Ca1 – 2xBi2xMo1 – xGexO4 solid solutions with a scheelite-like structure (space group I41/a) and the homogeneity range х = 0.0–0.4 were prepared using standard ceramic technology. The unit cell parameter с and unit cell volume increase as the dopant concentration increases due to the changing size of Ca/BiO8 polyhedra. The predominant thermal expansion of Ca/BiO8 polyhedra was inferred from the temperature-dependent unit cell parameters and Raman spectral patterns. The Ca/Bi–O and Mo/Ge–O bond lengths were calculated. The increasing dopant concentration decreases the thermal expansion coefficient of the ceramics and increases the electrical conductivity and activation energy of the complex oxides compared to the matrix compound. The effective oxygen diffusion coefficient is determined.