Tetragonality induced superconductivity in anti-ThCr2Si2-type RE2O2Bi (RE = rare earth) with Bi square nets

Superconductivity and improved electrical conduction in anti-ThCr2Si2-type RE 2O2Sb and RE 2O2Bi with pnictogen square net

Layered compounds have shown rich physical properties such as high-temperature superconductivity. Recently, monatomic honeycomb lattice systems, such as graphene, have been studied extensively, whereas monatomic pnictogen square nets in layered compounds also exhibit interesting electronic properties owing to their unusual negative valence states. Among them, anti-ThCr2Si2-type RE 2O2 Pn (RE = rare earth, Pn = Sb, Bi) with monoatomic Pn square nets were recently found to exhibit interesting electronic properties such as superconductivity and high carrier mobility. In this article, we review recent studies on crystal structures, electronic properties, and thin-film growth of RE 2O2 Pn.

Structural diversity among multinary pnictide oxides: a minireview focused on semiconducting and superconducting heteroanionic materials

Incorporating different anions with varied ionic sizes and charges is a rapidly growing approach to bring out unusual physical properties among various classes of solid-state materials, pnictides and chalcogenides in particular. This minireview is focused on hetero-anionic materials based on the pnictogens, which have been demonstrated to offer an impressive diversity of crystal chemistry and electronic structures. In addition, many pnictide oxides or oxypnictides, over the course of the last decade, have been shown to exhibit a broad spectrum of superconducting, magnetic, and semiconducting properties. However, the structural diversity of the mixed-anion materials is far greater than the several known structure types, or their variants, of the well-known layered superconductive materials. Therefore, with this treatise, we aim to provide a comprehensive overview of the crystal chemistry of pnictide oxides by recounting almost 40 different structures of such ternary and multinary compounds. In addition to the structural aspects, we also highlight some of the challenges associated with the synthesis, and briefly summarize reported, to date, physical properties of this remarkable class of solids.

Versatile control of the superconducting transition temperature in anti-ThCr2Si2-type Y2O2Bi via H, Li, or F doping

In Y₂O₂Bi with Bi square net, H substitution and Li intercalation led to higher superconducting transition temperature (T_c), while F substitution led to lower T_c, where T_c is universally scaled by unit cell tetragonality c/a. Li intercalated Y₂O₂Bi showed a higher T_c than previously reported Y₂O₂Bi even for the similar c/a.

Low-temperature topotactic oxidation using the solid-state oxidant Zr-doped CeO2

A new topotactic oxidation was developed using the solid-state oxidant Zr-doped CeO₂. For the anti-ThCr₂Si₂ type Y₂O₂Bi, which became superconducting via oxygen intercalation during solid-state oxidation at 1000 °C, the topotactic oxidation enabled not only the oxygen intercalation at a much lower temperature of 200 °C, hampering the segregation of impurity phases, but also the highest superconducting transition temperature for Y₂O₂Bi.

Increased hole mobility in anti-ThCr2Si2-type La2O2Bi co-sintered with alkaline earth metal oxides for oxygen intercalation and hole carrier doping

Metallic anti-ThCr₂Si₂-type RE₂O₂Bi (RE = rare earth) with Bi square nets show superconductivity while insulating La₂O₂Bi shows high hole mobility, by expanding the c-axis length through oxygen intercalation. In this study, alkaline earth metal oxides (CaO, SrO and BaO) were co-sintered with La₂O₂Bi. CaO and BaO served as oxygen intercalants without the incorporation of Ca and Ba in La₂O₂Bi. On the other hand, SrO served not only as an oxygen intercalant but also as a hole dopant via Sr substitution for La in La₂O₂Bi. The oxygen intercalation and hole doping resulted in the expansion of the c-axis length, contributing to the improved electrical conduction. In addition, the hole mobility was enhanced up to 150 cm² V^-1 s^-1 in La₂O₂Bi, which is almost double the mobility in a previous study.