Ryozo Aoki

Characterization and classification of ‘tervalent nickel complexes’, Ni(diamine)2ClX2 (X = Cl and CIO4)

Abstract The ESR, magnetic susceptibilities, IR and electronic spectra, and electric conductivities of solid state were measured for a series of nickel complexes of the general formula Ni(diamine) 2 ClX 2 which appeared to contain ‘tervalent nickel’ in order to elucidate to oxidation state of the nickel. Based on these data they were characterized and classified into the following three groups. A) Ni(en) 2 Cl 3 and Ni(tn) 2 Cl 3 , low-spin d 7 Ni(III) complexes; B) Ni(pn) 2 Cl 3 , Ni(cyn) 2 Cl 3 , Ni(btn) 2 Cl 3 and Ni(en) 2 Cl(ClO 4 ) 2 , Ni(II)Ni(IV) mixed valence complexes; and C) Ni(phn) 2 Cl 3 , probably Ni(II) complex with cation radical ligand.

The effect of La substitution on the superconductivity of Ba2YCu3Oy

Abstract The (Ba 1− x La x ) 2 YCu 3 O y solid solution has been characterized for its superconducting transition temperature T c , lattice parameters, oxygen content and carrier concentration. T c is found to have a relation to the oxygen introduction by La doping. The depression of T c in the region of x > x c ( x c =0.05) is attributed to the formation of [Cu(I)O 5 ] pyramids or [Cu(I)O 6 ] octahedra. A model is proposed to interpret the influence of [Cu(I)O 5 ] pyramids on the superconductivity. The fraction of uncooperative atoms in Cu(II)O 2 sheets is found to be a common parameter of T c for several kinds of cation substituted Ba 2 YCu 3 O y systems.

Negative Evidences for Charge/Spin Density Wave in ZrTe5

Experimental searches were made for evidences for the charge- or spin-density wave state in the trigonal-prismatic pseudo-linear chain compound ZrTe 5 . Negative evidences for such phase transitions were provided by the absence of lattice modulation, ohmic resistivity at high electric fields, and by temperature and angular dependences of electrical resistivity and magnetic susceptibility.

Metallic conductivity in perovskite-type compounds AMoO3 (A = Ba, Sr, Ca) down to 2.5K

Abstract The resistivities of perovskite-type compounds AMoO 3 (A = Ba, Sr, Ca) have been measured over the temperature range from room temperature to 2.5K. The metallic conductivity have been observed in these compounds. The order of resistivities of AMoO 3 is discussed from the viewpoint of overlap intergrals.

Observation of Multi-Stage Superconducting Gap States in Bi2Sr2CaCu2Ox Crystal Surface by LT-STM/STS

Low temperature STM/STS observation for BSCCO single crystal was carried out to investigate an intrinsic superconducting gap state of CuO 2 layer. The STM observation revealed out a mid-level-layer between the top and bottom BiO surfaces of the half unit cell in the crystal c-axis direction. The STS study on this mid-level surface brought a reproducible definite superconducting gap structure which shows a finite gap region with a low conductance level of about 5%, and which also shows a nature of wide range gap parameter of Δ max /Δ min ∼4 with Δ min ∼10 meV. This definite gap structure is considered to be a more direct reflection of the superconducting electronic states of the CuO 2 layer than the superconducting gap structure observed at the top BiO layer.

Non-Magnetic Localized State in Aluminum. : II. Specific Heat and Magnetic Susceptibility

The results of an experimental study on the residual resistance, specific heat and magnetic susceptibility of dilute solid solutions (ranging from 0.1 to 0.4 at.%) of V, Cr and Mn in aluminum are presented. The experimental data are analysed on basis of the Anderson model in order to estimate parameters which characterize the localized d -state, i. e. the mean conduction band- d -state ( s d ) admixture, the localized level width, the mean d -state occupation number and the intra-atomic d - d coulomb energy. The level width is evaluated to be about 0.2 eV. The results are combined with the change in the superconducting transition temperature measured in the same alloy system (reported in Part I) to discuss the properties of the localized d -state in light of recent theoretical studies by Ratto and Blandin, and Takanaka and Takano.

Raman scattering from 2H-NbS2 and intercalated NbS2

Abstract We have measured Raman scattering spectra from two polytypes of NbS2 and also NbS2 intercalated with organic molecules. It is found that the E2g(E) symmetry modes are much affected by the layer stacking and the intercalation. These effects are explained by the anion-cation bondings in the adjacent layers and the long range forces in addition to the van der Waals force.

One Dimensional Electric Conduction Mechanism in Mixed-Valence Complexes

Abstract The d.c. conductivity a along the chain of —M(II)—XM(IV)X— was observed with crystals of [M(II)(AA)23]·[M(IV)(AA)2X2]Y4; M=Pt, Pd, Ni, X=Cl, Br, I, (AA)=(en), (tn), Y=ClO4, BF4. Systematic change of [sgrave] from 10−8 to 10−15 (Ω-cm)−1 with M and X was characterized by an inter-ionic distance δ as [sgrave]∞exp [-αδ]. Its temperature change is expressed as [sgrave](T)=[sgrave]0 exp [-ΔE/kT] with ΔE=0.4 to 1.4 eV, which is in hν>2ΔE relation for the specturm absorption. Hydrostatic pressure on single crystal induces lattice contraction and [sgrave] enhancement of 103±1 times only by 7 kbar, suggesting dominant role of the orbital overlapping on [sgrave]. ESR singnal of gav=2.15±0.03 was observed for M=Pt, and its anisotropy with c-axis as gτ>g// indicates dz2 band contribution. The signal intensity change down to 77 K provides the carrier activation energy Δe=12±1 meV (X=I) and scarce activation number 1 per 104 Pt ion. Hence the conduction is considered as dominantly regulated by hopping process a...

Non-Magnetic Localized State in Aluminum. I. Superconducting Transition Temperature

The change in T c of the superconducting transition temperature of aluminum due to the addition of 3 d transitional impurities Ti, V, Cr, Mn, Fe and Ni is measured as a function of the residual resistance ratio ρ in the region of dilute concentrations ranging from 0.001 to 0.04 atomic percent. The contribution due to the smearing out of the energy gap anisotropy ( Δ T c ) anis is estimated by assuming that it can be accounted for by the theory of Markowitz and Kadanoff. ( Δ T c ) a anis thus estimated is found to depend only on the mean free path and very little on the type of impurity. The remaining part ( Δ T c ) v obtained by subtracting ( Δ T c ) anis from the observed change in the transition temperature, is found to be negative showing a dependence on impurity similar to that found for the residual resistance but differing that it shows a rather sharp minimum at Mn. Comparison with theories based on the Anderson model of localized states in metals are made. It is shown that the overall behavior show...

Superconductivity and magnetism in Co substituted YBCO compounds

Abstract Superconducting transition temperature Tc and magnetic susceptibility χ were measured on Co substituted YBCO system, YBa2[Cu1−xCox]3Oy. The observed characteristic dependence of Tc on the substitution concentration x w investigated taking the magnetic data into consideration. The operating mechanism of the Co ion at the Cu(I) site on the superconducting state in the [Cu(II)O] net-planes are inquired from the two viewpoints: (1) changes in electronic state and (2) magnetic moment induction at the Cu(II) site. The possibility of both being induced by displacement of the oxygen atom O(1) between Cu(I) and Cu(II) is considered.