Pb0.4Bi1.6Sr2Ca1Cu2O8+xPb_{0.4}Bi_{1.6}Sr_{2}Ca_{1}Cu_{2}O_{8+x} and Oxygen Stoichiometry: Structure, Resistivity, Fermi Surface Topology and Normal State Properties

$Pb_{0.4}Bi_{1.6}Sr_2CaCu_2O_{8+x}$ ($Bi(Pb)-$2212) single crystal samples were studied using transmission electron microscopy (TEM), $ab-$plane ($\rho_{ab}$) and $c-$axis ($\rho_c$) resistivity, and high resolution angle-resolved ultraviolet photoemission spectroscopy (ARUPS). TEM reveals that the modulation in the $b-$axis for $Pb(0.4)-$doped $Bi(Pb)-$2212 is dominantly of $Pb-$type that is not sensitive to the oxygen content of the system, and the system clearly shows a structure of orthorhombic symmetry. Oxygen annealed samples exhibit a much lower $c-$axis resistivity and a resistivity minimum at $80-130$K. He-annealed samples exhibit a much higher $c-$axis resistivity and $d\rho_c/dT<0$ behavior below 300K. The Fermi surface (FS) of oxygen annealed $Bi(Pb)-$2212 mapped out by ARUPS has a pocket in the FS around the $\bar{M}$ point and exhibits orthorhombic symmetry. There are flat, parallel sections of the FS, about 60\% of the maximum possible along $k_x = k_y$, and about 30\% along $k_x = - k_y$. The wavevectors connecting the flat sections are about $0.72(\pi, \pi)$ along $k_x = k_y$, and about $0.80(\pi, \pi)$ along $k_x = - k_y$, rather than $(\pi,\pi)$. The symmetry of the near-Fermi-energy dispersing states in the normal state changes between oxygen-annealed and He-annealed samples.Comment: APS_REVTEX 3.0, 49 pages, including 11 figures, available upon request. Submitted to Phys. Rev. B

ATOMIC RESOLUTION STUDIES OF SOLUTE-ATOM SEGREGATION AT GRAIN BOUNDARIES : EXPERIMENTS AND MONTE CARLO SIMULATIONS

L'étude des relations entre la structure d'un joint de grains et la composition chimique, dans les alliages métalliques binaire c.c. et c.f.c., est réalisée à l'aide de trois techniques différentes : (a) microscopie électronique de transmission (MET) ; (b) microscopie de champ ionique avec temps de vol (APFIM) ; et (c) simulation Monte Carlo avec ordinateur. MET est utilisée pour déterminer les cinq degrés de liberté macroscopiques d'un joint de grains ; APFIM est employée pour mesurer la composition chimiques ; et les calculs Monte Carlos sont utilisés pour simuler les ségrégations des atomes à joints de grains qui sont étudiées expérimentalement dans les alliages métalliques c.f.c. Nous présentons ici des résultats détaillés pour les alliages W(Re) et Pt(Ni).The study of the relationships between grain boundary (GB) structure and chemical composition, in bcc and fcc metallic binary alloys, is accomplished via three different techniques : (a) transmission electron microscopy (TEM) ; (b) atom-probe field-ion microscopy (APFIM) ; and (c) Monte Carlo computer simulations. TEM is used to determine the five macroscopic degrees of freedom of a GB ; APFIM is employed to measure the chemical composition of the interface ; and Monte Carlo calculations are utilized to simulate solute-atom segregation at GB's that are studied experimentally in fcc binary metallic alloys. Detailed results are presented for W(Re) and Pt(Ni) alloys