Exploratory Synthesis Employing Unusual Synthesis Approaches

摘要

One of the areas we investigated for new superconductors is reduced oxides ofniobium, One unusual synthesis approach to prepare these materials has been ion exchange reactions and another has been quenching reactions from very high temperatures. Many reduced niobium oxides in A-Nb-O ternary systems where A is an alkaline or alkaline earth metal have been reported. Some examples are LiNbO2 (1), NaNbl0O18 (2,) BaNb8Oi4 (3), Ba2Nbi5O32 (4) and Ca0.75Nb3O6 (5). Some of strongly reduced niobates contain a Nb6O12O6 cluster with metal-metal bonding as found in NaNbl0Ol8 (2), BaNb8O14 (3), Ba2Nb15O32 (4) and Rb4Al2Nb36O70 (6). These cluster compounds seemed like particularly good candidates in view of the known superconducting Mo-S cluster compounds. Furthermore, it was reported that LiNbO2 changed from a semiconductor to a superconductor with a Tc = 4.5 K by deintercalation of Li+ ions (7). This confirms the potential for superconductivity in reduced niobates. Recently, we discovered a new reduced rubidium niobium oxide, Rb1.51Nb10O17, with a layered structure and having a Nb6O12JO6 cluster (8). This compound is not superconducting down to 4.2 K, but changing the electron concentration in the cluster seemed like a worthwhile goal. The Rb+ ions occupying the interlayer space appeared to be good candidates for deintercalation or ion exchange reactions.