Noncentrosymmetric materials have crystal structures lacking a center of inversion. The absence of this symmetry element can yield interesting intrinsic properties that are valued in applications such as laser technology, spintronics, and superconductivity. Ternary tetrel pnictides composed of metal, tetrel (group 14), and pnictogen (group 15) elements exhibit a high abundance of noncentrosymmetric crystal structures in contrast to binary tetrelides and pnictides. This is hypothesized to be a result of the structural flexibility of tetrel pnictide frameworks and the diversity in coordination environments of main group elements around the metal atoms. Rare earth tetrel pnictides often feature homoatomic pnictogen fragments, ranging in length and dimensionality, which can further promote the formation of noncentrosymmetric structures. This work presents the synthesis, structure, and properties of noncentrosymmetric multinary rare earth silicon arsenides. Employing an arc-melted precursor, these metastable compounds can be synthesized in high yield. Ternary LnSiAs3 (Ln = La, Ce) compounds have layered crystal structures featuring either one-dimensional cis-trans chains or two-dimensional square layers of arsenic atoms. Incorporating manganese, a 3d transition metal, into the crystal structure yields related quaternary materials where the presence of locally-noncentrosymmetric building blocks is accompanied by unusual coordination geometries around Mn by Si and As (linear and square-pyramidal). Properties of the ternary parent and quaternary derivative materials will be presented to highlight the role Mn plays in modifying transport and magnetic behavior. This study provides insight into the complexity of multinary metal tetrel pnictides upon combining metals of varying electronegativities – a potential method for obtaining novel noncentrosymmetric materials.

Structure-composition-property relationships in noncentrosymmetric rare earth silicon arsenides

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