Infinite-layer-structure epitaxial thin films of SrFeO2 and LaNiO2 respectively were prepared by low-temperature reduction with CaH2 from brownmillerite SrFeO2.5 and perovskite LaNiO3 epitaxial thin films grown on single-crystal substrates. The reduction process, removing oxygen ions from the perovskite-structure framework and causing rearrangements of oxygen ions, topotactically transforms the initial compounds to the c-axis oriented infinite-layer-structure epitaxial thin films. Consequently, the oxidation state of transition-metal ions in the film changed in wide ranges.

BaTiO3/SrTiO3(001) epitaxial thin films were prepared at various growth rates by pulsed laser deposition, and their heterostructures were evaluated by synchrotron x-ray diffraction measurements and cross-sectional scanning transmission electron microscopy observations. In a film grown at a low deposition rate (0.01 nm/s), misfit dislocations are found near the interface and a fully relaxed BaTiO3 thin film grows epitaxially on the substrate. On the other hand, a film grown at a high deposition rate (0.04 nm/s) consists of strained and relaxed BaTiO3 lattices. Our results showed that the critical thickness of BaTiO3/SrTiO3(001) epitaxial thin films can be controlled by the deposition rate and that the critical thickness increases with increasing the deposition rate, and by adjusting the deposition rate we were able to prepare epitaxial thin films consisting of fully strained BaTiO3, partially strained BaTiO3 or fully relaxed BaTiO3. We have also achieved the growth controlling of BaTiO3 thin films on SrTiO3(001) substrates with SrRuO3 bottom electrode layer.

A new multiferroic compound Bi2NiMnO6 was synthesized in both bulk and thin-film forms. Bulk samples were prepared under a high pressure condition at 6 GPa, and thin-film samples were epitaxially grown on single-crystal SrTiO3 substrates by a pulsed-laser deposition method. The crystal structure of the material is a double perovskite, in which Ni2+ and Mn4+ ions are ordered in a rock-salt configuration. Bi3+ ions at the A-site cause a noncentrosymmetric (C2) structural distortion which allows a spontaneous ferroelectric polarization at room temperature. Ni2+–O–Mn4+ magnetic paths lead to ferromagnetism through the superexchange interaction according to the Kanamori-Goodenough rule. A coupling between the ferromagnetic and ferroelectric interactions appears to exist, but it is quite small.

Variable-emittance radiators based on the metal-insulator transition of (La,Sr)MnO3 have been developed. The emittance property of the material was evaluated from infrared reflectance spectra; that is, (La,Sr)MnO3 shows low emittance at low temperature but high emittance at high temperature. Moreover, the emittance property significantly changes at the metal-insulator transition temperature, where the material changes from a highly reflective (i.e., low emissivity) metal to a less reflective (i.e., high emissivity) insulator. The (La,Sr)MnO3 thin-films fitted on a spacecraft surface can, therefore, be used to automatically control the emmisive heat transfer from the spacecraft without the need for electrical power. The developed (La,Sr)MnO3 thin-film radiator also greatly reduces the weight and production cost of the thermal control devices.

The degradation mechanism of Pb(Zr,Ti)O3 (PZT) under reducing conditions was revealed. In contrast to the significant decrease in the sample weight of SrBi2Ta2O9 due to decomposition, the weight of Pb(Zr,Ti)O3 samples change little during H2-annealing at typical process temperatures. Although no apparent changes were detected by thermogravimetric and x-ray diffraction measurements after annealing, the PZT material did actually change. The main mechanism of the degradation is introduction of oxygen defects into the materials. The oxygen defects produce a donor level within the band gap, and light absorption by this donor level accounts for the change in sample appearance from white to black. Different endurance behaviors of materials against reducing conditions were also found: PbZrO3 decomposes through oxygen dissociation more easily than PbTiO3. Oxygen atoms in PbZrO3 are more weakly bonded to Zr than to Ti in PbTiO3 because of a significant anti-bonding component in the hybridized orbitals.

LiMn2O4 has a phase transition at room temperature, which is caused by Jahn-Teller distortion. DC resistivity of LiMn2O4 shows an anomaly at the transition temperature, while no such anomaly is observed in samples with excess lithium. X-ray diffraction patterns of LiMn2O4reveal that the crystal structure changes from cubic at higher temperature to orthorombic, as a first approximation, at lower temperature. However, no differences in initial charge-discharge curve are observed, which means that the Jahn-Teller distortion has no effect on electrochemical characteristics. The authors have succeeded in mass-producing lithium ion secondary batteries with a manganese spinel cathode.

Thin-film samples of La1-xSrxMnO3 (x = 0.20 – 0.30) were grown by pulsed-laser deposition using various target compositions, substrate materials, growth temperatures, oxygen partial pressures, and laser-pulse repetition rates. The crystal structure and the transport and magnetic properties of these films were then examined. Of the growth conditions, the oxygen partial pressure (Po2) had the greatest influence on the electrical and magnetic properties. Films grown under a low Po2 had a low ferromagnetic transition temperature (Tc) and a wide resistive transition width. None of the heat treatments done after growth improved these films’ quality. The film morphology was significantly affected by the substrate material. Our x-ray diffraction analysis and AFM measurements revealed that the films deposited on both MgO (100) and LaAlO3 (100) were epitaxially grown but contained defect structures. In contrast, grain-free thin films were epitaxially grown on the SrTiO3 (100) substrates. The surface roughness of films grown on SrTiO3 was less than 0.3 nm, even for films up to 150 nm thick. Under optimized growth conditions, as-deposited films for x ≥ 0.2 showed a sharp transition in resistivity at Tc. Magnetoresistance at far below Tc was as low as that reported for single-crystal sample. Since large magnetoresistance was often observed in polycrystalline samples and believed to be a grain boundary effect, these results indicate the high quality of the films grown on the SrTiO3 substrates.

Tl2Ba2Cuo6+δ(T1-2201) single crystals are prepared by a KCI flux method. In-plane and out-of plane resistivities (ρabρc as well as the in-plane Hall coefficient are measured for the single crystal samples with various 7c's. The ρc values are as large as ∼10−1 Ω cm, which is larger than that of YBa2Cu3O7, but smaller than that of Bi2Sr2CaCu2O8. Temperature dependences of ρc show metallic behaviors for both normal metallic and 75-K superconducting samples. Temperature dependence of in-plane resistivity par changes from ∼T2 to ∼T1 with increasing Tc In-plane Hall coefficient RH shows a characteristic maximum at about 100 K for all samples. Although both ρab and RH have rather a complicated temperature dependence, inverse Hall mobility μH(=ρab/RH always exhibits clear T2 dependence for all samples. These results suggest that the intrinsic scattering rate of this material varies as ∼T2, just like in an ordinary Fermi liquid, and that the carrier concentration actually changes with temperature like that observed in nH(=1/RHe).