$A_2Ln_2Ti_3O_{10}$ (A = potassium or rubidium; Ln = lanthanum or rare earth): a new series of layered perovskites exhibiting ion exchange

Several layered perovskites $A_2Ln_2Ti_3O_{10}$ (A = K or Rb; Ln = rare earth) and their monohydrates, crystg. in tetragonal structures related to ${Sr_4Ti_3O_10}$, were prepd. The alkali ions in $K_2Ln_2Ti_3O_{10}$ are topochem. exchanged by protons in aq. acid or by other alkali ions in molten salts. $H_2Ln_2Ti_3O_{10}$ also adopt a tetragonal structure similar to the parent oxides. Dehydrated $H_2La_2Ti_3O_{10}$ crystallizes at 1000 giving a new defect perovskite, $La_2/3TiO_3$, possessing a tetragonal structure