Single crystal growth and properties of two layered oxytellurides*

We report on the synthesis, structure, and physical properties of two layered oxytellurides: Ba$_{3}$Yb$_{2}$O$_{5}$Te and Ba$_{2}$TeO. Both compound were grown in single crystalline form using a molten metal flux, and crystallize in a tetragonal space group: $P$4$/mmm$ for Ba$_{3}$Yb$_{2}$O$_{5}$Te and $P$4$/nmm$ for Ba$_{2}$TeO. Ba$_{3}$Yb$_{2}$O$_{5}$Te consists of Ba$_{2}$Yb$_{2}$O$_{5}$ perovskite double layers separated by a CsCl-type BaTe slab, while Ba$_{2}$TeO consists of an inverse PbO-type BaO layer separated by an NaCl-type BaTe slab. Ba$_{3}$Yb$_{2}$O$_{5}$Te displays short range 2D magnetic ordering below 4 K, and a sharp optical absorption feature at 1.27 eV consistent with a $^{2}F_{7/2}\rightarrow ^{2}F_{5/2}$ transition of Yb$^{3+}$. For Ba$_{2}$TeO, optical measurements display a sharp increase in absorbance, a manifest of a band edge. DOS corroborates the band gap, at 2.93 eV, indicating semiconducting behavior.