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Reactions of Lanthanides and Actinides in Molten Alkali Metal/Polychalcogenide Fluxes at Intermediate Temperatures (250−600 °C)

1997; American Chemical Society; Volume: 9; Issue: 1 Linguagem: Inglês

10.1021/cm960448s

1520-5002

Anthony C. Sutorik, Mercouri G. Kanatzidis,

Iron-based superconductors research

From the reaction of the elemental lanthanides and actinides in molten alkali metal/polychalcogenide salts, several new ternary compounds have been discovered. Specifically, these phases are K4USe8 (I) and ALnQ4 (II), where A = K, Ln = Ce or Tb, and Q = Se or A = Rb, Ln = Ce, Q = Te; and NaLnS3 (III), where Ln = La, Ce. The K4USe8 crystallizes in the orthorhombic space group Fdd2 (No. 43) with a = 17.331(4) Å, b = 20.584(3) Å, c = 8.811(3) Å, Z = 8. The KCeSe4 crystallizes in the tetragonal space group P4/nbm (No. 125) with a = 6.376(2) Å, c = 8.327(1) Å, Z = 2. The KTbSe4 crystallizes in the tetragonal space group P4/nbm (No. 125) with a = 6.255(2) Å, c = 8.227(1) Å, Z = 2. The RbCeTe4 crystallizes in the tetragonal space group P4/nbm (No. 125) with a = 6.952(3) Å, c = 9.084(4) Å, Z = 2. The NaCeS3 crystallizes in the orthorhombic space group Pmmn (No. 59) with a = 5.683(1) Å, b = 4.238(2) Å, c = 9.802(2) Å, Z = 2. The NaLaS3 crystallizes in the orthorhombic space group Pmmn (No. 59) with a = 5.752(4) Å, b = 4.2796(6) Å, c = 9.841(2) Å, Z = 2. Compound I features discrete [U(Se2)4]4- anions, while (II) and (III) possess extended structures in which the lanthanide and chalcogenide atoms form infinite two-dimensional layers. In II the lanthanide cations are in square antiprismatic coordination environments, connected into layers by Q−Q bonds. In III, the lanthanides bond to a mixture of mono- and disulfides in a bicapped trigonal prismatic geometry; these polyhedra subsequently connect in two dimensions, forming layers equivalent to those seen in the ZrSe3 structure type. Details of the synthesis, structure, and properties of these compounds are discussed.