Structure - Property Relationships of Thin Films of Epitaxial Ferroelectric Bismuth-Layered Perovskites with Even and Odd Aurivillius' Parameters

Abstract

AbstractThin films of bismuth-layered perovskites with the generic formula (Bi2O2)2+(An- 1BnO3n+1)2- with an even Aurivillius' parameter n like SrBi2Ta2O9 (n = 2) and BaBi4Ti4O15 (n= 4) and with an odd Aurivillius' parameter like Bi4Ti3O12 (n= 3) and Ba2Bi4Ti5O18 (n=5) have been grown by pulsed laser deposition on epitaxial conducting LaNiO3 electrodes on single crystalline (100) SrTiO3 or on top of epitaxial buffer layers on (100) silicon. The films are shown to grow epitaxially, however, they do not have a single crystallographic orientation but several preferred orientations. The films consist of both c-axis-oriented regions and mixed (110)-, (100)- and (001)-oriented regions. The regions with mixed orientation feature rectangular as well as equiaxed crystalline grains embedded in a c-oriented matrix, protruding out of its smooth surface. Macroscopic as well as microscopic measurements of the ferroelectric properties of regions with pure c-orientation and of regions with mixed orientations showed a clear relationship between their ferroelectric properties and their morphology and crystallographic orientation. In the regions with mixed orientation, the films exhibited saturated ferroelectric hysteresis loops with well-defined remanent polarization Pr and coercive field Ec. The regions having c-axis orientation with a smooth surface morphology, in contrast, exhibited a linear P-E curve with no hysteretic behavior for SrBi2Ta2O9 and BaBi4Ti4O15, and weak ferroelectric behavior for Bi4Ti3O12. These results might have a technological impact due to the relevance of bismuth-layered ferroelectric oxides for the fabrication of non-volatile FeRAM memories.