Compounds Sr₂Ln₄Ti₂Ta₄O₂₂ (Ln=La, Pr) with heteroblock slab perovskite-like structure

Phase ratios in systems Sr₂Ln₂Ti₂Ta₂O₁₄+Ln₂Ta₂O₈ (Ln = La, Pr), Sr₂Ln)2Ti₂Ta₂O₁₄+2LnTaO₄ (Ln = Nd, Sm), Sr₂La₂Ti₂Nb₂O₁₄ + 2LaNbO₄, and La₄Ti₄O₁₄ + 2LaNbO₄ are investigated. The formation of new compounds Sr₂Ln₄Ti₂Ta₄O₂₂ (Ln = La, Pr) with heteroblock layered perovskite like structure from the charge of co-precipitated hydroxycarbonates, whose hetero blocks include four layer block Sr₂Ln₂Ti₂Ta₂O₁₄ and two-layer block Ln₂Ta₂O₈, is established. The impossibility of a crystallochemical stabilization of two-layer blocks of high pressure modification Nd₂Ta₂O₈ and La₂Nb₂O₈ in ((4)(2)) hetero blocks of Sr-containing compounds is shown