Electron paramagnetic resonance and partial density of states of copper impurity ions in Рb$_2$МоО$_5$ crystals

The electron paramagnetic resonance (EPR) spectra of Cu$^{2+}$ impurity ions in crystals of double lead molybdate Рb$_2$МоО$_5$ have been investigated for the first time. It has been found that there is an additional splitting of the hyperfine structure lines due to the interaction of a copper electron spin with nuclei of the surrounding atoms. The components and directions of the principal axes of the $g$-factor, hyperfine interaction, and superhyperfine interaction tensors have been calculated based on measurements of the orientational dependences of the Cu$^{2+}$ EPR spectra. The anisotropy of the EPR spectra suggests that copper impurity ions are located in one of the two structurally nonequivalent sites Pb1 or Pb2. A numerical calculation of the partial density of states of copper impurity ions has been performed for two variants of the substitution centers Cu(Pb1) and Cu(Pb2). Based on the obtained results, the localization of copper centers in the structure of Рb$_2$МоО$_5$ crystals has been discussed.