Large room temperature ferroelectric polarization in thin films of solid solution of bismuth ferrite and lead titanate

BiFeO$_{3}$ and PbTiO$_{3}$ form a solid solution i.e. (1-x)BiFeO$_{3}$-xPbTiO$_{3}$ showing a morphotropic phase boundary (MPB) at x $=$ 0.30 with high Curie temperature (T$_{\mathrm{c}}$ $\sim$ 630 $^{\circ}$C).Here we present the results of our investigations on the structure and properties of thin films grown by pulsed laser deposition and chemical solution deposition method on Pt/Si substrates and show that the use of PbTiO$_{3}$ buffer layer leads to improvement in the room temperature (RT) ferroelectric response. X ray diffraction and Raman spectroscopy reveal structure to be tetragonal (\textit{P4mm}) at x $=$ 0.35, rhombohedral (\textit{R3c}) at x $=$ 0.25 and two phase (\textit{R3c}$+$\textit{P4mm)} at x $=$ 0.30 exhibiting giant tetragonality (c/a$=$1.17) in bulk. However, PLD grown films remain tetragonal (\textit{P4mm}) for all compositions with P$_{\mathrm{r}}=$40 microcoulombs/cm$^{2}$ while solution grown films showed the structure to be monoclinic (\textit{Cm})at x$=$0.25 and a coexistence of \textit{Cm} and \textit{P4mm} phases for x$=$0.30 and x$=$0.35 with c/a$=$1.02 resulting in large polarization with P$_{\mathrm{r}}=$80microcoulombs/cm$^{2}$ and E$_{\mathrm{c}}=$130 kV/cm.