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Quaternary selenide, Pb4In2.6Bi3.4Se13 (x = 2.4 member of the Pb4(InxBi6-xSe13 solid solution), was synthesized by a solid-state technique, and its structure was determined using powder X-ray diffraction (XRD). Pb4In2.6Bi3.4Se13 crystallizes in the orthorhombic space group Pbam (No. 55) with Z = 4. Lattice parameters and calculated density were determined to be a = 22.152(5) Å, b = 27.454(5) Å, and c = 4.1354(6) Å, V = 2515.0(11) Å3, and Dx = 7.490 g cm−3. The structure consists of Z-shaped ribbon units and corner-shared infinite one-dimensional [InSe4]∞ chains running parallel to the c-axis. The chains and ribbons are further connected by Pb atoms to form a three-dimensional network. Pb atoms are situated in the center of bicapped trigonal prisms. The compound exhibits a semiconductor feature. The Seebeck coefficient of Pb4In2.6Bi3.4Se13 was found to be −180 μV K−1 at 295 K and −380 μV K−1 at 600 K. Combining the values of Seebeck coefficient, electrical conductivity, and thermal conductivity yield a figure of merit, ZT, of about 0.175 at 700 K. The powder XRD pattern of Pb4In2.6Bi3.4Se13 was also determined. [ABSTRACT FROM AUTHOR]

X-ray reference powder patterns and structures have been determined for a series of cobalt- and tungsten-containing cubic alkaline-earth perovskites, (BaxSr1–x)2CoWO6 (x = 0.1, 0.2, 0.3, 0.5, 0.7, and 0.9). The structure of the end members of the series, Sr2CoWO6 and Ba2CoWO6, were tetragonal and cubic, respectively, agreeing with the literature data. From Rietveld refinements, it was found that when x = 0.1 and 0.2, the structure was tetragonal I4/m (a = 5.60481(6) and 5.62305(11) Å and c = 7.97989(12) and 7.9847(2) Å, respectively; Z = 2). When x > 0.2, the structure was cubic (Fm $\bar{3}$ m, No. 225; Z = 4) (from x = 0.3 to 0.9, a increases from 7.98399(13) to 8.08871(10) Å). This tetragonal series of compounds exhibit the characteristics of a distorted double-perovskite structure. The bond valence sum values for the alkaline-earth (Ba, Sr) sites in all (BaxSr1−x)2CoWO6 members are greater than the ideal value of 2.0, indicating over-bonding situation, whereas for the W sites, as x increases, a change from under-bonding to slightly over-bonding situation was observed. Density functional theory calculations revealed that while Sr2CoWO6 is a semiconductor, Ba2CoWO6 and SrBaCoWO6 are half-metals. Powder X-ray diffraction patterns of this series of compounds (BaxSr1−x)2CoWO6, with x = 0.1, 0.2, 0.3, 0.5, 0.7, and 0.9, have been submitted to be included in the Powder Diffraction File. [ABSTRACT FROM AUTHOR]

The structure and thermoelectric properties of a series of barium lanthanide cobaltites, BaRCo4O7 (R = Dy, Ho, Er, Tm, Yb, and Lu), which were prepared using the spark plasma synthesis technique, have been investigated. The space group of these compounds was re-determined and confirmed to be P31c instead of the reported P63mc. The lattice parameters a and c range from 6.26279(2) Å to 6.31181(6) Å, and from 10.22468(6) Å to 10.24446(15) Å for R = Lu to Dy, respectively. The crystal structure of BaRCo4O7 is built up from Kagome sheets of CoO4 tetrahedra, linked by triangular layers of CoO4 tetrahedra. The values of figure of merit (ZT) of the BaRCo4O7 samples were determined to be around 0.02 at 800 K. X-ray diffraction patterns of these samples have been determined and submitted to the Powder Diffraction File. [ABSTRACT FROM AUTHOR]

Two low-dimensional cobaltite series in the Sr–Ca–Co–O system have been investigated for their solid solution limit, structure, and compatibility phase relationships (850 °C in air). Thermoelectric properties have been measured for selected members of these solid solutions. In (Ca,Sr)3Co4O9, which has a misfit layered structure, Sr was found to substitute in the Ca site to a limit of (Ca0.8Sr0.2)3Co4O9. Compounds in the homologous series, An+2ConCo′O3n+3 [where A=Sr, Ca, (Ca,Sr), or (Sr,Ca)], consist of one-dimensional parallel Co2O66- chains that are built from successive alternating face-sharing CoO6 trigonal prisms and “n” units of CoO6 octahedra along the hexagonal c-axis. In the Can+2ConCo′O3n+3 series, only the n=1 phase (Ca3Co2O6) could be prepared under the present synthesis conditions. Sr substitutes in the Ca site of Ca3Co2O6 to a limit of (Ca0.9Sr0.1)3Co2O6. In the Srn+2ConCo′O3n+3 series, Ca substitutes in the Sr site of the n=2, 3, and 4 members to a limit of (Sr0.7Ca0.3)4Co3O9, (Sr0.67Ca0.33)5Co4O12, and (Sr0.725Ca0.275)6Co5O15, respectively. While the members of the Can+2ConCo′O3n+3 and Srn+2ConCo′O3n+3 series have reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical conductivity needs to be increased in order to achieve high ZT values. [ABSTRACT FROM AUTHOR]

The search for thermoelectric materials for power generation and for solid-state cooling has led to increased interest of layered cobalt-containing oxides because of their thermal stability at high temperature and their desirable thermoelectric properties. This paper examines the effect of substitution of Co in the layered pervoskite Ba2Ho(Cu3-xCox)O6+y (x=0.3, 0.4, 0.5, 0.6, and 1.0). Structural analysis using the neutron Rietveld refinement technique reveals that when x≤0.4, Co substitutes mainly for Cu in the “chain sites” of the Ba2Ho(Cu3-xCox)O6+y structure. As x>0.4, Co also enters in the Cu-O “plane sites” as well. The thermoelectric properties of polycrystalline Ba2Ho(Cu3-xCox)O6+y samples were studied in the temperature range of 10–390 K. In general, as the cobalt content x increases, the resistivity and Seebeck coefficient of these samples increase while the thermal conductivity decreases. Among the five Ba2Ho(Cu3-xCox)O6+y compositions, the x=0.4 member gives the highest figure of merit ZT of ≈0.02 at approximately 270 K. [ABSTRACT FROM AUTHOR]

Structure and optical properties have been successfully determined for a series of niobium- and tantalum-containing layered alkaline-earth silicate compounds, Ba3(Nb6− x Ta x )Si4O26 (x = 0.6, 1.8, 3.0, 4.2, 5.4). The structure of this solid solution was found to be hexagonal P -62 m (No. 189), with Z = 1. With x increases from 0.6 to 5.4, the lattice parameter a increases from 8.98804(8) to 9.00565(9) Å and c decreases from 7.83721(10) to 7.75212(12) Å. As a result, the volume decreases from 548.304(11) to 544.479(14) Å3. The (Nb/Ta)O6 distorted octahedra form continuous chains along the c -axis. These (Nb/Ta)O6 chains are in turn linked with the Si2O7 groups to form distorted pentagonal channels in which Ba ions were found. These Ba2+ ions have full occupancy and a 13-fold coordination environment with neighboring oxygen sites. Another salient feature of the structure is the linear Si–O–Si chains. When x in Ba3(Nb6− x Ta x )Si4O26 increases, the bond valence sum (BVS) values of the Ba sites increase slightly (2.09–2.20), indicating the size of the cage becoming progressively smaller (over-bonding). While SiO cages are also slightly smaller than ideal (BVS range from 4.16 to 4.19), the (Nb/Ta)O6 octahedral cages are slightly larger than ideal (BVS range from 4.87 to 4.90), giving rise to an under-bonding situation. The bandgaps of the solid solution members were measured between 3.39 and 3.59 eV, and the x = 3.0 member was modeled by density functional theory techniques to be 3.07 eV. The bandgaps of these materials indicate that they are potential candidates for ultraviolet photocatalyst. [ABSTRACT FROM AUTHOR]

Structural characterization and X-ray reference powder pattern determination have been conducted for the Co- and Zn-containing tridymite derivatives Ba(Co1−xZnx)SiO4 (x = 0.2, 0.4, 0.6, 0.8). The bright blue series of Ba(Co1−xZnx)SiO4 crystallized in the hexagonal P6 3 space group (No. 173), with Z = 6. While the lattice parameter " a" decreases from 9.126 (2) Å to 9.10374(6) Å from x = 0.2 to 0.8, the lattice parameter " c" increases from 8.69477(12) Å to 8.72200(10) Å, respectively. Apparently, despite the similarity of ionic sizes of Zn2+ and Co2+, these opposing trends are due to the framework tetrahedral tilting of (ZnCo)O4. The lattice volume, V , remains comparable between 626.27 Å3 and 626.017 (7) Å3 from x = 0 to x = 0.8. UV-visible absorption spectrum measurements indicate the band gap of these two materials to be ≈3.3 and ≈3.5 eV, respectively, therefore potential UV photocatalytic materials. Reference powder X-ray diffraction patterns of these compounds have been submitted to be included in the Powder Diffraction File (PDF). [ABSTRACT FROM AUTHOR]

X-Ray Rietveld refinements were conducted on a series of eleven lanthanide phases, [Sr.sub.2]RGa[Cu.sub.2][O.sub.y] (2112 phase, R= Pr, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, and Yb) that are […]

A series of double-perovskite oxides, Sr2 R NbO6 (R = Sm, Gd, Dy, Ho, Y, Tm, and Lu) were prepared and their crystal structure and powder diffraction reference patterns were determined using the Rietveld analysis technique. The crystal structure of each of the Sr2 R NbO6 phase is reported in this paper. The R = Gd, Ho, and Lu samples were studied using synchrotron radiation, while R = Sm, Dy, Y, and Tm samples were studied using laboratory X-ray diffraction. Members of Sr2 R NbO6 are monoclinic with a space group of P 21/ n and are isostructural with each other. Following the trend of "lanthanide contraction", from R = Sm to Lu, the lattice parameters " a " of these compounds decreases from 5.84672(10) to 5.78100(3) Å, b from 5.93192(13) to 5.80977(3) Å, c from 8.3142(2) to 8.18957(5) Å, and V decreases from 288.355(11) to 275.057(2) Å3. In this double-perovskite series, the R 3+ and Nb5+ ions are structurally ordered. The average Nb–O bond length is nearly constant, while the average R –O bond length decreases with the decreasing ionic radius of R 3+. Powder diffraction patterns for these compounds have been submitted to the Powder Diffraction File (PDF). [ABSTRACT FROM AUTHOR]