Exploration of a Ca1−x(NaCe)x/2Bi4Ti3.98(WNb)0.01O15 ceramic intermediate phase by temperature-dependent spectroscopic ellipsometry and Raman scattering

Abstract

Different doping concentrations of Ca1−x(NaCe)x/2Bi4Ti3.98(WNb)0.01O15 (x=0, 3%, 4%, 5%, and 6%) were prepared by a traditional solid state reaction method. The effects of doping on the crystal structure, dielectric constant, electronic transitions, and lattice dynamics of doped CaBi4Ti4O15 were investigated by x-ray diffraction, temperature-dependent spectroscopic ellipsometry, and Raman scattering. The results showed that, when x<4%, the substitution of Na [rNa=0.95 Å with a coordination number (CN) = 6] is dominant, and the crystal structure symmetry is weakened. When x>4%, the substitution of Ce (rCe=1.01 Å, CN=6) is dominant, and the crystal structure symmetry begins to increase. As the doping concentration increases, the optical bandgap initially increases and then decreases, which is consistent with the evolution of the structural symmetry. Finally, evidence of the existence of an intermediate phase transformation of CaBi4Ti4O15-based ceramics is extracted by analyzing the thermal evolution of the electronic transitions and Raman modes. Therefore, spectroscopic ellipsometry and Raman spectroscopy can be used to probe intermediate phase transformations in ferroelectrics.