Perovskite-like mixed metal ruthenates are of interest owing to their varied electronic and magnetic properties, which are heavily dependent on the ordering of the transition metals. We report the synthesis and structural characterization of the first 1:2 ordered perovskite ruthenate, Sr3CaRu2O9. The structure was determined from a combination of powder X-ray, electron and neutron diffraction data and is characterized by a 1:2 ordering of Ca2+ and Ru5+ over the sixcoordinate B-sites of the perovskite lattice. Sr3CaRu2O9 is the first example of this structure-type to include a majority metal with d electrons (Ru(V), d3). The relationship of this material to the K2NiF4-type Sr1.5Ca0.5RuO4 (i.e., Sr3CaRu2O8) highlights the dramatic effects of the ruthenium valence on the resultant structure. Remarkably, these two structures can be quantitatively interconverted by the appropriate choice of reaction temperature and atmosphere.

Titanium di- and sesquioxide films were epitaxially grown on the (001) surface of sapphire single-crystalline substrates by an activated reactive evaporation method. Formation range for each titanium oxide was determined as a function of oxygen pressure (Po2) by means of x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Films prepared at Po2 ≥ 2.0 × 10−4 Torr were stoichiometric (100)-oriented rutile of TiO2, and with decreasing Po2 they would accommodate more and more Ti3+ ions in the rutile structure. At Po2 = 0.6 × 10−4 Torr, on the other hand, (001)-oriented Ti2O3 was formed and an electrical transition was clearly detected at about 400 K. However, the large lattice mismatch between the substrate and these films leads to a periodic introduction of misfit dislocations in the case of the TiO2 films and a mixing of stacking sequences for the Ti2O3 films.

The modulated structure in solid solution Bi2+xSr2−xCu1+yO6+δ (0.1 < x < 0.6, y ∼ x/4) has been investigated by means of powder x-ray diffraction, electron diffraction, and transmission electron microscopy. The [010] component of the modulation vector decreases almost linearly with increasing x, from 5.2b (x = 0.1) to 4.2b (x = 0.5), where b is the unit length of the average structure along the [010] direction, and is little sensitive to excess oxygen content δ. A structure model of the modulation based on a periodic substitution of Sr for Bi and formation of Bi blocks whose size varies with x is proposed. Relations among various modulations appearing in other related phases such as the Pb-substituted 105 K Tc phase are discussed.

Phases and their relations in the Bi, Pb–Sr–Ca–Cu–O system have been studied to afford a sound material scientific base. Of particular interest is the chemically most representative system, Bi–Sr–Cu–O, in which a series of solid solutions expressed as Bi2+xSr2−xCu1+yOz are formed. The superconductor (Tc≃10K) corresponds to an extremely narrow range of 0.1<x<0.13. From the composition dependence of the one-dimensional modulation mode a new important factor controlling the modulation mode has been deduced. Substitution of Pb for Bi in the high-Tc phase has been found to induce a stepwise change of the modulation mode, thus suggesting an ordering of Pb in the BiO layer. [CuO2]∞ planes exist both in the holeand electron-carrier superconductors, but their role in the former type of superconductors has not been known. As one possible contribution to attacking this problem, ACuO2 (A: Ba1/3Sr2/3˜Sr˜Ca2/3Sr1/3 ) crystallizing in /A/CuO2/A/CuO2/A/ structure have been prepared using high pressures of 60kb.