Cation distributions and possible phase separation in Tl2Ba2CuO6+δ from synchrotron powder x-ray diffraction

Orthorhombic and tetragonal Tl2Ba2CuO6+δ (Tl-2201) samples have been studied using resonant synchrotron x-ray powder diffraction data at energies just below the Cu K and Tl LIII absorption edges. The resonant contributions enable us to demonstrate that Cu substitutes at the Tl site; the tetragonal structure is stabilized by a higher (5.5%) degree of substitution than the orthorhombic (<1%) material, in excellent agreement with electron probe microanalysis results. A slight splitting of some diffraction peaks of oxygen-rich orthorhombic Tl-2201 is consistent with a phase separation due to the segregation of interstitial oxygens.