Volume deviations of defects-induced ZnSe crystals were investigated using X-ray diffraction. Point defects were introduced due to annealing stoichiometric ZnSe in Zn or Se ambience. The lattice constant of the sample annealed in Se ambience decreased with deviation rates of 10(-5). On the other hand, the deviations for the sample annealed in Zn were small within the errors. Positron annihilation experiments showed that vacancy-type defects increased in the former whereas no increase was observed in the latter. The vacancy could induce crystals to shrink. The results suggest that tensile stresses would suppress generations of vacancies. The defect properties were discussed using photoluminescence spectra and secondary ion mass spectrometry. The Se-annealed samples would involve a self-activated (SA) center consisting of Zn-vacancy and Li-interstitial. (C) 2002 Elsevier Science B.V. All rights reserved.