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Incorporation of organic molecules into the lattice of inorganic crystalline hosts is a common phenomenon in biomineralization and is shown to alter various properties of the crystalline host. Taking this phenomenon as a source of inspiration, it is shown herein that incorporation of specific single amino acids into the lattice of manganese (II) carbonate strongly alters its inherent magnetic properties. At room temperature, the magnetic susceptibility of the amino-acid-incorporating paramagnetic MnCO 3 decreases, following a simple rule of mixtures. When cooled below the Néel temperature, however, the opposite trend is observed, namely an increase in magnetic susceptibility measured in a high magnetic field. Such an increase, accompanied by a drastic change in the Néel phase transformation temperature, results from a decrease in MnCO 3 orbital overlapping and the weakening of superexchange interactions. It may be that this is the first time that the magnetic properties of a host crystal are tuned via the incorporation of amino acids., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

The addition of Nb and Sn to Zr 2 AlC is investigated, targeting the synthesis of a Zr-rich bulk MAX phase free of ZrC. The 211 phase formation in the two quaternary Zr-Nb-Al-C and Zr-Al-Sn-C systems is evaluated. Solubility over the entire compositional range in (Zr, Nb) 2 AlC and Zr 2 (Al, Sn)C is observed. In terms of effectiveness, the addition of Sn is preferred over the addition of Nb, as the former is selectively incorporated into the 211 structure. A combinatorial approach results in the formation of phase-pure (Zr 0.8 , Nb 0.2 ) 2 (Al 0.5 , Sn 0.5 )C. The effect of the added solutes on the microstructure and crystallographic parameters is investigated. The addition of Nb and Sn reduces the distortion parameter of the trigonal prism compared to pure Zr 2 AlC. Therefore, an attempt is made to establish a more general stability criterion for the M 2 AC structure based on the steric relationship between the atoms in the M 6 A trigonal prism. Inspired by the Hume-Rothery rules, it is suggested that comparable atomic radii of the M- and A-atoms provide a good starting point to obtain a stable 211 MAX phase.