title: Control of Multipolar and Orbital Order in Perovskite-like [C(NH2)3]CuxCd1-x(HCOO)3 Metal-Organic Frameworks.
abstract: We study the compositional dependence of molecular orientation (multipolar) and orbital (quadrupolar) order in the perovskite-like metal-organic frameworks [C(NH2)3]CuxCd1-x(HCOO)3. Upon increasing the fraction x of Jahn-Teller-active Cu(2+), we observe an orbital disorder/order transition and a multipolar reorientation transition, each occurring at distinct critical compositions xo = 0.45(5) and xm = 0.55(5). We attribute these transitions to a combination of size, charge distribution, and percolation effects. Our results establish the accessibility in formate perovskites of novel structural degrees of freedom beyond the familiar dipolar terms responsible for (anti)ferroelectric order. We discuss the implications of cooperative quadrupolar and multipolar states for the design of relaxor-like hybrid perovskites.
authors.affiliation: Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QR, U.K.
authors.forename: Nicole L
authors.initials: NL
authors.lastname: Evans
authors.affiliation: Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QR, U.K.
authors.forename: Peter M M
authors.initials: PM
authors.lastname: Thygesen
authors.affiliation: Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QR, U.K.
authors.forename: Hanna L B
authors.initials: HL
authors.lastname: Boström
authors.affiliation: Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QR, U.K.
authors.forename: Emily M
authors.initials: EM
authors.lastname: Reynolds
authors.affiliation: Laboratory of Crystallography, University of Bayreuth , D-95440 Bayreuth, Germany.
authors.forename: Ines E
authors.initials: IE
authors.lastname: Collings
authors.affiliation: School of Physics and Astronomy, Queen Mary, University of London , 327 Mile End Road, London E1 4NS, U.K.
authors.forename: Anthony E
authors.initials: AE
authors.lastname: Phillips
authors.affiliation: Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QR, U.K.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Goodwin