Eisuke Bannai

Growth of high purity LaB6 single crystals by multi-float zone passage

Abstract High purity LaB 6 single crystals have been grown by multi-float zone passage. Crystal growth was done under a pressurized atmosphere to prevent vaporization and dissociation of LaB 6 . No seed crystals for the selection of a preferred growth axis were used. The existence of an easy axis of growth was not found. The impurity concentrations were analysed by emission spectrography and residual resistance ratio measurement. The results show that the purity of the crystals after three passes were improved by about one order of magnitude compared with the crystals after only one zone pass. The grown crystals consist of sub-grains whose crystal axes were slightly misorientated with respect to each other. Electrical resistivity measurements for the purest crystal reveal the characteristic feature of conduction property of LaB 6 , i.e., polar phonon scattering of electrons plays an important role in the scattering mechanism of LaB 6 in addition to impurity scattering and acoustic phonon scattering.

Carbon Layer on Lanthanum Hexaboride (100) Surface

Arrangements of carbon atoms segregated on a LaB6 (100) surface at elevated temperature have been examined by AES, LEED and ELS. At least two distinct states of carbon atoms occur: an epitaxial graphite layer and a stable form. The thickness of the epitaxial layer has been estimated, through analysis of the Auger singals, as about one or two monolayers. The character of the bonding between carbon and LaB6 in the two states is discussed.

Preparation of TiCxsingle crystal with homogeneous compositions

Abstract Single crystals of TiC x with various compositions have been prepared using a floating zone technique in a He ambient gas pressure of up to 30 atm. It was found that the composition of TiC x crystal rods, grown by the usual floating zone process, changes continuously along the growth direction of the crystal. The longitudinal variations in composition have been confirmed by chemical analysis of carbon, measurements of the electrical resistivity and the lattice constants by the X-ray diffraction method. The results were interpreted in terms of the phase diagram. Finally, the zone leveling technique has successfully been used to prepare the single crystals of TiC x with uniform composition.

Raman Scattering in Metallic LaB6

Raman spectra of the phonons were measured in a metallic LaB 6 single crystal using the 4880- and 5145-A excitations of an argon ion laser. From the group theoretical analysis, three Raman active modes of symmetries A 1 g , E g and F 2 g are expected and observed peaks have been assigned to these modes on the basis of the polarization measurements. The results are compared with those of some other metal hexaborides.

Observation of Shock-Induced Phases of Nb2O5 Single Crystal under High-Resolution Electron Microscopy

Shock-loading experiments on Nb2O5 single crystals were carried out up to 54 GPa by the gun method. The shock-loaded materials are recovered by using both closed and open recovery fixtures and were examined by powder X-ray diffraction analysis and high-resolution electron microscopy. Complete conversion to T-Nb2O5 of µm size, denser by 12% than H-Nb2O5, was found in the pressure range from 20–40 GPa. When single-crystal H-Nb2O5 was shocked perpendicular to the b-axis using the open-system recovery fixture, an unidentified phase referred to as the X-phase, besides T-Nb2O5 and shock-reduced NbxO2 with the rutile structure, was observed. The high-resolution image of the X-phase is interpreted as two-dimensionally disordered H-Nb2O5. The X-phase is probably formed in the rapid decompression process from the shock-induced high-pressure phase.

Preparation and properties of CrB2 single crystals

Abstract Single crystals of CrB2 were grown by a floating-zone technique under a pressurized gas atmosphere. Repeated zone passes lowered considerably the impurity concentrations of the crystals but caused a deviation from stoichiometry in the direction of boron deficiency. Electrical resistivities, Hall coefficients, and magnetic susceptibilities, which were measured along the crystal axes, show little anisotropy. The Neel temperature observed was about 88 K. The magnetic structure of CrB2 has not yet been determined but the results of the measurements suggest the itinerant model to be more likely.

Preparation of EuB6 single crystal

Single crystals of EuB6 have been prepared using a floating zone technique. The crystal was grown in an ambient Ar gas pressure of 20 atm. The obtained crystal has been characterized using X-ray diffraction, mass density measurement and chemical analyses of stoichiometry and impurity content. Measured electrical and magnetic properties of the crystal differ markedly from previous results performed on polycrystalline specimens by other authors.

Crystal growth of (La0.8Ca0.2)MnO3 by the TSFZ method

Abstract Single crystals of (La 0.8 Ca 0.2 )MnO 3 were grown by the travelling-solvent floating-zone method. The crystals were characterized by an electron-probe microanalyzer. The state of the melt at the crystal growth is briefly discussed.

Transverse Magnetoresistance of LaB6

The transverse magnetoresistance of LaB 6 , single crystals has been studied at 1.5 K in magnetic fields up to 60 kOe. Open orbits along [110] and [001] are observed for H along θ=27° (from [001]) in the (1\bar10) plane and at most field directions (except near θ=0°) in the (010) plane, respectively. The [001] direction is a singular field direction. The low frequency oscillations with the order of 10 4 gauss are superimposed on the monotonic magnetoresistance. Present results are consistent with a multiply-connected Fermi surface model proposed already from de Haas-van Alphen experiments.