T. Shishido

Variation of electrical properties on growth sectors of ZnO single crystals

We have grown almost dislocation-free ZnO crystals by the hydrothermal method. The variation of electrical properties on growth sectors of these crystals was studied by means of I-V and 1/C 2 -V measurement. Gold contacts were made at the polar faces on each growth sector. In the (0001) faces [O surface] of all the sectors, clear rectifying action was observed. In the (0001) faces [Zn surface] of all sectors, weak rectifying action or nearly ohmic characteristics were observed. These results indicate that the O surfaces tend to induce intrinsic defects like O vacancies and the rectifying characteristics become strong, while Zn surfaces tend to form a metallic face so that the Au contacts become ohmic. The variation of I-V and 1/C 2 -V characteristics on the growth sectors showed that the contacts of m growth sector have better characteristics than those of other sectors.

The effects of yttrium addition on high-temperature oxidation of heat-resistant alloy with sulfur

Abstract The effects of yttrium (10, 300 and 3700 ppmY) addition on high-temperature oxidation of Fe–20Cr–4Al alloy with sulfur (185 ppmS) were studied in air for 1800 ks at 1273, 1373 and 1473 K by mass-change measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Oxide scales on all of the alloys showed good adherence after oxidation at 1273 K. On the other hand, oxide scales on the 185 ppmS and 10 ppmY alloys spalled from the entire surface, and those on other alloys did not spall after oxidation at 1373 and 1473 K. Mass gains of the alloys with yttrium addition tended to increase with increasing content of yttrium. Oxide scales on the 185 ppmS alloy showed a convoluted morphology, however, surface morphologies of those on the other alloys with yttrium changed to planar with increasing yttrium content after oxidation at 1273 K. Oxide scales on all of the alloys were almost planar after oxidation at 1373 and 1473 K. Behavior of sulfur and yttrium will be presented after oxidation.

Czochralski growth of UV-grade CaF2 single crystals using ZnF2 additive as scavenger

Abstract CaF 2 single crystals suitable for excimer laser application in the ultraviolet range were grown by the Czochralski method. ZnF 2 additive and CF 4 gas were successfully used as scavengers for removing the water molecules in the growth environment, which otherwise cause various defects such as subgrain boundaries, bubbles and oxygen-related precipitates in the CaF 2 crystal. Czochralski-grown CaF 2 crystals had very good crystallinity and a high transmittance in the wavelength range of the ultraviolet laser. The defect structures of colored and colorless CaF 2 crystals were compared.

Structure studies of CeAlO3

Abstract The crystal structure of CeAlO3 was studied by single-crystal X-ray diffraction. The symmetry is tetragonal, a/c = 0.9922, with a small deformation from the ideal cubic lattice. The structure basically belongs to the socalled ideal perovskite type. The electron distribution of the bridging oxygen atoms of -Al-O-Al- of AlO6 octahedra running along the a axes is considerably distorted from a spherical form. The Ce and other oxygen atoms are also slightly distorted. The aluminium atom shows no distortion. These phenomena can be successfully explained using an average structure of two statistical atom arrangements. Each arrangement is characterized by small deviations of oxygen and Ce atoms from their ideal positions of the basic perovskite-type structure and resembles an orthorhombic perovskite-type structure.

Thermal conductivity of layered borides: The effect of building defects on the thermal conductivity of TmAlB4 and the anisotropic thermal conductivity of AlB2

Rare earth metal borides have attracted great interest due to their unusual properties, such as superconductivity and f-electron magnetism. A recent discovery attributes the tunability of magnetism in rare earth aluminoborides to the effect of so-called “building defects.” In this paper, we report data for the effect of building defects on the thermal conductivities of α-TmAlB4 single crystals. Building defects reduce the thermal conductivity of α-TmAlB4 by ≈30%. At room temperature, the thermal conductivity of AlB2 is nearly a factor of 5 higher than that of α-TmAlB4. AlB2 single crystals are thermally anisotropic with the c-axis thermal conductivity nearly twice the thermal conductivity of the a-b plane. Temperature dependence of the thermal conductivity near and above room temperature reveals that both electrons and phonons contribute substantially to thermal transport in AlB2 with electrons being the dominant heat carriers.

Magnetic and superconducting properties of the cubic perovskite YRh3B

The compound YRh3B with cubic perovskite structure is found to be a superconductor whose transition temperature is 0.76 K. The upper-critical-field-temperature curve indicates that this compound appears as an ordinary, type II superconductor.

Crystal growth of a new orthorhombic ErBa(Cu,Pt)O4 material: Crystal chemistry and characterization

Abstract A new compound in the quaternary oxide system, Er-Ba-Cu-Pt-O, was discovered. Single crystals were grown using CuO as a flux in a platinum crucible by a slow cooling method. The platinum was supplied from the inner wall of the platinum crucible. Chemical analysis revealed the chemical composition of this compound to be ErBa 1.03 Cu 0.77 Pt 0.46 O 4.34 . The crystal system was found to be orthorhombic (space group Pcmn) with average unit cell dimensions a = 10.287(3) A, b = 5.659(1) A and c = 13.157 (3) A. We propose the chemical formula of this compound as ErBa(Cu,Pt)O 4 . A large, but broad diamagnetic transition, which should come from the superconducting state, was observed below 80–90 K in single crystal aggregates.

Ab initio studies of structural, elastic, and electronic properties of RRh3BX (R=Sc, Y, La, and Ce)

The variations in the atomic and electronic structures as well as the elastic properties of perovskite-type RRh3BX (R=Sc, Y, La, and Ce) compounds are understood as a function of X in terms of the changes in the cohesive energy and the covalent and ionic bonding using ab initio calculations. A strong covalent bonding is obtained between B 2p and Rh 4d orbitals in all cases. For R=Ce, f-d hybridization is significant and the Fermi level lies in a pseudogap similar to the case where B is replaced by C, leading to further possibilities of designing such compounds.

Studies on the perovskite solid solution Er(Rh, M)3By (M ≡ Pd, Pt and 0 ⩽ y ⩽ 1)

Abstract The solid solution systems Er(Rh 1− x M x ) 3 B y (M ≡ Pd, Pt and 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), prepared by arc melting in an argon atmosphere, were investigated by X-ray diffraction analysis. The stability of perovskite-type compounds was established by varying the content of substituent metal M and boron in the solid solution systems. In some cases, the boron deficiency (1 − y ) at the octahedral site in the body-centred position depended on the particular substitution parameter x . This result cannot be explained by the stacking of atoms but can be explained by the valence electron concentration per unit cell (VEC). The high stability of the perovskite structure in borides is governed by a specific VEC value between 31 and 34.3. Thus we considered that boron might be an electron donor in these perovskite structures.

The effect of temperature on laws of minor hysteresis loops in nickel single crystals with compressive deformation

The temperature dependence of minor hysteresis loops of compressively deformed nickel single crystals has been investigated in a wide temperature range below the Curie temperature of 628 K. There exist power-law relations between the field-dependent parameters of minor-loops, and their exponents are independent of both temperature and strain after the compressive deformation. These observations indicate the presence of universal power laws in minor hysteresis loops. The minor-loop coefficients of the power laws show a similar temperature dependence of the coercive force, which is quantitatively related to the dislocation density. These properties of minor hysteresis loops are useful for the accurate and quantitative nondestructive evaluation of age degradation in ferromagnetic materials.