H. Giefers, University of Paderborn Introduction XAFS 12 in Malmö 24. June 2003 High-pressure EXAFS and XRD investigation of unit cell parameters of SnO Hubertus Giefers Physics Department, University of Paderborn, D Paderborn, Germany

H. Giefers, University of Paderborn Survey  SnO under pressure  Energy dispersive X-ray diffraction (EDXRD) of SnO  EXAFS of SnO under high pressure  Combination of EXAFS and EDXRD results for determination of z(Sn)  Conclusion & Acknowledgment

H. Giefers, University of Paderborn SnO under pressure D.M. Adams et al., Phys. Rev. B46, (1992). N.R. Serebryanaya et al., Dokl. Akad. Nauk SSSR 187, 307 (1969). E.V. Kapitanov, E.N. Yakovlev, Phys. Stat. Sol. A51, 641 (1979). a b c c a b - only a few high pressure (HP) studies on SnO in the literature - a tetragonal to orthorhombic phase transition is controversially discussed - no HP study on the atom position parameter z(Sn) is reported in the literature

H. Giefers, University of Paderborn Energy dispersive X-ray diffraction (EDXRD) of SnO High pressure (HP) EDXRD at beamline F3 at HASYLAB/DESY - EDXRD spectra recorded with lN 2 cooled Ge-detector - in this case beam: 0.2×0.2 mm 2 - diamond anvil cell - liquid N 2 as pressure transmitting medium - Gold powder as pressure marker - sample size Ø 0.4 mm 2

H. Giefers, University of Paderborn Energy dispersive X-ray diffraction (EDXRD) of SnO - strong texture with c-axis parallel to load axis - no obvious phase transition with pressure - but: lines (hkl) with h≠k broaden with pressure - the broadening depends on the pressure transmitting medium - we attribute this line broadening to nonhydrostatic conditions in the HP cell - SnO is very sensitive to shear stress

H. Giefers, University of Paderborn Birch equation-of-state for SnO: K 0 = 33.5(11) GPa K 0 ‘ = 6.1(5) compared to SnO 2 with K 0 = 205 GPa K 0 ‘ = 3.1 due to the strong preferred orientation of SnO in the HP cell, the free atomic position parameter z(Sn) could not be determined from the diffraction intensities that is the reason why we performed the EXAFS study Energy dispersive X-ray diffraction (EDXRD) of SnO

H. Giefers, University of Paderborn EXAFS of SnO under high pressure - versatile high pressure cell with B 4 C anvils - anvil flat diameter 2.5 mm - sample diameter 1.3 mm - gasket material Cu - polyethylene as pressure transmitting medium - Ag powder as pressure marker - pressure determination with EXAFS of Ag at Ag-K edge (25.5 keV)

H. Giefers, University of Paderborn EXAFS of SnO under high pressure EXAFS at beamline X1 at HASYLAB/DESY - Si (311) double monochromator - energy resolution of 14 eV at 29 keV - EXAFS at Sn-K edge (29.2 keV) - beam size of 0.8×0.8 mm 2

H. Giefers, University of Paderborn EXAFS of SnO under high pressure EXAFS of: sample SnO and pressure marker Ag together in the HP cell

H. Giefers, University of Paderborn EXAFS of SnO under high pressure

H. Giefers, University of Paderborn EXAFS of SnO under high pressure - the Sn-O distance decreases only by about 2 % - compressibility of the Sn-O bonding is quite small - the decrease is linear with pressure - the 2 nd cumulant decreases continuously with pressure → contradicts a phase transition to ortho- rhombic structure

H. Giefers, University of Paderborn Combination of EXAFS and EDXRD results of SnO - a and c from EDXRD - R Sn-O from EXAFS - z(Sn) increases due to the strong compression of the c-axis and the small reduction of the Sn-O distance - when the Sn-O-Sn layers come closer with pressure the repulsion increases and the increase of z(Sn) flattens in the same way as the decrease of the c-axis

H. Giefers, University of Paderborn Conclusion & Acknowledgment - SnO shows no obvious tetragonal to orthorhombic phase transiton with lN 2 as pressure transmitting medium under pressure - XRD line broadenings are induced by nonhydrostatic conditions in the HP cell - SnO is very sensitive to shear stresses - the combination of XRD and EXAFS reveals all 3 cell parameters (a, c, z(Sn)) of SnO under pressure Thanks to - Felix Porsch - Gerhard Wortmann - Edmund Welter and the EXAFS HASYLAB team