TEM Study of the Electron-Doped Layered La2-2xCA1+2xMn207 : Orthorhombic Phase in 0.8

Published

March 1, 2001

Author(s)

Leonid A. Bendersky, R Chen, I D. Fawcett, M Greenblatt

Abstract

A series of Ruddlesden-Popper compounds with n = 2 and stoichiometry La_2-2xCa_1+2xMn₂0₇ were synthesized by a citrate gel technique and studied by TEM for the composition range 0.8 (less than or equal to) x (less than or equal to) 1.0. In-situ experiments and analysis of substructure/twins identified structural changes of the 14/mmm phase at low temperatures (200-350 C). Analysis of the reciprocal space identified super-lattice reflections (not previously detected by x-ray) and possible space groups. The low-temperature phase belongs to the non-centrosymmetric Cmc2₁ or Ama₂ space group, and the transient Cmcm space group is also possible. These structural transitions do not coincide with the magnetic transitions, which occur below room temperature. A structural model based on tilting of almost-rigid octahedra is suggested for Cmcm and Cmc2₁. The proposed model for the low temperature Cmc2₁ phase has a Φ Φ { Psi} _z) / Φ {Phi } Ψ _z combination of tilts, while the transient Cmcm has a { Phi} Φ 0 / Φ Φ 0 combination of tilts.

Citation

Journal of Solid State Chemistry

Volume

157

Issue

No. 2

Pub Type

Journals

Keywords

crystallography, La(sub 2-2x)Ca(sub 1+2xMn(sub 2)0(sub 7, manganates, phase transition, TEM

Citation

Bendersky, L. , Chen, R. , Fawcett, I. and Greenblatt, M. (2001), TEM Study of the Electron-Doped Layered La_2-2xCA_1+2xMn₂0₇ : Orthorhombic Phase in 0.8 < x < 1.0 Composition Range, Journal of Solid State Chemistry (Accessed July 27, 2024)