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1. Lower pressure phases and metastable states of superconducting photo-induced carbonaceous sulfur hydride

Author

Smith, G. Alexander, Collings, Ines E., Snider, Elliot, Smith, Dean, Petitgirard, Sylvain, Smith, Jesse, White, Melanie, Jones, Elyse, Ellison, Paul, Lawler, Keith V., Dias, Ranga P., and Salamat, Ashkan

Subjects
Condensed Matter - Superconductivity
Abstract

Room-temperature superconductivity was recently discovered in carbonaceous sulfur hydride (C-S-H) close to 3\,Mbar. We report significant differences in the superconducting response of C-S-H, with a maximum $T_{C}$ of 191(1)\,K, below a 1\,Mbar. Variations in intensity of the C-H Raman modes reveal carbon content can vary between crystals synthesized with the same photo-induced method. Synchrotron single crystal x-ray diffraction identifies polymorphism with increasing degrees of covalency. These unique metastable states are highly sensitive to thermodynamic pathways.

Published
2021

3. Persistent spin dynamics in the pressurized spin-liquid candidate YbMgGaO$_4$

Author

Majumder, Mayukh, Simutis, Gediminas, Collings, Ines E., Orain, Jean-Christophe, Dey, Tusharkanti, Li, Yuesheng, Gegenwart, Philipp, and Tsirlin, Alexander A.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

Single-crystal x-ray diffraction, density-functional band-structure calculations, and muon spin relaxation ($\mu$SR) are used to probe pressure evolution of the triangular spin-liquid candidate YbMgGaO$_4$. The rhombohedral crystal structure is retained up to at least 10 GPa and shows a nearly uniform compression along both in-plane and out-of-plane directions, whereas local distortions caused by the random distribution of Mg$^{2+}$ and Ga$^{3+}$ remain mostly unchanged. The $\mu$SR data confirm persistent spin dynamics up to 2.6 GPa and down to 250 mK with no change in the muon relaxation rate. Longitudinal-field $\mu$SR reveals power-law behavior of the spin-spin autocorrelation function, both at ambient pressure and upon compression., Comment: published version

Published
2019
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6. Compositional dependence of anomalous thermal expansion in perovskite-like ABX3 formates

Author

Collings, Ines E., Hill, Joshua A., Cairns, Andrew B., Cooper, Richard I., Thompson, Amber L., Parker, Julia E., Tang, Chiu C., and Goodwin, Andrew L.

Subjects
Condensed Matter - Materials Science
Abstract

The compositional dependence of thermal expansion behaviour in 19 different perovskite-like metal-organic frameworks (MOFs) of composition [AI][MII(HCOO)3] (A = alkylammonium cation; M = octahedrally-coordinated divalent metal) is studied using variable-temperature X-ray powder diffraction measurements. While all systems show essentially the same type of thermomechanical response-irrespective of their particular structural details-the magnitude of this response is shown to be a function of AI and MII cation radii, as well as the molecular anisotropy of AI. Flexibility is maximised for large MII and small AI, while the shape of AI has implications for the direction of framework hingeing., Comment: 11 pages, 7 figures, 2 tables

Published
2015
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7. Structure-property relationships in framework materials : anomalous mechanics by design

Author

Collings, Ines E.

Subjects
547
Abstract

Framework materials that contain molecular bridging ligands between metal nodes-as seen in coordination polymers-not only give rise to enhanced structural diversity, but also to a range of useful and unusual mechanical properties. This thesis demonstrates the general structure-property relationships that are developed for coordination polymers in order to enable prediction and design of their mechanical properties, and hence structural flexibility. Variable-temperature and -pressure diffraction experiments are employed for the determination of their mechanical properties, namely by calculating thermal expansion and compressibility coefficients. The anomalous and varied mechanical responses observed are rationalised by the important structural features, or the so-called mechanical building units (XBUs), of the coordination polymers. The XBUs are considered within the setting of framework topology, geometry, and composition in order to establish general design principles for targeting different degrees of flexibility within coordination polymers. The XBUs are identified first in silver(I) 2-methylimidazolate, Ag(mim), a framework which is comprised of structural motifs of varying strength, namely argentophilic interactions, hinge points and metal- ligand bonding. The anomalous mechanical responses in Ag(mim) are shown to be rationalised entirely by the XBUs present in the structure. The XBU abstraction is then applied to a range of other coordination polymers and shown to correspond directly with the anomalous responses known in these materials. The metal-ligand-metal linker XBU is investigated further in both cadmium imidazolate, Cd(imh, and zinc cyanide, Zn(CN)2. Here, the linker chemistries are completely different between the two frameworks, but the diamondoid arrangement of the linkers, and thus the topology, is the same. The structural responses of the two frameworks are examined to unravel the extent of topology- and chemistry-driven mechanics. It is found that the topology dominates the atomic displacements of both frameworks, indicating the existence of common soft-mode dynamics which are likely to extend to other coordination polymers with the same topology. The three-dimensional framework-hinging XBUs in zinc isonicotinate, Zn(ISNh, and indium deuterium terephthalate, InD(BDCh, are considered next. These frameworks have the same topology but contrasting framework geometries, evident from the differing cia-lattice parameter ratios. In this case, a geometric formalism is derived which can predict the direction of framework mechanical anisotropy in Zn(ISNh and InD(BDCh and other uniaxial coordination polymers. Finally, a family of ABX3-type transition metal(II) formates are investigated, where both the B-site and A-site cations are varied. The chemical modifications give rise to variations in B- or A-site cation sizes, which are found to correlate with the magnitude of mechanical responses. These structure-mechanical property relationships-based upon framework topology, geometry and composition- are presented in separate chapters, and in each case generalised so that they can be applied to a range of coordination polymers. Hence the' design principles determined here can provide the materials science community with an intuition on the type and magnitude of responses possible in these materials under different external stimuli.

Published
2014

8. Static disorder and local structure in zinc(II) isonicotinate, a quartzlike metal-organic framework

Author

Collings, Ines E., Tucker, Matthew G., Keen, David A., and Goodwin, Andrew L.

Subjects
Condensed Matter - Materials Science
Abstract

Using a combination of Rietveld and RMC refinement of neutron total scattering data, we find that the 10 K structure of zinc(II) isonicotinate shows strong evidence of static disorder. This disorder takes the form of transverse displacements of the isonicotinate ligand and results in elongated atomic displacement parameters and dampened oscillations of the experimental G(r). We analyse the RMC configurations using an approach derived from geometric algebra. Complications regarding the inclusion of hydrogenous guest molecules within the pore structure are discussed. This study highlights the way in which structural flexibility can give rise to multiple low-energy ground states in MOF-type materials., Comment: 8 pages, 7 figures

Published
2011

10. On the identification of hyperhydrated sodium chloride hydrates, stable at icy moon conditions

Author

Journaux, Baptiste, primary, Pakhomova, Anna, additional, Collings, Ines E., additional, Petitgirard, Sylvain, additional, Boffa Ballaran, Tiziana, additional, Brown, J. Michael, additional, Vance, Steven D., additional, Chariton, Stella, additional, Prakapenka, Vitali B., additional, Huang, Dongyang, additional, Ott, Jason, additional, Glazyrin, Konstantin, additional, Garbarino, Gaston, additional, Comboni, Davide, additional, and Hanfland, Michael, additional

Published
2023
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12. High-pressure single-crystal synchrotron X-ray diffraction study of lillianite

Author

Zucchini, Azzurra, Balic-Zunic, Tonci, Collings, Ines E., Hanfland, Michael, Comodi, Paola, Zucchini, Azzurra, Balic-Zunic, Tonci, Collings, Ines E., Hanfland, Michael, and Comodi, Paola

Abstract

In this paper, high-pressure data from a synchrotron X-ray diffraction study on a lillianite (Pb3Bi2S6) single crystal up to similar to 21 GPa are presented. A phase transition from lillianite (space group Bbmm, LP lillianite) to the high-pressure form beta-Pb3Bi2S6 (space group Pbnm, HP lillianite) was confirmed and bracketed between 4.90 and 4.92 GPa. The transition is reversible but of first-order with a hysteresis of similar to 2.8 GPa. It showed weak effects of pseudo-merohedral twinning that disappeared upon decompression, testifying to a full recovery of the single crystal of lillianite This makes lillianite an interesting shape-memory material.With a bulk modulus K-4.9 = 78(3) GPa and K' = 5.1(4), beta-Pb3Bi2S6 is markedly less compressible than lillianite [K-0 = 44(2) GPa, K' = 7(1)]. Compressional anisotropy increases markedly in beta-Pb3Bi2S6 with compressibility along the b axis [M-0b = 130(6) GPa and M-b' = 19(3) in lillianite, M-4.9b = 145(4) GPa and M-b' = 16.0(7) in beta-Pb3Bi2S6] significantly larger than that along the other two axes [M-0a = 118(5) GPa, M-a' = 21(3), M-0c = 139(12) GPa, and M-c' = 31(10) in lillianite, M-4.9a = 242(12) GPa, M-a' = 8(1), M-4.9c = 242(5) GPa, and M-c' = 29(1) in beta-Pb3Bi2S6].The behavior of lillianite at high pressure is an interesting case study in relation to non-quenchable ultrahigh-pressure phases likely occurring in the inner Earth, like post-perovskite MgSiO3, the oxide homologue N = 1 of the lillianite series. The beta-Pb3Bi2S6 structure, on the other hand, is the N = 3 homologue of the meneghinite series to which the higher-pressure modification of the post-perovskite structure also belongs (homologue N = 1). This makes the two forms of Pb3Bi2S6 potential equivalents of high- and ultrahigh-pressure Mg silicates that could occur both in the deep earth and in other rocky extrasolar planetary bodies.

Published
2022

13. Effect of Alkali and Trivalent Metal Ions on the High-Pressure Phase Transition of [C2H5NH3]MI0.5MIII0.5(HCOO)3 (MI = Na, K and MIII = Cr, Al) Heterometallic Perovskites

Author

Ptak, Maciej, Svane, Katrine L., Collings, Ines E., and Paraguassu, Waldeci

Subjects
Article
Abstract

We report the high-pressure behavior of two perovskite-like metal formate frameworks with the ethylammonium cation (EtAKCr and EtANaAl) and compare them to previously reported data for EtANaCr. High-pressure single-crystal X-ray diffraction and Raman data for EtAKCr show the occurrence of two high-pressure phase transitions observed at 0.75(16) and 2.4(2) GPa. The first phase transition involves strong compression and distortion of the KO6 subnetwork followed by rearrangement of the −CH2CH3 groups from the ethylammonium cations, while the second involves octahedral tilting to further reduce pore volume, accompanied by further configurational changes of the alkyl chains. Both transitions retain the ambient P21/n symmetry. We also correlate and discuss the influence of structural properties (distortion parameters, bulk modulus, tolerance factors, and compressibility) and parameters calculated by using density functional theory (vibrational entropy, site-projected phonon density of states, and hydrogen bonding energy) on the occurrence and properties of structural phase transitions observed in this class of metal formates.

Published
2020

15. Metal–organic frameworks under pressure.

Author

Collings, Ines E. and Goodwin, Andrew L.

Subjects
*METAL-organic frameworks, *PRESSURE, *WATER pressure, *COMPRESSIBILITY, *AMORPHIZATION, *EXPERIMENTAL design
Abstract

Metal–organic frameworks (MOFs) are a broad and interesting class of materials known for their mechanical flexibility. As such, their response to pressure is usually extreme and often counterintuitive. This tutorial review surveys the structural response of MOFs to pressure as observed experimentally. It describes the experimental tools exploited in high-pressure crystallographic measurements and highlights some of the experiment design choices that influence the actual physics probed in these measurements. The main focus of the review is a description of the key pressure-driven structural responses exhibited by MOFs: isosymmetric compression, including negative compressibility; symmetry-lowering transitions; changes in connectivity; amorphization; and inclusion of the pressure-transmitting medium within the MOF pores. The review concludes both by highlighting some functional implications of these responses and by flagging some future directions for the field. [ABSTRACT FROM AUTHOR]

Published
2019
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17. Host–Guest Hydrogen Bonding in High-Pressure Acetone Clathrate Hydrates: In Situ Single-Crystal X-ray Diffraction Study

Author

Pakhomova, Anna, primary, Collings, Ines E., additional, Journaux, Baptiste, additional, Petitgirard, Sylvain, additional, Boffa Ballaran, Tiziana, additional, Huang, Dongyang, additional, Ott, Jason, additional, Kurnosov, Alexander, additional, Hanfland, Michael, additional, Garbarino, Gaston, additional, and Comboni, Davide, additional

Published
2022
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18. Competing phases in the room-temperature M2(2,6-ndc)2(dabco) metal–organic framework thin film synthesis

Author

Hamon, Lucile, primary, Andrusenko, Iryna, additional, Borzì, Aurelio, additional, Stiefel, Michael, additional, Carl, Stephan, additional, Frison, Ruggero, additional, Cervellino, Antonio, additional, Gemmi, Mauro, additional, Santiso-Quinones, Gustavo, additional, Hovestreydt, Eric, additional, Neels, Antonia, additional, and Collings, Ines E., additional

Published
2022
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19. Carbon content drives high temperature superconductivity in a carbonaceous sulfur hydride below 100 GPa

Author

Smith, G. Alexander, primary, Collings, Ines E., additional, Snider, Elliot, additional, Smith, Dean, additional, Petitgirard, Sylvain, additional, Smith, Jesse S., additional, White, Melanie, additional, Jones, Elyse, additional, Ellison, Paul, additional, Lawler, Keith V., additional, Dias, Ranga P., additional, and Salamat, Ashkan, additional

Published
2022
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22. Probing the Influence of Defects, Hydration, and Composition on Prussian Blue Analogues with Pressure

Author

Boström, Hanna, Collings, Ines E., Daisenberger, Dominik, Ridley, Christopher J., Funnell, Nicholas P., Cairns, Andrew B., Boström, Hanna, Collings, Ines E., Daisenberger, Dominik, Ridley, Christopher J., Funnell, Nicholas P., and Cairns, Andrew B.

Abstract

The vast compositional space of Prussian blue analogues (PBAs), formula A(x)M[M'(CN)(6)](y)center dot nH(2)O, allows for a diverse range of functionality. Yet, the interplay between composition and physical properties-e.g., flexibility and propensity for phase transitions-is still largely unknown, despite its fundamental and industrial relevance. Here we use variable-pressure X-ray and neutron diffraction to explore how key structural features, i.e., defects, hydration, and composition, influence the compressibility and phase behavior of PBAs. Defects enhance the flexibility, manifesting as a remarkably low bulk modulus (B-0 approximate to 6 GPa) for defective PBAs. Interstitial water increases B-0 and enables a pressure-induced phase transition in defective systems. Conversely, hydration does not alter the compressibility of stoichiometric MnPt(CN)(6), but changes the high-pressure phase transitions, suggesting an interplay between low-energy distortions. AMnCo(CN)(6) (A(I) = Rb, Cs) transition from F (4) over bar 3m to P (4) over bar n2 upon compression due to octahedral tilting, and the critical pressure can be tuned by the A-site cation. At 1 GPa, the symmetry of Rb0.87Mn[Co(CN)(6)](0.91) is further lowered to the polar space group Pn by an improper ferroelectric mechanism. These fundamental insights aim to facilitate the rational design of PBAs for applications within a wide range of fields.

Published
2021
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24. Spin crossover in the Prussian blue analogue FePt(CN)(6 )induced by pressure or X-ray irradiation

Author

Boström, Hanna L. B., Cairns, Andrew B., Liu, Lei, Lazor, Peter, Collings, Ines E., Boström, Hanna L. B., Cairns, Andrew B., Liu, Lei, Lazor, Peter, and Collings, Ines E.

Abstract

The spin state of the Prussian blue analogue (FePtIV)-Pt-II (CN)(6) is investigated in response to temperature, pressure, and X-ray irradiation. White cooling to 10 K maintains the high-spin state of Fe-II, compression at ambient temperature induces a first-order spin-crossover (SCO) transition with a small hysteresis loop (p up arrow = 0.8 GPa, p down arrow= 0.6 GPa). In addition, the high-spin to low-spin transition can be initiated at lower pressure through increased X-ray irradiation. Our study highlights a cooperative SCO with moderate pressure in a porous Prussian blue analogue.

Published
2020
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28. Pressure-Induced Polymerization of Polycyclic Arene–Perfluoroarene Cocrystals: Single Crystal X-ray Diffraction Studies, Reaction Kinetics, and Design of Columnar Hydrofluorocarbons

Author

Friedrich, Alexandra, primary, Collings, Ines E., additional, Dziubek, Kamil F., additional, Fanetti, Samuele, additional, Radacki, Krzysztof, additional, Ruiz-Fuertes, Javier, additional, Pellicer-Porres, Julio, additional, Hanfland, Michael, additional, Sieh, Daniel, additional, Bini, Roberto, additional, Clark, Stewart J., additional, and Marder, Todd B., additional

Published
2020
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32. Charting the Metal-Dependent High-Pressure Stability of Bimetallic UiO-66 Materials

Author

Rogge, Sven M. J., primary, Yot, Pascal G., additional, Jacobsen, Jannick, additional, Muniz-Miranda, Francesco, additional, Vandenbrande, Steven, additional, Gosch, Jonas, additional, Ortiz, Vanessa, additional, Collings, Ines E., additional, Devautour-Vinot, Sabine, additional, Maurin, Guillaume, additional, Stock, Norbert, additional, and Van Speybroeck, Veronique, additional

Published
2020
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35. Polymorphism in M(H2PO2)3 (M = V, Al, Ga) compounds with the perovskite-related ReO3 structure

Author

Evans, Hayden A, Deng, Zeyu, Collings, Ines E, Wu, Yue, Andrews, Jessica L, Pilar, Kartik, Tuffnell, Joshua M, Wu, Guang, Wang, John, Dutton, Siân E, Bristowe, Paul D, Seshadri, Ram, Cheetham, Anthony K, Deng, Zeyu [0000-0003-0109-9367], Wu, Yue [0000-0003-2874-8267], Dutton, Sian [0000-0003-0984-5504], Bristowe, Paul [0000-0002-3153-1387], and Apollo - University of Cambridge Repository

Subjects
0306 Physical Chemistry (incl. Structural)
Abstract

Trivalent metal hypophosphites with the general formula M(H2PO2)3 (M = V, Al, Ga) adopt the ReO3 structure, with each compound displaying two structural polymorphs. High-pressure synchrotron X-ray studies reveal a pressure-driven phase transition in Ga(H2PO2)3 that can be understood on the basis of ab initio thermodynamics.

Published
2019

36. Intrinsic Flexibility of the EMT Zeolite Framework Under Pressure

Author

Antony Nearchou, Cornelius, Mero-Lee U., Skelton, Jonathan M., Jones, Zöe L., Cairns, Andrew B., Collings, Ines E., Raithby, Paul R., Stephen Wells, and Asel Sartbaeva

Subjects
DYNAMICS, Biochemistry & Molecular Biology, crystallization, framework materials, Chemistry, Multidisciplinary, EMC-2, SOFTWARE, 0305 Organic Chemistry, Article, WINDOW, lcsh:QD241-441, TEMPLATE, lcsh:Organic chemistry, Crown Ethers, Pressure, PROGRAM, LOCATION, zeolite, Science & Technology, Organic Chemistry, flexibility window, Temperature, 18-CROWN-6, RAY-POWDER DIFFRACTION, X-ray diffraction, Chemistry, high pressure, FAU, Physical Sciences, Zeolites, compressibility, crystallisation, lattice dynamics, Life Sciences & Biomedicine
Abstract

The roles of organic additives in the assembly and crystallisation of zeolites are still not fully understood. This is important when attempting to prepare novel frameworks to produce new zeolites. We consider 18-crown-6 ether (18C6) as an additive, which has previously been shown to differentiate between the zeolite EMC-2 (EMT) and faujasite (FAU) frameworks. However, it is unclear whether this distinction is dictated by influences on the metastable free-energy landscape or geometric templating. Using high-pressure synchrotron X-ray diffraction, we have observed that the presence of 18C6 does not impact the EMT framework flexibility&mdash, agreeing with our previous geometric simulations and suggesting that 18C6 does not behave as a geometric template. This was further studied by computational modelling using solid-state density-functional theory and lattice dynamics calculations. It is shown that the lattice energy of FAU is lower than EMT, but is strongly impacted by the presence of solvent/guest molecules in the framework. Furthermore, the EMT topology possesses a greater vibrational entropy and is stabilised by free energy at a finite temperature. Overall, these findings demonstrate that the role of the 18C6 additive is to influence the free energy of crystallisation to assemble the EMT framework as opposed to FAU.

Published
2019
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37. Raman and single-crystal X-ray diffraction evidence of pressure-induced phase transitions in a perovskite-like framework of [(C H ) N] [Mn(N(CN) ) ]

Author

Mączka, Mirosław, Collings, Ines E., Leite, Fabio Furtado, and Paraguassu, Waldeci

Subjects
Materials science, Triclinic crystal system, Inorganic Chemistry, chemistry.chemical_compound, symbols.namesake, Crystallography, chemistry, Phase (matter), X-ray crystallography, symbols, Raman spectroscopy, Dicyanamide, Single crystal, Monoclinic crystal system, Perovskite (structure)
Abstract

The [TPrA][Mn(dca) ] perovskite shows highly anisotropic compression and the presence of three pressure-induced phase transitions near 0.4, 3 and 5 GPa into lower symmetry phases., We report complementary high-pressure Raman and single-crystal X-ray diffraction studies of a perovskite-like dicyanamide framework of [(C H ) N][Mn(N(CN) ) ] ([TPrA][Mn(dca) ]). Our studies show that the bulk modulus of the ambient pressure 4̄2 phase is = 8.1(11) GPa, and the -plane compresses by 54.4(15) × 10 GPa and the -axis by 8.0(12) × 10 GPa , indicating the low stiffness of the framework and its highly anisotropic nature. [TPrA][Mn(dca) ] transforms near 0.4 GPa into the phase. The driving forces for this symmetry change are partial ordering of the dicyanamide ( ) linkers, off-center shifts of TPrA cations and large changes in the columnar shifts of the MnN octahedra within the -plane. Upon further increase of pressure, [TPrA][Mn(dca) ] undergoes symmetry-lowering transitions into a monoclinic phase (space group 2 / ) near 3 GPa and a triclinic phase near 5 GPa. The observed structural changes are, however, very subtle.

Published
2019
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38. Pressure-enhanced ferroelectric polarisation in a polar perovskite-like [C2H5NH3]Na0.5Cr0.5(HCOO)3 metal-organic framework

Author

Ptak, Maciej, Collings, Ines E., Svane, Katrine L., Sieradzki, Adam, Paraguassu, Waldeci, Maczka, Mirosław, Ptak, Maciej, Collings, Ines E., Svane, Katrine L., Sieradzki, Adam, Paraguassu, Waldeci, and Maczka, Mirosław

Abstract

We report the high-pressure structure-related properties of a ferroelectric heterometallic formate perovskite framework templated by the ethylammonium cation (CH3CH2NH3+, EtA+). High-pressure X-ray diffraction studies show a first-order structural phase transition at 3.6(2) GPa from the polar Pn ambient phase to a centrosymmetric P21/n high-pressure phase. A high-pressure Raman scattering experiment indicates the same transition in the 4.0-4.4 GPa range. The mechanism of the phase transition involves strong compression and distortion of the NaO6 subnetwork and a decrease in the space available for the accommodated EtA+ cations, resulting in a change in their configuration within the pores at 3.7 GPa. Using density functional theory the value of the ferroelectric polarisation within the ac plane is calculated to be 0.9 μC cm-2 at ambient pressure, increasing in magnitude to a value of 1.1 μC cm-2 at a pressure of 3 GPa before vanishing at the phase transition.

Published
2019

40. Local Structure of Ferroic Iron Formates at Low Temperature and High Pressure Studied by Mössbauer Spectroscopy

Author

Collings, Ines E., primary, Vasiukov, Denis M., additional, McCammon, Catherine A., additional, Dubrovinsky, Leonid, additional, Cerantola, Valerio, additional, Petitgirard, Sylvain, additional, Hübschle, Christian B., additional, Schönleber, Andreas, additional, Chernyshov, Dmitry, additional, van Smaalen, Sander, additional, and Dubrovinskaia, Natalia, additional

Published
2019
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41. Crystal structure compression and pressure-induced polymerization of arene-perfluoroarene co-crystals leading to columnar hydrofluorocarbons

Author

Friedrich, Alexandra, primary, Collings, Ines E., additional, Dziubek, Kamil, additional, Fanetti, Samuele, additional, Radacki, Krzysztof, additional, Ruiz-Fuertes, Javier, additional, Pellicer-Porres, Julio, additional, Hanfland, Michael, additional, Sieh, Daniel, additional, Bini, Roberto, additional, Clark, Stewart J., additional, and Marder, Todd B., additional

Published
2019
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47. Polymorphism in M(H2PO2)3 (M = V, Al, Ga) compounds with the perovskite-related ReO3 structure

Author

Evans, Hayden A., primary, Deng, Zeyu, additional, Collings, Ines E., additional, Wu, Yue, additional, Andrews, Jessica L., additional, Pilar, Kartik, additional, Tuffnell, Joshua M., additional, Wu, Guang, additional, Wang, John, additional, Dutton, Siân E., additional, Bristowe, Paul D., additional, Seshadri, Ram, additional, and Cheetham, Anthony K., additional

Published
2019
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48. Crystal Structure and Non‐Hydrostatic Stress‐Induced Phase Transition of Urotropine Under High Pressure.

Author

Guńka, Piotr A., Olejniczak, Anna, Fanetti, Samuele, Bini, Roberto, Collings, Ines E., Svitlyk, Volodymyr, and Dziubek, Kamil F.

Subjects
PHASE transitions, FIRST-order phase transitions, CRYSTAL structure, ATOMIC models, CHEMICAL bond lengths, EQUATIONS of state
Abstract

High‐pressure behavior of hexamethylenetetramine (urotropine) was studied in situ using angle‐dispersive single‐crystal synchrotron X‐ray diffraction (XRD) and Fourier‐transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure‐transmitting media to study the effect of deviatoric stress on phase transformations. Up to 4 GPa significant damping of molecular librations and atomic thermal motion was observed. A first‐order phase transition to a tetragonal structure was observed with an onset at approximately 12.5 GPa and characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non‐hydrostatic conditions, induced by deviatoric or uniaxial stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage‐like molecules and may be considered a common feature of such systems. DFT computations were performed to model urotropine equation of state and pressure dependence of vibrational modes. The first successful Hirshfeld atom refinements carried out for high‐pressure diffraction data are reported. The refinements yielded more realistic C−H bond lengths than the independent atom model even though the high‐pressure diffraction data are incomplete. [ABSTRACT FROM AUTHOR]

Published
2021
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49. Spin crossover in the Prussian blue analogue FePt(CN)6 induced by pressure or X-ray irradiation.

Author

Boström, Hanna L. B., Cairns, Andrew B., Liu, Lei, Lazor, Peter, and Collings, Ines E.

Subjects
PRUSSIAN blue, SPIN crossover, X-rays, IRRADIATION, HYSTERESIS loop
Abstract

The spin state of the Prussian blue analogue FeIIPtIV(CN)6 is investigated in response to temperature, pressure, and X-ray irradiation. While cooling to 10 K maintains the high-spin state of FeII, compression at ambient temperature induces a first-order spin-crossover (SCO) transition with a small hysteresis loop (p↑ = 0.8 GPa, p↓ = 0.6 GPa). In addition, the high-spin to low-spin transition can be initiated at lower pressure through increased X-ray irradiation. Our study highlights a cooperative SCO with moderate pressure in a porous Prussian blue analogue. [ABSTRACT FROM AUTHOR]

Published
2020
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