[{"type":"speech","title":"Self-diffusion in amorphous silicon nitride","issued":{"date-parts":[["2006"]]},"author":[{"family":"Schmidt","given":"H."},{"family":"Gupta","given":"M."},{"family":"Bruns","given":"M."}],"note":"DPG Spring Meeting of the Divison Condensed Matter, 21st General Conf.of the Condensed Matter Division of the European Physical Society, Dresden, March 26-31, 2006 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.41(2006) MM 27.4","abstract":"Metal- and Material Physics\nSectional Programme Overview\nMM 27 Di\ufb00usion I\nTime: Thursday 10:15\u201311:15\nMM 27.1 Thu 10:15 IFW B\nTransient heterogeneity in long-range order kinetics with lim\u00a8\nited vacancy mobility \u2014 \u2022David Reith1 , Wolfgang Puschl1 ,\nFerdinand Haider2 , and Wolfgang Pfeiler1 \u2014 1 Institut f\u00a8r Mau\nterialphysik, Universit\u00a8t Wien, Boltzmanng. 5, AT-1090 Vienna, Austria\n\u2014 2 Institut f\u00a8r Physik, Universit\u00a8t Augsburg, Universit\u00a8tsstrasse 1, Du\n86159 Augsburg, Germany\nLimited availability and mobility of vacancies may imprint a heterogeneous character on phase transformations which are otherwise expected\nto be homogeneous. This e\ufb00ect was investigated by a MC residence\ntime algorithm for disorder-order and order-order transitions in longrange ordered intermetallics of L12 and B2 structure. The calculation\ncell was subdivided into coarse graining cells and heterogeneity assessed\nby the mean square deviation of the local long-range order parameter.\nA transient increase of this measure over the statistical \ufb02uctuation for\nthe respective annealing temperature was observed for the B2 structure,\nbut not in the L12 case. This can be understood in view of the majority\nsublattice as an easy di\ufb00usion highway. The e\ufb00ect in B2 is even more\npronounced when starting from a disordered state. For a homogenous\ncharacter of the kinetics to be restored, an earlier intuitive criterion relied on the overlap of regions bounded by the mean quadratic random\nwalk distances of neighboring vacancies. Whereas this condition is in fact\nmet at a very early stage in the kinetics, true homogeneity is reached only\nwhen a signi\ufb01cant fraction of lattice sites has been visited by a vacancy.\nMM 27.2 Thu 10:30 IFW B\nOrdering kinetics is a\ufb00ected when jump barrier heights depend\n\u00a8\non local environment \u2014 \u2022Martin Leitner1 , Wolfgang Puschl1 ,\nFerdinand Haider2 , and Wolfgang Pfeiler1 \u2014 1 Institut f\u00a8r Mau\nterialphysik, Universit\u00a8t Wien, Boltzmanng. 5, AT-1090 Vienna, Austria\n\u2014 2 Institut f\u00a8r Physik, Universit\u00a8t Augsburg, Universit\u00a8tsstrasse 1, Du\n86159 Augsburg, Germany\nKinetics of order-order transformations in a L12 long-range ordered\nmodel crystal was investigated by Monte-Carlo simulation employing a\nresidence-time algorithm. Atoms were supposed to jump into nearestneighbor vacancies. In doing so, they have to pass through a rectangular\nwindow of atoms which are nearest neighbors to both the initial and the\n\ufb01nal positions. ab initio calculations of jump pro\ufb01les [Mat. Res. Soc.\nSymp. Proc. 842, S5.28 (2005)] for Ni3 Al show that barrier heights are\nmarkedly in\ufb02uenced by the kind of atoms occupying this window as well\nas their relative position. These results were incorporated as a rule into\nthe MC algorithm, with a parameter characterizing the in\ufb02uence of the\nwindow atoms. If this parameter is increased from zero, three regimes\nof kinetic behavior can be discerned: a regime of \ufb01nite but small in\ufb02uence below a certain threshold, a critical region where behavior changes\nquickly and in a qualitative way, an asymptotic region where the kinetics\nis stable against a further increase. It is discussed under which conditions\nthe usual assumption of constant barrier height made in the literature\nwill have to be modi\ufb01ed.\nMM 27.3 Thu 10:45 IFW B\nNonisothermal Internal Oxidation of Iron in Palladium \u2014\n\u00a8\nIncomplete isothermal-isobaric internal oxidation of dilute homogeneous alloys is a frequently used experimental technique to measure the\ndi\ufb00usion coe\ufb03cient of oxygen in the base metal. Adopting this method,\nhowever, derivation of the Arrhenius equation requires a series of anneals\nat di\ufb00erent temperatures. In the present work, a recently introduced [1],\nsimpli\ufb01ed experimental procedure is applied to the binary Pd-Fe system:\nincomplete temperature-controlled isobaric internal oxidation. Mathematical evaluation of the time development of the subscale thickness,\nwhich follows from SEM micrographs of samples that are removed from\nthe furnace at several durations of the air annealing, is performed by\nmeans of an iterative computer model [2]. In this realistic process simulation, the sought quantity, i.e. the di\ufb00usivity DO of oxygen in palladium,\nis the \ufb01t parameter and found to be:\nDO = 0.532 \u00b7 exp (\u221218728.27\/T )\nHere, DO is expressed in cm2 \/s and temperature T ranges from 1073 to\n1473 K. This result is compared with literature references.\nRoom: IFW B\n[2] J. Gegner: New Computer Model for Internal Oxidation. Proc.\nMMT-2004, p. 1\/28-1\/37\nMM 27.4 Thu 11:00 IFW B\nSelf-di\ufb00usion in Amorphous Silicon Nitride \u2014 \u2022Harald\nSchmidt1 , Mukul Gupta2 , and Michael Bruns3 \u2014 1 Fakult\u00a8t f\u00a8r\na u\n42, D-38678 Clausthal-Zellerfeld, Germany \u2014 2 Laboratory for Neutron\n3\nAmorphous silicon nitride is a model system for a covalently bound\namorphous solid with extremely low atomic mobilities where reasonable\nvalues of self-di\ufb00usivities are still lacking. We used neutron re\ufb02ectometry on isotope enriched Si14 N4 \/Si15 N4 multilayers to determine nitrogen\n3\n3\nself-di\ufb00usivities ranging from 10\u221224 to 10\u221221 m2 \/s between 950 and 1250\nC. Time dependent di\ufb00usivities observed at 1150 o C indicate the presence of structural relaxation. For long annealing times (relaxed state)\nthe di\ufb00usivities follow an Arrhenius law with an activation enthalpy of\n3.6 eV. Possible di\ufb00usion mechanisms are discussed and the results are\ncompared to the Si and N di\ufb00usivities in polycrystalline silicon nitride\nas obtained by Secondary Ion Mass Spectrometry.","kit-publication-id":"230063947"}]