Papers by Keyword: Jahn-Teller Distortion

Abstract: The simple perovskite manganite Sr_1-xCe_xMnO₃ (SCMO) has a highly-correlated electronic system with a three-dimensional character. Because the presence of orbital-ordered states of e_g electrons can be expected in SCMO, the crystallographic features of SCMO samples with 0.09 ≤ x ≤ 0.20 have been investigated mainly by transmission electron microscopy. In addition to fundamental reflections due to the simple perovskite structure, their electron diffraction patterns at room temperature exhibited both the presence of superlattice reflections at k = ()_c in the cubic notation and the splitting of fundamental and superlattice reflections. The careful analysis of these reflections indicated that the superlattice reflections originated from the R₂₅-type rotational displacement of oxygen octahedra about one of the <100>_c directions. On the other hand, the splitting of the reflections was found to be due to a {110}_c banded structure consisting of two tetragonal bands with different c/a values.　Because one of two tetragonal bands had the c/a value of about 1.028, the splitting reflects the introduction of the Jahn-Teller distortion as a response of a lattice system to orbital ordering. It is thus understood that the C-type orbital ordering of e_g electrons should be involved in the state at room temperature for 0.09 ≤ x ≤ 0.20 in SCMO.

Abstract: We studied in detail the lattice transition and local lattice structure (including Jahn-Teller distortion) in LaMnO₃/SrMnO₃ surperlattices by classical atomistic simulation. For a certain doping density, it is found that the superlattices with short modulation period have small lattice energies and larger differences among lattice parameters a, b/√2 and c. The average La-Mn (Mn³⁺-O) distance is larger than the average Sr-Mn (Mn⁴⁺-O) distance for all doping densities and superlattice configurations at certain doping density. The standard deviation of Mn-O bond lengths and Jahn-Teller distortion of MnO₆ octahedra have been calculated. Both the standard deviation and Jahn-Teller distortion of Mn³⁺O₆ octahedra in the superlattices are much smaller than those of Mn³⁺O₆ octahedra in LaMnO₃, while Mn⁴⁺O₆ octahedra in the superlattices have the smallest lattice distortion, but larger than those in SrMnO₃.

Abstract: LiM(M=Fe,Al,Mg)XMn2-XO4 fine powders were synthesized by the ultrasonic spray pyrolysis using metal nitrate solution. LiMn2O4 powders obtained by this method have a spherical morphology with a submicron size. XRD revealed that as-prepared powders were crystallized to spinel structure with Fd3m space group. LiM(M=Fe,Al,Mg)XMn2-XO4 showed enhanced cycling performance at room temperature. Reduced Jahn-Teller distortion of LiMn2O4 by metal doping was responsible for enhanced cycle performance of LiMn2O4.