Crystal chemistry of the halite-related cation-deficient superstructure phase Yb7+δSe8 with δ = 0.24 and its relation to YbSe
Systematic phase studies on the system YbSe-Yb2Se3 revealed besides the two terminal compounds three intermediate phases Yb0.91Se, Yb0.83Se and Yb0.75Se, all of them without significant phase width, w
Thermodynamics of sublimation and formation of ytterbium (II) selenide
The congruent vaporization of solid ytterbium (II) selenide of practically stoichiometric composition was studied over the temperature range 1744-2040 K by the Knudsen effusion weight loss technique. Using enthalpy and entropy data for the gaseous species
Syntheses and crystal structures of the quaternary uranium lanthanide oxyselenides UYb2O2Se3 and U2Ln 2O4Se3 (Ln=Pr, Sm, Gd)
Single crystals of the new uranium lanthanide oxyselenide compounds UYb2O2Se3 and U2Ln2O 4Se3 (Ln=Pr, Sm, Gd) have been synthesized from an Sb 2Se3 flux. The structures have been determined from single-crystal X-ray diffraction data. UYb2O2Se 3 is isostructural to UYb2O2S3. The structure comprises layers of edge-sharing YbSe6 octahedra and double layers of disordered (U/Ln)O4Se4 square antiprisms. The U2Ln2O4Se3 (Ln=Pr, Sm, Gd) compounds are isostructural to U2Ln2O4S3 (Ln=LaGd) whose structure had been deduced previously from X-ray powder diffraction data. In the structure a dodecahedron of four O atoms and four Se atoms surrounds a site primarily occupied by U and a distorted bicapped octahedron of five Se atoms and three O atoms surrounds a site primarily occupied by the lanthanide. These compounds represent the first examples of quaternary uranium oxyselenides.
Thermodynamics of the thermal decomposition and formation of ytterbium (III) oxide selenide
The thermal decomposition of (YbO)2Se(s) was studied over the temperature range 1753-1997 K by the Knudsen effusion weight loss technique. It was found that the decomposition leads to a gas phase containing ytterbium and selenium with a molar ratio of 2:3 and to a residue of Yb2O3(s). Using literature and estimated enthalpy and entropy data for the gaseous species Yb, Se, YbSe and Se2, the principal decomposition reaction was established from the rates of effusion, and the second-law and third-law enthalpies and entropies were found for this reaction. A value of -1594±33 kJ mol-l is derived for the standard enthalpy of formation of (YbO)2Se(s). The feasibility of this value is discussed in view of the significant decrease in the formula volume accompanying the formation of (YbO)2Se from Yb2O3 and Yb2Se3.