In situ high temperature environmental scanning electron microscopic investigations of sintering behavior in barium titanate

First time in situ observations of sintering behavior occurring in barium titanate have been carried out in the environmental scanning electron microscope (ESEM). FEI XL-30 ESEM-FEG/LaB6 environmental scanning electron microscopes equipped with a 1500°C hot-stage furnace accessory has been used to perform these studies. Barium excess Barium titanate powders (Ba/Ti ratio 1.004) processed using conventional ceramic routes have been sintered in the ESEM at temperatures between 1320°C and 1375°C. Silica additions to the powders have facilitated observation of liquid phase sintering behavior. Dynamic observations of the materials have been made starting at ambient temperatures and following a typical furnace sintering cycle with temperatures exceeding 1300°C. Both solid state and liquid phase sintering mechanisms have been observed in the samples with the dynamics of these mechanisms exhibiting similarities found in ex-situ studies in the literature. In all materials, no noticeable changes are observed to occur at temperatures below ∼800°C. Phosphate contamination occurring in initial experiments has resulted in vapor-solid interactions with mixed phase end products being formed. A contamination mechanism has been proposed. Corrective measures have been implemented to allow sample surface observations. Solid state sintering experiments performed in the ESEM result in poor sintering and densification. This is attributed to changes in the defect chemistry of the sample in the ESEM chamber caused by low vacuum water vapor atmospheres used in the experiments. Liquid phase sintering observations performed in the ESEM result in dense large grained samples with microstructural similarities to conventional furnace sintered samples. Instrument capabilities allow the capture of rapid sequences at high resolution. Fluid real-time sequences studying ongoing sintering phenomenon can be obtained, vastly enhancing the ability to study these dynamic processes in real time. Platinum support materials have been observed to vaporize and condense on sample surfaces at temperatures exceeding 1300°C. The use of field emission instrumentation over LaB6 sources is recommended due to their improved imaging characteristics in harsh environments. These studies clearly demonstrate the versatility of the ESEM techniques and its ability to probe into harsh research environments providing the researcher with a valuable tool to understand them.