Christian Bocker, Christian Rüssel Otto-Schott-Institut Universität Jena

1. „Recent results of nano crystallization in transparent glass-ceramics containing BaF2 crystallites“ Christian Bocker, Christian Rüssel Otto-Schott-Institut Universität Jena

2. Motivation • Transparent glass ceramics have numerous photonic applications • Nano crystals with narrow size distribution homogeneously in a glassy matrix • Investigation of nano crystals by electron microscopy (100 - x)(8 Al2O3 ∙ 16 K2O ∙ 2 Na2O ∙ 74 SiO2) ∙ x BaF2

3. Transparent glass ceramics

4. Crystallite size as a function of heat treatment temperature

5. Corrected crystallite-size distribution P.L. Goldsmith „The calculation of true particle size distributions from the sizes observed in a thin slice“, Brit. J. Appl. Phys. 18, 1967

6. Narrow crystallite-size distribution

7. Concentration of crystalline BaF2 as a function of temperature

8. Crystallite size as a function of time

9. Concentration of crystalline BaF2 as a function of time

10. Tg as a function of annealing time (at 500 °C)

11. diffusion barrier nucleus Model of nano crystallization residual glassy phase

12. Indirect prove for a layer around the crystallites Bright field TEM image Si Map 13.4 nm 16.9 nm 69.56 SiO2 - 7.52 Al2O3 - 15.04 K2O - 1.88 Na2O - 6 BaF2 annealed at 700 °C for 2 h

13. BaF2 glass-ceramics – EELS spectra Si-L2,3 Ba-N4,5

14. Simulation of Si Mapping around BaF2 nano crystal Hollow sphere SiO2 (inner Ø: 12 nm, 1 nm thick) Sphere BaF2 and SiO2 BaF2 Sphere (diameter: 12 nm) FWHM 13.1 nm FWHM 16 nm FWHM 10.3 nm

15. TEM micrograph of the sample annealed at 700 °C for 2 h Line scan length 100 nm

16. Line scan • Linescan at 120 kV (monochromated probe-corrected microscope) • Collection semi-angle 15 mrad, convergence semi angle 15 mrad • spot diameter: ca. 0,3 nm • Experiment: J.R. Jinschek @ DTU Denmark BaF2 crystal Si content [a.u.]

17. Viscosity as a function of temperature Sample with 6 mol% BaF2

18. Viscosity as a function of BaF2 concentration

19. Composition of the glasses • Assumption of 40% fluoride loss

20. Diffusion of fluoride and barium fluoride barium (1.3 ± 0.2) ∙ 10-15 m2∙s-1 (30 ± 3) ∙ 10-15 m2∙s-1 (4.5 ± 1.1) ∙ 10-15 m2∙s-1 (0.035 ± 0.008) ∙ 10‑15 m2∙s-1

21. Diffusion coefficient as a function of temperature

22. Activation energy of diffusion and viscosity

23. Conclusions • Narrow crystallite-size distribution observed in TEM micrographs • Proof of diffusion barrier around crystallites • Diffusion coefficient of fluoride two orders of magnitude larger than that of barium • Activation energy of diffusion of barium is about 85 kJ∙mol‑1 larger than that of fluoride • In comparison to the activation energy of viscosity: • In agreement within the limits of error for the activation energies of barium • Viscosity as a function of barium fluoride concentrationand temperature • How to solve the problem of the dependence of viscosity from the fluoride concentration taking into account the fluoride loss during preparing the glass?

24. Acknowledgement This project is funded by the EC

25. Appendix

26. 700 °C, 2 h Si content [a.u.] Line scan length: 106 nm (nm)

27. 700 °C, 2 h Si content [a.u.] (nm)

28. 700 °C, 2 h Si content [a.u.] (nm)

29. Determination of entropy jump frequencyt0 = 10-13 s jump distanceD = 0.2 nm barium: DS  17R fluorine: DS  11R

30. Stokes - Einstein

31. Glass with heat treatment at 640 °C for 40 h B3 B0

32. Contents • Motivation • Studies on crystallization • Viscosity • Diffusion • Recent results from IOM

33. Christian Bocker B6(3) 69.56 SiO2 - 7.52 Al2O3 - 15.04 K2O - 1.88 Na2O - 6 BaF2 glass annealed at 700°C for 2 hr

34. BaF2-Glass Ceramics – EELS spectra Si-L2,3 Ba-N4,5

35. B6(3), 700°C, 2h Line scan length: 106 nm Si content [a.u.] (nm)

36. B6(3), 700°C, 2h Si content [a.u.] (nm)

37. B6(3), 700°C, 2h Si content [a.u.] (nm)