Three-dimensional analysis of porous BaTiO3 ceramics using FIB nanotomography

Three-dimensional (3D) data represent the basis for reliable quantification of complex microstructures. Therefore, the development of high-resolution tomography techniques is of major importance for many materials science disciplines. In this paper, we present a novel serial sectioning procedure for 3D analysis using a dual-beam FIB (focused ion beam). A very narrow and reproducible spacing between the individual imaging planes is achieved by using drift correction algorithms in the automated slicing procedure. The spacing between the planes is nearly of the same magnitude as the pixel resolution on scanning electron microscopy images. Consequently, the acquired stack of images can be transformed directly into a 3D data volume with a voxel resolution of 6x7x17 nm. To demonstrate the capabilities of FIB nanotomography, a BaTiO3 ceramic with a high volume fraction of fine porosity was investigated using the method as a basis for computational microstructure analysis and the results compared with conventional physical measurements. Significant differences between the particle size distributions as measured by nanotomography and laser granulometry indicate that the latter analysis is skewed by particle agglomeration/aggregation in the raw powder and by uncertainties related to calculation assumptions. Significant differences are also observed between the results from mercury intrusion porosimetry (MIP) and 3D pore space analysis. There is strong evidence that the ink-bottle effect leads to an overestimation of the frequency of small pores in MIP. FIB nanotomography thus reveals quantitative information of structural features smaller than 100 nm in size which cannot be acquired easily by other methods.