B. G. Aitken

Corning Incorporated, 코닝, New York, United States

Are you B. G. Aitken?

Claim your profile

Publications (88)184.65 Total impact

  • A. W. Mao · D. C. Kaseman · B. G. Aitken · S. Sen
    [Show abstract] [Hide abstract]
    ABSTRACT: Off-stoichiometric glasses in the Ba-Ga-Ge-Se system with Se excess or deficiency (BGGS ± Se) are synthesized and their structure is characterized using Raman and multinuclear (77Se, 71Ga) magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The results reveal that the structure of these off-stoichiometric BGGS ± Se glasses consists of a charge-compensated, partially covalent network of corner-sharing (Ga/Ge)Se4 tetrahedra where [GaSe4]- tetrahedra charge balance the Ba2 + cations. Addition of excess Se to a stoichiometric BaSe-Ga2Se3-GeSe2 glass with BaSe:Ga2Se3 > 1 results in the formation of Se-Se linkages, while Se deficiency is accommodated via the formation of homopolar Ge-Ge bonds, in agreement with the continuously-alloyed structural scenario of purely covalent chalcogenide glasses. Such composition-dependent structural evolution is shown to be consistent with the corresponding variation in density and glass transition temperature.
    No preview · Article · Oct 2015 · Journal of Non-Crystalline Solids
  • A.W. Mao · D. C. Kaseman · I. Hung · Z. Gan · B. G. Aitken · S. Sen
    [Show abstract] [Hide abstract]
    ABSTRACT: The nature of the selenium coordination environments in the structure of binary Ga2Se3–GeSe2 chalcogenide glasses is investigated using two-dimensional 77Se magic angle turning-phase adjusted spinning sidebands/Carr–Purcell–Meiboom–Gill (MATPASS/CPMG) nuclear magnetic resonance (NMR) spectroscopy. The structural network of these glasses consists of corner and edge-sharing (Ga/Ge)Se4 tetrahedra in which the coordination numbers of Ga, Ge, and Se atoms are primarily 4, 4, and 2, respectively. Consequently, the addition of Ga2Se3 to GeSe2 results in the formation of Ge–Ge homopolar bonds to satisfy the coordination constraints of the constituent atoms. These Ge–Ge bonds are randomly distributed throughout the network such that any clustering of (Se3/2)Ge–Ge(Se3/2) ethane-like units is avoided to the maximum extent. However, for glasses containing ≥ 30 mol% Ga2Se3, the appearance of three-coordinated Se atoms provides an alternate mechanism to accommodate for the Se deficiency in the limit where the Ge–Ge bonds are nearly saturated. These three-coordinated Se atoms are formed by corner-sharing between three GaSe4 tetrahedra that is reminiscent of oxygen triclusters shared by three AlO4 tetrahedra reported in peraluminous oxide glasses and liquids.
    No preview · Article · Feb 2015 · Journal of Non-Crystalline Solids
  • [Show abstract] [Hide abstract]
    ABSTRACT: The short-range structure, connectivity and chemical order in AsxTe100-x (25≤x≤65) glasses are studied using high-resolution two-dimensional projection magic-angle-turning (pjMAT) 125Te nuclear magnetic resonance (NMR) spectroscopy. The 125Te pjMAT NMR results indicate that the coordination of Te atoms obey the 8-N coordination rule over the entire composition range. However, in strong contrast with the analogous glass-forming As-S and As-Se chalcogenides, significant violation of chemical order is observed in As-Te glasses over the entire composition range in the form of homopolar As-As (Te-Te) bonds, even in severely As (Te) -deficient glasses. The speciation of the Te coordination environments can be explained with a dissociation reaction model As2Te3->2As +3TeII, characterized by a dissociation constant that is independent of glass composition. These structural characteristics can be attributed to the high metallicity of Te and the strong energetic similarity between the Te-Te, Te-As and As-As bonds and they are consistent with the monotonic and often nearly linear variation of physical properties observed in telluride glasses as a function of the Te content.
    No preview · Article · Jan 2015 · The Journal of Physical Chemistry B
  • J. Galbraith · J.W. Zwanziger · B.G. Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: The stress-induced birefringence, known as the stress-optic response, of glasses in the Ge–P–S and Ge–Sb–S families were measured and correlated with structure. Birefringence of the samples was measured as a function of stress load, using the Sénarmont method. In addition, density, index of refraction, and shear moduli were determined. It was found that the glass structure correlated well with the stress-optic response, through a combination of the bond lengths and coordination numbers, as found previously for oxides. However, the zero stress-optic threshold behavior and magnitude of the effect differ from oxides, and these features are explained based on bonding differences and the smaller shear moduli in sulfides.
    No preview · Article · Nov 2014 · Journal of Non-Crystalline Solids
  • A.W. Mao · S.C. Currie · B.G. Aitken · S. Sen
    [Show abstract] [Hide abstract]
    ABSTRACT: Chalcogenide glasses in the system Na2Se-Ga2Se3-GeSe2 (NGGS) have been synthesized and characterized using Raman spectroscopy as well as density and glass transition temperature measurements. Results are compared to those from the analogous system BaSe-Ga2Se3-GeSe2 (BGGS) in an attempt to shed light on the comparative roles of Na and Ba as modifying elements in chalcogenide networks. In general, both NGGS and BGGS glasses exhibit the corner-sharing network of (Ga/Ge)Se4 tetrahedra that is characteristic of glasses containing Ga–Ge–Se. Some amount of tetrahedral edge-sharing and Ge–Ge bonding exists, but the concentration of Ge–Ge bonds in the network is heavily dependent on both the ratio R = Na2Se(BaSe)/Ga2Se3 and the type of the modifying element. The addition of Na2Se to an NGGS glass with R < 1 efficiently removes Ge–Ge bonding such that their concentration essentially goes to zero by the chemical threshold R = 1. In contrast, the addition of BaSe to a BGGS glass with R < 1 removes the Ge–Ge bonds less efficiently, such that a non-zero concentration still exists at R = 1. On the other hand, compared to BGGS glasses, increasing R results in a rapid drop in the glass transition temperature of NGGS glasses with R > 1 indicating that Na2Se is a much more efficient modifier that lowers the connectivity of the Ga–Ge–Se tetrahedral network via the formation of non-bridging Se atoms.
    No preview · Article · Nov 2014 · Journal of Non-Crystalline Solids
  • [Show abstract] [Hide abstract]
    ABSTRACT: The structures of Ge-doped arsenic selenide glasses with Se contents varying between 25 and 90 at.% are studied using a combination of high-resolution, two-dimensional 77Se nuclear magnetic resonance (NMR) and Raman spectroscopy. The results indicate that, in contrary to the conventional wisdom, the compositional evolution of the structural connectivity in Se-excess glasses do not follow the chain-crossing model and chemical order is likely violated with the formation of a small but significant fraction of As-As bonds. The addition of As to Se results in a nearly random crosslinking of Se chains by AsSe3 pyramids and a highly chemically ordered network consisting primarily of corner-shared AsSe3 pyramids is formed at the stoichiometric composition. Further increase in As content, up to 40 at. % Se, results in the formation of a significant fraction of As4Se3 molecules with As-As homopolar bonds and consequently the connectivity and packing efficiency of the network decreases and anharmonic interactions increase. Finally, in the highly As-rich region with <40 at.% Se, the relative concentration of the As4Se3 molecules decrease rapidly and large clusters of As atoms connected via Se-Se-As and As-Se-As linkages dominate. These three composition regions with distinct structural characteristics and the corresponding mixing entropy of the Se environments are reflected in the appearance of multiple extrema in the compositional variation of a wide range of physical properties of these glasses, including density, glass transition temperature, thermal expansivity and fragility.
    No preview · Article · Feb 2014 · The Journal of Physical Chemistry B
  • A W Mao · B G Aitken · R E Youngman · D C Kaseman · S Sen
    [Show abstract] [Hide abstract]
    ABSTRACT: Structure of glasses in the pseudobinary system Ga2Se3-GeSe2 with Ga2Se3 content ranging from 6.3 to 30 mol % is investigated using a combination of Raman and multinuclear ((71)Ga, (77)Se) solid state nuclear magnetic resonance (NMR) spectroscopy. The results indicate that the structure of these glasses consists primarily of a corner sharing network of (Ge/Ga)Se4 tetrahedra with some fraction of edge-sharing GeSe4 tetrahedra and of ethane-like (Se3)Ge-Ge(Se3) units, in which the Ga, Ge, and Se atoms adopt coordination numbers of 4, 4, and 2, respectively. As expected, the concentration of metal-metal bonds increases with addition of Ga2Se3 as the glass structure becomes too deficient in Se to satisfy the tetrahedral coordination of both Ga and Ge by Se atoms alone. These metal-metal bonds are mostly limited to Ge-Ge homopolar bonds, indicating a violation of chemical order. At relatively high degrees of Se-deficiency, however, spectroscopic evidence suggests the formation of triply coordinated Se atoms as an alternate mechanism to accommodate the tetrahedral coordination of Ga and Ge atoms. This observation indicates a violation of the 8-N coordination rule and is reminiscent of oxygen triclusters in isoelectronic Al2O3-SiO2 glasses. Compositional variation of physical properties such as density, molar volume, optical band gap, glass transition temperature, and fragility are shown to be consistent with the proposed structural model.
    No preview · Article · Dec 2013 · The Journal of Physical Chemistry B
  • A.W. Mao · D.C. Kaseman · R.E. Youngman · B.G. Aitken · S. Sen
    [Show abstract] [Hide abstract]
    ABSTRACT: The structure of chalcogenide glasses in the system BaSeGa2Se3GeSe2 is investigated using a combination of Raman spectroscopy, 71Ga and 77Se NMR spectroscopy and neutron scattering. The results of these experiments, when taken together, indicate that the structure of these glasses consists primarily of a corner-shared network of (Ga/Ge)Se4 tetrahedra with minor edge-sharing. Homopolar metal–metal bonds are detected in glasses even with BaSe:Ga2Se3 > 1, implying violation of chemical order; however, such bonding is primarily limited to Ge atoms, in the form of GeGe bonds. A comparison between these glasses and crystalline Ba2GeSe4, of their Raman and NMR spectroscopic signatures, suggest the formation of a modified network with non-bridging Se atoms upon increasing the BaSe content. Therefore, the structure of BGGS glasses undergoes network modification characteristic of oxides as well as continuous alloying and homopolar bond formation characteristic of non-oxide chalcogenides.
    No preview · Article · Sep 2013 · Journal of Non-Crystalline Solids
  • A.W. Mao · B.G. Aitken · S. Sen
    [Show abstract] [Hide abstract]
    ABSTRACT: Chalcogenide glasses in the system BaSe–Ga2Se3–GeSe2 have been synthesized and their optical band gap, density, glass transition temperature and fragility have been measured. The band gap and density exhibit nearly linear variation with Ba:Ga ratio at a fixed GeSe2 content. On the other hand, the glass transition temperature and fragility display either a clear maximum or a break in slope near 2Ba/Ga = 1. The compositional dependence of these physical properties are consistent with a scenario where the atomic structure of these glasses transforms across 2Ba/Ga = 1 that behaves as a chemical threshold between a Se-poor network with Ge/Ga–Ge/Ga bonding and a network characterized by Se–Se bonding and/or the formation of non-bridging Se atoms.
    No preview · Article · Jun 2013 · Journal of Non-Crystalline Solids
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Pressure induced densification in a molecular arsenic sulfide glass is studied at ambient temperature using x-ray scattering, absorption and Raman spectroscopic techniques in situ in a diamond anvil cell. The relatively abrupt changes in the position of the first sharp diffraction peak, FSDP, and the pressure-volume equation of state near ∼2 GPa suggest a phase transition between low- and high-density amorphous phases characterized by different densification mechanisms and rates. Raman spectroscopic results provide clear evidence that the phase transition corresponds to a topological transformation between a low-density molecular structure and a high-density network structure via opening of the constituent As(4)S(3) cage molecules and bond switching. Pressure induced mode softening of the high density phase suggests a low dimensional nature of the network. The phase transformation is hysteretically reversible, and therefore, reminiscent of a first-order phase transition.
    Full-text · Article · Dec 2012 · The Journal of Chemical Physics
  • Source
    B. Kalkan · S. Sen · B. G. Aitken · S. V. Raju · S. M. Clark
    [Show abstract] [Hide abstract]
    ABSTRACT: The crystalline, liquid and amorphous phase stabilities and transformations of the Ge1Sb2Te4 (GST124) alloy are investigated as a function of pressure and temperature using synchrotron diffraction experiments in a diamond anvil cell. The results indicate that the solid-state amorphization of the cubic GST124 phase under high pressure may correspond to a metastable extension of the stability field of the GST124 liquid along a hexagonal crystal-liquid phase boundary with a negative P-T slope. The internal pressures generated during phase change are shown to be too small to affect phase stability. However, they may be important in understanding reliability issues related to thermomechanical stress development in phase change random access memory structures.
    Full-text · Article · Jul 2011 · Physical review. B, Condensed matter
  • T. G. Edwards · E. L. Gjersing · S. Sen · S. C. Currie · B. G. Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: The local coordination environments of Te atoms have been investigated in crystalline and glassy binary and ternary tellurides in the system Ge–As–Sb–Te using 125Te solid-state wideline nuclear magnetic resonance (NMR) spectroscopy. The average 125Te NMR chemical shifts in these materials range from 300 to 1050, 90 to 700 and − 2000 to − 4100 ppm for 2, 3 and 6-coordinated environments, respectively. Te atoms are predominantly 2-coordinated in binary Ge–Te, As–Te and ternary Ge–As–Te glasses. The 125Te NMR spectrum of the cubic Ge1Sb2Te4 phase with rock salt structure is consistent with a random distribution of Ge/Sb vacancies in the lattice. Besides the coordination number, the 125Te chemical shifts in these materials are also found to be sensitive to the chemical identity of the nearest neighbors. 125Te NMR spectroscopy shows significant future promise in its application as a technique complementary to diffraction and EXAFS in understanding the short-range structure of amorphous Ge–As–Sb tellurides.
    No preview · Article · Jul 2011 · Journal of Non-Crystalline Solids
  • [Show abstract] [Hide abstract]
    ABSTRACT: A neutron diffraction investigation has been performed of the structure of four chalcogenide glasses, using the D4c diffractometer on the high-flux reactor at the Institut Laue-Langevin (ILL). Vitreous Ge3As52S45 is shown to have a structure based on As4S3 molecules, whereas that of its selenide analogue, vitreous Ge3As52Se45, involves far fewer As4Se3 molecules. Two As2X3 reference glasses (X = S or Se) have purely network structures. As–X, and As–As bond lengths have been extracted, together with their associated co-ordination numbers, from peak fits to the real space correlation functions, T(r), and suggest that all four glasses are chemically ordered; i.e. that they contain the maximum possible number of As–X (and Ge–X) bonds. The molecular nature of vitreous Ge3As52S45 is evident from the enhanced first diffraction peak relative to the As2S3 reference glass, and has been further investigated by comparing its interference function, Qi(Q), with that expected for an isolated As4S3 molecule. On the other hand, the second diffraction peak for vitreous Ge3As52S45 is not reproduced by a random orientation molecular model, indicating that there is orientational correlation between adjacent molecules, and this is discussed with respect to the structure of the corresponding As4S3 crystalline phases. The neutron-weighted vibrational density of states (VDOS) for vitreous Ge3As52S45, obtained with the ISIS MARI spectrometer, unambiguously confirms the existence of As4S3 molecules, as revealed by a peak at ~34meV arising from the triangle of As atoms that form the base of the molecule. MARI data recorded at ambient temperature also reveal a strong quasi-elastic component in the scattered intensity, which has been further investigated using the IN5 quasi-elastic scattering spectrometer (ILL) and indicates the presence of rotational diffusion of the As4S3 molecules; i.e. that, at ambient temperature, vitreous Ge3As52S45 behaves as a plastic glass. A possible structural model for vitreous Ge3As52S45 comprises a two-dimensional tangled GeS2 net with As4S3 molecules trapped in its folds whereas, for vitreous Ge3As52Se45, a clathrate model appears more appropriate.
    No preview · Article · Jul 2011 · Journal of Non-Crystalline Solids
  • E L Gjersing · S Sen · B G Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: The structure of phosphorus selenide glasses with compositions close to the P(4)Se(3) stoichiometry with and without doping with a few atom % Ge has been investigated with Raman and (31)P NMR spectroscopic techniques. The results indicate that the structure of these glasses consists predominantly of P(4)Se(3) cage molecules. However, in spite of this structural similarity, doping with Ge results in a remarkably large increase in T(g). The dynamical behavior of the constituent P(4)Se(3) molecules in the Ge-free composition is investigated with a (31)P NMR hole-burning technique in the supercooled liquid state. These molecules perform large angle rotational reorientations near and above the glass transition with time scales similar to those expected for shear relaxation. Such coupling between molecular rotation and shear relaxation processes near T(g) is reminiscent of the dynamical behavior of organic molecular glass-forming liquids. However, this behavior is in stark contrast with the large temporal decoupling between molecular rotation and shear relaxation previously reported for a Ge-doped arsenic sulfide liquid that contained similarly structured As(4)S(3) cage molecules.
    No preview · Article · Mar 2011 · The Journal of Physical Chemistry B
  • S Sen · S. Soyer Uzun · C J Benmore · B G Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: High-energy x-ray diffraction is employed to study the atomic structure of bulk GexAs2xTe100 − 3x glasses with compositions in the range 25 ≤ 3x ≤ 70. The coordination environments of Te atoms suggest significant violation of chemical order in these glasses. Analyses of the nearest-neighbor coordination environments and the parameters for the first sharp diffraction peak indicate that these telluride glasses are structurally and chemically more disordered as compared with their sulfide or selenide analogs. The compositional evolution of the structural parameters is shown to be consistent with the corresponding variation in molar volume and glass transition temperature.
    No preview · Article · Oct 2010 · Journal of Physics Condensed Matter
  • S. Sen · E.L. Gjersing · B.G. Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: Ternary GexAs2xTe100 − 3x glasses with 20 ≤ 3x ≤ 70 have been investigated to determine the compositional dependence of select physical properties. Molar volume, viscosity, optical band gap and thermophysical properties display a monotonic and often linear variation with the Te content in these glasses. Such compositional dependence is hypothesized to be due to the progressive replacement of a three-dimensional network of corner-shared Ge and As centered coordination polyhedra by –Te–Te–Te– chains as the Te content increases. This topologic change arises as Ge/As–Ge/As bonds in Te-deficient glasses are gradually replaced by Ge/As–Te bonds and ultimately the Te–Te bonds in Te-excess glasses. The compositional evolution of the Raman spectra of these glasses is shown to be consistent with this structural scenario. Furthermore, detailed analysis of the Raman spectra shows significant violation of chemical order in the form of the presence of Te–Te (Ge/As–Ge/As) bonds in Te-deficient (-excess) glasses. Such behavior in ternary Ge–As telluride glasses is unique in comparison with their sulfide and selenide counterparts.
    No preview · Article · Sep 2010 · Journal of Non-Crystalline Solids
  • E. L. Gjersing · S. Sen · B. G. Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: High-resolution 77Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary GexSe100−x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se−Se−Se and Ge−Se−Se linkages as well as Ge−Se−Ge sites where the Se atom is shared by two GeSe4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77Se MAS NMR spectrum of crystalline β-GeSe2. Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of GexSe100−x glasses in this composition range can be described as a randomly interconnected network of GeSe4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.
    No preview · Article · May 2010 · The Journal of Physical Chemistry C
  • E L Gjersing · S Sen · H Maekawa · B G Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: The dynamics of As2P2S8 quasi-molecular units caged in an As-S network in the supercooled chalcogenide liquid of composition (As2S3)90(P2S5)10 have been studied near the glass transition region (Tg=468<or=T<or=628 K) using 31P NMR line shape analysis and spin-lattice relaxation techniques. 31P NMR line shape analysis indicates the presence of isotropic rotational reorientation of As2P2S8 quasi-molecular units at frequencies on the order of tens of kilohertz at T<540 K. At higher temperatures, the time scale of intramolecular bond-breaking and rearrangement is coupled to that of shear/structural relaxation of the surrounding network. On the other hand, over the entire temperature range, the 31P NMR spin-lattice relaxation results from fast cage-rattling dynamics of the same molecules at frequencies in the megahertz to gigahertz range. When taken together, these results imply the presence of serial hierarchical dynamics in which the fast rattling of As2P2S8 quasi-molecular units trapped in their cages coexists with slower isotropic rotational reorientation. The shear or alpha-relaxation involves cooperative rearrangement of the surrounding As-S network and, consequently, relaxation of the cages that provides feedback to the fast rattling dynamics over the entire temperature range.
    No preview · Article · Jun 2009 · The Journal of Physical Chemistry B
  • R.E. Youngman · B.G. Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: Quaternary glasses containing only the glass forming oxides B 2O3, Al2O3, P2O 5 and SiO2, have been studied by multinuclear NMR as a function of B for Al substitution at 7-5 mol% P2O5 and 70 mol% SiO2. Clear glasses along this join can be obtained for all B:Al ratios, except near the 1:1 composition, where liquidus temperatures are unusually high. As B+Al is always in excess of P in these glasses, P was found almost exclusively in symmetric Q4 units with all bridging oxygen atoms and B or Al next nearest neighbours. 27B and 27Al NMR showed a clear preference for Al-P instead of B-P associations, regardless of the B:Al ratio, in contrast to the situation in AlBP ternary glasses where B has been determined to be more strongly associated with P.
    No preview · Article · Jun 2009 · European Journal of Glass Science and Technology Part B Physics and Chemistry of Glasses
  • E.L. Gjersing · S. Sen · B.G. Aitken
    [Show abstract] [Hide abstract]
    ABSTRACT: Raman spectroscopic measurements have been performed on Ge20Se80 glass and supercooled liquid at temperatures ranging between 298 and 500 K. Temperature dependent softening of vibrational mode frequencies has been used in conjunction with the available vibrational density of states data at ambient temperature to estimate the relative contributions of vibrational and configurational entropies across glass transition. Nearly 20% of the additional entropy above glass transition is estimated to be vibrational. Thermal expansion effect on vibrational mode softening is found to be insufficient to account for the anharmonic component of vibrational entropy implying possible coupling between the vibrational and configurational entropies at temperatures above Tg. These results may have important consequences in shaping our understanding of various aspects of glass transition.
    No preview · Article · May 2009 · Journal of Non-Crystalline Solids

Publication Stats

1k Citations
184.65 Total Impact Points


  • 1995-2015
    • Corning Incorporated
      코닝, New York, United States
    • University of Georgia
      • Department of Physics and Astronomy
      Атина, Georgia, United States
  • 2007
    • Dalhousie University
      • Department of Chemistry
      Halifax, Nova Scotia, Canada
  • 2003
    • Indiana University Bloomington
      • Department of Chemistry
      Bloomington, Indiana, United States