HRTEM investigation of the 90° domain structure and ferroelectric properties of multi-layered PZT thin films

Multi-layered epitaxial Pb(Zr_x,Ti_1-x)O₃ (PZT) films with x = 0.2-0.5 were deposited on La_0.5Sr_0.5CoO_3-x (LSCO)/(001)STO and LSCO/CeO₂/YSZ/(001)Si substrates with buffer layers. We investigated using HRTEM and XRD how the 90° domain structure and the P-E hysteresis character depend on the difference in the thermal expansion coefficient by changing the Zr/Ti composition and the substrate. XTEM analysis showed that large 90° domains 8-30 nm in width penetrate the columnar grain and the PZT layer in the PZT stacked film Zr/Ti = 20/80,30/70,40/60. On the other hand, close-packed small 90° domains 4-5 nm in width were present in epitaxial columnar grains in the PZT50/50 stacked film. The P-E hysteresis loops of PZT20/80 stacked films deposited on STO and Si substrates show a remanent polarization of 2Pr = 136 and 80 μC/cm², respectively. On the other hand, those of PZT50/50 stacked films deposited on STO and Si substrates show a polarization of 2Pr = 125 and 36 μC/cm², respectively. Thus, the P-E hysteresis loop of PZT50/50 exhibits remarkable differences in 2Pr values between the substrates.