Magnetic, optical, and electrical properties of solid solutions VxFe1−x BO3

Complex studies of magnetic, electrical, and optical properties of V_x Fe_1?x BO₃ solid solutions are carried out in the entire range of concentrations between the extreme compounds VBO₃ and FeBO₃. A concentration semiconductor-insulator transition accompanied by a change in the magnetic structure is observed. It is found that the physical properties of the solid solution under investigation differ from those predicted in the model of a virtual crystal in the form of an aggregate of V and Fe centers taken with the weight of x and 1?x, respectively. The systems of electron energy levels of the VB₆O₆ and FeB₆O₆ clusters are calculated from first principles using the Hartree-Fock method. The calculated electron structure forms the basis for simulating the optical absorption spectra, which are in good agreement with experimental results. A qualitative explanation is given for the entire body of data on electrical conductivity and magnetization.