[en] Treatment at high pressures and temperatures of 6 GPa and 1120 K, typically, have proved to be useful to find new layered complex cupric oxides. Among these, SrCuO₂ crystallizing in the infinite-layer structure may be considered to be the key material not only because of its sample composition and structure but also because of the fact that interesting homologous series of high-pressure phases like Sr_n+1Cu_nO_2n+1+δ and Sr_n+1Cu_n+1O_2n converge to SrCuO₂ as n increases. 15 refs., 8 figs

[en] We studied the resistivity under pulsed high electric field for thin films and micro-meter sized wires of perovskite-type manganese oxide, Pr_0.65Ca_0.35MnO₃ (PCMO). The thin films were prepared by the pulsed laser deposition method. Wires of the oxides were fabricated by the electron-beam lithography and Ar-ion etching methods. By applying a pulsed electric field upto 5x10⁵ V/cm with a duration of 10 ms, the resistivity of the wire with the size of 10 μmx10 μm reduced by 60% at 150 K

[en] We measured the resistivity under pulsed high electric field up to 4000 V/cm in La_1/3Sr_2/3FeO₃ thin film which exhibits charge disproportionation (CD) at 185 K. To eliminate the self-heating effect, we adopted thin films (rather than bulk samples) and micro-fabrication with the focused ion beam technique. Current-voltage characteristics showed non-linear behavior above 1000 V/cm at 170 K; this behavior appears only in CD phase. The threshold field E_th increases as temperature is decreased. Negative differential resistivity and delay in pulse wave form which are characteristic for de-pinned charge density wave were also observed. These suggest an occurrence of collective motion of carriers under CD phase

[en] Short communication

[en] Use of high pressure stabilizes ACuO₂ in the so-called infinite-layer structure for a wide composition range of A=Ba_1/3Sr_2/3 ∼ Sr_1/3Ca_2/3 and stabilizes R₂CuO₄ in the Nd₂CuO₄ structure for small rare earth ions like Y, Ho∼Tm. In addition to these new homologous series of phases Sr_n-1Cu_n+1O_2n in which Cu-O double chains periodically intersect the regular CuO₂ sheet seen in SrCuO₂ (n=∞) have been found. The Cu_n+1O_2n sheets would show frustrated anti ferromagnetic behavior without any carrier doping. Very recent new oxide superconductors were found in the Sr-Cu-O and the Sr-R-Cu-O systems treated under high pressure. Importance of high-pressure effects to find new layered cupric oxides should thus be recognized. (author). 7 refs.; 6 figs

[en] The effect of the La substitution for Bi in newly found triclinic perovskite BiNiO₃ was examined. The charge disproportionation of Bi ions into Bi³⁺ and Bi⁵⁺ was suppressed by 20% substitution. Bi_0.8La_0.2NiO₃ showed a metal-insulator transition at around 300 K

[en] The ATF damping ring has been operated since January in 1997 at KEK, and several beam studies have been started. For the orbit measurement, button-type beam position monitors (BPM) are installed in the ATF damping ring together with a conventional readout electronics. This readout electronics includes clipping circuits with Schottky diodes to measure a charge induced in each button-type electrode of a BPM by a beam. But Schottky diodes can hardly respond to high frequency components in a BPM signal. This fact finally limits the position resolution of BPM. However, the high position resolution will be increasingly required. Hence we tried to use an FET as a clipping device instead of a Schottky diode, and found out a few good properties to improve performance of the clipping circuit. (author)

[en] Magnetic susceptibility and specific heat measurements are presented for some Cu-containing phosphates with different copper frameworks, M₂Cu(PO₄)₂ (M=Sr and Ba: linear 1D uniform chains), BaCuP₂O₇ (double 1D uniform chains), MCuP₂O₇ (M=Ca, Sr, and Pb: zig-zag 1D uniform chains), and Sr_9.1Cu_1.4(PO₄)₇ (isolated Cu²⁺ ions). We observed short- and long-range magnetic ordering in these compounds in which the main Cu-Cu interactions are transferred through PO₄ groups. In M₂Cu(PO₄)₂ and BaCuP₂O₇, J/k_B values of about 100-140 K and k_BT_N/J<1% were obtained

[en] Our Moessbauer effect studies on the electronic state of Fe⁴⁺ ions in perovskite-type oxides, Casub(1-x)Srsub(x)FeO₃(0<=x<=1), Srsub(1-y)Lasub(y)FeO₃(0<=y<=0.6), and some others, are summarized and discussed. The Fe⁴⁺ ions take a high spin state, tsub(2g)³esub(g)¹, and the esub(g) electrons are accommodated in a narrow σ* band. The quarter-filled σ* band state is stable down to the lowest t emperature in SrFeO₃ However, when the Sr-content is enough decreased, the esub(g) electrons get localized at low temperatures in a special way to form a mixed valence state, that is, a charge disproportionation of the Fe⁴⁺ ions into Fe³⁺(tsub(2g)³esub(g)²) and Fe⁵⁺(tsub(2g)³) ions which can be seen typically in CaFeO₃ and Srsub(0.7)Lasub(0.3)FeO₃. In the intermediate composition ranges of 0< x<1 and 0< y<0.3 quite unusual intermediate states are realized and, hence, the chemical formulas of these oxides at low temperatures can be expressed conveniently as Casub(1-x)Srsub(x)Fesub(0.5) sup((3+Δ)+)Fesub(0.5) sup((5-Δ)+)O₃ and Srsub(1-y)Lasub(y)Fesub((1+y)/2)sup((3+delta)+)Fesub((1-y)/2)sup((5-delta)+)O₃. (author)

[en] Perovskite-structure oxides containing unusually high valence states of iron are reviewed. Fe⁴⁺ in oxides has very low-lying 3 d levels and thus makes covalent electronic states with ligand holes. Charge disproportionation or charge transfer lifts the degenerated ligand hole states and intriguing physical properties often appear. (author)