Sigalit Aharon

The quest for new superconductors is of both fundamental and technological importance. Recently, an artificial intelligence method correctly predicted PtPb3Bi to be a superconductor. In this work, we find superconductivity in the newly synthesized MPb4–xBix (M = Au, Pd, and Rh), of which PtPb3Bi is a member. When M = Ni, whose radius is considerably smaller, the structure instead collapses into the different Pb-substituted NiBi3 type. Interestingly, the stoichiometric parameter x shifts across the three compounds to keep the total valence-electron count close to 20 per formula unit. The superconducting transitions occur at 4.9, 4.2, and 3.4 K, for M = Au, Pd, and Rh, respectively. Using electrical resistivity, magnetization, and specific heat measurements, we establish the bulk nature of the superconducting state and determine the critical fields, characteristic length scales, and anisotropy ratios. All three compounds are moderately anisotropic conventional type-II superconductors, with modest upper critical field anisotropies of Hc2∥c/Hc2⊥c ≈ 1.2 to 1.5. These results establish MPb4–xBix as a family of anisotropic superconductors and a platform for studying how site disorder and Pb–Bi mixing govern superconductivity in heavy-element intermetallics.

Core–shell nanomaterials provide a versatile platform for tuning physical properties and integrating complementary functionalities in nanoscale systems, but their synthesis often requires multistep procedures and precise control over composition, morphology, and interfaces. Achieving core–shell architectures in nanosheets is particularly challenging due to the difficulty of controlling growth direction and interfacial formation. Here, we describe a one-step chemical exfoliation process that produces core–shell nanosheets from the highly air-sensitive compound Li_1+x MnTe₂. Brief sonication in Milli-Q water under ambient conditions yields a dark gray suspension of nanosheets within 10 min, which remains stable in air for at least 31 days. Powder X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, inductively coupled plasma–optical emission spectrometry, and transmission electron microscopy indicate the formation of few-layer crystalline Mn­(OH)₂ cores encapsulated by amorphous Te–O shells. Magnetic measurements show antiferromagnetic ordering in the restacked nanosheets. The suspension can be readily deposited onto coated glass, polyethylene terephthalate, and Si/SiO₂ substrates to form uniform films, with electrical transport measurements indicating resistances on the order of megaohms at room temperature. These results demonstrate chemical exfoliation as an effective approach for producing core–shell nanosheets with magnetic and electronic functionality.

The preparation of kinetically favored inorganic crystals remains a major challenge, as high‐temperature methods often prevent access to metastable phases with unique properties. To address this, post‐synthetic processes that enable the preparation of kinetically favored structures have been developed. In this work, we employ a low‐temperature (200 C) post‐synthetic ion exchange process to transform the parent layered kagome material, RbPdSe, into the nonlayered mineral CuPdSe. This mineral has previously only been synthesized under extreme conditions or was found in nature. Achieving such a structural transformation via ion exchange is unconventional; typical ion exchange reactions mediate transitions between closely related structures. Moreover, the ion exchange procedure developed here does not involve solvents, and the full ion exchange is accomplished at low temperature by the proper choice of a eutectic mixture of salts. Analysis of products synthesized under different conditions show that the CuPdSe decomposition is limited at 200 C when the mixture of CuCl and KCl is used, resulting in a pure‐phase product. The magnetic and electrical characteristics of CuPdSe are presented here for the first time and confirm our density functional theory calculations. Our findings demonstrate that low‐temperature molten salt‐mediated ion exchange may unlock new regions of the solid‐state materials landscape.

The term defect tolerance (DT) is used often to rationalize the exceptional optoelectronic properties of halide perovskites (HaPs) and their devices. Even though DT lacked direct experimental evidence, it became a “fact” in the field. DT in semiconductors implies that structural defects do not translate to electrical and optical effects (e.g., due to charge trapping), associated with such defects. We present pioneering direct experimental evidence for DT in Pb-HaPs by comparing the structural quality of 2-dimensional (2D), 2D-3D, and 3D Pb-iodide HaP crystals with their optoelectronic characteristics using high-sensitivity methods. Importantly, we get information from the materials’ bulk because we sample at least a few hundred nanometers, up to several micrometers, from the sample’s surface, which allows for assessing intrinsic bulk (and not only surface-) properties of HaPs. The results point to DT in 3D, 2D-3D, and 2D Pb-HaPs. Overall, our data provide an experimental basis to rationalize DT in Pb-HaPs. These experiments and findings will help the search for and design of materials with real DT.

The anharmonic lattice dynamics of oxide and halide perovskites play a crucial role in their mechanical and optical properties. Raman spectroscopy is one of the key methods used to study these structural dynamics. However, despite decades of research, existing interpretations cannot explain the temperature dependence of the observed Raman spectra. We demonstrate the nonmonotonic evolution with temperature of the scattering intensity and present a model for second-order Raman scattering that accounts for this unique trend. By invoking a low-frequency anharmonic feature, we are able to reproduce the Raman spectral line shapes and integrated intensity temperature dependence. Numerical simulations support our interpretation of this low-frequency mode as a transition between two minima of a double-well potential surface. The model can be applied to other dynamically disordered crystal phases, providing a better understanding of the structural dynamics, leading to favorable electronic, optical, and mechanical properties in functional materials.

Adding a 2D character to halide perovskite (HaP) active layers in ambient‐protected cells can improve their stability drastically, which is not obvious from the hydrophobicity of the large cations that force the HaP into a 2D structure. Results of two‐photon confocal microscopy are reported to study inherent photo‐stability of 2D Pb iodide HaPs in the interior of single crystals. Compared to 3D HaP crystals, 2D ones have higher photo‐stability and, under a few sun‐equivalent conditions, self‐heal efficiently after photo‐damage. Using both photoluminescence (PL) intensities (as function of time after photo‐damage) and spectra, self‐healing dynamics of 2D HaP (C₄H₉NH₃)₂PbI₄, 2D/3D (C₄H₉NH₃)₂(CH₃NH₃)₂Pb₃I₁₀ and 3D MAPbI₃ are compared. Differences in response to photo‐damage and self‐healing ability from different degrees of photo‐damage are found between these HaPs. Based on the findings, a possible chemical mechanism for photo‐damage and self‐healing of the 2D HaPs is suggested: the layered lattice arrangement limits out‐diffusion of degradation products, facilitating damage reversal, leading to better 2D HaP photo‐stability and self‐healing uniformity than for 2D/3D HaPs. One implication of the layered structures’ resilience to photo‐damage is transfer of their increased stability to devices made with them, such as photovoltaic solar cells and light‐emitting diodes.

The influence of the Schottky contact is studied for hole transport material (HTM) free CH₃NH₃PbI₃ perovskite solar cells (PSCs), by using drift-diffusion and small signal models. The basic current-voltage and capacitance-voltage characteristics are simulated in reasonable agreement with experimental data. The build in potential of the finite CH₃NH₃PbI₃ layer is extracted from a Mott-Schottky capacitance analysis. Furthermore, hole collector conductors with work-functions of more than 5.5 eV are proposed as solutions for high efficiency HTM-free CH₃NH₃PbI₃ PSCs.