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Ca28Ga11, a structure with three types of coordination polyedra around the Gallium atoms
No full textPhases in the Al-Yb-Zn system between 25 and 50 at% Yb
No full textPhases YbZn1-xAlx, YbZn2-xAlx and YbZn3-xAlx were studied by electron microprobe analysis and X-ray single crystal and powder methods. The compound YbZn0.8Al0.2 crystallizes with the CsCl-type, a=3.635(2) Å. Four phases were investigated by single crystal X-ray diffraction: YbZn0.996(6)Al1.004(6), MgNi2-type, P63/mmc, a=5.573(1), c=18.051(3) Å, Z=8, wR2=0.040 and YbZn0.88(3)Al1.12(3), MgCu2-type, Fd over(3, -) m, a=7.860(2) Å, Z=8, wR2=0.060, both showing mixed Zn/Al occupancy; YbZn2.50(1)Al0.50(1), CeNi3-type, P63/mmc, a=5.496(1), c=17.336(2) Å, Z=6, wR2=0.036 and YbZn1.92(2)Al1.08(2), PuNi3- or NbBe3-type, R over(3, -) m, a=5.499(1), c=26.134(5) Å, Z=9, wR2=0.053, where the zinc atoms are ordered in the CaCu5 segment, while share the sites with aluminium in the Laves phase segment. In the pseudobinary section YbZn2-xAlx four structures occur in sequence with increasing the electron concentration: CeCu2 or KHg2 (x=0-0.3), MgZn2 (x=0.33-0.54), MgNi2 (x=0.68-1.01) and MgCu2 (x=1.12-2). This sequence agrees with the results of first-principles calculations, already reported in the literature for other similar series. In the YbZn3-xAlx section CeNi3-type compounds occur with x=0.40-0.88 followed by PuNi3-type compounds with x=0.92-1.10. The stability ranges of these phases are related to the valence electron concentration
Phases around the 1:1:1 composition in the Yb-Au-Ge and Ca-Au-Ge systems
No full textThe systems YbAu2-xGex and CaAu2-xGex with 0.7<x<1.3 were structurally examined by X-rays on powders and single crystals. In this range of composition nine phases occur, belonging to six closely related structure types: CeCu2, AlB2, EuAuGe (occupation derivative), SrAgGe, α-YbAuGe and β-YbAuGe (the last two being centrosymmetric variants of the CaCuGe type). The equiatomic compound CaAuGe shows a phase transition at 1238 K. YbAuGe crystallizes in three different structural modifications as a function of temperature: α-YbAuGe up to 1003 K, β-YbAuGe in the range 1003 to 1308 K and γ-YbAuGe at T>1308 K. Resistance measurements carried out in the range 14-400 K for the high-temperature forms of YbAuGe and CaAuGe show normal metallic behaviour. Magnetic susceptibility data of YbAuGe are in agreement with the occurrence of divalent ytterbium. © 1998 Elsevier Science S.A
On the physico-chemical characterization of high Tc superconducting defect-perovskite YBa2Cu3O7-x
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