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SUMMARY:Comparison of thermal expansion of Tc and Re salts.
DTSTART;VALUE=DATE-TIME:20171102T050000Z
DTEND;VALUE=DATE-TIME:20171102T051500Z
DTSTAMP;VALUE=DATE-TIME:20260305T170738Z
UID:indico-contribution-1134@events01.synchrotron.org.au
DESCRIPTION:Speakers: Gordon Thorogood (ANSTO)\n99Tc is the most significa
 nt long-lived product of uranium fission\, producing the largest fraction 
 of the total long-lived radiation emissions of nuclear waste.  Tc 7+ compo
 unds are highly mobile in the environment.  Relatively little is known reg
 arding the solid state chemistry of Tc. Recently we studied the structural
  properties of (NH4)TcO4 (Tc7+) and confirmed that this is isostructural w
 ith (NH4)ReO4 adopting a tetragonal scheelite type structure in space grou
 p I41/a.  The unit cell parameters of (NH4)TcO4 are strongly temperature d
 ependent with the structure showing negative thermal expansion along both 
 the a- and c-axis\, albeit at different temperatures  This behavior is sig
 nificantly different to that previously reported for the isostructural oxi
 de (NH4)ReO4\, although we note that the data for (NH4)ReO4 was collected 
 at much lower resolution.  Nevertheless it is clear in the literature that
  the thermal expansion behavior of (NH4)ReO4 is highly anisotropic.  Despi
 te the difference in the thermal expansion between what we have observed f
 or (NH4)TcO4 and that described by others for (NH4)ReO4 it is likely that 
 the origin of the anomalous thermal expansion in is the same in both cases
 \, namely it is a consequence of re-orientation of the ammonium ions in th
 e surrounding cage of eight oxygen atoms.  To verify this for (NH4)TcO4 re
 quires we replace the ammonium cation with another small cation.  Therefor
 e we have compared the thermal behavior of AReO4 with ATcO4 to determine i
 f Re oxides are suitable surrogates to predict the behavior of Tc oxides a
 nd how they may behave in the environment.\n\nhttps://events01.synchrotron
 .org.au/event/51/contributions/1134/
LOCATION:
URL:https://events01.synchrotron.org.au/event/51/contributions/1134/
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