Na₂Ln₂Ti_3-xMn_xO₁₀ (Ln = Sm, Eu, Gd, and Dy; 0 ≤, x ≤ 1): A new series of ion-exchangeable layered perovskites containing B-site manganese

Na₂Ln₂Ti_3-xMn_xO₁₀ (Ln = Sm, Eu, Gd, and Dy; 0 ≤ x ≤ 1), a new series of triple-layer Ruddlesden-Popper phases, were synthesized by direct solid-state reaction. The smaller lanthanides enhance manganese solubility in the parent titanate, and an optimized synthetic approach allows Na₂Ln₂Ti_3-xMn_xO₁₀ to be stabilized relative to competing single-layer and cubic phases. The X-ray diffraction patterns of Na₂Ln₂Ti_3-xMn_xO₁₀ can be indexed on a tetragonal unit cell with a doubled a axis. The Na₂Ln₂Ti_3-xMn_xO₁₀ phases undergo ion exchange, forming A₂Ln₂Ti_3-xMn_xO₁₀ (A = Li, NH₄) by exchange in the molten nitrates. Na₂Ln₂Ti_3-xMn_xO₁₀ is also amenable to divalent ion exchange, evidenced by the formation of A^IIGd₂Ti₂MnO₁₀ (A^II = Mg, Ca) by ion exchange in aqueous MgCl₂ and Ca(NO₃)₂, respectively. Temperature-dependent magnetic susceptibility measurements indicate that the Na₂Ln₂Ti_3-xMn_xO₁₀ phases are paramagnetic and suggest the onset of weak magnetic ordering at low temperatures (<10 K).