Effects of Annealing Conditions on the Properties of Bi1-xLaxTi3O12 Thin Films

Bismuth layered structure ferroelectric thin films, La-substituted $Bi_{4}Ti_{3}O_{12}$ ($Bi_{1-x}La_{x}Ti_{3}O_{12}$, x=0.75, BLT) were prepared on the $Pt(111)/Ti/SiO_2/Si(100)$ substrates by a sol-gel spin coating process. The thin films were annealed in various conditions, i.e., oxygen, nitrogen and vacuum atmospheres for various annealing time. We investigated the annealing condition effects on the grain orientation and ferroelectric properties. The measured XRD patterns revealed that the BLT thin films showed only $Bi_{4}Ti_{3}O_{12}$-type phase with random orientation. $La^{3+}$ ion substitution for $Bi^{3+}$ ion in perovskite layers of $Bi_{4}Ti_{3}O_{12}$ decreased the degree of c-axis orientation and increased the remanent polarization ($2P_{r}$). The remanent polarization ($2P_{r}$) and the coercive field ($2E_{c}$) of the BLT thin film annealed at $650^{\circ}C$ for 5 min in oxygen atmosphere were $87{\mu}C/cm^2$ and 182 kV/cm, respectively, at an applied electric field of 240 kV/cm. For all of the BLT thin films annealed in various conditions, the fatigue resistance was shown. The improvement of ferroelectric properties with La substitution in $Bi_{4}Ti_{3}O_{12}$ could be attributed to the changes in space charge densities and grain orientation in the thin film.

열처리 조건이 Bi1-xLaxTi3O12 (x=0.75) 박막의 특성에 미치는 효과