H. Giefers, Universität Paderborn Einleitung Hochdruck-Kristallographie und Synthese 28. August 2003 Reaktionskinetik der Disproportionierung von SnO unter Druck Hubertus Giefers Universität Paderborn Department Physik AG Wortmann

H. Giefers, Universität Paderborn Survey 1.The system tin – oxide 2.The disproportionation of SnO at ambient pressure -set up -analysis of the spectra 3.The disproportionation of SnO under pressure 4.Summary 5.Acknowledgement

H. Giefers, Universität Paderborn 1. The system tin and tin oxide SnSnOSn 2 O 3 SnO 2 thermodyn. stable thermodyn. metastable thermodyn. metastable thermodyn. stable 7.31 g/cm³6.4 g/cm³7.03 g/cm³5.9 g/cm³ GPa bct Sn-I GPa bct Sn-II 45 - >120 GPa bcc Sn-III under hydrostatic pressure tetragonal  -PbO at least to 60 GPa under nonhydrostatic compression orthorhombic splitting triclinic structure a phase transition at ca. 9 GPa to unkown structure two low pressure phases: tetragonal and orthorhombic high pressure phase (>10 GPa) fcc

H. Giefers, Universität Paderborn 1. The system tin and tin oxyde under pressure our high pressure study on: SnO to 50 GPa tetragonal + orth. splitting z(Sn) was determined with EXAFS Sn 2 O 3 to 30 GPa triclinic, unkown SnO 2 to 50 GPa tetragonal, orthorhomic, cubic

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure SnO Sn 2 O 3 + Sn SnO 2 + Sn T > ca. 250 °C SnO is metastable and disproportionates to the 2 stable materials SnO 2 and Sn at elevated temperatures. Depending on temperature and also on the synthesis condition of SnO, the metastable compound Sn 2 O 3 is formed in the disproportionation reaction, which decomposes to SnO 2 and Sn at higher temperature.

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure The disproportionation of SnO was studied ex situ and in situ with Energy Dispersive X-Ray Diffraction (EDXRD) at beamline F3 at HASYLAB/DESY in Hamburg. 22

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure ←heating band ceramic spacer → collimator ↓ HP cell → ←thermocouple ↓ Al foil

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure irradiated SnO at 131 °C & 0 GPa after 15 h Gasket SnO decomposed SnO (shape of SR beam) Sample environment 0.2 mm

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure We analysed the normalized diffraction line intensities of the 3 samples SnO, Sn 2 O 3 and SnO 2. Sn was liquid or showed no reproducible line intensities. We used the fluoreszence lines of Sn to normalize the bragg peaks. This is an advantage of EDXRD. A time resolution of 100 s was achieved.

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure At low T (< 250 °C) SnO decomposes due to the synchrotron radiation(!) to nanocrystalline SnO 2 and Sn. No Sn 2 O 3 is produced. At high T (>370 °C) the reaction is dominated by thermal disproportionation. Sn 2 O 3 is produced.

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure Sharp-Hancock plot of the reaction progress 

H. Giefers, Universität Paderborn „activation energy E A “ radiation induced range : 27(2) kJ/mol thermal induced range: 225(32) kJ/mol Arrhenius: k = A exp(-E A /RT) 2. Disproportionation of SnO at ambient pressure - up to ca. 275 °C the in situ reaction is radiation induced - above 370 °C the in situ reaction is mainly thermal induced

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure t = 180 s t = 615 s t = 825 s t =1020 s t =1220 s t =1425 s t =1620 s - at beamline F3 it is possible to do angle dispersive XRD (ADXRD) - the CCD camera is from GeoForschungsZentrum Potsdam with a time resolution of 150 s per frame - one test measurement was carried out at ambient pressure in the HP cell

H. Giefers, Universität Paderborn 2. Disproportionation of SnO at ambient pressure ADXRD kinetic study on the disproportionation of SnO with 2 different SnO samples in the HP cell at 434 °C

H. Giefers, Universität Paderborn 3. Disproportionation of SnO at high pressure Reaction kinetics under pressure - high pressure cell made of a Ti-alloy - temperatures up to 500 °C can be reached - temperature at sample position was calibrated by the melting points of Pb, Sn, Zn - diamond flats of 1 mm and 0.5 mm were used - pressures of 20 GPa were reached - NaCl or MgO for pressure determination (Au was alloyed with Sn) - lN 2 as pressure transmitting medium

H. Giefers, Universität Paderborn under pressure: - no nanocrystalline SnO 2 and Sn at low T - no radiation induced disproportionation - no production of Sn 2 O 3 under pressure due to the low crystallographic density 3. Disproportionation of SnO at high pressure some examples under pressure

H. Giefers, Universität Paderborn 3. Disproportionation of SnO at high pressure Sharp-Hancock plot of m: reaction exponent k: reaction rate  : reaction progress

H. Giefers, Universität Paderborn 3. Disproportionation of SnO at high pressure - the reaction kinetic changes strongly under pressure - the reaction exponent m is very low at 3 GPa - in the measured p,T range the reaction exponent m is T independent reaction exponent m: diffusion m ≈ 0.5 phase-boundary ≈ 1 nucleation and growth ≈ 2

H. Giefers, Universität Paderborn The reaction rate k of the disproportionation of SnO depends on the phase of metallic Sn (liquid, Sn-I, Sn-II). 3. Disproportionation of SnO at high pressure

H. Giefers, Universität Paderborn 4. Summary - EDXRD provides a tool to study reaction kinetics in situ even at high pressure - results are: reaction rates k and reaction mechanism m (nucleation, growth…) the existence of intermediate products or not (Sn 2 O 3 ) the formation of high pressure phases at lower pressure (here SnO 2 -fcc)

H. Giefers, Universität Paderborn - Felix Porsch: EDXRD Messungen - H.-D. Niggemeier: ex situ Proben -Ulrich Ponkratz: ADXRD Messungen 5. Acknowledgement