KLn 2 Ti 3 O 9·5 (Ln = La,Nd,Sm,Gd,Dy): New family of layered perovskite oxides

A novel kind of layered perovskite type oxides KLn₂Ti₃O_9·5 (Ln = La, Nd, Sm, Gd, Dy) was fabricated by a stearic acid sol–gel method at a relatively low temperature (400–800°C) with reduced time (2–6 h) using Ti(OBu)₄, KOH, Ln₂O₃ and stearic acid as raw materials. The obtained KLn₂Ti₃O_9·5 nanocrystals with good dispersibility took on a square-like appearance, and the average size was about 20×20 nm. The unit cell data of KLn₂Ti₃O_9·5 were estimated by Jade.5, and the effect of lanthanide on the microstructure of KLn₂Ti₃O_9·5 was discussed on the basis of the tolerance factor t of perovskite type oxides. It was found that the obtained KLn₂Ti₃O_9·5 (Ln = La, Nd, Sm Gd, Dy) possessed the same layered perovskite type structure for t≥0·788. However, when Ln = Er (t<0·778), the product was Er₂Ti₂O₇ other than KEr₂Ti₃O_9·5. Possible reasons were proposed.