Probing local symmetry changes in LaMnO3.12 rhombohedric-orthorhombic phase transition

A.M.L. Lopes 2,5Joao P. Araujo 3E. Rita 1,5J. G. Correia 1,5V. S. Amaral 2Yuan Li 2J. M. Vieira 4R. Suryanarayanan 6ISOLDE Collaboration 5

1. Instituto Técnológico Nuclear (ITN), Sacavém 2686, Portugal
2. Universidade de Aveiro, Departamento de Fisica and CICECO (UA), Campus de Santiago, Aveiro 3810-193, Portugal
3. Departamento de Fisica and IFIMUP, Universidade do Porto (UP), Rua do Campo Alegre, 687, Porto 4169-007, Portugal
4. Universidade de Aveiro, Departamento de Engenharia Cerâmica e do Vidro and CICECO (UA), Campus de Santiago, Aveiro 3810-193, Portugal
5. European Centre for Nuclear Research (CERN), Geneva CH1211, Switzerland
6. Laboratoire de Physico-Chimie de l'Etat Solide, bât 414, Université Paris-Sud, Orsay 91405, France


It is well established that the LaMnO3+δ system presents a rich variety of structural (rhombohedral, orthorhombic) and magnetic (antiferromagnetic or ferromagnetic) phase as a function of the oxygen content (δ) or as a function of temperature (T). To deeply understand the Rh-Orth phase transition we combined High Resolution TEM, Perturbed Angular Correlation (PAC) and X-ray powder diffraction (XRD) studies in the temperature range 10-323 K in polycrystalline sample prepared by solid state reaction method. From the PAC signal we determined the Electrical Field Gradient (EFG) parameters which are sensitive to the charge distribution around the probe vicinity and therefore to the local symmetry of the crystal. In the 10-323 K temperature range two different EFG were measured revealing two different local environments. Phase coexistence was found in large temperature range. The measured EFG were assigned to the Rh/Orth local environment. Within the same temperature range the ED-HRTEM and bright/dark field imaging results showed the existence of laths and twinning domains of different crystalline simmetry. This data and the complementary 2 line shifts observed by XRD suggest a displacive martensite like Rh-Orth phase transition.

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Presentation: poster at E-MRS Fall Meeting 2003, Symposium D, by Armandina L. Lopes
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-28 03:40
Revised:   2009-06-08 12:55
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