We have prepared by pulsed laser deposition La0.67Sr0.33MnO3 (LSMO)/SrTiO3 (STO)/LSMO tunnel junctions epitaxially grown on (001) STO. LSMO is rhombohedral in bulk (pseudo cubic with an angle of 89.74 degrees); its epitaxy on STO raises two kinds of questions: (1) are the interfaces chemically abrupt? (2) How is the geometrical mismatch (rhombohedron on cube) accommodated? We have investigated these issues using cross-sectional high-resolution transmission electron microscopy (HRTEM). We have shown previously that interdiffusion was absent, and that interfacial roughness was restricted to single unit cell steps [J.-L. Maurice, R. Lyonnet, J.-P. Contour, J. Mag. Mag. Mat. 211 (2000) 91]. Here, we present our results on atomic plane distortion measurements using quantitative Fourier analysis of the HRTEM micrographs. We show that a progressive twinning occurs that gives a full rhombohedral relaxation at a thickness of about 30 nm, with no need of dislocations.