Chessboard/Diamond Nanostructures and the A-site Deficient, Li_1/2–3x Nd_1/2+xTiO₃, Defect Perovskite Solid Solution

Abstract

The crystal chemical origin of nanoscale chessboard/diamond ordering in perovskite-related solid solutions of composition Li 0.5−3x Nd 0.5+x TiO 3 (LNT, x ∼ 0.02−0.12) is investigated. Experimental and simulated scanning transmission electron microscopy (STEM) images are found to be consistent with the compositional modulation model proposed by previous authors. However, these earlier models do not satisfactorily explain other features observed in high-resolution STEM and TEM images, such as the two-dimensional {100} lattice fringes with the same periodicity, √2a p × √2a p , as the local LNT unit cell viewed along the [001] direction (where a p is the parent perovskite unit cell parameter). Based on bond valence sum calculations, we propose a new set of crystal structures for LNT in which Li ions are primarily bonded to only two O ions, and order one-dimensionally with √2a p periodicity. Bright-field STEM image simulations performed for this new model reproduced the experimentally observed √2a p lattice fringes, thus strongly suggesting that the finer features of the highresolution (S)TEM images are the result of Li ion ordering and associated local structural relaxation. In this new model, the LNT chessboard supercell then results from the ordered combinations of two sublattices: the Li ion sublattice and its translational variants on the one hand, and the Nd 0.5 TiO 3 sublattice and its oxygen octahedral tilt twin variants on the other. Dielectric measurements indicate the presence of long-lived polar clusters that are easily activated under an applied electric field. This suggests that these clusters consist of spatially correlated Li ions.

Characterization of Ordering in A-Site Deficient Perovskite Ca1–xLa2x/3TiO3 Using STEM/EELS

“…48 Taking up a morphology described as "nanochessboard", these domains were shown to correspond to strain arising from modulations in the octahedral titling, and not from chemical segregation, as suggested in earlier studies on similar systems. 49,50 In Nd 2/3−x Li 3x TiO 3 perovskites, analogous features in the microstructure, i.e. one-or twodimensional stripe patterns and nanochessboard arrangements, were correlated with parallel ordering and spinodal decomposition along different crystallographic directions.…”

Perovskite Based Photocatalyst for Wastewater Treatment: Green Approach of Environmental Sustainability

“…A good photocatalyst should have absorbance near 520 nm as the major portion of solar light consists of visible and NIR region [14]. The photocatalytic activity of perovskite material may be tuned in different ways of design due to their chemical stability and band structure characteristics [13,15,16]. The band gap of perovskite can be modified by the replacement of 'A' or 'B' or 'O' atoms or introduction of different kind atoms [14,17].…”

Coupled Compositional and Displacive Modulations in KLaMnWO6 Revealed by Atomic Resolution Imaging

“…In the case of the Nd 2/3– x Li 3 x TiO 3 , Guiton et al concluded nanoscale compositional ordering arising from interparticle phase segregation into Nd 1/2 Li 1/2 TiO 3 and Nd 2/3 TiO 3 coupled with periodic twinning of octahedral tilts to form domains in a chessboard like pattern. , Further investigations using a combination of techniques (mainly powder neutron diffraction and scanning transmission electron microscopy) opened an intense debate on the origin of the modulation of the crystal structure of these perovskites, supporting a displacive modulation of the octahedral tilting coupled to B-site cation displacements driven by second-order Jahn–Teller distortions. − However, the presence of a periodic modulation of the octahedral tilts does not preclude a compositional modulation. In fact, crystal chemistry considerations suggest that the two should be linked.…”