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Recently, superconductivity at high temperatures is observed in bulk La3Ni2O7−δ under high pressure. However, the attainment of high‐purity La3Ni2O7−δ single crystals remains a formidable challenge. Here, the crystal structure and physical properties of single crystals of Sr‐doped La3Ni2O7 synthesized at high pressure (20 GPa) and high temperature (1400 °C) are reported. Through single crystal X‐ray diffraction, it is shown that high‐pressure‐synthesized paramagnetic Sr‐doped La3Ni2O7 crystallizes in an orthorhombic structure with Ni─O─Ni bond angles of 173.4(2)° out‐of‐plane and 175.0(2)°and 176.7(2)°in plane. The substitution of Sr alters in band filling and the ratio of Ni2+/Ni3+ in Sr‐doped La3Ni2O7, aligning them with those of "La3Ni2O7.05", thereby leading to significant modifications in properties under high pressure relative to the unsubstituted parent phase. At ambient pressure, Sr‐doped La3Ni2O7 exhibits insulating properties, and the conductivity increases as pressure goes up to 10 GPa. However, upon further increasing pressure beyond 10.7 GPa, Sr‐doped La3Ni2O7 transits back from a metal‐like behavior to an insulator. The insulator–metal–insulator trend under high pressure dramatically differs from the behavior of the parent compound La3Ni2O7−δ, despite their similar behavior in the low‐pressure regime. These experimental results underscore the considerable challenge in achieving superconductivity in nickelates. [ABSTRACT FROM AUTHOR]

Author(s): Myles R. Allen (corresponding author) [1]; Peter A. Stott [2]; John F. B. Mitchell [2]; Reiner Schnur [3]; Thomas L. Delworth [4] Forecasts of climate change are inevitably uncertain. [...]

Electrochemically driven chemical transformations play the key role in controlling storage of energy in chemical bonds and subsequent conversion to power electric vehicles and consumer electronics. The promise of coupling anionic oxygen redox with cationic redox to achieve a substantial increase in capacities has inspired research in a wide range of electrode materials. A key challenge is that these studies have focused on polycrystalline materials, where it is hard to perform precise structural determinations, especially related to the location of light atoms. Here a different approach is utilized and a highly ordered single crystal, Na2−xIrO3 is harnessed, to explore the role of defects and structural transformations in layered transition metal oxide materials on redox‐activity, capacity, reversibility, and stability. Within a combined experimental and theoretical framework, it is demonstrated that 1) it is possible to cycle Na2−xIrO3, offering proof of principle for single‐crystal based batteries 2) structural phase transitions coincide with Ir 4+/Ir 5+ redox couple with no evident contribution from anionic redox 3) strong irreversibility and capacity fade observed during cycling correlates with the Na + migration resulting in progressive growth of an electrochemically inert O3‐type NaIrO3 phase. [ABSTRACT FROM AUTHOR]

The iron arsenide Ca[Fe.sub.4][As.sub.3] has featured a three-dimensional network derived from intergrown [Fe.sub.2][As.sub.2] layers and Ca ions in channels. Complex magnetic interactions between Fe atoms have provided unexpected transitions and novel direction-dependent magnetic behavior.

We present a short biography of Sir John Mason, part of Weather's series of pen portraits of Past Presidents of the Royal Meteorological Society. This biography is longer than a normal pen portrait to reflect Sir John Mason's exceptional and wide‐ranging achievements and to show how he contributed to the debate about climate change. We include a discussion of his early years, particularly his pioneering work in cloud physics. We particularly review the key activities of the Met Office with which he was closely involved in his years as Director General, followed by his activities after retirement and his main awards. [ABSTRACT FROM AUTHOR]

A one-dimensional model of an incommensurately modulated insulator is investigated in perturbation theory using tight-binding theory with overlap. Results applicable in the sinusoidal regime are discussed in terms of the ‘‘structural resonance’’ of McConnell and Heine (Ref. ). The method of moments is used to explore ordering in one-dimensional chains, suggesting a novel electronic explanation of the driving force for the transition from disorder to order as a function of electron count (band filling). © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The method of moments is used to study the electronic driving force for disorder to order transitions. Building on the moments foundation by introducing a mean-field approximation and a Landau-like order parameter, it is shown that ordering is energetically favorable for certain electron counts, minimizing the fourth moment of the crystal density of states. A straightforward method for calculating the moments to arbitrary order is presented, relying only on a knowledge of the low-temperature ordering pattern and a finite number of possible short-range ordering patterns. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have grown (110)-oriented thin films of the bilayer manganite La1.2Sr1.8Mn2O7 [n=2 phase of the Ruddlesden-Popper (RP) family] by pulsed laser deposition. The structural, magnetic, and magnetotransport properties of these films depend strongly on the growth conditions as well as the film thickness. Optimal growth conditions of 900 °C and 100 mTorr O2 balance the oxygenation of the n=2 phase without causing its decomposition into the n=1 and ∞ phases of the RP family. With increasing film thickness, the film evolves from a mixture of the n=1, 2, and ∞ phases to a film composed primarily of the n=2 phase. The thicker films possess bulklike properties with a ferromagnetic/paramagnetic transition that coincides with a resistivity maximum at a reduced Tc∼90 K (vs 120 K in bulk) and an anisotropy ratio, ρc/ρab∼20–200 over the temperature range 5–380 K. [ABSTRACT FROM AUTHOR]

Abstract: Methylammonium lead iodide (MAPbI3) perovskites are organic–inorganic semiconductors with long carrier diffusion lengths serving as the light‐harvesting component in optoelectronics. Through a substitutional growth of MAPbI3 catalyzed by polar protic alcohols, evidence is shown for their substrate‐ and annealing‐free production and use of toxic solvents and high temperature is prevented. The resulting variable‐sized crystals (≈100 nm–10 µm) are found to be tetragonally single‐phased in alcohols and precipitated as powders that are metallic‐lead‐free. A comparatively low MAPbI3 yield in toluene supports the role of alcohol polarity and the type of solvent (protic vs aprotic). The theoretical calculations suggest that overall Gibbs free energy in alcohols is lowered due to their catalytic impact. Based on this alcohol‐catalyzed approach, MAPbI3 is obtained, which is chemically stable in air up to ≈1.5 months and thermally stable (≤300 °C). This method is amendable to large‐scale manufacturing and ultimately can lead to energy‐efficient, low‐cost, and stable devices. [ABSTRACT FROM AUTHOR]

Ultrafast time-domain thermoreflectance (TDTR) is utilized to extract the through-plane thermal conductivity ( ΛLSCO) of epitaxial La0.5Sr0.5CoO3− δ (LSCO) of varying thickness (<20 nm) on LaAlO3 and SrTiO3 substrates. These LSCO films possess ordered oxygen vacancies as the primary means of lattice mismatch accommodation with the substrate, which induces compressive/tensile strain and thus controls the orientation of the oxygen vacancy ordering (OVO). TDTR results demonstrate that the room-temperature ΛLSCO of LSCO on both substrates (1.7 W m−1 K−1) are nearly a factor of four lower than that of bulk single-crystal LSCO (6.2 W m−1 K−1). Remarkably, this approaches the lower limit of amorphous oxides (e.g., 1.3 W m−1 K−1 for glass), with no dependence on the OVO orientation. Through theoretical simulations, origins of the glass-like thermal conductivity of LSCO are revealed as a combined effect resulting from oxygen vacancies (the dominant factor), Sr substitution, size effects, and the weak electron/phonon coupling within the LSCO film. The absence of OVO dependence in the measured ΛLSCO is rationalized by two main effects: (1) the nearly isotropic phononic thermal conductivity resulting from the imperfect OVO planes when δ is small; (2) the missing electronic contribution to ΛLSCO along the through-plane direction for these ultrathin LSCO films on insulating substrates. [ABSTRACT FROM AUTHOR]