ABSTRACT
Reversible switching of room-temperature electrical resistivity due to crystal-amorphous transition is demonstrated in various chalcogenides for development of non-volatile phase change memory. However, such reversible thermal switching of room-temperature electrical resistivity has not reported in transition metal oxides so far, despite their enormous studies on the electrical conduction like metal-insulator transition and colossal magnetoresistance effect. In this study, a thermally reversible switching of room-temperature electrical resistivity is reported with gigantic variation in a layered nickelate Sr2.5 Bi0.5 NiO5 (1201-SBNO) composed of (Sr1.5 Bi0.5 )O2 rock-salt and SrNiO3 perovskite layers via unique crystalline phase changes between the conducting 1201-SBNO with ordered (O-1201), disordered Sr/Bi arrangements in the (Sr1.5 Bi0.5 )O2 layer (D-1201), and insulating oxygen-deficient double perovskite Sr2 BiNiO4.5 (d-perovskite). The O-1201 is reentrant by high-temperature annealing of ≈1000 °C through crystalline phase change into the D-1201 and d-perovskite, resulting in the thermally reversible switching of room-temperature electrical resistivity with 102 - and 109 -fold variation, respectively. The 1201-SBNO is the first oxide to show the thermally reversible switching of room-temperature electrical resistivity via the crystalline phase changes, providing a new perspective on the electrical conduction for transition metal oxides.
ABSTRACT
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.
ABSTRACT
We report a series of layered superconductors, anti-ThCr2Si2-type RE2O2Bi (RE = rare earth), composed of electrically conductive Bi square nets and magnetic insulating RE2O2 layers. Superconductivity was induced by separating the Bi square nets as a result of excess oxygen incorporation, irrespective of the presence of magnetic ordering in RE2O2 layers. Intriguingly, the transition temperature of all RE2O2Bi including nonmagnetic Y2O2Bi was approximately scaled by unit cell tetragonality (c/a), implying a key role in the relative separation of the Bi square nets to induce superconductivity.
