 3 (100 À x)[3B 2 O 3 ÁPbO] system with 0 6 x 6 50 mol% have been prepared using the melt quenching method, succeeded by heat treatment applied at 625°C and 675°C, respectively, for 48 h. The influence of europium ions on structural behavior of the lead-borate glass ceramics has been investigated using infrared spectroscopy and DFT calculations. The addition of europium ions into the host glass ceramics matrix leads to an increase of the glass network polymerization due to the replacement of BAOAB bonds by the more resistant BAOAPb bonds.

Research paper thumbnail of The improvement of the amorphous environment of the germanate–tellurate glasses in the presence of the gadolinium ions

Journal of Materials Science, 2011

Glasses in the system xGd 2 O 3 Á(100x)[TeO 2 Á GeO 2 ] with 0 B x B 50 mol% have been prepared f... more Glasses in the system xGd 2 O 3 Á(100x)[TeO 2 Á GeO 2 ] with 0 B x B 50 mol% have been prepared from melt quenching method. In this paper, we investigated changes of the coordination numbers of germanium, tellurium, and gadolinium ions by investigations of FTIR, EPR, and UV-VIS spectroscopy. By analyzing the structural changes resulted from the IR spectra we found that the bending modes of [GeO 4 ] structural units and the deformed modes of the Te-O-Te linkages produce intercalation of the [GdO n ] entities in the germanate-tellurate chain network and densification of the glasses by increasing the number of [GeO 6 ] structural units. EPR spectra of the studied samples reveal that the gadolinium ions play a role of network former. The UV-VIS spectra show broad UV absorption bands located in the 250-350 nm region. Their intensity increase with the increasing of Gd 2 O 3 content showing that these stronger transitions can be due to the presence of the O=Ge bonds (n-p* excitations) of [GeO 5 ] structural units. The [GeO 5 ] structural units are more stable thermodynamically than their analogues and the [GeO 6 ] structural units produce the improvement of the amorphous character of these glasses.

Research paper thumbnail of The local structure of gadolinium vanado-tellurite glasses

Journal of Materials Science, 2008

In this work we report on a vibrational spectroscopic, X-ray diffraction, and density measurement... more In this work we report on a vibrational spectroscopic, X-ray diffraction, and density measurement study of the structural properties of the ternary xGd 2 O 3 (100x)[7TeO 2 Á3V 2 O 5 ] systems for various x values up to 70 mol%. Structural changes, as recognized by analyzing band shapes of X-ray diffraction and IR spectra, revealed that Gd 2 O 3 causes a higher extent of network polymerization as far as x B 40 mol%, while for x between 40 and 50 mol% showed a drastic structural modification which lead to the apparition of the GdVO 4 crystalline phase.

Research paper thumbnail of Effect of the introduction of vanadium pentaoxide in phospho-tellurite glasses containing gadolinium ions

Journal of Materials Science, 2008

A range of phospho-tellurite glasses containing gadolinium was prepared and infrared absorption s... more A range of phospho-tellurite glasses containing gadolinium was prepared and infrared absorption spectra were measured. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Gd 2 O 3 causes a higher extent of network polymerization as far as x B 15 mol% because the conversion of [TeO 4 ] to [TeO 3 ] structural units is supported by the increase of metaphosphate structural groups. While for x between 20 and 30 mol% Gd 2 O 3 show some drastic structural modifications which lead to the increase in the glass fragility. Thus the addition of V 2 O 5 resulted in gradual depolymerization of the phosphate chains and formation of short phosphate units, which are linked to vanadium through P-O-V bonds. The formation of P-O-V bonds increases the cross-link between the phosphate chains and the bending mode of Te-O-Te or O-Te-O linkages.

Research paper thumbnail of Structural role of europium ions in lead–borate glasses inferred from spectroscopic and DFT studies

Chemical Physics Letters, 2008

a b s t r a c t Glasses in the system xEu 2 O 3 Á (100 À x)[3B 2 O 3 ÁPbO] with 0 6 x 6 35 mol% h... more a b s t r a c t Glasses in the system xEu 2 O 3 Á (100 À x)[3B 2 O 3 ÁPbO] with 0 6 x 6 35 mol% have been prepared from melt quenching method. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Eu 2 O 3 causes a change from the continuous borate network to the continuous lead-borate network, interconnected through Pb-O-B and B-O-B bridges. DFT calculations show that lead atoms occupy three different sites in the proposed model. Comparing the theoretical and experimental data, we conclude that the performance of the method/basis sets used on the prediction of the structural data and vibrational modes is good.

Research paper thumbnail of Diagnosis and Control by Using Biomarkers

IFMBE Proceedings, 2009

Non-invasive and semi-invasive methods were developed for diagnosis of some diseases by using sel... more Non-invasive and semi-invasive methods were developed for diagnosis of some diseases by using selected ion monitoring (SIM)-GC-MS. A method for PKU and MSUD diagnosis in neonatal blood samples, a method for liver dysfunction test and one for quantitative measuring of biomarkers in asthma were developed. GC-MS was used for the diagnosis by metabolite profiling and fingerprint or quantitative analyses of

Research paper thumbnail of Toward Modeling Phosphate Tellurate Glasses: The Devitrification and Addition of Gadolinium Ions Behavior

The Journal of Physical Chemistry A, 2008

Glasses in the xGd2O3 x (100 - x)[7TeO2 x 3P2O5] system with 0 < or = x < or = 20 m... more 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.

Research paper thumbnail of Structural and Optical Behavior of Vanadate-Tellurate Glasses Containing PbO or Sm2O3

Infrared Spectroscopy - Materials Science, Engineering and Technology, 2012

Research paper thumbnail of Dinuclear manganese centers in the manganese–lead–tellurate glasses

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011

a b s t r a c t FTIR, UV-VIS and EPR spectra of manganese doped lead-tellurate glasses with compo... more a b s t r a c t FTIR, UV-VIS and EPR spectra of manganese doped lead-tellurate glasses with composition xMnO·(100 − x)[4TeO 2 ·PbO 2 ] where x = 0, 1, 5, 10, 20, 30, 40 mol% have been studied. The FTIR spectra show the formation of the Mn-O-Pb and Mn-O-Te bridging bonds by increasing of MnO concentration. The UV-VIS spectra show the Mn +3 species exhibit pronounced absorption, which masks the Mn +2 spin-forbidden absorption bands when Mn +2 ions are in high concentrations in these glasses. The EPR spectra exhibit resonance signals characteristic of Mn +2 ions. The resonance signal located at g ≈ 2 is due to Mn +2 ions in an environment close to octahedral symmetry, whereas the resonance at g ≈ 4.3 and 3.3 are attributed to the rhombic surroundings of the Mn +2 ions. The increase in the MnO content gives rise to absorption at g ≈ 2.4 and the paramagnetic ions are involved in dinuclear manganese centers.

Research paper thumbnail of Amino Acids Profiles in Biological Media

An accurate analytical method was developed to determine amino acids in some biological specimens... more An accurate analytical method was developed to determine amino acids in some biological specimens by GC/MS technique. Stable isotopes provide useful tools for a variety of studies, offering ideal internal standards in quantitative information. Isotopic dilution gas chromatography-mass spectrometry (ID-GC/MS) is the techniques used for quantitative analysis of compounds labeled with stable isotopes. A Trace DSQ Thermo Finnigan quadrupole mass spectrometer coupled with a Trace GC was used. Amino acids were separated on a Rtx-5 MS capillary column, 30 m×0.25 mm, 0.25 mum film thickness, using a temperature program from 50 °C, 1 min, 6 °C/min at 100 °C, 4 °C/min at 200 °C, 20 °C/min at 300 °C, (3 min). The transfer line temperature was 250 °C, the injector temperature 200 °C and ion source temperature 250 °C splitter: 10:1. Electron energy was 70 eV and emission current, 100 muA. The amino acids were purified on a Dowex 50W-W8 exchange resin and were derivatized in a procedure following two steps to obtain trifluoroacetyl butyl esters. The identification of amino acids was obtained by using NIST library but also by using amino acid standards.

Research paper thumbnail of Structural properties of the boro-bismuthate glasses containing gadolinium ions

Vibrational Spectroscopy, 2008

The structural properties of the xGd 2 O 3 (100Àx)[4Bi 2 O 3 ÁB 2 O 3 ] vitreous system, with 0 x... more The structural properties of the xGd 2 O 3 (100Àx)[4Bi 2 O 3 ÁB 2 O 3 ] vitreous system, with 0 x 30 mol% were investigated by FT-IR spectroscopy, density measurements and ab initio calculations.

Research paper thumbnail of EPR AND MAGNETIC SUSCEPTIBILITY STUDIES OF Gd 3+ IONS-DOPED BISMUTH–GERMANATE GLASS MATRIX

Modern Physics Letters B, 2008

Glasses of the xGd2O3 · (100-x)[4Bi2O3 · GeO2] system, with 1 &am... more Glasses of the xGd2O3 · (100-x)[4Bi2O3 · GeO2] system, with 1 <= x <= 30 mol% were obtained and investigated by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The EPR spectra of the studied glasses reveal resonance sites with an unexpected high crystalline field in addition to the "U" spectrum, typical for Gd3+ ions in glasses. This absorption line

Research paper thumbnail of LOW-TEMPERATURE STUDY OF MAGNETIC BEHAVIOR OF EUROPIUM IN LEAD-BISMUTHATE GLASSES

Modern Physics Letters B, 2006

Glasses of the xEu2O3(1-x)[3Bi2O3PbO] system with x=0-0.25 were prepared and studied using low-te... more Glasses of the xEu2O3(1-x)[3Bi2O3PbO] system with x=0-0.25 were prepared and studied using low-temperature magnetization measurements. The obtained data suggest the presence of both Eu3+ and Eu2+ ions in the host glass matrix. The determined fraction of the Eu2+ ions/total number of europium ions was very small (2.1-3.4%). Magnetization data show that the europium ions exert superexchange interactions and show an

Research paper thumbnail of Semi conducting properties amd microstructure of x%V2O5·(100−x)% (As2O3·B203) glasses

Materials Chemistry and Physics, 1985

Research paper thumbnail of Structure of TeO2·B2O3 glasses inferred from infrared spectroscopy and DFT calculations

Journal of Non-Crystalline Solids, 2008

a b s t r a c t Glasses in the system (1 À x)TeO 2 Á xB 2 O 3 glasses (with x = 0.3 and 0.4) have... more a b s t r a c t Glasses in the system (1 À x)TeO 2 Á xB 2 O 3 glasses (with x = 0.3 and 0.4) have been prepared from melt quenching method. The structural changes were studied by FTIR spectroscopy and DFT calculations. From the analysis of the FTIR spectra it is reasonable to assume that when increasing boron ions content the tetrahedral [BO 4 ] units are gradually replaced by trigonal [BO 3 ] units. The increase in the number of non-bridging oxygen atoms would decrease the connectivity of the glass network, would depolymerize of borate chains and would necessite quite a radical rearrangement of the network formed by the [TeO 6 ] octahedral. This is possible considering that tellurium dioxide brings stoichiometrically two oxygen atoms in [TeO 4 ] and needs an additional oxygen atom for the formation of [TeO 6 ] octahedra. This additional oxygen atom is evidently taken off from the boron co-ordination and thus boron atoms transfer their [BO 4 ] co-ordination into [BO 3 ] co-ordination. We used the FTIR spectroscopic data in order to compute two possible models of the glasses matrix. We propose two possible structural models of building blocks for the formation of continuous random network glasses used by density functional theory (DFT) calculations.

Research paper thumbnail of Experimental and theoretical investigations of the copper–lead–germanate glasses

Journal of Molecular Structure, 2010

Research paper thumbnail of The local structure of europium–lead-borate glass ceramics

Journal of Molecular Structure, 2009

Glass ceramics in the xEu 2 O 3 (100 À x)[3B 2 O 3 ÁPbO] system with 0 6 x 6 50 mol% have been pr... more Glass ceramics in the xEu 2 O 3 (100 À x)[3B 2 O 3 ÁPbO] system with 0 6 x 6 50 mol% have been prepared using the melt quenching method, succeeded by heat treatment applied at 625°C and 675°C, respectively, for 48 h. The influence of europium ions on structural behavior of the lead-borate glass ceramics has been investigated using infrared spectroscopy and DFT calculations. The addition of europium ions into the host glass ceramics matrix leads to an increase of the glass network polymerization due to the replacement of BAOAB bonds by the more resistant BAOAPb bonds.

Research paper thumbnail of The improvement of the amorphous environment of the germanate–tellurate glasses in the presence of the gadolinium ions

Journal of Materials Science, 2011

Glasses in the system xGd 2 O 3 Á(100x)[TeO 2 Á GeO 2 ] with 0 B x B 50 mol% have been prepared f... more Glasses in the system xGd 2 O 3 Á(100x)[TeO 2 Á GeO 2 ] with 0 B x B 50 mol% have been prepared from melt quenching method. In this paper, we investigated changes of the coordination numbers of germanium, tellurium, and gadolinium ions by investigations of FTIR, EPR, and UV-VIS spectroscopy. By analyzing the structural changes resulted from the IR spectra we found that the bending modes of [GeO 4 ] structural units and the deformed modes of the Te-O-Te linkages produce intercalation of the [GdO n ] entities in the germanate-tellurate chain network and densification of the glasses by increasing the number of [GeO 6 ] structural units. EPR spectra of the studied samples reveal that the gadolinium ions play a role of network former. The UV-VIS spectra show broad UV absorption bands located in the 250-350 nm region. Their intensity increase with the increasing of Gd 2 O 3 content showing that these stronger transitions can be due to the presence of the O=Ge bonds (n-p* excitations) of [GeO 5 ] structural units. The [GeO 5 ] structural units are more stable thermodynamically than their analogues and the [GeO 6 ] structural units produce the improvement of the amorphous character of these glasses.

Research paper thumbnail of The local structure of gadolinium vanado-tellurite glasses

Journal of Materials Science, 2008

In this work we report on a vibrational spectroscopic, X-ray diffraction, and density measurement... more In this work we report on a vibrational spectroscopic, X-ray diffraction, and density measurement study of the structural properties of the ternary xGd 2 O 3 (100x)[7TeO 2 Á3V 2 O 5 ] systems for various x values up to 70 mol%. Structural changes, as recognized by analyzing band shapes of X-ray diffraction and IR spectra, revealed that Gd 2 O 3 causes a higher extent of network polymerization as far as x B 40 mol%, while for x between 40 and 50 mol% showed a drastic structural modification which lead to the apparition of the GdVO 4 crystalline phase.

Research paper thumbnail of Effect of the introduction of vanadium pentaoxide in phospho-tellurite glasses containing gadolinium ions

Journal of Materials Science, 2008

A range of phospho-tellurite glasses containing gadolinium was prepared and infrared absorption s... more A range of phospho-tellurite glasses containing gadolinium was prepared and infrared absorption spectra were measured. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Gd 2 O 3 causes a higher extent of network polymerization as far as x B 15 mol% because the conversion of [TeO 4 ] to [TeO 3 ] structural units is supported by the increase of metaphosphate structural groups. While for x between 20 and 30 mol% Gd 2 O 3 show some drastic structural modifications which lead to the increase in the glass fragility. Thus the addition of V 2 O 5 resulted in gradual depolymerization of the phosphate chains and formation of short phosphate units, which are linked to vanadium through P-O-V bonds. The formation of P-O-V bonds increases the cross-link between the phosphate chains and the bending mode of Te-O-Te or O-Te-O linkages.

Research paper thumbnail of Structural role of europium ions in lead–borate glasses inferred from spectroscopic and DFT studies

Chemical Physics Letters, 2008

a b s t r a c t Glasses in the system xEu 2 O 3 Á (100 À x)[3B 2 O 3 ÁPbO] with 0 6 x 6 35 mol% h... more a b s t r a c t Glasses in the system xEu 2 O 3 Á (100 À x)[3B 2 O 3 ÁPbO] with 0 6 x 6 35 mol% have been prepared from melt quenching method. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Eu 2 O 3 causes a change from the continuous borate network to the continuous lead-borate network, interconnected through Pb-O-B and B-O-B bridges. DFT calculations show that lead atoms occupy three different sites in the proposed model. Comparing the theoretical and experimental data, we conclude that the performance of the method/basis sets used on the prediction of the structural data and vibrational modes is good.