Ordered Rock-Salt Related Nanoclusters in CaMnO₂

Abstract

Oxygen engineering techniques performed under adequate controlled atmosphere show that the CaMnO(3)-CaMnO(2) topotactic reduction-oxidation process proceeds via oxygen diffusion while the cationic sublattice remains almost unaltered. Extra superlattice reflections in selected area electron diffraction patterns indicate doubling of the CaMnO(2) rock-salt cell along the cubic directions of a distorted rhombohedral cell originated by ordering of Ca(2+) and Mn(2+) ions distributed in nanoclusters into a NaCl-type matrix, as evidenced by dark field electron microscope images. The local nature of the information provided by the transmission electron microscopy techniques used to characterize the rock-salt type Ca(1-x)Mn(x)O(2) solid solution clearly hints at the existence of subtle extra ordering in other upper oxides of the Ca-Mn-O system. The combination of local characterization techniques like electron microscopy with more average ones like powder X-ray and neutron diffraction allows a very complete characterization of the system.

Mn(I) in an Extended Oxide: The Synthesis and Characterization of La1–xCaxMnO2+δ(0.6 ≤x≤ 1)

“…X-ray powder diffraction data, collected from the washed products of the reactions between La 1Àx Ca x MnO 3 phases and NaH (Figure 1), could be readily indexed using the unit cells listed in Table 1. Data collected from the x = 1 and x = 0.9 samples are consistent with reduced materials adopting rock-salt structures with disordered cation 25 Structural models based on cationdisordered rock salt structures gave good statistical fits to the X-ray (x = 1, 0.9) and neutron (x = 0.9) powder diffraction data collected from these reduced samples, confirming this structural assignment as detailed in the Supporting Information. In contrast to data from the calcium-rich phases, X-ray powder diffraction data collected from reduced phases of composition La 1Àx Ca x MnO 3Ày (0.6 e x e 0.7) could be indexed using primitive tetragonal unit cells, suggesting that the cation lattice of the parent perovskite materials has been retained in these reduced products.…”

CaxLa1–xMn1–yMyO3−δ (M = Mg, Ti, Fe, or Cu) as Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)

“…The regeneration of the parent perovskite CM upon oxidation (bottom of Figure 11) is in accordance with several studies. 20,24, 31,32 (2) In the case of A-and B-site-doped particles (CLMT, CLMF, and CLMM), the XRD patterns looked very similar to one another in all cases without any evidence of CaMnO 2 formation after reduction by synthesis gas. This suggests that the doubly doped compounds are less prone to phase separation, as opposed to their undoped and singly doped analogues.…”

Structural Characterization and Evolution of the Electronic Behavior of New Sr2−xGdxMnTiO6 (0≤x≤1) Perovskites

“…ED and microscopy techniques have been applied in the literature to evaluate the possible cation ordering in a local range, as established in other related compounds like CaMnO 2 29 . A microstructural study has then been carried out on all samples in order to explore the possible existence of defects and/or structural disorder, which are key features in order to understand the electronic properties.…”