In the present work, tetragonal beta type Bi( III)(2-2x) Dy( II)(2x)O3- x square x (square: empty oxygen site) solid solutions have been synthesized in the ranges 0.06 <= x <= 0.08 at 750 degrees C and 0.05 <= x <= 0.09 at 800 degrees C by doping small amounts of Dy2O3 into monoclinic alpha-Bi2O3. X-ray powder diffraction (XRD) has been used for characterisation of the doped Dy2O3 powders as well as for calculation of the unit cell parameters. The polymorphic phase transitions, crystallographic properties, particle sizes, the scanning electron microscope (SEM) microprobe analysis and Dy2O3 content dependence of the lattice parameters of the observed beta-phase has been reported. The obtained solid solutions had nonstoichiometric character and nonstoichiometry increases with the increasing amount of Dy2O3 addition. The experimental results suggested that oxygen vacancies are present in the crystal structure of Dy2O3 doped type solid solutions. (C) 2005 Springer Science + Business Media, Inc.