Positron annihilation lifetime and Doppler broadening spectroscopies were applied in solid mixtures and solutions of AIK(SO4)(2) . 12H(2)O and CrK(SO4)(2) . 12H(2)O. For the solid solutions of the general formula Al(1 - x)Cr(x)K(SO4)(2) . 12H(2)O (x = Cr(III)), a strong inhibition of positronium formation is observed with increasing chromium complex concentration. In the solid mixtures, the positronium formation decreases linearly with CrK(SO4)(2) . 12H(2)O concentration, while the positronium lifetime remains constant for both solid binary mixtures and solutions. The experimental results are satisfactorily explained on basis of the spur model. (c) 2005 Elsevier B.V. All rights reserved.