Phase studies in the Rb–Sr–U–O system: characterisation of new phases

The subsolidus phase relations in the Rb–Sr–U–O system were determined at 900 °C. Two new quaternary phases Rb2Sr2U4O15 and Rb8Sr2U6O24 in the Rb–Sr–U–O system were synthesized by heating the respective oxides at 900 °C in air. A pseudo-ternary phase diagram of Rb2O–SrO–UO3 was drawn using the new quaternary compounds, and various phase fields were established by X-ray powder diffraction analysis. X-ray powder diffraction (XRD) data of Rb2Sr2U4O15 were indexed by a monoclinic system with cell parameters, a=0.7875(4) nm, b=1.3199(4) nm, c=0.6667(5) nm and β=104.93(8)°, whereas XRD data of Rb8Sr2U6O24 were indexed by a cubic cell with a=0.8743(1) nm. The structure of Rb8Sr2U6O24 was derived from the powder data and structural parameters were refined by the Rietveld profile method.