Lithium-Stuffed Diamond Polytype Zn–Tt Structures (Tt = Sn, Ge): The Two Lithium–Zinc–Tetrelides Li3Zn2Sn4 and Li2ZnGe3

Cubic Stuffed-Diamond Semiconductors LiCu3TiQ4 (Q = S, Se, and Te)

Lithium chalcogenides have been understudied, owing to the difficulty in managing the chemical reactivity of lithium. These materials are of interest as potential ion conductors and thermal neutron detectors. In this study, we describe three new cubic lithium copper chalcotitanates that crystallize in the P4̅3m space group. LiCu₃TiS₄, a = 5.5064(6) Å, and LiCu₃TiSe₄, a = 5.7122(7) Å, represent two members of a new stuffed diamond-type crystal structure, while LiCu₃TiTe₄, a = 5.9830(7) Å crystallized into a similar structure exhibiting lithium and copper mixed occupancy. These structures can be understood as hybrids of the zinc-blende and sulvanite structure types. In situ powder X-ray diffraction was utilized to construct a "panoramic" reaction map for the preparation of LiCu₃TiTe₄, facilitating the design of a rational synthesis and uncovering three new transient phases. LiCu₃TiS₄ and LiCu₃TiSe₄ are thermally stable up to 1000 °C under vacuum, while LiCu₃TiTe₄ partially decomposes when slowly cooled to 400 °C. Density functional theory calculations suggest that these compounds are indirect band gap semiconductors. The measured work functions are 4.77(5), 4.56(5), and 4.69(5) eV, and the measured band gaps are 2.23(5), 1.86(5), and 1.34(5) eV for the S, Se, and Te analogues, respectively.

Exploring the frontier between polar intermetallics and Zintl phases for the examples of the prolific ALnTnTe3-type alkali metal (A) lanthanide (Ln) late transition metal (Tn) tellurides

Understanding electronic structures is important in order to interpret and to design the chemical and physical properties of solid-state materials. Among those materials, tellurides have attracted an enormous interest, because several representatives of this family are at the cutting edge of basic research and technologies. Despite this relevance of tellurides with regard to the design of materials, the interpretations of their electronic structures have remained challenging to date. For instance, most recent research on tellurides, which primarily comprise post-transition elements, revealed a remarkable electronic state, while the distribution of the valence electrons in tellurides comprising group-I/II elements could be related to the structural features by applying the Zintl-Klemm-Busmann concept. In the cases of tellurides containing transition metals the applications of the aforementioned idea should be handled with care, as such tellurides typically show characteristics of polar intermetallics rather than Zintl phases. And yet, how may the electronic structure look like for a telluride that consists of a transition metal behaving like a p metal? To answer this question, we examined the electronic structure for the quaternary RbTbCdTe3 and provide a brief report on the crystal structures of the isostructural compounds RbErZnTe3 and RbTbCdTe3, whose crystal structures have been determined by means of X-ray diffraction experiments for the very first time.

Synthesis and Characterization of NaCd0.92Sn1.08, Na(Cd0.28Sn0.72)2 and Na2CdSn5 with Three-Dimensional Cd-Sn Frameworks

The crystal structures of three new ternary compounds, NaCd0.92Sn1.08 (I), Na(Cd0.28Sn0.72)2 (II), and Na2CdSn5 (III) synthesized in a sodium-cadmium-tin system were determined by single-crystal X-ray analysis to be the following: (I) LiGeZn-type structure (hexagonal, a = 4.9326(1) Å, c = 10.8508(3) Å, space group P-6m2); (II) CaIn2-type structure (hexagonal, a = 4.8458(2) Å, c = 7.7569(3) Å, P63/mmc); and (III) isotype with tI-Na2ZnSn5 (tetragonal, a = 6.4248(1) Å, c = 22.7993(5) Å, I-42d). Each compound has a three-dimensional framework structure mainly composed of four-fold coordinated Cd and Sn atoms with Na atoms located in the framework space. Elucidation of the electrical properties of the polycrystalline samples indicated that compounds (I) and (II) are polar intermetallics with metallic conductivity, and compound (III) is a semiconducting Zintl compound. These properties were consistent with the electronic structures calculated using the ordered structure models of the compounds.

Mn-induced spin glass behavior in metallic Ir3Sn7-xMnx

Transition metal stannides are usually semiconductors with a narrow band gap. We report experimental investigation on metallic Ir₃Sn_7-xMn_x(x= 0 and 0.56). Single crystal x-ray diffraction refinement indicates that Ir₃Sn_7-xMn_xcrystals form a cubic structure (space groupIm3̄m) with the lattice parametera= 9.362(4) Å forx= 0 and 9.328(6) Å forx= 0.56. The electrical resistivity shows metallic behavior between 2 K and 300 K withT²dependence atT< 30 K forx= 0, reflecting the Fermi-liquid ground state. While Ir₃Sn₇exhibits weak diamagnetism, partial substitution of Sn by Mn results in spin glass behavior in Ir₃Sn_7-xMn_xbelowT_g∼ 13 K forx= 0.56. Remarkably, an upturn in the resistivity is observed inx= 0.56 below ∼2T_g, suggesting strong spin fluctuation. This fluctuation is suppressed by the application of magnetic field, which is reflected in the observation of negative magnetoresistance. The unusual properties that emerge due to Mn doping are discussed.

Switching the Structure Type upon Ag Substitution: Synthesis and Crystal as well as Electronic Structures of Li12AgGe4

Li-rich compounds of metals and semimetals are interesting candidates for anode materials for rechargeable batteries. The investigation of the Li-rich part of the Li-Ag-Ge phase diagram led to the discovery of the new compound Li12AgGe4, which represents the Li-richest phase in the ternary phase system. The phase-pure compound is synthesized by high-temperature reaction of Li with stoichiometric amounts of premelted reguli of Ag and Ge. The structure was determined by single-crystal X-ray diffraction. Li12AgGe4 crystallizes in the Li13Si4 structure type in the space group Pbam (no. 55) with lattice parameters of a = 8.0420(2) Å, b = 15.1061(4) Å, and c = 4.4867(1) Å and exhibits the unique Zintl anion [AgGe2](7-)-iso(valence) electronic to the CO2 molecule-and Ge2 dumbbells. Li12AgGe4 adopts the atom packing of the lighter homologue Li13Si4 and not that of Li13Ge4 by the selective substitution of one out of seven Li positions by Ag. The calculation of the electronic structure indicates metallic property and the presence of strong covalent bonds between Ag and Ge in the linear triatomic Ge-Ag-Ge unit as well as π character between the Ge atoms of the dumbbells. The Ag-Ge bond order of the linear AgGe2 unit reaches its maximum at EF of Li12AgGe4 with full occupancy of all atomic positions (in contrast to the related Li12Ag1-xSi4), indicating that the formation of covalent Ag-Ge bonds is the driving force for the formation of the structure type.

Fully and partially Li-stuffed diamond polytypes with Ag-Ge structures: Li2AgGe and Li2.53AgGe2

In view of the search for and understanding of new materials for energy storage, the Li-Ag-Ge phase diagram has been investigated. High-temperature syntheses of Li with reguli of premelted Ag and Ge led to the two new compounds Li(2)AgGe and Li(2.80-x)AgGe(2) (x = 0.27). The compounds were characterized by single-crystal X-ray diffraction. Both compounds show diamond-polytype-like polyanionic substructures with tetrahedrally coordinated Ag and Ge atoms. The Li ions are located in the channels provided by the network. The compound Li(2)AgGe crystallizes in the space group R3̅m (No. 166) with lattice parameters of a = 4.4424(6) Å and c = 42.7104(6) Å. All atomic positions are fully occupied and ordered. Li(2.80-x)AgGe(2) crystallizes in the space group I4(1)/a (No. 88) with lattice parameters of a = 9.7606(2) Å and c = 18.4399(8) Å. The Ge substructure consists of unique (1)(∞)[Ge(10)] chains that are interconnected by Ag atoms to build a three-dimensional network. In the channels of this diamond-like network, not all of the possible positions are occupied by Li ions. Li atoms in the neighborhood of the vacancies show considerably enlarged displacement vectors. The occurrence of the vacancy is traced back to short Li-Li distances in the case of the occupation of the vacancy with Li. Both compounds are not electron-precise Zintl phases. The density of states, band structure, and crystal orbital Hamilton population analyses of Li(2.80-x)AgGe(2 )reveal metallic properties, whereas a full occupation of all Li sites leads to an electron-precise Zintl compound within a rigid-band model. Li(2)AgGe reveals metallic character in the ab plane and is a semiconductor with a small band gap along the c direction.