SmxY2-xO3 solid solutions are semimagnetic semiconducting materials with wide energy gaps. Magnetic properties of these materials are coupled with their structural and microstructural parameters. Evidently, it is of interest to investigate these parameters in order to explain magnetic properties of diluted magnets. All mixed sesquioxides SmxY2-xO3 (x = 0.2, 0.5, 0.7, 1.0, 1.4 and 1.7) crystallize in C-M2O3 crystal type in space group Ia3 with Y3+ and Sm3+ cations in 24(d) and 8(b) Wyckoff positions, respectively. The X-ray diffraction data were used to establish the distribution of magnetic ions over crystallographic positions 8(b) and 24(d). A random distribution was found. The same data were used for evaluation of the crystal size, microstrain and paracrystallinity. The concentration dependence of these values was concluded. Results show that unit cell parameters obey Vegard's rule, That fact leads to indirect information about well mixing of Y2O3 and Sm2O3. Agreement of the unit cell parameters with Vegard's rule is connected with the difference between cationic radii and electronegativity, The Sm3+-O2--Sm3+ bond geometry, important for the superexchange interaction, strongly depends on Sm3+ concentration. By comparing difference of unit cell parameters of the constitutive components Y2O3 and Sm2O3 and values of microstrains of their solid solutions it can be concluded that clusters are randomly formed.