Local structure of a switchable dielectric Prussian blue analogue

Duncan, Helen D.; Beake, Edward O. R.; Playford, Helen Y.; Dove, Martin T.; Phillips, Anthony E.

doi:10.1039/c7ce01883e

Cited by 19 publications

(13 citation statements)

References 33 publications

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“…6 Often, at least in the first phases found on cooling below the melting point, the disorder is dynamic, with the molecules or molecular ions undergoing rotational motion across a continuous distribution of molecular orientations, or jump rotations between a well-defined set of distinct orientations. Examples range from molecular crystals [1] such as fullerenes [2] to polyatomic ions in metal-organic frameworks [3] and even hemes in proteins [4]. Orientational disorder may lead to anomalous materials properties, such as reversible amorphisation under pressure [5] and giant barocaloric effects [6].…”

Section: Orientationally Disordered Crystalsmentioning

confidence: 99%

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Neutron scattering study of the orientational disorder in potassium cyanide

et al. 2020

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We report the results of a combined neutron diffraction and total scattering study of the orientational order-disorder phase transitions in potassium cyanide, KCN. The diffraction data are analysed in terms of the spontaneous strains that accompany the phase transitions. The total scattering data are analysed using the Reverse Monte Carlo method, which gives direct access to the distribution of atomic positions and hence molecular orientations in each phase. Incorporating information from diffuse scattering in this way provides a means to measure the coefficients of the orientation distribution function up to almost arbitrarily high orders, and furthermore has the advantage that this function is naturally positive everywhere. The results for the cubic phase show that the distribution of orientations never exceeds 25% difference from an isotropic distribution.

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Section: Orientationally Disordered Crystalsmentioning

confidence: 99%

“…( ) and N y , , 3 4 N 1 4 ( ) . The atomic structure of the partially-ordered Immm phase has atomic coordinates K (0, 0, 0) and ( ) with fractional occupancy of 1/12 for both atom types, as an over-simplified model in order to be able extract lattice parameters.…”

Section: Rietveld Analysis Of Kcn: Lattice Parameters and Spontaneousmentioning

confidence: 99%

Neutron scattering study of the orientational disorder in potassium cyanide

et al. 2020

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“…(2.1), this phase corresponds to ferroquadrupolar order. To a large extent, the focus of these earlier studies has been the evolution of dipolar order on cooling from room temperature, which is associated with an anomaly in the corresponding dielectric response [31,49,50]. While the imidazolium cations are free to rotate (within their confined plane) in the ambient R3m phase, in this low-temperature state each cation adopts a single orientation.…”

Section: (D) Monte Carlo Simulationsmentioning

confidence: 99%

Ferroic Multipolar Order and Disorder in Cyanoelpasolite Molecular Perovskites

Coates¹,

Gray²,

Bulled³

et al. 2018

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<div>We use a combination of variable-temperature high-resolution synchrotron X-ray powder diffraction measurements and Monte Carlo simulations to characterise the evolution of two different types of ferroic multipolar order in a series of cyano elpasolite molecular perovskites. We show that ferroquadrupolar order in [C3N2H5]2Rb[Co(CN)6] is a first-order process that is well described by a 4-state Potts model on the simple cubic lattice. Likewise, ferrooctupolar order in [NMe4]2B[Co(CN)6] (B = K, Rb, Cs) also emerges via a first-order transition that now corresponds to a 6-state Potts model. Hence, for these particular cases, the dominant symmetry breaking mechanisms are well understood in terms of simple statistical mechanical models. By varying composition, we find that the effective coupling between multipolar degrees of freedom—and hence the temperature at which ferromultipolar order emerges—can be tuned in a chemically sensible manner.</div><div><br></div>

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“…We here report measurements on the imidazolium salts (C 3 H 5 N 2 ) 2 K[M III (CN) 6 ], M = Fe,Co. We have previously measured the local 9 and long-range crystallographic structure 10 of these materials, while Zhang and co-workers have reported crystallographic, electrical, and NMR data. 1,11 The target materials have three phases: a low-temperature (LT) phase crystallising in space group C2/c, where the imidazolium ions are ordered ( Fig.…”

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confidence: 99%

“…The crystallographic differences between these phases are extremely subtle: on cooling from the HT to the IT phase, the cyanide ions move slightly away from the lost mirror plane 10 and bend somewhat less at the metal ion. 9 On the other hand, 2 H-NMR shows a distinct shift in the dynamics at the HT-IT transition, which has been attributed to librations of the imidazolium ion out of its plane.…”

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confidence: 99%