Colossal Negative Area Compressibility in the Ferroelastic Framework Cu(tcm).

Copper(I) tricyanomethanide, Cu(tcm), is a flexible framework material that exhibits the strongest negative area compressibility (NAC) effect ever observed─a remarkable property with potential applications in pressure sensors, artificial muscles, and shock-absorbing devices. Under increasing pressure, Cu(tcm) undergoes two sequential phase transitions (tetragonal → orthorhombic → monoclinic): It has an initial tetragonal structure (4) at ambient conditions, but this structure only persists within a narrow pressure range; at 0.12(3) GPa, a pressure-induced ferroelastic phase transition occurs, transforming Cu(tcm) into a low-symmetry orthorhombic structure (2).

An extended thermal pressure equation of state for sodium fluoride.

The effect of pressure and temperature on the unit-cell volume of NaF has been measured by X-ray powder diffraction at ambient pressure between 12 and 300 K and neutron powder diffraction up to 5 GPa between 140 and 350 K. These data have been combined with high-pressure volume data at 300 and 950 K to 25 GPa and adiabatic bulk modulus data to 650 K to define an equation of state for NaF relating molar volume to both temperature and pressure. The model combines a fourth-order Birch-Murnaghan equation of state at 295 K with a Mie-Grüneisen-Debye model for thermal pressure.

Exploring the full range of N⋯I⋯X halogen-bonding interactions within a single compound using pressure.

The response of the trimethylammonium-iodinechloride and diiodide (TMA-ICl/I) crystal structures have been examined under high pressure using neutron powder diffraction. TMA-ICl exhibits impressive pressure-driven electronic flexibility, where the N⋯I-Cl interactions progressively encompass all the distances represented in analogous structures recorded in the Cambridge Structural Database. Comparison with the TMA-I complex reveals that this flexibility is owed to the electronegativity of the chlorine atom which induces increased distortion of the iodine electron cloud.

The pressure response of Jahn-Teller-distorted Prussian blue analogues.

Jahn-Teller (JT) distorted Cu-containing compounds often display interesting structural and functional behaviour upon compression. We use high-pressure X-ray and neutron diffraction to investigate four JT-distorted Prussian blue analogues: Cu[Co(CN)], CuPt(CN), and ACuCo(CN) (A = Rb, Cs), where the first two were studied in both their hydrated and dehydrated forms. All compounds are less compressible than the JT-inactive Mn-based counterparts, indicating a coupling between the electronic and mechanical properties.

Neutron scattering study of polyamorphic THF·17(HO) - toward a generalized picture of amorphous states and structures derived from clathrate hydrates.

From crystalline tetrahydrofuran clathrate hydrate, THF-CH (THF·17HO, cubic structure II), three distinct polyamorphs can be derived. First, THF-CH undergoes pressure-induced amorphization when pressurized to 1.3 GPa in the temperature range 77-140 K to a form which, in analogy to pure ice, may be called high-density amorphous (HDA).

Radiation effects, zero thermal expansion, and pressure-induced phase transition in CsMnCo(CN).

The Prussian blue analogue CsMnCo(CN) is studied using powder X-ray and neutron diffraction under variable temperature, pressure, and X-ray exposure. It retains cubic 4̄3 symmetry in the range 85-500 K with minimal thermal expansion, whereas a phase transition to 4̄2 occurs at ∼2 GPa, driven by octahedral tilting. A small lattice contraction occurs upon increased X-ray dose.

Phase behaviour of ammonium bromide-under high pressure and low temperature; an average and local structure study.

We revisit the pressure-induced order-disorder transition between phases II and IV in ammonium bromide-using neutron diffraction measurements to characterise both the average and local structures. We identify a very sluggish transition that does not proceed to full conversion and local structure correlations indicate a slight preference for ammonium cation ordering along ⟨110⟩ crystallographic directions, as pressure is increased. Simultaneous cooling below ambient temperature appears to facilitate the pressure-induced transition.

Direct evidence for distinct colour origins in ROY polymorphs.

ROY is one of the most well-studied families of crystal structures owing to it being the most polymorphic organic material on record. The various red, orange, and yellow colours of its crystal structures are widely-believed to originate from molecular conformation, though the orange needle (ON) polymorph is thought to be an exception. We report high-pressure, single-crystal X-ray measurements which provide direct experimental evidence that the colour origin in ON is intermolecular, revealing that the molecule undergoes minimal deformation but still exhibits a pronounced, reversible, pale orange → dark red colour change between ambient pressure and 4.

Extracting interface correlations from the pair distribution function of composite materials.

Using a non-negative matrix factorisation (NMF) approach, we show how the pair distribution function (PDF) of complex mixtures can be deconvolved into the contributions from the individual phase components and also the interface between phases. Our focus is on the model system Fe∥FeO. We establish proof-of-concept using idealised PDF data generated from established theory-driven models of the Fe∥FeO interface.

Probing the Influence of Defects, Hydration, and Composition on Prussian Blue Analogues with Pressure.

The vast compositional space of Prussian blue analogues (PBAs), formula AM[M'(CN)]·HO, allows for a diverse range of functionality. Yet, the interplay between composition and physical properties-e.g.

Structure and spectroscopy of methionyl-methionine for aquaculture.

The amino acid L-methionine is an essential amino acid and is commonly used as a feed supplement in terrestrial animals. It is less suitable for marine organisms because it is readily excreted. It is also highly water soluble and this results in loss of the feed and eutrophication of the water.

high pressure neutron diffraction and Raman spectroscopy of 20BaO-80TeO glass.

The short-range structure of 20BaO-80TeO glass was studied by high pressure neutron diffraction and high pressure Raman spectroscopy. Neutron diffraction measurements were performed at the PEARL instrument of the ISIS spallation neutron source up to a maximum pressure of 9.0 ± 0.

A simple system for neutron diffraction at 4 K and elevated pressures.

We describe a unique cryogen-free closed-cycle refrigerator system using a beryllium-copper VX1 variant of the Paris-Edinburgh press, which enables approximately 3 GPa to be generated on a sample volume of 66 mm, over the temperature range of 4 K-300 K. The main advantage of this system is its versatility; it has been designed to be fully compatible with the PEARL neutron powder-diffraction instrument at the ISIS facility, but is also compatible with several other instruments at the facility with minor modifications. We provide a full description of the system, along with representative data collected on PEARL from MnF at 13 K and 2.

Alloxan under pressure-squeezing an extremely dense molecular crystal structure.

The crystal structure of the small organic molecule, alloxan, has been explored using high-pressure neutron diffraction; its already efficiently-packed structure provides a 'chemical head-start' on the pressure experiment. At the highest pressure measured, alloxan reaches a density of 2.36 g cm-3-unprecedented for a C, H(D), N, O-containing organic material of appreciable molecular weight.

Nanocomposite structure of two-line ferrihydrite powder from total scattering.

Ferrihydrite is one of the most important iron-containing minerals on Earth. Yet determination of its atomic-scale structure has been frustrated by its intrinsically poor crystallinity. The key difficulty is that physically-different models can appear consistent with the same experimental data.

Elucidation of the pressure induced amorphization of tetrahydrofuran clathrate hydrate.

The type II clathrate hydrate (CH) THF·17 HO (THF = tetrahydrofuran) is known to amorphize on pressurization to ∼1.3 GPa in the temperature range 77-140 K. This seems to be related to the pressure induced amorphization (PIA) of hexagonal ice to high density amorphous (HDA) ice.

Negative Hydration Expansion in ZrW_{2}O_{8}: Microscopic Mechanism, Spaghetti Dynamics, and Negative Thermal Expansion.

We use a combination of x-ray diffraction, total scattering, and quantum mechanical calculations to determine the mechanism responsible for hydration-driven contraction in ZrW_{2}O_{8}. The inclusion of H_{2}O molecules within the ZrW_{2}O_{8} network drives the concerted formation of new W─O bonds to give one-dimensional (─W─O─)_{n} strings. The topology of the ZrW_{2}O_{8} network is such that there is no unique choice for the string trajectories: the same local changes in coordination can propagate with a large number of different periodicities.

In situ neutron diffraction study of the formation of HoGeO pyrochlore at high temperature and pressure.

The formation of the spin-ice pyrochlore HoGeO by two different high temperature, high pressure routes has been explored using in situ neutron diffraction. The first route involves the solid-state reaction of HoO and GeO, and formation of the pyrochlore phase is observed at 994(27) °C and 3.81(2) GPa, which are significantly milder conditions than those previously reported.

Mesoscale Polarization by Geometric Frustration in Columnar Supramolecular Crystals.

Columnar supramolecular phases with polarization along the columnar axis have potential for the development of ultrahigh-density memories as every single column might function as a memory element. By investigating structure and disorder for four columnar benzene-1,3,5-trisamides by total X-ray scattering and DFT calculations, we demonstrate that the column orientation, and thus the columnar dipole moment, is receptive to geometric frustration if the columns aggregate in a hexagonal rod packing. The frustration suppresses conventional antiferroelectric order and heightens the sensitivity towards collective intercolumnar packing effects.

Reversible piezochromism in a molecular wine-rack.

The highly-polymorphic, strongly-coloured 'ROY' system exhibits a yellow → orange → red piezochromic response under hydrostatic compression. The 'Y' (yellow) polymorph accommodates the effect of pressure via a wine-rack-type mechanism, made accessible by the conformational flexibility of the molecule, while retaining the crystal symmetry of the parent Y form. Decompression from 1.

Flexibility transition and guest-driven reconstruction in a ferroelastic metal-organic framework†Electronic supplementary information (ESI) available: Atomic coordinates and lattice parameter data. CCDC 1016797. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4ce01572jClick here for additional data file.

The metal-organic framework copper(i) tricyanomethanide, Cu(tcm), undergoes a ferroelastic transition on cooling below = 240 K. Thermal expansion measurements reveal an order-of-magnitude variation in framework flexibility across . The low-temperature phase α-Cu(tcm) exhibits colossal positive and negative thermal expansion that is the strongest ever reported for a framework material.