The additional secondary phase found in the sample calcined at 1200 °C (reflection at 2𝜃=29.5° in Figure ) could not be conclusively identified as one of the room-temperature stable polytitanates (BaTi2O5, BaTi4O9, and BaTi5O11) currently known to exist in the BaO-TiO2 phase diagram . The observed phase might in fact be a mixture of several phases, either formed due to sluggish diffusion or after eutectoid decomposition of (Ba,Ca)6(Zr,Ti)17O40 or (Ba,Ca)4(Zr,Ti)13O30. Furthermore, the substituted Ca 2+ -ions and Zr 4+ -ions could influence the structure and thermodynamic stability of these secondary phases . To verify the phase composition, we synthesized a sample with the nominal composition (Ba,Ca)6(Zr,Ti)17O40 (Figure ). The recorded diffraction pattern agrees well with the reflection of the secondary phase, visible in the BCZT sample, confirming that the additional reflections can be attributed to Ti-excess. However, no clear identification of either residual Ba6Ti17O40 or the expected stable phases BaTi2O5 and BaTi4O9 was possible and a significant fraction of BCZT perovskite phase was also present in the system. While we could confirm that the formation of the polytitanate secondary phase found in BCZT is related to an intrinsic B-site excess in the material, the exact structure and composition could not be conclusively identified yet.