The crystal and oxygen defect structure of the n=2 Ruddlesden-Popper phase Sr3Fe2O6+delta have been studied by in situ high temperature neutron powder diffraction in the temperature range 20 <= T <= 900 degrees 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 theFeO, planes of the perovskite layers. The oxygen vacancies on the O(3) site increase with temperature up to similar to 0.25 per formula unit at T = 900 degrees C. This result supports previously proposed oxygen ion diffusion mechanism in Sr3Fe2O6-delta that involves the migration of vacancies from an 0(3) site to an adjacent 0(l) site. The total linear expansion along the c axis alpha(c) = 17.7(5) center dot 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 alpha(v)/3 = 20(1) center dot 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-delta. (c) 2006 Elsevier B.V. All rights reserved.