Structures and Phase Transitions in Pertechnetates

Brendan J Kennedy; Sean Injac; Gordon J Thorogood; Helen E A Brand; Frederic Poineau

doi:10.1021/acs.inorgchem.9b01257

Structures and Phase Transitions in Pertechnetates

Inorg Chem. 2019 Aug 5;58(15):10119-10128. doi: 10.1021/acs.inorgchem.9b01257. Epub 2019 Jul 9.

Authors

Brendan J Kennedy¹, Sean Injac¹, Gordon J Thorogood², Helen E A Brand³, Frederic Poineau⁴

Affiliations

¹ School of Chemistry , F11 The University of Sydney , Sydney , New South Wales 2006 , Australia.
² Australian Nuclear Science and Technology Organisation , Lucas Heights , New South Wales 2234 , Australia.
³ Australian Synchrotron , Australian Nuclear Science and Technology Organisation, ANSTO , 800 Blackburn Road , Clayton , Victoria 3168 , Australia.
⁴ University of Nevada Las Vegas , Department of Chemistry and Biochemistry , 4505 Maryland Parkway , Las Vegas , Nevada 89154 . United States.

PMID: 31287289
DOI: 10.1021/acs.inorgchem.9b01257

Abstract

The temperature dependence of the structures of four pertechnetates (ATcO₄ A = Ag, Tl, Rb, Cs) from 90 K to their melting points is described. Synchrotron X-ray diffraction measurements show that RbTcO₄ undergoes a I4₁/a to I4₁/amd transition near 530 K that is associated with a change in the orientation of the TcO₄^- tetrahedra about the scheelite b axis. AgTcO₄ also exhibits a tetragonal scheelite type structure, and this is retained between 90 and 750 K, above which it melted. CsTcO₄ has an orthorhombic pseudo-scheelite structure at room temperature and this undergoes a first-order orthorhombic to tetragonal transformation (Pnma to I4₁/a) near 430 K. TlTcO₄ is isostructural with CsTcO₄ at 90 K, but the orthorhombic to tetragonal transformation proceeds via an intermediate orthorhombic phase. The different behavior found here and described previously for the analogous Re oxide TlReO₄ highlights the differences in the chemistry of these two systems.