Crystal structure, microstructure, and electrical properties in nonstoichiometric SBT thin films

Abstract

The relation between the electrical properties and the microstructure of the layered-perovskite SBT thin films were studied. The crystal structure of the powder SBT samples were also analyzed by the Rietveld refinement method for clarifying the relationship between the two. The Rietveld refinement results for the Sr₁Bi₂Ta₂O₉, Sr_0.7Bi_2.2Ta₂O₉, Sr_0.7Bi₂Ta₂O₉ and (Sr_0.87Bi_0.13)Bi₂(Ta_1.93Bi_0.07)O₉ samples showed that excess-Bi occupies the Sr site forming (Sr_1−3/2xBi_x)Bi₂Ta₂O₉ solid solution. The Sr_0.7Bi₂Ta₂O₉ and (Sr_0.87Bi_0.13)Bi₂(Ta_1.93Bi_0.07)O₉ samples produced minor impurity phases in addition the major SBT phase. The SBT thin films with molar ratio (Sr:Bi:Ta) of 1:2:2, 0.7:2.2:2, 1.87:2.2:1.93, 1:2.2:2 and 0.7:2:2 were prepared by MOD method. The spin-coated films were crystallized at 750°C for 1 hour under O₂. Remanent polarization of the thin films critically depended on the crystallinity and grain size, while the leakage current density depended on the minor impurity phase contained in the thin films. The 0.7:2.2:2 thin films showed the best electrical properties: 2P_r = 8.2 μC/cm², E_c = 43.6KV/cm, J_{leakage current} = 6.4x10⁻⁸ A/cm² at 3V.

Key Words:

• nonstoichiometric SBT
• thin films
• crystal structure
• ferroelectric properties
• Rietveld refinement
• spin-coating