Protonated Forms of Layered Perovskite-Like Titanate NaNdTiO4: Neutron and X-ray Diffraction Structural Analysis

Oleg I Silyukov,Iana A Minich,Sergey A Kurnosenko,Ivan A Rodionov,Irina A Zvereva

doi:10.3390/solids2030017

Abstract

Structures of partially and completely protonated Ruddlesden–Popper phases, H0.7Na0.3NdTiO4·0.3H2O and HNdTiO4, have been established by means of neutron and X-ray diffraction analysis and compared among themselves as well as with that of the initial titanate NaNdTiO4. It was shown that while interlayer sodium cations in the partially protonated form are coordinated by nine oxygen atoms, including one related to intercalated water, in the fully protonated compound the ninth oxygen proves to be an axial anion belonging to the opposite slab of titanium-oxygen octahedra. Moreover, the partially protonated titanate was found to significantly differ from the other two in the octahedron distortion pattern. It is characterized by a weakly pronounced elongation of the octahedra towards the Nd-containing interlayer space making Ti4+ cations practically equidistant from both axial oxygen atoms, which is accompanied by a low-frequency shift of the bands relating to the asymmetric stretching mode of axial Ti–O bonds observed in the Raman spectra.

Highlights

H0.7 Na0.3 NdTiO4 ·0.3H2 O and HNdTiO4, have been established by means of neutron and X-ray diffraction analysis and compared among themselves as well as with that of the initial titanate
Ion-exchangeable layered perovskites are crystalline solids possessing a block-type structure, which consists of negatively charged intergrowth slabs with a thickness of n corner-shared perovskite octahedra regularly alternating with interlayer spaces populated by alkali cations
In view of the foregoing, the present paper focuses on a structural study of two protonated forms of the layered perovskite-like titanate NaNdTiO4, namely the partially protonated form

Summary

Introduction

H0.7 Na0.3 NdTiO4 ·0.3H2 O and HNdTiO4 , have been established by means of neutron and X-ray diffraction analysis and compared among themselves as well as with that of the initial titanate. Ion-exchangeable layered perovskites are crystalline solids possessing a block-type structure, which consists of negatively charged intergrowth slabs with a thickness of n corner-shared perovskite octahedra regularly alternating with interlayer spaces populated by alkali cations. The structure of the Ruddlesden–Popper phases, described by a formula A’2 [An−1 Bn O3n+1 ], represents alternation of perovskite slabs with the layers adopting the crystal arrangement of rock salt. The reactivity of the Ruddlesden–Popper perovskites is known to be lower in comparison with that of the Dion–Jacobson ones, it appears to be enough for ion exchange and intercalation of small molecules via the soft chemistry approaches [36,37,38,39,40,41]

Methods

Results

Conclusion