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The structure of triphenyl phosphite studied using spallation neutron diffraction

The structure of triphenyl phosphite studied using spallation neutron diffraction. Qiang Mei Prasanna Ghalsasi Chris J. Benmore Jeffery L. Yarger. Introduction. A candidate of polyamorphic material Theory 1– defect-ordered crystal due to topological frustration (Kivelson et al.)

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The structure of triphenyl phosphite studied using spallation neutron diffraction

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  1. The structure of triphenyl phosphite studied using spallation neutron diffraction Qiang Mei Prasanna Ghalsasi Chris J. Benmore Jeffery L. Yarger

  2. Introduction • A candidate of polyamorphic material • Theory 1– defect-ordered crystal due to topological frustration (Kivelson et al.) • Theory 2– a mixture of nanocrystal and supercooled liquid (Hedoux et al.) • Theory 3– Transformation of one supercooled liquid to a glassy state of another liquid ( Tanaka et al.)

  3. Experiments • Fully deuterated P(OC6D5)3 and 67% deuterated P2/3(OC6D5)2+P1/3(OC6H5) were prepared • Neutron diffraction experiments were performed at low temperature (190K-250K) using GLAD at ANL • H/D substitution technique was used to elucidate the structural differences

  4. The temperatures at which the measurements were taken Tg:203 K Tc:238K Tm:294K

  5. Theory and data analysis (1) (2) where =1 if =H and =0 if =P, C or O (3)

  6. TPP molecule structure

  7. Measured neutron Intensity • Excellent signal • Slope is due to inelastic scattering

  8. Structure factor for D-TPP • Crystal • Glacial (c) Supercooled liquid (d) Glass (e) Liquid

  9. First order difference structure factors

  10. Total correlation function for D-TPP • Phenyl ring is more rigid in the glacial and glass compare to crystal • The main differences are observed at 3.0 and 4.5 Å

  11. Comparison of neutron scattering crystal data and a model structure

  12. Comparison of neutron scattering crystal data and a model structure

  13. Faber Ziman neutron weighting factors Normalized Faber Ziman neutron weighting factors for the first order difference DH(r) function shows the scattering signal is dominated by the C-H and H-H interactions. The total D(r) function for D-TPP has 10 weighted partial structure factors, the main contributions coming from C-H (41%) and C-C (25%).

  14. TPP molecule structure Black lines: C-H and H-H correlations between distances of 2.8 and 3.4Å

  15. Schematic picture of intermolecular hydrogen related bonds • Thin line: two shortest H-O intermolecular hydrogen bonds at 2.81 and 2.97 Å • Thick line: the shortest intermolecular C-H and H-H correlations below 3.15 Å

  16. Hydrogen related correlation functions • Crystal • Supercooled liquid • Glass • The peaks in the range of 2.8-3.2Å arise from intermolecular C-H or H-H correlations

  17. Different stages of glacial phase

  18. Explanations based on LPS • LPS – Locally preferred structure • LPS1– TPP molecule cluster which has a low local free energy due to its optimal molecular conformation (in glacial) • LPS2– TPP molecule cluster linked by two intermolecular hydrogen bonds (in crystal)

  19. Conclusions • Glacial phase is not a simple mixture of nanocrystalline and supercooled liquid • The neutron results show the most significant differences in structure between the glacial and crystalline states appear at 3.0 and 4.5 Å. These features are due to inter-phenyl ring C-H and H-H interactions, most probably associated with the formation of weak intermolecular hydrogen bonds observed in Raman scattering. • Intermolecular hydrogen bonds can be formed through a slight loss of rigidity in the phenyl ring.

  20. Future Work • Investigate the structure evolution of the glacial state as a function of time using neutron and x-ray scattering experiments

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