Doris Möncke | Alfred University (original) (raw)
Papers by Doris Möncke
Scientific Reports, Dec 15, 2017
In many daily applications glasses are indispensable and novel applications demanding improved st... more In many daily applications glasses are indispensable and novel applications demanding improved strength and crack resistance are appearing continuously. Up to now, the fundamental mechanical processes in glasses subjected to high strain rates at room temperature are largely unknown and thus guidelines for one of the major failure conditions of glass components are non-existent. Here, we elucidate this important regime for the first time using glasses ranging from a dense metallic glass to open fused silica by impact as well as quasi-static nanoindentation. We show that towards high strain rates, shear deformation becomes the dominant mechanism in all glasses accompanied by Non-Newtonian behaviour evident in a drop of viscosity with increasing rate covering eight orders of magnitude. All glasses converge to the same limit stress determined by the theoretical hardness, thus giving the first experimental and quantitative evidence that Non-Newtonian shear flow occurs at the theoretical strength at room temperature.
Scientific Reports, Dec 15, 2017
In many daily applications glasses are indispensable and novel applications demanding improved st... more In many daily applications glasses are indispensable and novel applications demanding improved strength and crack resistance are appearing continuously. Up to now, the fundamental mechanical processes in glasses subjected to high strain rates at room temperature are largely unknown and thus guidelines for one of the major failure conditions of glass components are non-existent. Here, we elucidate this important regime for the first time using glasses ranging from a dense metallic glass to open fused silica by impact as well as quasi-static nanoindentation. We show that towards high strain rates, shear deformation becomes the dominant mechanism in all glasses accompanied by Non-Newtonian behaviour evident in a drop of viscosity with increasing rate covering eight orders of magnitude. All glasses converge to the same limit stress determined by the theoretical hardness, thus giving the first experimental and quantitative evidence that Non-Newtonian shear flow occurs at the theoretical strength at room temperature.
Journal Of Non-crystalline Solids: X, Jun 1, 2023
International Journal of Applied Glass Science, 2023
Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by m... more Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by melt‐quenching for a detailed investigation of the Pb2+ ions’ optical properties. UV–Vis absorption and photoluminescence spectroscopy reveal variations in the s–p transition of Pb2+, which are shown to correlate with the optical basicity of the host glass in both borates and phosphates. Pb2+ emission differs significantly for borate and phosphate glasses, as the nature of the charged sites available to accommodate Pb2+ cations vary. Optical basicity values were determined from the composition (Λth) and the measured refractive index (Λn). The UV‐cutoff shifts toward higher wavelengths with increasing optical basicity and lead content. In borate glasses, the frequency of the stretching modes due to nonbridging oxygen atoms of trigonal metaborate species is identified to be inversely proportional to the excitation wavelength (directly proportional to the excitation energy) of Pb2+. Lead‐containing alkali and alkaline‐earth borate glasses show additional correlations between the Pb2+ emission wavelength and the weighted average of the field strength of the modifier(s). Complementary to the investigation of optical properties, radiation and neutron shielding parameters were calculated, suggesting the potential utility of some of the studied compositions for radiation shielding applications.
De Gruyter eBooks, Jun 7, 2022
De Gruyter eBooks, Jun 7, 2022
The Royal Society of Chemistry eBooks, May 4, 2022
The Royal Society of Chemistry eBooks, May 4, 2022
Key Engineering Materials, Jul 1, 2016
We report on the mechanical properties of xCuO-(50-x)PbO-50B2O3 (x from 0 to 30 mol%) copper-lead... more We report on the mechanical properties of xCuO-(50-x)PbO-50B2O3 (x from 0 to 30 mol%) copper-lead-borate glasses. Their mechanical properties were investigated by the mechanical resonance technique and by the indentation measurement. The replacement of lead by copper improves the packing efficiency, and enhances the elastic moduli, hardness and the fracture toughness of glasses.
Frontiers in Materials, Jul 28, 2020
Alkali-borosilicate glasses are one of the most used types of glasses with a high technological i... more Alkali-borosilicate glasses are one of the most used types of glasses with a high technological importance. In order to optimize glasses for diverse applications, an understanding of the correlation between microscopic structure and macroscopic properties is of central interest in materials science. It has been found that the crack initiation in borosilicate glasses can be influenced by changes in network interconnectivity. In the NBS2 borosilicate glass system (74.0SiO 2-20.7B 2 O 3-4.3Na 2 O-1.0Al 2 O 3 in mol%) two subnetworks are present, i.e., a silicate and a borate network. Increasing cooling rates during processing were found to improve glasses crack resistance. Simultaneously, an increase in the network interconnectivity accompanied by an increasing capacity for densification were noticed. Their individual contribution to the mechanic response, however, remained unclear. In the present study the borosilicate glasses were systematically modified by addition of up to 4.0 mol% Al 2 O 3. Changes in the network connectivity as well as the short-and medium-range order were characterized using Raman and NMR spectroscopy. Both the Raman and the 11 B NMR results show that four-fold-coordinated boron is converted into threefold coordination as the Al 2 O 3 content increases. Additionally, 27 Al NMR experiments show that aluminum is dominantly present in four-fold coordination. Aluminum-tetrahedra are thus charge balanced by sodium ions and incorporated into the silicate network. Finally, nanoindentation testing was employed to link the inherent glass structure and its network configuration to the mechanical glass response. It was found that the glass softens with increasing Al 2 O 3 content, which enhances the crack resistance of the borosilicate glass.
International Journal of Applied Glass Science, 2023
Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by m... more Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by melt‐quenching for a detailed investigation of the Pb2+ ions’ optical properties. UV–Vis absorption and photoluminescence spectroscopy reveal variations in the s–p transition of Pb2+, which are shown to correlate with the optical basicity of the host glass in both borates and phosphates. Pb2+ emission differs significantly for borate and phosphate glasses, as the nature of the charged sites available to accommodate Pb2+ cations vary. Optical basicity values were determined from the composition (Λth) and the measured refractive index (Λn). The UV‐cutoff shifts toward higher wavelengths with increasing optical basicity and lead content. In borate glasses, the frequency of the stretching modes due to nonbridging oxygen atoms of trigonal metaborate species is identified to be inversely proportional to the excitation wavelength (directly proportional to the excitation energy) of Pb2+. Lead‐containing alkali and alkaline‐earth borate glasses show additional correlations between the Pb2+ emission wavelength and the weighted average of the field strength of the modifier(s). Complementary to the investigation of optical properties, radiation and neutron shielding parameters were calculated, suggesting the potential utility of some of the studied compositions for radiation shielding applications.
RSC smart materials, Nov 28, 2016
Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range ... more Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range order and in superstructural units such as chains or rings. Variations in this atomic arrangement depend on the glass composition and directly influence glass properties, including thermal behaviour or dissolution rates. This chapter describes the structure and properties of three important groups of melt-derived glasses used as biomaterials: silicate, phosphate and borate glasses, as well as some commonly used mixed glass former systems, including phosphosilicate and borosilicate glasses. In addition, the structural features of sol–gel derived silicate glasses are considered.
RSC smart materials, Nov 28, 2016
Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range ... more Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range order and in superstructural units such as chains or rings. Variations in this atomic arrangement depend on the glass composition and directly influence glass properties, including thermal behaviour or dissolution rates. This chapter describes the structure and properties of three important groups of melt-derived glasses used as biomaterials: silicate, phosphate and borate glasses, as well as some commonly used mixed glass former systems, including phosphosilicate and borosilicate glasses. In addition, the structural features of sol–gel derived silicate glasses are considered.
Journal of Non-crystalline Solids, Dec 1, 2015
Abstract Fluoride–phosphate (FP) glasses have been developed (in terms of glass forming ability) ... more Abstract Fluoride–phosphate (FP) glasses have been developed (in terms of glass forming ability) as a more stable alternative to fluoride glasses. Benefitting from the low polarizability of the fluoride anion, high electronic band-gap and low phonon energy, they present one of the most important host species for the inclusion of rare-earth and other optically active dopants into fiber and bulk glass. A major limitation, however, has been the mechanical performance of these glasses and their susceptibility to damage and fracture. Here, we provide comprehensive data on elasticity, plasticity and fracture of a series of mixed fluoride–phosphate glasses with strongly ionic bonding character, spanning the compositional join of strontium metaphosphate and alkaline earth aluminum fluoride. Simplistic models such as that of Makishima and Mackenzie can reproduce the mechanical properties of these glasses within a limited compositional range. This break-down is explained in the context of glass structure, in particular, the role of intermediate VIAl3 + species which act as bridges between the fluoride and the phosphate sub-networks. A simple binominal model is implemented to estimate the atomic fractions of aluminum as well as of magnesium cations, which are linked to two or more phosphate units, and used as an indicator for the connectivity between the anion sub-networks. Such adjustment of the Makishima–Mackenzie model provides an unambiguous rational for the elastic properties, but also for the susceptibility to inelastic deformation and fracture of FP glasses.
Springer handbooks, 2019
Glass is a fascinating material, not only because of its transparency and for its formability, bu... more Glass is a fascinating material, not only because of its transparency and for its formability, but also because of the manifold facets of bright colors it can display. Just remember how the colored glasses of cathedral windows made us dream in our childhood, and how much we could quarrel in the schoolyard over a marble or a bead necklace.
Optical Materials, Feb 1, 2018
Red opaque glasses of two different sites in central Germany, a medieval glassworks in Glashütten... more Red opaque glasses of two different sites in central Germany, a medieval glassworks in Glashütten, Taunus Mountains, and an early modern glassworks in Wieda, Harz Mountains, were analysed with regard to their optical appearance. By scanning electron microscopy and X-ray diffraction, metallic copper nanoparticles were identified as a conspicuous constituent in these glasses. In addition, similar opaque red glasses were reproduced in the laboratory in order to better understand the manufacturing process. Detailed analysis of the optical scattering was conducted in order to evaluate the role of Cu 0 nanoparticles in the colouring mechanism relative to other possible reasons of colouration. We find clear differences between the possible contributions of Cu 2 O (cuprite) particles and metallic copper (Cu 0) nanoparticles. Through simulated backscattering spectra we were able to calculate an average copper particle radius in the archaeological glass samples resulting in a value of up to 95 nm, which matches well the results of SEM investigation (minimum 65 nm). Using the methods we applied in this study, it becomes possible to reconstruct various processing conditions as they were applied in medieval manufacture of these particular materials.
Optical Materials, Dec 1, 2016
Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with dif... more Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with different alkaline earth modifiers were prepared by melt quenching. The structure of the prepared glasses was investigated by FT-IR and Raman, as well as by optical spectroscopy. The effect of the optical basicity of the host glass matrix on the added active dopants was studied, as was the effect doping had on the phosphate structural units. The optical edge shifts toward higher wavelengths with an increase in the optical basicity due to the increased polarizability of the glass matrix, but also with increasing CeO 2 concentration as a result of Ce 3þ /Ce 4þ inter valence charge transfer (IV-CT) absorption. The optical band gap for direct and indirect allowed transitions was calculated for the undoped glasses. The glass sample containing Mg 2þ modifier ions is found to have the highest value (4.16 eV) for the optical band gap while Ba 2þ has the lowest value (3.61 eV). The change in the optical band gap arises from the structural changes and the overall polarizability (optical basicity). Refractive index, molar refractivity R m and molar polarizability a m values increase with increasing optical basicity of the glasses. The characteristic absorption peaks of Sm 3þ were also investigated. For Sm/Ce co-doped glasses, especially at high concentration of CeO 2 , the absorption of Ce 3þ hinders the high energy absorption of Sm 3þ and this effect becomes more obvious with increasing optical basicity.
Journal of Non-crystalline Solids, Jul 1, 2015
Plastic deformation, densification, and cracking of sodium borosilicate (NBS) glasses were examin... more Plastic deformation, densification, and cracking of sodium borosilicate (NBS) glasses were examined during indentation with a three-sided pyramidal indenter. Compositions of 74.0SiO 2-10.0B 2 O 3-16.0Na 2 O (NBS1), and 74.0SiO 2-20.7B 2 O 3-4.3Na 2 O-1.0Al 2 O 3 (NBS2) (mol%) were investigated. The effect of thermal history was additionally considered for the NBS2 composition, which lies near the boron anomaly line. Hardness, elastic modulus, and fracture toughness were estimated with instrumented indentation techniques. Atomic force microscopy (AFM), Raman micro-spectroscopy, and post-indent annealing experiments were used to analyze surface topographies, densification, and recovery of deformed material. The results indicate that NBS1 exhibits a greater hardness and elastic modulus, and undergoes less densification than the NBS2 glasses. Different casting conditions influenced the plastic deformation and onset of crack initiation in NBS2. Interpretation of fracture toughness measured by indentation is complicated by residual stresses, densification during contact, and model assumptions. However, distinct differences in elastic modulus, plastic deformation and cracking between the glasses were noticeable. Such results and observations are discussed in terms of structural changes in the glass.
Scientific Reports, Dec 15, 2017
In many daily applications glasses are indispensable and novel applications demanding improved st... more In many daily applications glasses are indispensable and novel applications demanding improved strength and crack resistance are appearing continuously. Up to now, the fundamental mechanical processes in glasses subjected to high strain rates at room temperature are largely unknown and thus guidelines for one of the major failure conditions of glass components are non-existent. Here, we elucidate this important regime for the first time using glasses ranging from a dense metallic glass to open fused silica by impact as well as quasi-static nanoindentation. We show that towards high strain rates, shear deformation becomes the dominant mechanism in all glasses accompanied by Non-Newtonian behaviour evident in a drop of viscosity with increasing rate covering eight orders of magnitude. All glasses converge to the same limit stress determined by the theoretical hardness, thus giving the first experimental and quantitative evidence that Non-Newtonian shear flow occurs at the theoretical strength at room temperature.
Scientific Reports, Dec 15, 2017
In many daily applications glasses are indispensable and novel applications demanding improved st... more In many daily applications glasses are indispensable and novel applications demanding improved strength and crack resistance are appearing continuously. Up to now, the fundamental mechanical processes in glasses subjected to high strain rates at room temperature are largely unknown and thus guidelines for one of the major failure conditions of glass components are non-existent. Here, we elucidate this important regime for the first time using glasses ranging from a dense metallic glass to open fused silica by impact as well as quasi-static nanoindentation. We show that towards high strain rates, shear deformation becomes the dominant mechanism in all glasses accompanied by Non-Newtonian behaviour evident in a drop of viscosity with increasing rate covering eight orders of magnitude. All glasses converge to the same limit stress determined by the theoretical hardness, thus giving the first experimental and quantitative evidence that Non-Newtonian shear flow occurs at the theoretical strength at room temperature.
Journal Of Non-crystalline Solids: X, Jun 1, 2023
International Journal of Applied Glass Science, 2023
Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by m... more Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by melt‐quenching for a detailed investigation of the Pb2+ ions’ optical properties. UV–Vis absorption and photoluminescence spectroscopy reveal variations in the s–p transition of Pb2+, which are shown to correlate with the optical basicity of the host glass in both borates and phosphates. Pb2+ emission differs significantly for borate and phosphate glasses, as the nature of the charged sites available to accommodate Pb2+ cations vary. Optical basicity values were determined from the composition (Λth) and the measured refractive index (Λn). The UV‐cutoff shifts toward higher wavelengths with increasing optical basicity and lead content. In borate glasses, the frequency of the stretching modes due to nonbridging oxygen atoms of trigonal metaborate species is identified to be inversely proportional to the excitation wavelength (directly proportional to the excitation energy) of Pb2+. Lead‐containing alkali and alkaline‐earth borate glasses show additional correlations between the Pb2+ emission wavelength and the weighted average of the field strength of the modifier(s). Complementary to the investigation of optical properties, radiation and neutron shielding parameters were calculated, suggesting the potential utility of some of the studied compositions for radiation shielding applications.
De Gruyter eBooks, Jun 7, 2022
De Gruyter eBooks, Jun 7, 2022
The Royal Society of Chemistry eBooks, May 4, 2022
The Royal Society of Chemistry eBooks, May 4, 2022
Key Engineering Materials, Jul 1, 2016
We report on the mechanical properties of xCuO-(50-x)PbO-50B2O3 (x from 0 to 30 mol%) copper-lead... more We report on the mechanical properties of xCuO-(50-x)PbO-50B2O3 (x from 0 to 30 mol%) copper-lead-borate glasses. Their mechanical properties were investigated by the mechanical resonance technique and by the indentation measurement. The replacement of lead by copper improves the packing efficiency, and enhances the elastic moduli, hardness and the fracture toughness of glasses.
Frontiers in Materials, Jul 28, 2020
Alkali-borosilicate glasses are one of the most used types of glasses with a high technological i... more Alkali-borosilicate glasses are one of the most used types of glasses with a high technological importance. In order to optimize glasses for diverse applications, an understanding of the correlation between microscopic structure and macroscopic properties is of central interest in materials science. It has been found that the crack initiation in borosilicate glasses can be influenced by changes in network interconnectivity. In the NBS2 borosilicate glass system (74.0SiO 2-20.7B 2 O 3-4.3Na 2 O-1.0Al 2 O 3 in mol%) two subnetworks are present, i.e., a silicate and a borate network. Increasing cooling rates during processing were found to improve glasses crack resistance. Simultaneously, an increase in the network interconnectivity accompanied by an increasing capacity for densification were noticed. Their individual contribution to the mechanic response, however, remained unclear. In the present study the borosilicate glasses were systematically modified by addition of up to 4.0 mol% Al 2 O 3. Changes in the network connectivity as well as the short-and medium-range order were characterized using Raman and NMR spectroscopy. Both the Raman and the 11 B NMR results show that four-fold-coordinated boron is converted into threefold coordination as the Al 2 O 3 content increases. Additionally, 27 Al NMR experiments show that aluminum is dominantly present in four-fold coordination. Aluminum-tetrahedra are thus charge balanced by sodium ions and incorporated into the silicate network. Finally, nanoindentation testing was employed to link the inherent glass structure and its network configuration to the mechanical glass response. It was found that the glass softens with increasing Al 2 O 3 content, which enhances the crack resistance of the borosilicate glass.
International Journal of Applied Glass Science, 2023
Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by m... more Lead‐containing alkali/alkaline‐earth borate and barium lead phosphate glasses were prepared by melt‐quenching for a detailed investigation of the Pb2+ ions’ optical properties. UV–Vis absorption and photoluminescence spectroscopy reveal variations in the s–p transition of Pb2+, which are shown to correlate with the optical basicity of the host glass in both borates and phosphates. Pb2+ emission differs significantly for borate and phosphate glasses, as the nature of the charged sites available to accommodate Pb2+ cations vary. Optical basicity values were determined from the composition (Λth) and the measured refractive index (Λn). The UV‐cutoff shifts toward higher wavelengths with increasing optical basicity and lead content. In borate glasses, the frequency of the stretching modes due to nonbridging oxygen atoms of trigonal metaborate species is identified to be inversely proportional to the excitation wavelength (directly proportional to the excitation energy) of Pb2+. Lead‐containing alkali and alkaline‐earth borate glasses show additional correlations between the Pb2+ emission wavelength and the weighted average of the field strength of the modifier(s). Complementary to the investigation of optical properties, radiation and neutron shielding parameters were calculated, suggesting the potential utility of some of the studied compositions for radiation shielding applications.
RSC smart materials, Nov 28, 2016
Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range ... more Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range order and in superstructural units such as chains or rings. Variations in this atomic arrangement depend on the glass composition and directly influence glass properties, including thermal behaviour or dissolution rates. This chapter describes the structure and properties of three important groups of melt-derived glasses used as biomaterials: silicate, phosphate and borate glasses, as well as some commonly used mixed glass former systems, including phosphosilicate and borosilicate glasses. In addition, the structural features of sol–gel derived silicate glasses are considered.
RSC smart materials, Nov 28, 2016
Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range ... more Despite glasses having an amorphous structure, their atoms are arranged in a certain short-range order and in superstructural units such as chains or rings. Variations in this atomic arrangement depend on the glass composition and directly influence glass properties, including thermal behaviour or dissolution rates. This chapter describes the structure and properties of three important groups of melt-derived glasses used as biomaterials: silicate, phosphate and borate glasses, as well as some commonly used mixed glass former systems, including phosphosilicate and borosilicate glasses. In addition, the structural features of sol–gel derived silicate glasses are considered.
Journal of Non-crystalline Solids, Dec 1, 2015
Abstract Fluoride–phosphate (FP) glasses have been developed (in terms of glass forming ability) ... more Abstract Fluoride–phosphate (FP) glasses have been developed (in terms of glass forming ability) as a more stable alternative to fluoride glasses. Benefitting from the low polarizability of the fluoride anion, high electronic band-gap and low phonon energy, they present one of the most important host species for the inclusion of rare-earth and other optically active dopants into fiber and bulk glass. A major limitation, however, has been the mechanical performance of these glasses and their susceptibility to damage and fracture. Here, we provide comprehensive data on elasticity, plasticity and fracture of a series of mixed fluoride–phosphate glasses with strongly ionic bonding character, spanning the compositional join of strontium metaphosphate and alkaline earth aluminum fluoride. Simplistic models such as that of Makishima and Mackenzie can reproduce the mechanical properties of these glasses within a limited compositional range. This break-down is explained in the context of glass structure, in particular, the role of intermediate VIAl3 + species which act as bridges between the fluoride and the phosphate sub-networks. A simple binominal model is implemented to estimate the atomic fractions of aluminum as well as of magnesium cations, which are linked to two or more phosphate units, and used as an indicator for the connectivity between the anion sub-networks. Such adjustment of the Makishima–Mackenzie model provides an unambiguous rational for the elastic properties, but also for the susceptibility to inelastic deformation and fracture of FP glasses.
Springer handbooks, 2019
Glass is a fascinating material, not only because of its transparency and for its formability, bu... more Glass is a fascinating material, not only because of its transparency and for its formability, but also because of the manifold facets of bright colors it can display. Just remember how the colored glasses of cathedral windows made us dream in our childhood, and how much we could quarrel in the schoolyard over a marble or a bead necklace.
Optical Materials, Feb 1, 2018
Red opaque glasses of two different sites in central Germany, a medieval glassworks in Glashütten... more Red opaque glasses of two different sites in central Germany, a medieval glassworks in Glashütten, Taunus Mountains, and an early modern glassworks in Wieda, Harz Mountains, were analysed with regard to their optical appearance. By scanning electron microscopy and X-ray diffraction, metallic copper nanoparticles were identified as a conspicuous constituent in these glasses. In addition, similar opaque red glasses were reproduced in the laboratory in order to better understand the manufacturing process. Detailed analysis of the optical scattering was conducted in order to evaluate the role of Cu 0 nanoparticles in the colouring mechanism relative to other possible reasons of colouration. We find clear differences between the possible contributions of Cu 2 O (cuprite) particles and metallic copper (Cu 0) nanoparticles. Through simulated backscattering spectra we were able to calculate an average copper particle radius in the archaeological glass samples resulting in a value of up to 95 nm, which matches well the results of SEM investigation (minimum 65 nm). Using the methods we applied in this study, it becomes possible to reconstruct various processing conditions as they were applied in medieval manufacture of these particular materials.
Optical Materials, Dec 1, 2016
Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with dif... more Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with different alkaline earth modifiers were prepared by melt quenching. The structure of the prepared glasses was investigated by FT-IR and Raman, as well as by optical spectroscopy. The effect of the optical basicity of the host glass matrix on the added active dopants was studied, as was the effect doping had on the phosphate structural units. The optical edge shifts toward higher wavelengths with an increase in the optical basicity due to the increased polarizability of the glass matrix, but also with increasing CeO 2 concentration as a result of Ce 3þ /Ce 4þ inter valence charge transfer (IV-CT) absorption. The optical band gap for direct and indirect allowed transitions was calculated for the undoped glasses. The glass sample containing Mg 2þ modifier ions is found to have the highest value (4.16 eV) for the optical band gap while Ba 2þ has the lowest value (3.61 eV). The change in the optical band gap arises from the structural changes and the overall polarizability (optical basicity). Refractive index, molar refractivity R m and molar polarizability a m values increase with increasing optical basicity of the glasses. The characteristic absorption peaks of Sm 3þ were also investigated. For Sm/Ce co-doped glasses, especially at high concentration of CeO 2 , the absorption of Ce 3þ hinders the high energy absorption of Sm 3þ and this effect becomes more obvious with increasing optical basicity.
Journal of Non-crystalline Solids, Jul 1, 2015
Plastic deformation, densification, and cracking of sodium borosilicate (NBS) glasses were examin... more Plastic deformation, densification, and cracking of sodium borosilicate (NBS) glasses were examined during indentation with a three-sided pyramidal indenter. Compositions of 74.0SiO 2-10.0B 2 O 3-16.0Na 2 O (NBS1), and 74.0SiO 2-20.7B 2 O 3-4.3Na 2 O-1.0Al 2 O 3 (NBS2) (mol%) were investigated. The effect of thermal history was additionally considered for the NBS2 composition, which lies near the boron anomaly line. Hardness, elastic modulus, and fracture toughness were estimated with instrumented indentation techniques. Atomic force microscopy (AFM), Raman micro-spectroscopy, and post-indent annealing experiments were used to analyze surface topographies, densification, and recovery of deformed material. The results indicate that NBS1 exhibits a greater hardness and elastic modulus, and undergoes less densification than the NBS2 glasses. Different casting conditions influenced the plastic deformation and onset of crack initiation in NBS2. Interpretation of fracture toughness measured by indentation is complicated by residual stresses, densification during contact, and model assumptions. However, distinct differences in elastic modulus, plastic deformation and cracking between the glasses were noticeable. Such results and observations are discussed in terms of structural changes in the glass.