Abstract
The crystal structures of seven samples of orthorhombic (Pnma) Ln2TiO5 compounds with Ln=La, Pr, Nd, Sm, Gd, Tb and Dy were refined by Rietveld analysis of synchrotron X-ray powder diffraction (S-XRD) data. With increasing size of the lanthanide cation, the lattice parameters increase systematically: c by only ~1.5% whereas both a and b by ~6% from Dy2TiO5 to La2TiO5.The mean Ti–O bond length only increases by ~1% with increasing radius of the Ln cation from Gd to La, primarily due to expansion of the pair of Ti–O3 bonds to opposite corners of the Ti–O5 square based pyramid polyhedra. For Dy2TiO5 and Tb2TiO5, a significant variation in Ti–O1 and Ti–O4 bond lengths results in an increased deformation of the Ti–O5 base.The particular configuration consists of large rhombic shaped tunnels and smaller triangular tunnels along the b axis, which have implications for defect formation and migration caused by radiation damage or the ionic conductivity.
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