Solid Solubility of Holmium, Yttrium, and Dysprosium in BaTiO 3

The solid solubility of R ions (R = Ho 3+ , Dy 3+ , and Y 3+ ) in the BaTiO 3 perovskite structure was studied by quantitative electron‐probe microanalysis (EPMA) using wavelength‐dispersive spectroscopy (WDS), scanning electron microscopy (SEM), and X‐ray diffractometry (XRD). Highly doped BaTiO 3 samples were prepared using mixed‐oxide technology including equilibration at 1400° and 1500°C in ambient air. The solubility was found to depend mainly on the starting composition. In the TiO 2 ‐rich samples a relatively low concentration of R incorporated preferentially at the Ba 2+ lattice sites (solubility limit ∼Ba 0.986 R 0.014 Ti 0.9965 (V ″ Ti ″ ) 0.0035 O 3 at 1400°C). In BaO‐rich samples a high concentration of R entered the BaTiO 3 structure at the Ti 4+ lattice sites (solubility limit ∼BaTi 0.85 R 0.15 O 2.925 (V O •• ) 0.075 at 1500°C). Ho 3+ , Dy 3+ , and Y 3+ incorporated preferentially at the Ti 4+ lattice sites stabilize the hexagonal polymorph of BaTiO 3 . The phase equilibria of the Ho 3+ –BaTiO 3 solid solutions were presented in a BaO–Ho 2 O 3 –TiO 2 phase diagram.