[en] Yttrium-doped uranium brannerite (U_1-xY_xTi₂O₆) and thorutite (Th_1-xY_xTi₂O_6-δ) phases were synthesized in air at 1400 deg. C. Powder X-ray diffraction revealed that these phases crystallized to form monoclinic (C2/m) structures. Crystal structures of U_0.54Y_0.46Ti₂O₆ (1) (a=9.8008(2); b=3.7276(1); c=6.8745(1); β=118.38(1); V=220.97(1); Z=2; R_P=7.3%; R_B=4.6%) and Th_0.91Y_0.09Ti₂O_6-δ (2) (a=9.8002(7); b=3.7510(3); c=6.9990(5); β=118.37(4); V=226.40(3); Z=2; R_P=4.5%; R_B=2.9%) were refined from powder neutron diffraction data. These two phases were isostructural, revealing planes of corner and edge-sharing TiO₆ octahedra separated by irregular eight-fold coordinate U/Y or Th/Y atoms. The oxygen sites within the structure of 1 were found to be fully occupied, confirming that the doping of lower valence Y atoms occurs in conjunction with the oxidation of U(IV) to U(V). Y doping of the thorutite phase 2 does not lead to oxidation but rather the formation of oxygen vacancies within the structure