High pressure FAST of nanocrystalline barium titanate

This work studies the microstructural evolution of nanocrystalline (< 1 mu m) barium titanate (BaTiO3), and presents high pressure in field-assisted sintering (FAST) as a robust methodology to obtain > 100 nm BaTiO3 compacts. Using FAST, two commercial similar to 50 nm powders were consolidated into compacts of varying densities and grain sizes. Microstructural inhomogeneities were investigated for each case, and an interpretation is developed using a modified Monte Carlo Potts (MCP) simulation. Two recurrent microstructural inhomogeneities are highlighted, heterogeneous grain growth and low-density regions, both ubiqutously present in all samples to varying degrees. In the worst cases, HGG presents an area coverage of 52%. Because HGG is sporadic but homogenous throughout a sample, the catalyst (e.g., the local segregation of species) must be, correspondingly, distributed in a homogenous manner. MCP demonstrates that in such a case, a large distance between nucleating abnormal grains is required otherwise abnormal grains prematurely impinge on each other, and their size is not distinguishable from that of normal grains. Compacts sintered with a pressure of 300 MPa and temperatures of 900 degrees C, were 99.5% dense and had a grain size of 90 +/- 24 nm. These are unprecedented results for commercial BaTiO3 powders or any starting powder of 50 nm particle size other authors have used 16 nm lab-produced powder to obtain similar results. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.