[en] The solid solubilities of some or all of Cs, Sr, Y, La, U, Th, and Na in each of barium hollandite, zirconolite and titanite were investigated by X-ray diffraction in samples prepared by ceramic techniques at 1100-1400⁰C. Various charge compensation schemes were used in attempts to incorporate aliovalent ions. Cs and Sr, but not the other ions, have extensive solid solubilities in barium hollandite. Zirconolite dissolves relatively large amounts of Na, as well as actinides and the smaller rare earths. Appreciable amounts of Sr, Na, rare earths, and actinides can be accommodated in titanite. Titanite is compatible with zirconolite but not with barium hollandite at about 1200⁰C