Microstructure and Electrical Properties of Sodium-Diffused and Potassium-Diffused SrTiO3 Barrier-Layer Capacitors Exhibiting Varistor Behavior |
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Authors: | Masayuki Fujimoto Yet-Ming Chiang Alexana Roshko W David Kingery |
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Affiliation: | Ceramics Division, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 |
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Abstract: | In sodium-diffused strontium titanate internal-boundary-layer capacitors exhibiting good varistor properties, high-resolution transmission electron microscopy and scanning transmission electron microscopy revealed sodium segregation at grain boundaries in the absence of intergranular phases. The segregation layer is narrow (≅10 nm), unlike much broader diffused boundary layers which have also been observed. The nonohmic behavior in these and in potassium-diffused specimens suggests that segregated acceptor alkali ions act as grain-boundary electron traps leading to varistor electrical barriers. |
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