Shigetoshi Muranaka

Temperature-induced A-B intersite charge transfer in an A-site-ordered LaCu 3 Fe 4 O 12 perovskite

Changes of valence states in transition-metal oxides often cause significant changes in their structural and physical properties. Chemical doping is the conventional way of modulating these valence states. In ABO3 perovskite and/or perovskite-like oxides, chemical doping at the A site can introduce holes or electrons at the B site, giving rise to exotic physical properties like high-transition-temperature superconductivity and colossal magnetoresistance. When valence-variable transition metals at two different atomic sites are involved simultaneously, we expect to be able to induce charge transfer—and, hence, valence changes—by using a small external stimulus rather than by introducing a doping element. Materials showing this type of charge transfer are very rare, however, and such externally induced valence changes have been observed only under extreme conditions like high pressure. Here we report unusual temperature-induced valence changes at the A and B sites in the A-site-ordered double perovskite LaCu3Fe4O12; the underlying intersite charge transfer is accompanied by considerable changes in the material’s structural, magnetic and transport properties. When cooled, the compound shows a first-order, reversible transition at 393 K from LaCu2+3Fe3.75+4O12 with Fe3.75+ ions at the B site to LaCu3+3Fe3+4O12 with rare Cu3+ ions at the A site. Intersite charge transfer between the A-site Cu and B-site Fe ions leads to paramagnetism-to-antiferromagnetism and metal-to-insulator isostructural phase transitions. What is more interesting in relation to technological applications is that this above-room-temperature transition is associated with a large negative thermal expansion.

Influence of substrate temperature and film thickness on the structure of reactively evaporated In2O3 films

Abstract Indium oxide films 25–550 A thick were reactively evaporated at an oxygen pressure of about 0.27 Pa and at a substrate temperature between room temperature and 400°C. The dependence of the structure of the films on the substrate temperature and on the film thickness was studied using transmission electron microscopy and electron diffraction. It was found that thick films (about 550 A) were amorphous at room temperature, partially crystallized at 50–125°C and crystalline at 150–400°C. The crystallinity of the films deposited at 150–250°C also depended markedly on the film thickness. Very thin films about 25 A thick were quasi-amorphous, but with increasing film thickness the amorphous phase transformed into a crystalline phase. The thermal transformation of the amorphous films after deposition was also studied. Amorphous films about 550 A thick deposited at room temperature and 100°C crystallized at 230°C and 210°C respectively.

Spin‐Ladder Iron Oxide: Sr3Fe2O5

14 SPIN-LADDER IRON OXIDE: Sr3Fe2O5 H. Kageyama, T. Watanabe, Y. Tsujimoto, A. Kitada, Y. Sumida, K. Kanamori, K. Yoshimura, N. Hayashi, S. Muranaka, M. Takano , M. Ceretti, W. Paulus, C. Ritter, G. Andre Department of Chemistry, Graduate School of Science, Kyoto University, Japan Graduate School of Human and Environmental Studies, Kyoto University, Japan 3 Institute for Chemical Research, Kyoto University, Uji, Japan 4 Institute for Integrated Cell-Materials Sciences and Research Institute for Production Development, Japan 5 University of Rennes1, Sciences Chimiques de Rennes UMR CNRS 6226, Campus de Beaulieu, Rennes 6 Institute Laue Langevin, BP 156, 38042, Grenoble, France 7 Laboratoire Leon Brillouin, CEA-CNRS Saclay, 91191, Gif-sur-Yvette, France

Preparation by reactive deposition and some physical properties of amorphous tin oxide films and crystalline SnO2 films

Tin oxide films were reactively deposited at oxygen pressures of (0.3–5) × 10-3 Torr and at substrate temperatures of 60–420 °C. The dependence of the crystalline phase of the films on the deposition conditions was studied by X-ray diffraction. It was found that, depending on the substrate temperature, amorphous films or crystalline SnO2 films were deposited at pressures above about 10-3 Torr. The amorphous films were non-conducting but their resistivity could be reduced to less than 1 Ω cm by heat treatment in air at 250 or 300 °C. This decrease in resistivity was accompanied by an increase in the light transmission to about 90%. The crystalline SnO2 films were conducting, had a resistivity of the order of 10-2 Ω cm and were highly transparent with an average light transmission of about 90%.

Effects of oxygen gas pressure on structural, electrical, and thermoelectric properties of (ZnO)3In2O3 thin films deposited by rf magnetron sputtering

Zinc indium oxide films were deposited by the rf magnetron sputtering method using a (ZnO)3In2O3 target. The films were prepared at 573 K in various Ar/O2 sputtering gases (O2 content: 0%–25%). The effect of the oxygen gas content in the sputtering gas on the structural, optical, electrical, and thermoelectric properties of the films was investigated. The films had a c-axis oriented layer structure. The films deposited at 0%–3% oxygen gas contents exhibited a high electrical conductivity with a high carrier concentration, n≈1020 cm−3, while the conductivity of the films significantly decreased above the 3% oxygen gas content, having a carrier concentration below 1018 cm−3. From the optical transmission measurement, the band gap of the films was estimated to be 3.01 eV. The films deposited at 3%–8% oxygen gas contents showed a high Seebeck coefficient, −300 μV/K, while the maximum power factor, 4.78×10−5 W/m K2, was obtained at the 2% oxygen gas content. The Seebeck coefficient and the power factor were ca...

Magnetic susceptibility and torque measurements of FeV2S4, FeV2Se4 and FeTi2Se4

Abstract Magnetic susceptibility and torque measurements of FeV2S4, FeV2Se4 and FeTi2Se4 were made using the powder and the single crystal samples. The inverse susceptibility of FeV2S4, FeV2Se4 and FeTi2Se4 changed its slope at 850, 820 and 700 K, respectively, at which temperature the order-disorder transition of cation vacancies should seem to take place. Above these temperatures the paramagnetic moment obtained for these compounds was in the range of 5.26–5.37 μB, close to that of the high spin state Fe2+. Below these temperatures the paramagnetic moment was reduced to 4.23–4.35 μB. The antiferromagnetic spin axis of FeV2S4 was in the neighborhood of the [101] direction and that of FeV2Se4 and FeTi2Se4 in the direction of the c-axis. The large magnetic anisotropy observed and the preference of the magnetic moments for the direction of the c-axis were attributed to the spin-orbit interaction of Fe2+ electrons in the trigonal crystal field.

Order-disorder transition of vacancies in FeTi2S4

Vacancy-ordered FeTi2S4 was prepared by a prolonged heat treatment. X-ray and magnetic measurements showed the transition of vacancies to the disordered state at about 450°C. The magnetic property was antiferromagnetic, having the Neel temperature at 138K. The increase of ferromagnetic character was associated with the disordering of vacancies.

57Fe Mössbauer Spectroscopic Study on Fe2+-Oxides with Infinite-Layer and Ladder Structures

On the basis of Mossbauer spectroscopy, we studied the magnetic properties of a pair of square-planar coordinated Fe 2+ ( S = 2)-oxides, SrFeO 2 (112) and Sr 3 Fe 2 O 5 (325). The infinite layered structure for the 112 phase and the two-legged ladder structure for the 325 phase are suggestive of magnetic low dimensionality but, in fact, both these oxides have been found to have high Neel temperatures of T N = 468 K (112) and 296 K (325). Significantly strong FeO 4 face-to-FeO 4 face interactions between the layers (112) and between the ladders (325) have thus been suggested. The intrinsic isomer shift, a Mossbauer spectroscopic parameter measuring the s electron density at the 57 Fe nucleus, was estimated to be so small as ∼0.7 mm s -1 for both 112 and 325, indicating the specificity of the square planer coordination.

Influence of oxygen pressure on the structure of reactively deposited indium oxide films

Indium oxide films have been reactively deposited at oxygen pressures of 3 × 10–3–0.3 Pa and at substrate temperatures of 25–200 °C. The influence of the oxygen pressure on the structure of the films was studied using transmission electron microscopy and electron diffraction. Below an oxygen pressure of 2 × 10–2 Pa, films were deposited in an In phase at room temperature, and in a In–In2O3 phase mixture at 100 °C and above. Above 2 × 10–2 Pa, films were amorphous or quasi-amorphous below 150 °C, while they were crystalline In2O3 at 150 and 200 °C. The lattice parameters of the In and In2O3 phases in the films were also determined by X-ray diffraction.

Mass spectrometric study on chemical transport of VO2

Abstract The analysis of gas in the chemical transport reaction of VO2 using TeCl4 as a transport agent was carried out with a quadrupole mass spectrometer. In the transport reaction from 600 to 500°C, it was found that the oxygen and vanadium of VO2 were transported in the form of VOCl3 and TeOCl2 gases; the transport reaction was VO 2 + 3 2 TeCl 4 = VOCl 3 + TeOCl 2 + 1 2 TeCl 2 . The transport reaction from 900°C to 800°C was assumed to be VO 2 + 3 2 TeCl 2 = VOCl 3 + 1 2 O 2 + 3 4 TeCl 2 . In the transport at high temperature, the oxygen partial pressure estimated from the mass spectrum was considerably higher than that in equilibrium with VO2 phase. In this paper a study of the chemical transport of the system VO2-TeCl4 is presented.