Intercalation route to nano-hybrids: inorganic/organic-high Tc cuprate hybrid materials

A systematic application of intercalation techniques to layered superconducting oxides enables us to open a new chapter in the development of nano-hybrids with various functions. Recently we were successful in preparing a new series of inorganic-inorganic nano-hybrids, M-X-Bi 2 Sr 2 Ca m–1 Cu m O y (M=Hg, Ag, Au; X=Br, I; m=1-3) and organic-inorganic ones, R 2 HgI 4 -Bi 2 Sr 2 Ca m–1 Cu m O y (R=organic cation). Our synthetic strategies are based on (1) HSAB (hard-soft acid-base) interactions and (2) interlayer complexation concepts. Since the iodine species in IBi 2 Sr 2 Ca m–1 Cu m O y are stabilized as I3– (soft base) with a charge transfer between host and guest, soft Lewis acids like Ag + , Au + , and Hg 2+ can be further intercalated into the iodine layers inbetween the (Bi-O) double layers. On the other hand, new organic-inorganic nano-hybrids (R 2 HgI 4 -Bi 2 Sr 2 Ca m–1 Cu m O y ) have also been achieved through the intercalative complex-salt formation reaction between preintercalated HgI 2 molecules and R + I – salts in the interlayer space of Bi 2 Sr 2 Ca m–1 Cu m O y . Compared to the pure compounds the superconducting transition temperatures of the organic-salt intercalates are little changed even with a large basal increment upon intercalation, indicating a two-dimensional nature of the high-T c superconductivity. From the viewpoint of application, the intercalation of large organic molecules provides a new synthetic route to high-T c superconducting thin-film and nano-particles by separating superconducting blocks into isolated single sheets.