[15p-2L-1~13] 6.1 Ferroelectric thin films

[15p-2L-2] Fabricatation of Novel Lead-free Ferroelectric Bi₂ZnTi_1-xMn_xO₆ Thin Films

〇ken tominaga¹, Hajime Hojo¹, Keisuke Shimizu¹, Narumi Matsuda¹, Masaki Azuma¹ (1.Tokyo Tech)

Keywords:piezoelectric material,BZT

Ceramics based on PbZr1-xTixO3 (PZT) are used in sensors and actuators due to their high piezoelectric coefficient, which arises at so-called “morphotropic phase boundary” (MPB) between rhombohedral and tetragonal phases. It is generally believed that the crystal structure of PZT at MPB is monoclinic, and the lack of a symmetry axis allows a rotation of ferroelectric polarization vector between the polar axes of the rhombohedral and tetragonal phases, resulting in excellent piezoresponse. Bi2ZnTiO6 is a PbTiO3-type tetragonal perovskite compound, but its giant c/a ratio of 1.21 due to the 6s2 lone pair of Bi3+ and the second order Jahn-Teller (SOJT) effect of Ti4+ prevents the polarization being reversed by the electric field. Substituting Ti4+ with SOJT inactive d3 or d6 ions should be effective in reducing the c/a ratio, while keeping the insulating properties. In this study, we have prepared polycrystalline Bi2ZnTi1-xMnxO6 (BZTMO) by high pressure synthesis. In order to evaluate the ferro/piezoelectric properties, we have also prepared BZTMO in the form of thin films, which generally suffers less leakage current at grain boundaries. Polycrystalline BZTMO samples were prepared with a cubic anvil-type high-pressure apparatus. X-ray diffraction (XRD) and synchrotron XRD patterns were collected for phase identification and refinement of the lattice parameters. We confirmed that crystal structure is monoclinic for the composition of x=0.2~0.4. The c/a ratio is as small as 1.065 at x=0.4. Therefore, we can expect improved piezoresponse in BZTMO by polarization rotation mechanism. BZTMO films were prepared on SrTiO3(001) substrate using pulse laser deposition followed by post-annealing. Using this method, we have successfully obtained (00l)-oriented BZTMO films with perovskite structure. Detailed crystal structure analysis and electrical properties will be reported in the presentation.