Lithium iron arsenide phases with compositions close to LiFeAs exhibit superconductivity at temperatures at least as high as 16 K, demonstrating that superconducting [FeAs](-) anionic layers with the anti-PbO structure type occur in at least three different structure types and with a wide range of As-Fe-As bond angles.

A new layered iron arsenide NaFeAs isostructural with the superconducting lithium analogue displays evidence for the coexistence of superconductivity and magnetic ordering.

A series of layered oxychalcogenide and oxypnictide solids is described that contain oxide layers separated by distinct layers, which contain the softer chalcogenide (S, Se, Te) or pnictide (P, As, Sb, Bi) anions. The relationships between the crystal structures adopted by these compounds are described, and the physical and chemical properties of these materials are related to the structures and the properties of the elements. The properties exhibited by the oxychalcogenide materials include semiconductor properties, for example, in LaOCuCh (Ch = chalcogenide) and derivatives, unusual magnetic properties exhibited by the class Sr 2MO 2Cu 2-deltaS 2 (M = Mn, Co, Ni), and redox properties exhibited by the materials Sr 2MnO 2Cu 2 m-0.5 S m+1 ( m = 1-3) and Sr 4Mn 3O 7.5Cu 2Ch 2 (Ch = S, Se). Recent results in the oxychalcogenide area are reviewed, and some new results on the intriguing series of compounds Sr 2MO 2Cu 2-deltaS 2 (M = Mn, Co, Ni) are reported. Oxypnictides have received less recent attention, but this is changing: a new frenzy of research is underway following the discovery of high-temperature superconductivity (>40 K) in derivatives of the layered oxyarsenide LaOFeAs. The early results in this exciting new area will be reviewed.

AgBiI4 powder, crystals, and polycrystalline films were synthesized by sealed tube solid state reactions, chemical vapor transport (CVT), and solution processing, respectively, and their structural, optical and electronic properties are reported. The structure of AgBiI4 is based unambiguously upon a cubic close packed iodide sublattice, but it presents an unusual crystallographic problem: we show that the reported structure, a cubic defect-spinel, cannot be distinguished from a metrically cubic layered structure analogous to CdCl2 using either powder or single crystal X-ray crystallography. In addition, we demonstrate the existence a noncubic CdCl2-type polymorph by isolation of nontwinned single crystals. The indirect optical band gap of AgBiI4 is measured to be 1.63(1) eV, comparable to the indirect band gap of 1.69(1) eV measured for BiI3 and smaller than that reported for other bismuth halides, suggesting that structures with a close-packed iodide sublattice may give narrower band gaps than those with perovskite structures. Band edge states closely resemble those of BiI3; however, the p-type nature of AgBiI4 with low carrier concentration is more similar to MAPbI3 than the n-type BiI3. AgBiI4 shows good stability toward the AM1.5 solar spectrum when kept in a sealed environment and is thermally stable below 90 °C.

Since the emergence of lead halide perovskites for photovoltaic research, there has been mounting effort in the search for alternative compounds with improved or complementary physical, chemical, or optoelectronic properties. Here, we report the discovery of Cu 2 AgBiI 6 : a stable, inorganic, lead-free wide-band-gap semiconductor, well suited for use in lead-free tandem photovoltaics. We measure a very high absorption coefficient of 1.0 × 10 5 cm –1 near the absorption onset, several times that of CH 3 NH 3 PbI 3 . Solution-processed Cu 2 AgBiI 6 thin films show a direct band gap of 2.06(1) eV, an exciton binding energy of 25 meV, a substantial charge-carrier mobility (1.7 cm 2 V –1 s –1 ), a long photoluminescence lifetime (33 ns), and a relatively small Stokes shift between absorption and emission. Crucially, we solve the structure of the first quaternary compound in the phase space among CuI, AgI and BiI 3 . The structure includes both tetrahedral and octahedral species which are open to compositional tuning and chemical substitution to further enhance properties. Since the proposed double-perovskite Cs 2 AgBiI 6 thin films have not been synthesized to date, Cu 2 AgBiI 6 is a valuable example of a stable Ag + /Bi 3+ octahedral motif in a close-packed iodide sublattice that is accessed via the enhanced chemical diversity of the quaternary phase space.