The sintering phenomena, electrical resistivity, dielectric and piezoelectric properties of lead titanate ceramics modified by the partial substitution of La for Pb and Mn for Ti, ($Pb_{1-1.5x}La_x$) ($Ti_{1-y}Mn_y$) $O_3$ ceramics, have been investigated. The specimens were prepared by the conventional mixed oxide technique and atmosphere sintering method.
The specimens were sintered at 1200℃, 1220℃ 1240℃ 1260℃ and 1280℃ for 1hr respectively.
Replacement of $Pb^{2+}$ by $La^{3+}$ in $(Pb_{1-1.5x}La_x$) ($Ti_{1-y}Mn_y$) $O_3$ solid solutions is accompanied by the creation of cation vacancies. These vacancies seem to facilitate material transport and aid sintering.
In $(Pb_{1-1.5x}La-x$) ($Ti_{0.99}Mn_{0.01}$) $O_3$ system, with increasing lanthanum content, the relative bulk density increased, but the Curie point and tetragonality (c/a) decreased. The tetragonal-to-cubic phase transition boundary existed in the range of $0.20 < x < 0.25$. The electromechanical anisotropy ($k_t/k_p$) was observed in the tetragonal region and electromechanical coupling factor ($k_t$) had a maximum value at x=0.05.
In $(Pb_{.925} La_{0.05})\; (Ti_{1-y}Mn_y)$ $O_3$ system, the electromechanical coupling factor ($k_t$) and electrical resistivity had maximum values at y=0.01, but dielectric constant and dissipation factor had minimum values.
It was concluded that lanthanum enhanced the sinterability of lead titanate and $MnO_2$ improved the piezoelectric properties.
