Synthesis of Nanosized (1−x)NaNbO3−xSrTiO3 Solid Solution by Mechanochemical Activation, Processing of Ceramics, and Phase Transitions

A novel mixed technique based on wet-chemistry plus mechanochemical activation has been applied to obtain the Na 1- x Sr x Nb 1- x Ti x O 3 solid solution with x = 0.1, 0.25, 0.5, 0.75, and 0.9. The wet-chemistry step aims at a better mixing of the constituent elements before the mechanical treatment, and thus, at a better reactivity during the activation step. Milled powders were studied by thermogravimetry (TG), differential thermal analysis (DTA), and X-ray diffraction (XRD). Incipient formation of a perovskite-type oxide of the NaNbO 3 −SrTiO 3 system by mechanosynthesis at room temperature was observed in the whole range of compositions. Mechanical treatment was followed by annealing at different temperatures to establish the optimized protocol for the synthesis of each member of the solid solution, as a single phase, with very important decreases in the formation temperatures (up to 600 °C) and reaction times (several days), as compared with the traditional ceramic method due to the high reactivity of the mechanically activated powders. Dense ceramics can be processed from these mechanosynthesized precursors. The ceramic samples were used to study phase transitions in the solid solution by measurement of the dielectric permittivity as a function of the temperature.