BaTiO3 solid solutions co-doped with Gd3+ and Eu3+: Synthesis, structural evolution and dielectric properties

Abstract

In this paper, the synthesis, structural evolution, and dielectric properties of BaTiO3 solid solutions co-doped with rare earth elements (Gd3+ and Eu3+) prepared using the solid-state reaction method are presented. Chemically pure precursor powders of BaCO3, TiO2, Gd2O3, and Eu2O3 were mixed in stoichiometric proportions, ground in an agate mortar before being uniaxially pressed at 250 MPa and sintered at 1300 °C in air atmosphere for 6 h to obtain Ba1–3xGd2xTi1–3xEu4xO3 (x = 0, 0.0015, 0.01 and 0.1). X-ray diffraction (XRD) and Rietveld's refinement results reveal the crystal phase ferroelectric tetragonal BaTiO3 for the samples with x = 0, 0.0015 and 0.01, as well as a consistent increment in the lattice parameters caused by the doping. The solubility limit of Gd3+ and Eu3+ in the BaTiO3 structure is reached for the sample with x > 0.01, and the orthorhombic Eu2TiO5 and monoclinic BaTi2O5 secondary phases were identified. The Raman results show the characteristic peaks of ferroelectric tetragonal BaTiO3 around 716 cm−1 (LO of A1 symmetry), 515 cm−1 (TO of A1 symmetry), and 305 cm−1 (B1). The maximum relative permittivity measured at 1 kHz was recorded to be 6151.8 for the sample with x = 0.0015, and a decrease in the Curie temperature to 105 °C with respect to the undoped sample was observed. The punctual microanalysis for the samples with x = 0.0015, 0.01, and 0.1 reveals grains composed of Ba, Ti, O, Gd, and Eu homogeneously distributed in the BaTiO3 structure. The Ba/Ti ratios for samples with x = 0.0015, 0.01 and 0.1 are 2.86, 2.91, and 0.68, respectively, indicating substitution at the Ti site for samples with x = 0.0015 and 0.01 and a substitution at the Ba site for the sample with x = 0.1.