W. Wong-Ng

Structure and X-ray reference diffraction patterns of (Ba 6− x Sr x ) R 2 Co 4 O 15 ( x = 1, 2) ( R = lanthanides)

The structure and X-ray patterns of two series of barium lanthanide cobaltates, namely, Ba4Sr2R2Co4O15 (R = La, Nd, Sm, Eu, Gd, and Dy), and Ba5SrR2Co4O15 (R = La, Nd, Sm, Eu, and Gd) have been determined. These compounds crystallize in the space group P6(3)mc; the unit-cell parameters of Ba4Sr2R2Co4O15 (R from La to Dy) decrease from a = 11.6128(2) angstrom to 11. 5266(9) angstrom, c = 6.869 03(11) to 6. 7630(5) angstrom, and V = 802.23(3)angstrom(3) to 778.17(15) angstrom(3), respectively. In the Ba5SrR2Co4O15 series (R = La to Gd), the unit-cell parameters decrease from a = 11.735 44(14) angstrom to 11.619 79(12) angstrom, c = 6.942 89 (14) angstrom to 6.836 52(8) angstrom, and V = 828.08(3) angstrom(3) to 799.40(2) angstrom(3). In the general structure of (Ba6-xSrx) R2Co4O15, there are four Co ions per formula unit occupying one CoO6 octahedral and three CoO4 tetrahedral units. Through corner-sharing of these polyhedra, a larger Co4O15 unit is formed. Sr2+ ions adopt both octahedral and 8-fold coordination environment. R3+ ions adopt 8-fold coordination (mixed site with Sr), while the larger Ba2+ ions assume both 10- and 11-fold coordination environments. The samples were found to be insulators. X-ray diffraction patterns of these samples have been determined and submitted to the Powder Diffraction File (PDF)

X-ray diffraction patterns of LuNi 2 B 2 C and YNi 2 B 2 C

(Received 25 August 1995; accepted 20 November 1995) Reference X-ray diffraction patterns for the quarternary intermetallic superconductor phases of compositions LuNi2B2C and YNi2B2C are reported. Both materials were synthesized by the arc-melting technique. The patterns of these metallic phases exhibit preferred orientation in an ordinarily pressed sample, which was minimized through special specimen preparation. The observed intensities and the calculated values for both phases agree reasonably well with each other. Both compounds were refined in the space group IAImmm, with a = 3.4647(1) A and c = 10.6330(4) A for LuNi2B2C and a =3.5271(1) A, c = 10.5361(7) A for YNi2B2C.

Structures and thermoelectric properties of double-filled (Ca{sub x}Ce{sub 1−x})Fe{sub 4}Sb{sub 12} skutterudites

Abstract The structures and thermoelectric properties of the double-filled (Ca x Ce 1− x )Fe 4 Sb 12 series ( x =0, 0.25, 0.5, 0.75, and 1) have been studied using a combined experimental and computational methods. Compounds of (Ca x Ce 1− x )Fe 4 Sb 12 were obtained only for x =0, 0.5, and 1. Composition with x =0.25 was found to be a mixture of x =0 and 0.5 compounds, and composition with x =0.75 was found to be a mixture of x =1 and 0.5 compounds, respectively. Our conclusions on phase formation are supported by density functional theory (DFT) calculations. In Ca 0.5 Ce 0.5 Fe 4 Sb 12, Ca substitution in the Ce site of CeFe 4 Sb 12 leads to high hole concentrations, resulting in stronger semimetal transport as compared to CeFe 4 Sb 12 . Ca 0.5 Ce 0.5 Fe 4 Sb 12 yields a slightly higher ZT value than that of CeFe 4 Sb 12 , which is attributed to its lower lattice thermal conductivity. Phonon mode calculations adopting a three-particle bending model suggest that thermal conductivity is reduced upon Ca substitution because of an additional vibration mode which involves both Ca and Ce atoms.

X-Ray and Neutron Powder Diffraction Studies of (Ba1-xSrx)Y2CuO5

This paper reports the results of crystallography and crystal chemistry investigation of the (Ba 1− x Sr x )Y 2 CuO 5 (“green phase”) solid solution series by X-ray powder diffraction (XPD) and neutron powder diffraction techniques. The single phase regions for (Ba 1− x Sr x )Y 2 CuO 5 were determined to be 0⩽ x ⩽0.3 for samples prepared at 810 °C in 100 Pa p O2 , and 0⩽ x ⩽0.7 for samples prepared at 930 °C in air. All single phase (Ba 1− x Sr x )Y 2 CuO 5 samples are isostructural to BaY 2 CuO 5 and can be indexed using an orthorhombic cell with the space group Pnma. Lattice parameters, a , b , c and the cell volume, V , of the (Ba 1− x Sr x )Y 2 CuO 5 members decrease linearly with increasing Sr substitution ( x ) on the Ba site. The general structure of (Ba 1− x Sr x )Y 2 CuO 5 can be considered as having a three-dimensional interconnected network of [YO 7 ],[(Ba,Sr)O 11 ], and [CuO 5 ] polyhedra. The copper ions are located inside distorted [CuO 5 ] “square” pyramids. These pyramids are connected by the [Y 2 O 11 ] groups that are formed from two monocapped [YO 7 ] trigonal prisms sharing a triangular face. The Ba 2+ ions are found to reside in distorted 11-fold coordinated cages. The oxygen sites are essentially fully occupied. XPD reference patterns of two members of the series, (Ba 0.3 Sr 0.7 )Y 2 CuO 5 and (Ba 0.7 Sr 0.3 )Y 2 CuO 5 , were prepared for inclusion in the powder diffraction file.