Solid Solubility of Holmium, Yttrium, and Dysprosium in BaTiO3

The solid solubility of R ions (R = Ho3+, Dy3+, and Y3+) in the BaTiO3 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 BaTiO3 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 TiO2-rich samples a relatively low concentration of R incorporated preferentially at the Ba2+ lattice sites (solubility limit ∼Ba0.986R0.014Ti0.9965(V″Ti″)0.0035O3at 1400°C). In BaO-rich samples a high concentration of R entered the BaTiO3 structure at the Ti4+ lattice sites (solubility limit ∼BaTi0.85R0.15O2.925(VO••)0.075at 1500°C). Ho3+, Dy3+, and Y3+incorporated preferentially at the Ti4+ lattice sites stabilize the hexagonal polymorph of BaTiO3. The phase equilibria of the Ho3+–BaTiO3 solid solutions were presented in a BaO–Ho2O3–TiO2phase diagram.

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