title: Rational design of materials with extreme negative compressibility: selective soft-mode frustration in KMn[Ag(CN)2]3.
abstract: We show that KMn[Ag(CN)(2)](3) exhibits the strongest negative linear compressibility (NLC) effect over the largest pressure range yet observed. Variable pressure neutron powder diffraction measurements reveal that its crystal lattice expands along the c axis of its trigonal cell under increasing hydrostatic pressure, while contracting along the a axis. This corresponds to a "wine-rack"-like mechanism for NLC that we find also results in anisotropic negative thermal expansion (NTE) in the same material. Inclusion of extra-framework K(+) counterions has minimal effect on framework flexibility (and hence the magnitude of NTE/NLC) but selectively frustrates the soft phonon modes responsible for destroying NLC in the related material Ag(3)[Co(CN)(6)].
authors.affiliation: Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, UK.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Cairns
authors.forename: Amber L
authors.initials: AL
authors.lastname: Thompson
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Tucker
authors.forename: Julien
authors.initials: J
authors.lastname: Haines
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Goodwin