Perovskites are attracting an increasing interest in the wide community of photovoltaics, optoelectronic, and detection, traditionally relying on lead‐based systems. This Minireview provides an overview of the current status of experimental and computational results available on Ge‐containing 3D and low‐dimensional halide perovskites. While stability issues analogous to those of tin‐based materials are present, some strategies to afford this problem in Ge metal halide perovskites (MHPs) for photovoltaics have already been identified and successfully employed, reaching efficiencies of solar devices greater than 7 % at up to 500 h of illumination. Interestingly, some Ge‐containing MHPs showed promising nonlinear optical responses as well as quite broad emissions, which are worthy of further investigation starting from the basic materials chemistry perspective, where a large space for properties modulation through compositions/alloying/fnanostructuring is present.

Metamorphic rocks are the records of plate tectonic processes whose reconstruction relies on correct estimates of the pressures and temperatures (P-T) experienced by these rocks through time. Unlike chemical geothermobarometry, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on overstepping of reaction boundaries and to identify other examples of non-equilibrium behavior in rocks. Here we introduce a method that exploits the anisotropy in elastic properties of minerals to determine the unique P and T of entrapment from a single inclusion in a mineral host. We apply it to preserved quartz inclusions in garnet from eclogite xenoliths hosted in Yakutian kimberlites (Russia). Our results demonstrate that quartz trapped in garnet can be preserved when the rock reaches the stability field of coesite (the high-pressure and high-temperature polymorph of quartz) at 3 GPa and 850 °C. This supports a metamorphic origin for these xenoliths and sheds light on the mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that interpreting P and T conditions reached by a rock from the simple phase identification of key inclusion minerals can be misleading.

The elucidation of the structure–property correlation in 2D metal halide perovskite is a key issue to understand the dependence of optical properties on structural distortions and to design novel tailored materials. To extend the actual knowledge on this kind of correlation for lead-free materials, here we report four novel 2D germanium bromide perovskites, namely A₂GeBr₄ with A = phenylethylammonium, PEA, Br-phenylethylammonium, BrPEA, F-phenylethylammonium, FPEA, and benzylammonium BZA. A dependence of the band gap value and emission characteristics in terms of Stokes shift and peak width has been highlighted and correlated with the octahedral distortion parameters. In addition, by comparing the actual results with previous data on analogous Sn- and Pb-based materials, we observed an intrinsic increased distortion induced by germanium, particularly on the octahedral bond elongation and bond angle variance, and less on the Ge–Br–Ge bond angle. The structural and optical investigation, together with density functional theory simulations, clarified the role of different structural distortion parameters on the optical properties for a series of 2D Ge-containing perovskites, thus providing novel clues for the future design of layered lead-free materials.

Significance: The origin of diamonds in ureilites is still a debated issue among the scientific community, with significant implications for the sizes of early Solar System bodies. We investigated three diamond-bearing ureilites by a multimethodological approach using scanning electron microscopy, micro X-ray diffraction, transmission electron microscopy, and micro-Raman spectroscopy, with the aim of determining the origin of the diamonds. Our results show that formation of both microdiamonds and nanodiamonds in ureilites can be explained by impact shock events on a small planetesimal and does not require long growth times at high static pressures within a Mercury- or Mars-sized body.