Structural evolution of Ba₈Ti₃Nb₄O ₂₄ from BaTiO₃ using a series of Ba(Ti_{1-5 x}Nb_4x)O₃ solid solutions

In this work, the structural evolution of hexagonal phase Ba ₈Ti₃Nb₄O₂₄ by adding Nb ₂O₅ to perovskite structure of BaTiO₃ was investigated. The compositions Ba(Ti_1-5xNb_4x)O₃ ceramics, with 0.00025 ≤ x ≤ 0.125 were prepared by the conventional solid state route in air atmosphere, the powders precursors, BaTiO₃, BaCO₃ and Nb₂O₅, were mixed in stoichiometric proportions and ground in a ball mill using alumina balls and acetone. The mixed powders were calcined at temperatures up to 1500°C. The phase transformation of Ba₈Ti₃Nb₄O₂₄ from BaTiO₃ was studied by DRX, Raman spectroscopy, SEM, electrical measurements (relative permittivity and P-E hysteresis loops); Rietveld's refinement was used to structurally characterize the samples. For the devices obtained capacitance was measured at 1 kHz; with these values we calculated the relative permittivity. The samples show typical P-E hysteresis loops at room temperature accompanied by saturation polarization (Ps) and remnant polarization (Pr). The DRX and Rietveld's refinement results show x ≤ 0.01 has a ferroelectric behavior. When the doped level is increased x ≥ 0.02, a peak displacement is observed, this is due to the phase transformation of tetragonal to cubic into the unit cell. Finally, with x = 0.125 the crystal structure transforms to the characteristic hexagonal phase Ba₈Ti ₃Nb₄O₂₄ which resonates at microwave frequencies.