Solid materials are commonly classified as crystalline or amorphous based on the presence or absence of long-range order.Metal-organic frameworks (MOFs), like other solids,also display markedly different properties and functions in these two phases. Here, we identify a previously unrecognized structural state that retains long-range in-plane translational order while losing order along the stacking direction. Hypothesized since 1941 but not experimentally verified, this intermediate phase emerges in a crystalline MOFs via controlled thermal desolvation, which selectively disrupts the intrinsically weak interlayer interactions while preserving macroscopic structural coherence. Although the resulting material appears amorphous under conventional characterization, systematic synchrotron PXRD, total X-ray scattering, and low-dose high resolution TEM reveal clear in-plane periodicity. This material spontaneously delaminates in water into uniform, high-quality two-dimensional crystalline nanosheets, forming stable colloidal suspensions and exhibiting superlubricity comparable to graphene - but at less than 0.1

The interest in spin crossover for solid-state cooling is growing. We investigate the spin crossover transitions of [Fe(pyridine)2Fe(CN)5NO] and [Fe(pyrazine)Fe(CN)5NO] by single-crystal X-ray diffraction, high-pressure X-ray diffraction, magnetometry, and high-pressure calorimetry. The dehydrated form of the latter compound shows a reversible cooling effect (∆Tad,rev) of ∼15K at 1.2 kbar. This is high in the context of other reported spin-crossover barocalorics, and competitive within the field at large. The excellent performance results from a large barocaloric coefficient (dT1/2/dp = 35K kbar−1). In addition, the one-pot synthesis is simple and free from toxic solvents.

There is increasing need for higher performance dielectric polymers for devices in power conversion systems for renewable energy generation and electric vehicles. In particular, materials with higher dielectric permittivity, lower loss and the ability to operate at higher temperatures. We have developed a counter intuitive method to achieve this, the melt blending of multiple immiscible polymers, in an approach that mimics high entropy materials design. We demonstrate that using this approach we can significantly exceed the rule-of-mixtures for the dielectric constant (>250%), whilst surprisingly retaining a low loss tangent. The materials show increased thermal stability up to 150 °C, which opens up the possibility of the wider application of dielectric polymers. We provide a consistent model to describe the behaviour based on the use of polymers with different glass transition temperatures to frustrate the de-blending of the immiscible polymers during melt processing. This produces highly amorphous and disordered polymer blends with increased inter-chain spacing (free volume) and increased rotational freedom of the polar groups in polar nano regions. This approach has wide applicability to other polar polymer blends and is scalable.

The title paper [Phys. Rev. B 110, 064104 (2024)] examines the negative thermal expansion and phase transitions in ScF3 and related materials through density functional theory calculations. The calculations of negative thermal expansion in the noncubic materials are in error for two important reasons. First, these calculations use a formulation of Gr & uuml;neisen theory that is only applicable to isotropic systems. Not only is this formulation wrong, but the choice of volume change in the derivatives of phonon frequencies is automatically arbitrary. A second error is the neglect of LO/TO splitting of the phonon frequencies at zero wave vector, which in the software chosen by the authors leads to an error that spreads across the Brillouin zone. These are both common errors in the literature, which we wish to highlight so that future authors can perform these calculations correctly. We further make two comments on the interpretation of these results. First, in systems that show phase transitions, the thermal expansion is likely dominated by spontaneous strains associated with the phase transition and not through a tension-effect mechanism. Finally, we point out that negative thermal expansion in ScF3 is much better understood than acknowledged in the title paper. Indeed, on the basis of recent work, we can easily and automatically understand why the negative thermal expansion would be much reduced, should the thermal expansion be associated with a tension effect, in related materials that are distorted as a result of a displacive phase transition.

Our society is experiencing an accelerated technological transition to reach net zero emissions by 2050, where the decarbonization of heating and cooling systems is a key aspect. In this work, we describe two new solid-state barocaloric materials, [C12H25NH3](2)MnCl4 and [C12H25NH3](2)MnBr4, with colossal barocaloric effects of Delta S > 200 J K-1 kg(-1), which are already reversible under operating pressures of 500 bar. In addition, we introduce the first 3D printable barocaloric composite using a pressure transmitting matrix and thermal conductive additives, which is formed in the shape of a heat exchange gyroid. This innovative proof-of-concept demonstrates a new strategy to enhance the thermal performance, chemical stability and technological integration of the emerging family of barocaloric compounds. In addition, we identify emerging technologies (beyond traditional refrigeration) where thermal management is critical and that match the operating temperature and pressure range of the barocaloric materials obtained here, namely, lithium-ion batteries and hydrogen fuel cells.

Neutron diffraction studies of the low-temperature relaxor ferroelectric phases of [NH 4 ]M(HCO 2 ) 3 , where M = Mn 2+ and Zn 2+ , show that a third of the NH 4 + cations remain subtly structurally disordered to low temperature. All NH 4 + cations within the channels are well separated from each other, with significant hydrogen bonds only with the anionic M(HCO 2 ) 3 framework. Complementary studies of the dynamics using 2 H solid state NMR and quasielastic neutron scattering indicate significant rotational motion in both paraelectric and ferroelectric phases, which evolves gradually with increasing temperature with no abrupt change at the phase transition. Nudged elastic band calculations suggest that the activation barrier for flipping between “up” and “down” orientations of the NH 4 + cations is low in the ferroelectric phase, with the NH 4 + cations primarily interacting with the framework rather than neighbouring NH 4 + cations. It is likely this motion that is responsible for scrambling the NH 4 + cation orientation locally in the ferroelectric phase. We propose that this disorder, with the same basic motion active above and below the phase transition, induces the significant dielectric relaxation in these materials. This suggests that orientational disorder may be an effective substitution for compositional disorder commonly associated with relaxor ferroelectrics in molecular materials.

Methylammonium lead iodide crystallises in three phases. The high-temperature phase is cubic with a high degree of orientational disorder of the molecular ions. The intermediate phase shows progressive alignment of the molecules, but still with disorder.

Correction for ‘Local structure and lithium-ion diffusion pathway of cubic Li 7 La 3 Zr 2 O 12 studied by total scattering and the Reverse Monte Carlo method’ by Haolai Tian et al. , J. Mater. Chem. A , 2023, 11 , 25516–25533, https://doi.org/10.1039/D3TA04495E.

We report detailed structural studies of the low-temperature ferroelectric phases of [NH4]M(HCO2)3, where M = Mn2+ and Zn2+, finding that a third of the NH4+ cations remain subtly rotationally disordered to low temperature in both compounds. All NH4+ cations within the channels are well separated from each other, with significant hydrogen bonds only with the anionic M(HCO2)3 framework. Complementary studies of the dynamics using 2H solid state NMR and quasielastic neutron scattering indicate significant motion in both paraelectric and ferroelectric phases, which evolves gradually with increasing temperature with no abrupt change at the phase transition. Nudged elastic band calculations suggest that the activation barrier for flipping between “up” and “down” orientations of the NH4+ cations is low in the ferroelectric phase, with the NH4+ cations primarily interacting with the framework rather than the neighbouring molecular cations. It is likely this motion that is responsible for scrambling the NH4+ cation orientation locally in the ferroelectric phase. We propose that this disorder, with the same basic motion active above and below the phase transition, induces the significant dielectric relaxation associated with these materials’ relaxor-like dielectric properties.

Samarium hexaboride, SmB6, is a negative thermal expansion (NTE) material whose structure is similar to other known NTE materials such as the family of Prussian blues. In the Prussian blues, NTE is due to a phonon mechanism, but we recently showed from DFT calculations that this is unlikely in SmB6 (Li et al., Phys. Chem. Chem. Phys. 2023, 25, 10749). We now report experimental X-ray diffraction and pair distribution function analysis of this material in the temperature range 20-300 K. The interatomic distances shown by both methods are consistent with the NTE instead arising from an electronic effect, by which the samarium atoms lose electrons and thus have a smaller ionic radius as the temperature increases. Using X-ray diffraction and measurements of the pair distribution function we show that negative thermal expansion in SmB6 arises from charge transfer rather than the traditional tension effect.

Organometallic-sandwich salts are well-known materials that undergo order-disorder phase transitions, leading to a high-temperature phase characterized by the total or partial disorder of ionic species. Their potential for barocaloric applications has not previously been explored. Here, we focus on two salts derived from metallocenes with the formula [Cp2M][PF6] where Cp: cyclopentadienyl anion (C5H5)(-) and M: Fe3+ or Co3+. These molecular salts exhibit two solid-solid phase transitions, shifting from a well-ordered crystalline phase at low temperatures to an orientationally disordered phase in the case of the Fe-compound, and a partially disordered phase in the case of the Co-compound above room temperature. We find a significant entropy change (similar to 40 J K-1 kg(-1)) and a moderate volume change (similar to 2%) associated with these phase transitions. Additionally, we observe that these transitions are highly sensitive to external applied pressure, leading to substantial barocaloric effects (exceeding 20 K kbar(-1)). Very interestingly, we obtain substantial values for reversible adiabatic temperature change (Delta T-rev > 10 K) under an applied pressure as low as 1 kbar, comparable to those observed in the most promising barocaloric materials. We prove that the unique structure and chemical bonding of these sandwich organometallic cations are responsible for their interesting and unusual barocaloric response. These findings position the metallocenium family as promising candidates for eco-friendly solid-state refrigeration technologies.

This work introduces a completely rewritten version of the program RMCProfile (version 7), big-box, reverse Monte Carlo modelling software for analysis of total scattering data. The major new feature of RMCProfile7 is the ability to refine multiple phases simultaneously, which is relevant for many current research areas such as energy materials, catalysis and engineering. Other new features include improved support for molecular potentials and rigid-body refinements, as well as multiple different data sets. An empirical resolution correction and calculation of the pair distribution function as a back-Fourier transform are now also available. RMCProfile7 is freely available for download at https://rmcprofile.ornl.gov/.

Conventional vapour-compression cooling techniques are inefficient and environmentally damaging.Hydrohaloalkane refrigerants are greenhouse gases and ozone depleters, while cooling processes that use them comprise about 20% of global energy consumption and yield 10% of carbon emissions.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Using calculations of the phonon distribution in ScF3 across the whole of reciprocal space, we show that the important phonons for the negative thermal expansion in this material are those associated with the rigid unit modes (RUMs) and associated quasi-RUMs. We discuss the role of the bond-bending flexibility within the ScF6 octahedra, and how this enables other phonons to make an additional but ultimately much weaker contribution to negative thermal expansion. These results inform recent discussions on the role of correlated atomic motions in giving rise to negative thermal expansion in ScF3.

High-entropy order-disorder phase transitions can be used for efficient and eco-friendly barocaloric solid-state cooling. Here the barocaloric effect is reported in an archetypal plastic crystal, adamantane. Adamantane has a colossal isothermally reversible entropy change of 106 J K-1 kg(-1). Extremely low hysteresis means that this can be accessed at pressure differences less than 200 bar. Configurational entropy can only account for about 40% of the total entropy change; the remainder is due to vibrational effects. Using neutron spectroscopy and supercell lattice dynamics calculations, it is found that this vibrational entropy change is mainly caused by softening in the high-entropy phase of acoustic modes that correspond to molecular rotations. We attribute this difference in the dynamics to the contrast between an 'interlocked' state in the low-entropy phase and sphere-like behaviour in the high-entropy phase. Although adamantane is a simple van der Waals solid with near-spherical molecules, this approach can be leveraged for the design of more complex barocaloric molecular crystals. Moreover, this study shows that supercell lattice dynamics calculations can accurately map the effect of orientational disorder on the phonon spectrum, paving the way for studying the vibrational entropy, thermal conductivity, and other thermodynamic effects in more complex materials.

The cubic phase of Li 7 La 3 Zr 2 O 12 shows fast diffusion of the lithium ions. Combining total scattering measurements analysed by the RMC method with molecular dynamics simulations gives a detailed picture of the distribution of the Li + ions.

In the search for stable materials with high porosity, attention has moved toward atomic networks that utilize molecular linkages. PAF-1, with linkages of biphenyl moieties, forms an amorphous network with phenomenal porosity and stability. Until now there still has been no clear picture of its atomic structure. We report here on a study using both neutron scattering and molecular dynamics simulation methods. We demonstrate that PAF-1 forms a continuous random network, in which tetrahedral carbon sites are connected by the biphenyl linkers. The molecular dynamics simulations show local structure with avoidance of close contacts between hydrogen atoms. We observe a distinct peak in the scattering at Q = 0.45 angstrom(-1), corresponding to the first sharp diffraction peak in amorphous silica. This suggests there is structural analogy between the amorphous tetrahedral networks of PAF-1 and silica.

We report the results of a neutron powder diffraction study of the phase transitions in deuterated methylammonium lead iodide, with a focus on the system of orientational distortions of the framework of PbI6 octahedra. The results are analysed in terms of symmetry-adapted lattice strains and normal mode distortions. The higher-temperature cubic-tetragonal phase transition at 327 K is weakly discontinuous and nearly tricritical. The variations of rotation angles and spontaneous strains with temperature are consistent with a standard Landau theory treatment. The lower-temperature transition to the orthorhombic phase at 165 K is discontinuous, with two systems of octahedral rotations and internal distortions that together can be described by 5 order parameters of different symmetry. In this paper we quantify the various symmetry-breaking distortions and their variation with temperature, together with their relationship to the spontaneous strains, within the formalism of Landau theory. A number of curious results in the low-temperature phase are identified, particularly regarding distortion amplitudes that decrease rather than increase with lowering temperature.