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Hybrid organic-inorganic perovskite (HOIP) ferroelectrics are attracting considerable interest because of their high performance, ease of synthesis, and lightweight. However, the intrinsic thermodynamic origins of their ferroelectric transitions remain insufficiently understood. Here, we identify the nature of the ferroelectric phase transitions in displacive [(CH

Hybrid organic–inorganic compounds attract a lot of interest for their flexible structures and multifunctional properties. For example, they can have coexisting magnetism and ferroelectricity whose possible coupling gives rise to magnetoelectricity. Here using first-principles computations, we show that, in a perovskite metal–organic framework (MOF), the magnetic and electric orders are further coupled to optical excitations, leading to an Electric tuning of the Magneto-Optical Kerr effect (EMOKE). Moreover, the Kerr angle can be switched by reversal of both ferroelectric and magnetic polarization only. The interplay between the Kerr angle and the organic–inorganic components of MOFs offers surprising unprecedented tools for engineering MOKE in complex compounds. Note that this work may be relevant to acentric magnetic systems in general, e.g., multiferroics.

We perform density functional theory calculations on a recently synthesized metal-organic framework (MOF) with a perovskite-like topology ABX3, i.e., [CH3CH2NH3]Mn(HCOO)3, and predict a multiferroic behavior, i.e., a coexistence of ferroelectricity and ferromagnetism. A peculiar canted ordering of the organic A-cation dipole moments gives rise to a ferroelectric polarization of ~2 μC/cm(2). Starting from these findings, we show that by choosing different organic A cations, it is possible to tune the ferroelectric polarization and increase it up to 6 μC/cm(2). The possibility of changing the magnitude and/or the canting of the organic molecular dipole opens new routes toward engineering ferroelectric polarization in the new class of multiferroic metal-organic frameworks.

Modeling of nanocrystals supported by advanced morphological and chemical characterization is a unique tool for the development of reliable nanostructured devices, which depends on the ability to synthesize and characterize materials on the atomic scale. Among the most significant challenges in nanostructural characterization is the evaluation of crystal growth mechanisms and their dependence on the shape of nanoparticles and the distribution of doping elements. This paper presents a new strategy to characterize nanocrystals, applied here to antimony-doped tin oxide (Sb-SnO(2)) (ATO) by the combined use of experimental and simulated high-resolution transmission electron microscopy (HRTEM) images and surface energy ab initio calculations. The results show that the Wulff construction can not only describe the shape of nanocrystals as a function of surface energy distribution but also retrieve quantitative information on dopant distribution by the dimensional analysis of nanoparticle shapes. In addition, a novel three-dimensional evaluation of an oriented attachment growth mechanism is provided in the proposed methodology. This procedure is a useful approach for faceted nanocrystal shape modeling and indirect quantitative evaluation of dopant spatial distribution, which are difficult to evaluate by other techniques.

A new procedure for the synthesis of MoS(2) nanotubes is reported, and additionally demonstrated for MoSe(2), WS(2), and WSe(2). Highly concentrated sunlight creates continuous high temperatures, strong temperature gradients, and extended hot annealing regions, which, together with a metallic (Pb) catalyst, are conducive to the formation of different inorganic nanotubes. Structural characterization (including atomic resolution images) reveals a three-step reaction mechanism. In the first step, MoS(2) platelets react with water-air residues, decompose by intense solar irradiation, and are converted to molybdenum oxide. Subsequently, the hot annealing environment leads to the growth of Pb-stabilized MoO(3-x) nanowhiskers. Shortly afterward, the surface of the MoO(3-x) starts to react with the sulfur vapor supplied by the decomposition of nearby MoS(2) platelets and becomes enveloped by MoS(2) layers. Finally, the molybdenum oxide core is gradually transformed into MoS(2) nanotubes. These findings augur well for similar syntheses of as yet unattained nanotubes from other metal chalcogenides.