See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/343449983 Structure and Bonding in TeO2 Melt and Glass (Talk Slides) Presentation · August 2020 CITATIONS READS 0 37 1 author: Oliver L. G. Alderman Science and Technology Facilities Council 91 PUBLICATIONS 329 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Nuclear Materials View project Germanate glasses and melts View project All content following this page was uploaded by Oliver L. G. Alderman on 05 August 2020. The user has requested enhancement of the downloaded file.
Structure and Bonding in TeO 2 Melt and Glass Oliver L.G. Alderman ISIS Neutron and Muon Source oliver.alderman@stfc.ac.uk Alderman, O.L.G., et al ., J. Phys. Chem. Lett., 2020. 11 : 427 ACerS Virtual Glass Summit August 3 rd - 5 th 2020 1
Main collaborators Special Thanks: Emma Barney University of Nottingham Rick Weber Anthony Tamalonis Vrishank Walia E. I. Kamitsos Chris J. Benmore Materials Development Inc. E. Simandiras Advanced Photon Source D. G. Liakos National Hellenic Research Foundation Funding U.S. DOE SBIR DE-SC0015241 SBIR DE-SC0018601 Steven Feller Martha Jesuit NSF-DMR 1746230 Makayla Boyd NSRF 2014-2020 MIS 5002409 Michael Packard Coe College 2
Single-oxide glass formers Angell Plot VFT fits • 12 Oxides of only 8 elements from glasses B 2 O 3 , SiO 2 , SiO 2 m = 25 GeO 2 , P 2 O 5 , V 2 O 5 , As 2 O 5 , As 2 O 3 , Sb 2 O 3 , TeO 2 10 B 2 O 3 m = 37 TeO 2 m = 145 log 10 viscosity (Pa s) 8 • TeO 2 vastly more fragile cf . canonical oxide glass 6 formers SiO 2 , GeO 2 , B 2 O 3 4 • Correlates with relatively poor glass forming ability 2 0 • So what makes TeO 2 so different? -2 What is the structure of the liquid and its glass? -4 0.0 0.2 0.4 0.6 0.8 1.0 T g / T (K/K) Veber & Mangin, Mater. Res. Bull. 2008, 43 , 3066 Macedo & Napolitano, J. Chem. Phys. 1968, 49 , 1887 Doremus, J. Appl. Phys. 2002, 92 , 7619 3
Single-oxide glass formers • Zachariasen predicted most single-oxide glass formers, based on crystal structures known in 1932! W. H. Zachariasen J. Am. Chem. Soc., 1932. 54 : 3841 • Corner-sharing M O 3 triangles or M O 4 tetrahedra, oxygen 2-coordinated (O M 2 ) • M – O – M bond angles deform easily (with little energy cost) → small thermodynamic driving force for crystallization Cation Zachariasen Confirmed Valence Predicted Glass N N – 2 N = Group • The ones Zachariasen got wrong were only due to lack Number of knowledge of crystal structures 4
Lone-pair-oxides & glass formation TeO 2 is an N – 2 glass former Te 4+ is a lone-pair cation • • Electron lone-pairs tend to be stereochemically active which leads to low coordination numbers to oxygen, & increased glass forming tendency • Excellent non-linear optical properties high index, infrared transmission etc. Cation Zachariasen Confirmed Valence Predicted Glass N N – 2 N = Group = Cationic electron Number lone-pair in oxide 5
TeO 2 crystal polymorphs α P4 1 2 1 2 1 β Pbca γ P2 1 2 1 2 1 δ Fm-3m • • • • Layered structure 4 bond lengths Oxygen sublattice Stable phase disorder • • • 2 bond lengths 4 bond lengths 2 asymmetric • oxygen bridges Many bond lengths • • 2 asymmetric 1 asymmetric • • oxygen bridges Less stable than α Many asymmetric oxygen bridge & β – obtained by oxygen bridges • • ‘ Paratellurite ’ ‘Tellurite’ mineral crystallization of • glass/doped-glass crystallization of mineral doped-glass 6
TeO 2 crystal polymorphs α P4 1 2 1 2 1 β Pbca γ P2 1 2 1 2 1 δ Fm-3m γ -TeO 2 Showing connectivity of the [TeO 4 ] polyhedra through asymmetric Te-O-Te bridges 7
Trigonal pyramidal site in Na 2 TeO 3 crystal Terminal bonds Na 2 TeO 3 If present in pure TeO 2 , such a Showing isolated [TeO 3 ] 2- site could involve [(Te=O)O 2/2 ] polyanion neutral groups with terminal oxygen : : Te Te O O O O O O 8
TeO 2 glass & liquid • What about the disordered liquid & glassy structures? • Te – O coordination number varies between reports 3.6 < n TeO ≲ 4.0 in the glass • Where n TeO < 4, there must exist low coordination sites, e.g. 3-fold TeO 3 not seen in the crystal polymorphs • Plan to measure Te – O coordination in glass & liquid by HEXRD High-Energy X-ray Diffraction • Expected dominant species as follows: Solids Liquid Gas : : : Te Te Te O O O O O O O O O • Raman evidence suggests increase in 3-fold TeO 3 with liquid temperature 9
Aerodynamic levitation – containerless melting • Float sample on gas stream & heat with CO 2 laser 10.6 μ m • Access to high T refractory melts Avoid contamination, alloying & background scattering of x-ray/neutron probe beams • Extend glass forming regions & supercooling heterogeneous Recalescence nucleation at melt-container interface eliminated Glass formation 2.5 mm 6.0 mm Alderman, O.L.G. , et al. , J. Am. Ceram. Soc., 2018. 101 : 3357 10
Diffraction from amorphous substances 3.5 Pulsed neutron diffraction measurement GEM, ISIS Sine Fourier transform B – O 11 B 4 O 7 Ba 2 O – O ℱ { Q·S ( Q ) – 1} = D ( r ) 2.8 i ( Q ) / Barns per atom per steradian Neutron T(r) / barns per Å 1.5 11 B 4 O 7 Ba 2.1 1.0 Polycrystalline r = interatomic separation 1.4 Glass 0.5 | Q | = (4 π / λ ) sin ϑ Polycrystalline 0.7 scalar momentum transfer/ ħ Glass 0.0 (glass is isotropic) 0.0 1 2 3 4 5 6 7 8 2 ϑ = scattering angle -0.5 r / Å 0 5 10 15 20 λ = wavelength -1 Q / Å • Short & medium range order very • Both crystals and glass show diffuse similar in this case scattering • Resolution Δ r = 3.791/ Q max ∼ 1/ Q max • Only crystals show Bragg peaks 11 Hannon, A.C., Nucl. Instrum. Meth. A, 2005. 551 : 88
High-energy x-ray diffraction (HEXRD) 10 4 • Advanced Photon Source (APS) 90 to 100 keV synchrotron x-rays + rapid large-area TeO 2 Mass attenuation coefficient / cm 2 g -1 Coherent Argonne National Laboratory Incoherent detector APS beamline 6-ID-D, λ ∼ 0.14 to 0.12 Å 215 Photoelectric 10 2 Total • High resolution pair distribution functions X-ray weighted 1.47 10 0 distributions of the interatomic separations • Each measurement made in seconds or minutes 100 keV Cu K 1 10 -2 10 0 10 1 10 2 10 3 Photon energy / keV 0.8 Te-Te 0.6 Pair weightings W ij ( Q ) 0.4 Te-O 2 ϑ 0.2 | Q | = (4 π / λ ) sin ϑ O-O Momentum transfer = ħ Q 0.0 0 5 10 15 20 25 Q / Å -1 Energy = hc / λ Alderman, O.L.G., et al., J. Am. Ceram. Soc., 2018. 101 : 3357 12
Findings 8 • T ( r ) (Å -2 ) Observe only subtle differences between TeO 2 glass & melt in terms of Te – O units • Shift of Te – Te peak to longer distance 6 Te-Te qualitatively consistent with thermal expansion • Shaded region represents uncertainty in 4 Te-O liquid density 2 O-O Glass Melt 0 0 2 4 6 8 10 r (Å) Alderman, O.L.G. , et al. , J. Phys. Chem. Lett., 2020. 11 : 427 13
Te – O bond length distribution Glass 12 Melt g -TeO 2 c O rT TeO ( r ) (Å -1 ) Radial Ab initio 8 clusters Distribution • More short, strong Te – O bonds in the melt fewer long, weak bonds Function (RDF) 4 But very similar mean n TeO ≈ 4 poorly defined due to lack of plateau • in n TeO ( r ) as seen for all ordered crystals (& e.g. SiO 2 ) 0 • Qualitatively consistent with Raman spectroscopic observations 6 Running Te – O n TeO ( r ) • coordination Good agreement with ab-initio cluster calculations 100 atom, high 4 level of accuracy (blue open points ) number n TeO ( r ) 2 • The long weak bonds are more important in satisfying the bonding requirements in the solid 0 4 V Te ( r ) or v Te ( r ) ( e ) • Difficult to distinguish Te=O from Te-O·····Te by any means Running Te – O bond-valence 2 Bond valence sum asymptote V Te ( r →∞ ) > 4 due to lone pair • sum V TeO ( r ) • O – O contribution not important (neutron-x-ray difference analysis) 0 2.0 2.5 3.0 r (Å) Alderman, O.L.G. , et al. , J. Phys. Chem. Lett., 2020. 11 : 427 14
Conclusions • TeO 2 glass & liquid incorporate short-range disorder as well as long-range disorder • TeO 2 is therefore distinct from the canonical glass forming oxides SiO 2 , B 2 O 3 … Alderman, O.L.G. , et al. , J. Phys. Chem. Lett., 2020. 11 : 427 Questions? Email me: oliver.alderman@stfc.ac.uk 15
α - TeO 2 recovered and starting materials Figure S1: X-ray diffraction patterns for polycrystalline TeO 2 beads Recovered after melting in O 2 12000 recovered after melting and liquid diffraction measurement in O 2 gas, and Prior to melting in Ar prior to the same in Ar gas. Both patterns indicate the presence of α -TeO 2 , Elemental Te although with considerable preferred orientation, especially in the case of 10000 g -TeO 2 the former. In each case 2-dimensional diffraction patterns were averaged -TeO 2 over the full azimuthal range to reduce the effects of preferred orientation, 8000 no background subtraction has been made and arbitrary scaling factors I ( d ) (a.u.) have been applied. The calculated powder diffraction patterns for elemental Te, α -TeO 2 and γ -TeO 2 are shown for comparison. 6000 4000 2000 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 d -spacing (Å) Alderman, O.L.G. , et al. , J. Phys. Chem. Lett., 2020. 11 : 427 16
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