Introduction to the special issue on energy materials

Papers in this special issue focus on a broad range of research devoted to Energy Materials, investigating the role and application of structural science in one of the most important scientific challenges of our age: the identification of secure, sustainable and affordable sources of energy.

Metal–organic frameworks: the pressure is on

Metal–organic frameworks (MOFs) demonstrate a wide variety of behavior in their response to pressure, including anomalous mechanical properties, negative linear compressibility, pressure-induced crystal-to-crystal and crystal-to-amorphous structural transitions. The discovery of framework materials combining novel pressure responses and high mechanical stability is key in the quest for applications of MOFs at the industrial level.

Structural studies of metal–organic frameworks under high pressure

Here we present a review on the effect of high pressure on metal–organic framework materials.

Structure and spectroscopy of CuH prepared via borohydride reduction

We show by a combination of diffraction and spectroscopic methods that CuH produced by borohydride reduction of a Cu^II salt consists of a core of CuH with the Wurtzite structure and a shell of water. We also demonstrate that the shell is exchangeable for ethanol.

Crystal engineering on superpolyhedral building blocks in metal–organic frameworks applied in gas adsorption

This paper reports on metal–organic frameworks which can be designed and synthesized to investigate structure predictability using a SBB (supermolecular building blocks) approach.

The crystal chemistry of inorganic metal boro­hydrides and their relation to metal oxides

Single- and poly-cation inorganic homoleptic metal borohydrides are discussed on the basis of their structural relationship to metal oxides.

Intrinsic flexibility of porous materials; theory, modelling and the flexibility window of the EMT zeolite framework

Framework materials possess intrinsic flexibility which can be investigated using geometric simulation. We review framework flexibility properties in energy materials and present novel results on the flexibility window of the EMT zeolite framework containing 18-crown-6 ether as a structure directing agent (SDA).

Using neutron powder diffraction and first-principles calculations to understand the working mechanisms of porous coordination polymer sorbents

A combination of neutron powder diffraction and first-principles density functional theory calculations is used to understand the gas-sorption mechanisms of porous coordination polymers. This work overviews experimental and computational approaches taken to study these materials and the type of information that is obtained. This information includes the guest-responsive behaviour of the framework and the interaction between the host and the guest molecules, and between the guest molecules, that govern the gas sorption properties of the solid.

Lithium chromium pyrophosphate as an insertion material for Li-ion batteries

A carbon-coated lithium chromium polyanion, LiCrP₂O₇/C, was electrochemically tested versus lithium and found to be active with a specific charge of 105 mAh g⁻¹ in the 1.5–4.5 V versus Li⁺/Li potential window. Operando X-ray diffraction experiments showed a reversible insertion reaction mechanism attributed to the LiCr^IIIP₂O₇/Li₂Cr^IIP₂O₇ couple leading to amorphization in the potential region of 1.8–2.2 V versus Li⁺/Li.

Structural diversity in hybrid organic–inorganic lead iodide materials

The structures of seven hybrid organic–inorganic lead iodide compounds and solvates, related to the photovoltaic material methylammonium lead iodide, have been elucidated. The dimensionality of the inorganic lead iodide component varies from zero-dimensional, discrete [PbI₆]⁴⁻ anions to two-dimensional [PbI₄]²⁻ sheets depending on the geometry and hydrogen-bonding behaviour of the counter organic molecular cation.

Type II Bi_1 − xW_xO_{1.5 + 1.5x}: a (3 + 3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bis­muth oxide

Type II Bi_1 − xW_xO_{1.5 + 1.5x} is the first commensurate case among the known (3 + 3)-dimensional modulated δ-Bi₂O₃-related phases. The ability to refine a supercell model serves to validate the previously proposed crystal chemistry and modulated structure descriptions of these phases.

Spinel materials for Li-ion batteries: new insights obtained by operando neutron and synchrotron X-ray diffraction

Here we address the use of operando diffraction techniques to understand the mechanisms involved for important electrode materials such as the spinels Li_1 + xMn_2 − xO₄ (0 ≤ x ≤ 0.10) and LiNi_0.4Mn_1.6O₄.

Polymorph engineering of CuMO₂ (M = Al, Ga, Sc, Y) semiconductors for solar energy applications: from delafossite to wurtzite

Structure–property relationships in Cu-based ternary oxides are explored using first-principles materials modelling.

Disorder in the composite crystal structure of the manganese `disilicide' MnSi_1.73 from powder X-ray diffraction data

The crystal structure of the higher manganese silicide MnSi_1.7 is disordered incommensurate composite at temperatures not higher than 1273 K.

Oxyanion induced variations in domain structure for amorphous cobalt oxide oxygen evolving catalysts, resolved by X-ray pair distribution function analysis

Amorphous thin-film oxygen evolving catalysts, OECs, of first-row transition metals show promise to serve as self-assembling materials in solar-driven, photoelectrochemical `artificial leaf' devices. This report demonstrates the ability to use high-energy X-ray scattering and atomic pair distribution function analyses, PDF, to resolve structure in amorphous metal oxide catalysts films, and is applied here to resolve domain structure differences induced by oxyanion substitution during the electrochemical assembly of amorphous cobalt oxide catalyst films.

Microwave-assisted synthesis and electrochemical evaluation of VO₂ (B) nanostructures

An in-situ X-ray absorption spectroscopy comparison of nanostructured VO₂ (B) positive intercalation electrodes synthesized by solvothermal and microwave assisted routes, highlighting the effect of morphological differences on electrochemical performance and oxidation state evolution, is presented.

Structure–property relationships in lithium superionic conductors having a Li₁₀GeP₂S₁₂-type structure

Based on neutron diffraction data, the present study reports the structural characteristics and related effects on conductivity for Li₁₀GeP₂S₁₂ (LGPS)-type lithium superionic conductors.

Closing the gap between electron and X-ray crystallography

The development of a proper refinement algorithm that takes into account dynamical scattering guarantees, for electron crystallography, results approaching X-rays in terms of precision, accuracy and reliability. The combination of such dynamical refinement and electron diffraction tomography establishes a complete pathway for the structure characterization of single sub-micrometric crystals.

Structure refinement using precession electron diffraction tomography and dynamical diffraction: tests on experimental data

The method of structure refinement from electron diffraction tomography using dynamical diffraction theory is tested on a number of examples. General guidelines for the application of the method to new structures are provided.

Structural chemistry and number theory amalgamized: crystal structure of Na₁₁Hg₅₂

The structurally most complex crystal structure of the sodium amalgam Na₁₁Hg₅₂ is best described via group-theoretic sublattices which are generated and concisely represented, including their point group symmetry, by number-theoretic formulae taken from the field of modular arithmetics developed by Gauß.

Crystal chemistry of hydrothermally grown ternary alkali rare earth fluorides

Hydrothermally grown single crystals of compositions ARE₂F₇ and ARE₃F₁₀ (A = K, Rb, Cs; RE = Y, La–Lu) have been studied by single-crystal X-ray diffraction. The study has identified a new structure type describing ARE₂F₇ compounds, and has extended the limits of the ARE₃F₁₀ structure types, while underscoring the importance of synthetic technique to directing the structure type.

On the transferability of electron density in binary vanadium borides VB, V₃B₄ and VB₂

The similarities and differences between the electron density features in VB, V₃B₄ and VB₂ derived from X-ray diffraction data as well as from theoretical calculations are analysed using quantum theory of atoms in molecules (QTAIM) descriptors.

Photocrystallography and IR spectroscopy of light-induced linkage NO isomers in [RuBr(NO)₂(PCyp₃)₂]BF₄

Photocrystallographic, IR analysis and DFT calculations reveal selective light-induced NO linkage isomerism in the dinitrosyl compound [RuBr(NO)₂(PCyp₃)₂]BF₄.

Crystal behavior of potassium bromate under compression

The crystal behavior of potassium bromate was studied up to 15 GPa pressure by both angle-dispersive X-ray diffraction experiments and ab initio total-energy calculations.

A temperature-induced order–disorder phase transition in a 4-substituted 4,2′:6′,4′′-terpyridine

A temperature driven, single-crystal to single-crystal, first-order phase transition is reported and the structures and interaction schemes in both phases analyzed. A π⋯π ↔ C—H⋯π `switching' is deemed to be a possible driving force of the transition.