The recent discovery of superconductivity in the Ruddlesden-Popper bilayer nickelate, specifically La₃Ni₂O₇, has generated significant interest in the exploration of high-temperature superconductivity within this material family. In this study, we present the crystallographic and electrical resistivity properties of two distinct Ruddlesden-Popper nickelates: the bilayer La₃Ni₂O₇ (referred to as 2222-phase) and a previously uncharacterized phase, La₃Ni₂O₇ (1313-phase). The 2222-phase is characterized by a pseudo F-centered orthorhombic lattice, featuring bilayer perovskite [LaNiO₃] layers interspaced by rock salt [LaO] layers, forming a repeated ...2222... sequence. Intriguingly, the 1313-phase, which displays semiconducting properties, crystallizes in the Cmmm space group and exhibits a pronounced predilection for a C-centered orthorhombic lattice. Within this structure, the perovskite [LaNiO₃] layers exhibit a distinctive long-range ordered arrangement, alternating between single- and trilayer configurations, resulting in a ...1313... sequence. This report contributes to novel insights into the crystallography and the structure-property relationship of Ruddlesden-Popper nickelates, paving the way for further investigations into their unique physical properties.

Stacking two-dimensional (2D) van der Waals (vdW) materials in a layered bulk structure provides an appealing platform for the emergence of exotic physical properties. As a vdW crystal with exceptional plasticity, InSe offers the opportunity to explore various effects arising from the coupling of its peculiar mechanical behaviors and other physical properties. Here, we employ neutron scattering techniques to investigate the correlations of plastic interlayer slip, lattice anharmonicity, and thermal transport in InSe crystals. Not only are the interlayer slip direction and magnitude well captured by shifts in the Bragg reflections, but we also observe a deviation from the expected Debye behaviour in the heat capacity and lattice thermal conductivity. Combining the experimental data with first-principles calculations, we tentatively attribute the observed evidence of strong phonon-phonon interactions to a combination of a large acoustic-optical frequency resonance and a nesting effect. These findings correlate the macroscopic plastic slip and the microscopic lattice dynamics, providing insights into the mechano-thermo coupling and modulation in 2D vdW materials.

Superconducting states onsetting at moderately high temperatures have been observed in epitaxially stabilized RENiO₂-based thin films. However, recently, it has also been reported that superconductivity at high temperatures is observed in bulk La₃Ni₂O_7-δ at high pressure, opening further possibilities for study. Here we report the reduction profile of La₃Ni₂O₇ in a stream of 5% H₂/Ar gas and the isolation of the metastable intermediate phase La₃Ni₂O_6.45, which is based on Ni²⁺. Although this reduced phase does not superconduct at ambient or high pressures, it offers insights into the Ni-327 system and encourages future study of nickelates as a function of oxygen content.

Single crystals of a new layered compound, ${\mathrm{Cr}}_{1.21}{\mathrm{Te}}_2$, were synthesized via a vapor transport method. The crystal structure and physical properties were characterized by single crystal and powder x-ray diffraction, temperature- and field-dependent magnetization, zero-field heat capacity, and angle-resolved photoemission spectroscopy. ${\mathrm{Cr}}_{1.21}{\mathrm{Te}}_2$, containing two Cr sites, crystalizes in a trigonal structure with a space group P-3 (No. 147). The Cr site in the interstitial layer is partially occupied. Physical property characterizations indicate that ${\mathrm{Cr}}_{1.21}{\mathrm{Te}}_2$ is metallic with hole pockets at the Fermi energy and undergoes a ferromagnetic phase transition at $\sim 173\mathrm{K}$. The magnetic moments align along the $c$ axis in the ferromagnetic state. Based on low-temperature magnetization, the spin stiffness constant, D, and spin excitation gap, $\mathrm{\Delta }$, were estimated according to Bloch's law to be $D=94\pm 17\mathrm{meV}{\AA }^2$ and $\mathrm{\Delta }=0.45\pm 0.33$ meV, suggesting its possible application as a low dimensional ferromagnet.

We reported recently that two imidazolium room-temperature ionic liquids (RTILs) exhibit the direct piezoelectric effect (J. Phys. Chem. Lett., 2023, 14, 2731-2735). We have subsequently investigated several other RTILs with pyrrolidinium and imidazolium cations and tetrafluoroborate and bis(trifluoromethylsulfonyl)imide anions in an effort to gain insight into the generality and mechanism of the effect. All the RTILs studied exhibit the direct piezoelectric effect, with a magnitude (d₃₃) and threshold force that depend on the structures of both the cation and anion. The structure-dependence and existence of a threshold force for the piezoelectric effect are consistent with a pressure-induced liquid-to-crystalline solid phase transition in the RTILs, and this is consistent with experimental X-ray diffraction data.