Polymorphism in Novel Li2-II-IV-S4 Diamond-Like Semiconductors

Diamond-like semiconductors (DLSs) have structures that are derived from either the cubic or hexagonal form of diamond. The I2-II-IV-VI4 diamond-like semiconductors are particularly interesting systems for their tunable nature and technological applications in photovoltaic solar cells, spintronics, and non-linear optics, specifically second harmonic generation. Polymorphism, which may affect important physicochemical properties in these materials, has been commonly reported in binary and ternary systems, while investigations of polymorphism in quaternary DLSs have been less prevalent. Polymorphs have been observed crystallizing in the stannite (I-42m) and wurtzstannite (Pmn21) structure types, which differ in the closest-packed arrangement of the anions, cubic versus hexagonal respectively. Polymorphism may also be observed in quaternary DLSs that maintain the same anion packing, but differ only in the cation ordering arrangements within the tetahedral holes. In the hexagonally derived quaternary DLSs, the different cation ordering gives rise to at least three different structure types, wurtzstannite (Pmn21), wurtzkesterite (Pn), and cobalt (II) lithium silicate (Pna21). In this work, high-temperature solid-state synthesis in a Li2-II-IV-VI4 system lead to the discovery of two new polymorphic compounds, crystallizing in the Pna21 and Pn space groups. The two polymorphs were analyzed using single crystal X-ray diffraction, synchrotron X-ray powder diffraction, and optical diffuse reflectance UV/Vis/NIR spectroscop

Polymorphism and second harmonic generation in a novel diamond-like semiconductor: Li2MnSnS4

© 2015 Elsevier Inc. All rights reserved. High-temperature, solid-state synthesis in the Li2MnSnS4 system led to the discovery of two new polymorphic compounds that were analyzed using single crystal X-ray diffraction. The α-polymorph crystallizes in Pna21 with the lithium cobalt (II) silicate, Li2CoSiO4, structure type, where Z=4, R1=0.0349 and wR2=0.0514 for all data. The β-polymorph possesses the wurtz-kesterite structure type, crystallizing in Pn with Z=2, R1=0.0423, and wR2=0.0901 for all data. Rietveld refinement of synchrotron X-ray powder diffraction was utilized to quantify the phase fractions of the polymorphs in the reaction products. The α/β-Li2MnSnS4 mixture exhibits an absorption edge of ∼2.6-3.0 eV, a wide region of optical transparency in the mid- to far-IR, and moderate SHG activity over the fundamental range of 1.1-2.1 μm. Calculations using density functional theory indicate that the ground state energies and electronic structures for α- and β-Li2MnSnS4, as well as the hypothetical polymorph, γ-Li2MnSnS4 with the wurtz-stannite structure type, are highly similar

Polymorphism and Second Harmonic Generation in a Novel Diamond-like Semiconductor: Li2MnSnS4

High-temperature, solid-state synthesis in the Li2MnSnS4 system led to the discovery of two new polymorphic compounds that were analyzed using single crystal X-ray diffraction. The α-polymorph crystallizes in Pna21 with the lithium cobalt (II) silicate, Li2CoSiO4, structure type, where Z=4, R1=0.0349 and wR2=0.0514 for all data. The β-polymorph possesses the wurtz-kesterite structure type, crystallizing in Pn with Z=2, R1=0.0423, and wR2=0.0901 for all data. Rietveld refinement of synchrotron X-ray powder diffraction was utilized to quantify the phase fractions of the polymorphs in the reaction products. The α/β-Li2MnSnS4 mixture exhibits an absorption edge of ∼2.6–3.0 eV, a wide region of optical transparency in the mid- to far-IR, and moderate SHG activity over the fundamental range of 1.1–2.1 μm. Calculations using density functional theory indicate that the ground state energies and electronic structures for α- and β-Li2MnSnS4, as well as the hypothetical polymorph, γ-Li2MnSnS4 with the wurtz-stannite structure type, are highly similar