ABSTRACT
CuMnO2 is a prototype ABO2-type crednerite compound featured by transition metal ions of variable valence states essential for creating novel properties and optimum performance. However, the phase stabilization region of CuMnO2 has not yet been well established, restricting one's ability in comprehending this unique structure for functional applications. Here, layered Cu1-zMn1+zO2 crednerite was systematically synthesized and characterized by accurately regulating the reaction parameters of hydrothermal conditions, which led to a first demonstration of the phase diagram for CuMnO2 crednerite. The pure phase layered structure was uncovered to be stabilized under hydrothermal conditions as the temperature varies between 85 and 175 °C and the molar ratio of Cu to (Cu + Mn) varies between 0.45 and 0.55. For Cu1-zMn1+zO2, there appeared non-stoichiometric occupation of transition metal ions. Strikingly, different from many other layered oxides, the samples at a molar ratio of Cu:(Cu + Mn) = 0.55 showed a special structure, in which excess Cu2+ occupied the position of the Mn3+ site to form a Cu2+ (3d9)/Mn4+ (3d3) ionic pair and traces of corresponding cationic ordered phases. Such a configuration (3d9/3d3 ionic pair) gives rise to an optimum super-capacitor performance, as represented by a highest mass specific capacitance of 428.4 F/g at a current density of 1 A/g. The strategy reported in this work for mapping the phase diagram of layered CuMnO2 crednerite is fundamentally important, which may offer guidance to explore the potentials of other ABO2-type compounds for functional applications.
ABSTRACT
CsCu2I3 mixed with Cs3Cu2I5 has shown potential applications as white-light-emitting materials, while their growth, structural evolution behaviors, and their impact on photoluminescence of CsCu2I3 nanocrystals (NCs) are still not known. In this work, we investigated the growth and structural evolution of CsCu2I3 nanocrystals with increasing reaction temperature. At low temperature and in the presence of a high dosage of oleic acid and oleylamine, Cs3Cu2I5 nanoparticles, rather than CsCu2I3 NCs, preferred to form in the hot-injection reaction system. Increasing the reaction temperature promoted the formation of CsCu2I3 nanorods. Phase-pure CsCu2I3 nanorods were steadily obtained at 180 °C. Structural evolution from less copper-containing NCs to copper-rich ones in the low-temperature reaction condition is highly related to the coordination of copper ions with OAm. More importantly, accompanying the growth of nanorods and structural evolution from Cu3Cs2I5 to CsCu2I3, the color of photoluminescence emission of NCs changed from blue to nearly white and to yellow, but their photoluminescence quantum yield decreased from 36.00 to 9.86%. The finding in this work would give a view to the structural evolution of copper-containing perovskite-like halides, being helpful for adjusting their photoluminescence in white LEDs.
