Structural characterization of further high temperature superionic phases of Ag2HgI4 and Cu2HgI4

Authors
Citation
S. Hull et Da. Keen, Structural characterization of further high temperature superionic phases of Ag2HgI4 and Cu2HgI4, J PHYS-COND, 13(24), 2001, pp. 5597-5610
Citations number
45
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
JOURNAL OF PHYSICS-CONDENSED MATTER
ISSN journal
09538984 → ACNP
Volume
13
Issue
24
Year of publication
2001
Pages
5597 - 5610
Database
ISI
SICI code
0953-8984(20010618)13:24<5597:SCOFHT>2.0.ZU;2-9
Abstract
The high temperature crystal structure of the superionic compounds Ag2HgI4 and Cu2HgI4 has been investigated using powder neutron diffraction. In addi tion to the widely studied beta --> alpha superionic transitions observed i n both compounds just above ambient temperature, we have characterized the transitions to phases (labelled S) in Ag2HgI4 and Cu2HgI4 which occur at si milar to 410 and similar to 578 K, respectively. Prior to melting, Ag2HgI4 undergoes an additional transition at similar to 445 K to a phase labelled epsilon. The crystal structure of the delta phases comprises a slightly dis torted h.c.p. anion sublattice with the two cation species dynamically diso rdered over the octahedral and tetrahedral interstices. In epsilon -Ag2HgI4 the cations are distributed over the tetrahedral and trigonal interstices formed by a b.c.c. anion sublattice and can, therefore, be considered to be a 'cation-deficient' alpha -AgI-type superionic phase. The implications of these experimental findings in the wider context of the family of copper- and silver-based superionic conductors and for previous suggestions of 'unu sual' behaviour of the alpha <----> delta transition are discussed.