Neutron powder Diffraction Study at High Temperature of the Ruddlesden-Popper Phase Sr3Fe2O7-d

F. PRADO; L. MOGNI; G. CUELLO; A. CANEIRO

SOLID STATE IONICS

Elsevier

Año: 2007 vol. 178 p. 77 - 82

0167-2738

The crystal and oxygen defect structure of the n = 2 Ruddlesden-Popper phase Sr3Fe2O6+ have been studied by in-situ high temperature neutron powder diffraction in the temperature range 20  T  900 °C in air. The analysis of the neutron diffraction data revealed the presence of structural oxygen vacancies on both the O(1) sites linking the octahedra along the c-axis and the O(3) sites in the FeO2 planes of the perovskite layers. The oxygen vacancies on the O(3) site increase with temperature up to  0.25 per formula unit at T = 900 °C. This result supports previously proposed oxygen ion diffusion mechanism in Sr3Fe2O6+that involves the migration of vacancies from an O(3) site to an adjacent O(1) site. The total linear expansion along the c axis c =17.7(5)∙10?6 K?1 mainly affects the perovskite block while the width of the rock salt layers remains stable with temperature. The total volumetric expansion v/3 = 20 (1) 10?6 K?1 is around the average of the TEC values (14.8-27.1 K-1) reported for the perovskite system La1?xSrxCo1?yFeyO3?.