Functional properties of barium titanate ceramics alloyed with nickel ferrite

The paper studies the effect of nickel ferrite addition and sintering temperature on the density, dielectric and piezoelectric characteristics of barium titanate ceramics. A density jump is detected, when with an increase in the ferrite content the density first increases and then drops sharply. Moreover, if at a sintering temperature of 1200 °C the maximum density (5.38 g/cm³) occurs at a ferrite concentration of 0.05 mol.%, then at a sintering temperature of 1300 °C the maximum density (5.62 g/cm³) shifts to the region of higher ferrite concentrations and is 0.1 mol.%. Thus, it can be stated that at a sintering temperature of 1300 °C the ferrite addition in an amount of 0.1 mol.% acts as a sintering activator. X-ray phase analysis showed that in alloyed barium titanate the tetragonal splitting of lines is expressed more strongly, and the calculated lattice parameters a and c differ significantly from the parameters of pure barium titanate. The addition of 0.1 mol.% ferrite lowers the Curie temperature of the phase transition from the cubic phase to the tetragonal phase from 117 to 108.5 °C. Activation of the sintering process with the addition of ferrite up to ~0.1 mol.% makes it possible to reduce the sintering temperature to 1300 °C and obtain ceramics with high functional characteristics. Relative density is 93%, specific resistance is ~10¹⁰ Ohm·m, permittivity is 1500, piezoelectric modulus d₃₁ is 85 pC/N, electromechanical coupling coefficient is 0.37.