Homogeneous fields of Sr4 - x M x Nb 2O9 (M = Cd, Cu, Ni, or Zn) solid solutions were determined using powder X-ray diffraction. Phase fields were plotted proceeding from the tolerance factor t and electronegativity ratio κ̄ A/κ̄B with a satisfactory fit of experimental results. Thermogravimetry was used to establish the major kinetic laws of solid-phase synthesis (conversion, rate-controlling stage, and effective activation energy) in (4 - x)SrCO3 + xMO + Nb2O 5 powdery mixtures. Direct radiometry was used to determine 90Sr, 63Ni, and 65Zn self-diffusion coefficients in solid solutions based on the Sr4Nb2O 9 phase. Electrical conductivity was measured as a function of temperature for all Sr4Nb2O9-"M 4Nb2O9" samples. The conductivity of Sr4 - x M x Nb2O9 (M = Cd, Cu, Ni, or Zn) solid solutions has a mixed ion-electron character. © 2010 Pleiades Publishing, Ltd.