Anthony E. Phillips

Zero thermal expansion in a flexible, stable framework : tetramethylammonium copper(I) zinc(II) cyanide.

Tetramethylammonium copper(I) zinc(II) cyanide, which consists of N(CH(3))(4)(+) ions trapped within a cristobalite-like metal cyanide framework, has been studied by variable-temperature powder and single-crystal X-ray diffraction. Its coefficient of thermal expansion is approximately zero over the temperature range 200-400 K and comparable with the best commercial zero thermal expansion materials. The atomic displacement parameters, apparent bond lengths, and structure of a low-temperature, low-symmetry phase reveal that the low-energy vibrational modes responsible for this behavior maintain approximately rigid Zn coordination tetrahedra but involve significant distortion of their Cu counterparts.

Ru-OSO coordination photogenerated at 100 K in tetraammineaqua(sulfur dioxide)ruthenium(II) (±)-camphorsulfonate.

The photoinduced O-bound coordination mode in RuSO(2) complexes, previously observed only at 13 K, has been generated at 100 K in tetraammineaqua(sulfur dioxide)ruthenium(II) (±)-camphorsulfonate. This coordination state, often denoted MS1, decays to the η(2)-bound MS2 state, with an estimated half-life of 3.4(8) h and a long-lived population of 2.9(4)% at 120 K.

Common origin of negative thermal expansion and other exotic properties in ceramic and hybrid materials

Hong Fang,1 Martin T. Dove,1, 2, 3, ∗ and Anthony E. Phillips2, 3 1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, U.K. 2Centre for Condensed Matter and Materials Physics, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, U.K. 3Materials Research Institute, Queen Mary University of London, Mile End Road, London, E1 4NS, U.K. (Dated: May 16, 2014)

Flexibility of zeolitic imidazolate framework structures studied by neutron total scattering and the reverse Monte Carlo method

The zeolitic imidazolate framework ZIF-4 undergoes an amorphization transition at about 600 K, and then transforms at about 700 K to ZIF-zni, the densest of the crystalline ZIFs. This series of long-range structural rearrangements must give a corresponding series of changes in the local structure, but these have not previously been directly investigated. Through analysis of neutron total diffraction data by reverse Monte Carlo modelling, we assess the changes in flexibility across this series, identifying the key modes of flexibility within ZIF-4 and the amorphous phase. We show that the ZnN4 tetrahedra remain relatively rigid, albeit less so than SiO4 tetrahedra in silicates. However, the extra degrees of freedom afforded by the imidazolate ligand, compared to silicate networks, vary substantially between phases, with a twisting motion out of the plane of the ligand being particularly important in the amorphous phase. Our results further demonstrate the feasibility of reverse Monte Carlo simulations for studying intermolecular interactions in solids, even in cases, such as the ZIFs, where the pair distribution function is dominated by intramolecular peaks.

Control of Multipolar and Orbital Order in Perovskite-like [C(NH2)3]CuxCd1–x(HCOO)3 Metal–Organic Frameworks

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.

Temperature-dependent pressure-induced softening in Zn(CN) 2

We study the temperature dependence of the pressure-induced softening in the negative thermal expansion material Zn(CN)

The heat capacity of matter beyond the Dulong–Petit value

{}_{2}

Bayesian analysis of the evidence for minor components in crystallographic models: an alternative to the Hamilton {\cal R} test

using neutron powder diffraction and molecular dynamics simulations. Both the simulation and experiment show that the pressure-induced softening only occurs above a minimum temperature and also weakens at high temperatures.

Local structure study of the orbital order/disorder transition in LaMnO3

We propose a simple new way to evaluate the effect of anharmonicity on a systems thermodynamic functions, such as heat capacity. In this approach, the contribution of all the potentially complicated anharmonic effects to the constant-volume heat capacity is evaluated using one parameter only: the coefficient of thermal expansion. Importantly, this approach is applicable not only to crystals, but also to glasses and viscous liquids. To support this proposal, we perform molecular dynamics simulations of several crystalline and amorphous solids as well as liquids, and find a good agreement between the results from theory and simulations. We observe an interesting non-monotonic behavior of the liquid heat capacity with a maximum, and explain this effect as being a result of competition between anharmonicity at low temperature and decreasing number of transverse modes at high temperature.

Crossover between tilt families and zero area thermal expansion in hybrid Prussian blue analogues

A simple test based on Bayesian statistics for the presence of minority populations in single-crystal structure refinement is presented. The test is illustrated by analysis of photocrystallographic experiments on single crystals of ruthenium-sulfur-dioxide-based complexes. In data sets collected after irradiation with light, conventional refinements of the populations of different metastable states to values below 4% are shown to be statistically significant. The results also confirm that the photo-induced states are absent from data collected in the dark.