Thus, the apparent solubility limit of tungsten in SrTiO3 should be below 6 mol %. These precipitates are found preferentially inside pores of as-fired samples, as illustrated by Figure 4, and corresponding EDS maps confirm that the segregated particles (50−300 nm) are enriched in tungsten. XRD (Figure 1B) suggests that these are metallic W, and the high refractoriness of metallic tungsten might explain the ability to retain nearly nanostructure particles after the sintering cycle. In addition, EDS maps show that these precipitates are also Sr-rich, possibly corresponding to the residual liquid phase upon precipitation of metallic W particles. In any case, spontaneous segregation of nanostructured W-rich precipitates, achieved by sintering under reducing atmospheres, may be favorable for suppressing the thermal conductivity, by providing efficient phonon scattering at the formed interfaces, as shown below.