Probing Jahn-Teller Distortions and Antisite Defects in LiNiO with Li NMR Spectroscopy and Density Functional Theory.

The long- and local-range structure and electronic properties of the high-voltage lithium-ion cathode material for Li-ion batteries, LiNiO, remain widely debated, as are the degradation phenomena at high states of delithiation, limiting the more widespread use of this material. In particular, the local structural environment and the role of Jahn-Teller distortions are unclear, as are the interplay of distortions and point defects and their influence on cycling behavior. Here, we use Li NMR measurements in combination with density functional theory (DFT) calculations to examine Jahn-Teller distortions and antisite defects in LiNiO.

Jahn-Teller Distortions and Phase Transitions in LiNiO: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction.

The atomistic structure of lithium nickelate (LiNiO), the parent compound of Ni-rich layered oxide cathodes for Li-ion batteries, continues to elude a comprehensive understanding. The common consensus is that the material exhibits local Jahn-Teller distortions that dynamically reorient, resulting in a time-averaged undistorted 3̅ structure. Through a combination of ab initio molecular dynamics (AIMD) simulations and variable-temperature X-ray diffraction (VT-XRD), we explore Jahn-Teller distortions in LiNiO as a function of temperature.

O3 to O1 Phase Transitions in Highly Delithiated NMC811 at Elevated Temperatures.

Nickel-rich layered oxide cathodes such as NMC811 (LiNiMnCoO) currently have the highest practical capacities of cathodes used commercially, approaching 200 mAh/g. Lithium is removed from NMC811 via a solid-solution behavior when delithiated to > 0.10, maintaining the same layered (O3 structure) throughout as observed via operando diffraction measurements.

Formation of new crystalline qtz-[Zn(mIm)2] polymorph from amorphous ZIF-8.

The structure of a new ZIF-8 polymorph with quartz topology (qtz) is reported. This qtz-[Zn(mIm)2] phase was obtained by mechanically amorphising crystalline ZIF-8, before heating the resultant amorphous phase to between 282 and 316 °C. The high-temperature phase structure was obtained from powder X-ray diffraction, and its thermal behaviour, CO gas sorption properties and dye adsorption ability were investigated.

Negative X-ray expansion in cadmium cyanide.

Cadmium cyanide, Cd(CN), is a flexible coordination polymer best studied for its strong and isotropic negative thermal expansion (NTE) effect. Here we show that this NTE is actually X-ray-exposure dependent: Cd(CN) contracts not only on heating but also on irradiation by X-rays. This behaviour contrasts that observed in other beam-sensitive materials, for which X-ray exposure drives lattice expansion.

Spin-ice physics in cadmium cyanide.

Spin-ices are frustrated magnets that support a particularly rich variety of emergent physics. Typically, it is the interplay of magnetic dipole interactions, spin anisotropy, and geometric frustration on the pyrochlore lattice that drives spin-ice formation. The relevant physics occurs at temperatures commensurate with the magnetic interaction strength, which for most systems is 1-5 K.

High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate).

Single-component molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and crystal structure of the single-component crystal [Ni(dddt)] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)], which is the first example of a single-component molecular crystal that exhibits nodal line semimetallic behavior under high pressure.

Synthesis, PtS-type structure, and anomalous mechanics of the Cd(CN) precursor Cd(NH)[Cd(CN)].

We report the nonaqueous synthesis of Cd(CN)2 by oxidation of cadmium metal with Hg(CN)2 in liquid ammonia. The reaction proceeds via an intermediate of composition Cd(NH3)2[Cd(CN)4], which converts to Cd(CN)2 on prolonged heating. Powder X-ray diffraction measurements allow us to determine the crystal structure of the previously-unreported Cd(NH3)2[Cd(CN)4], which we find to adopt a twofold interpenetrating PtS topology.