The effect of B-doping on the electrical conductivity of polymer-derived Si(B)OC ceramics

In this work the room temperature electrical conductivity of Si(B)OC glasses made via polymer pyrolysis at 1200 degrees C and 1400 degrees C (maximum temperature) and having different amount of boron was measured. When B content is increased from zero (pure SiOC glass) up to B/Si=0.5 the electrical conductivity increases in 2 orders of magnitude from 4.09 +/- 0.64910(-5) up to 2.93 +/- 1.91910(-3) with a corresponding decrease in the activation energy from about 1.08 to 0.51 eV. This results shows for the first time that the electrical conductivity of Si-based polymer-derived ceramics can be controlled by the amount of the doping element. The structure of the Si(B) OC glasses has been studied with different techniques including FT-IR, XRD and Raman spectroscopy. The Raman study indicates that B partially substitutes C into the sp(2) C planes of the free carbon phase forming trigonal BC3 units. Accordingly, the evolution of the electrical properties with the B content has been correlated with the corresponding structural evolution and a hypothesis is presented to rationalize the role of boron on the electrical conductivity of SiOBC glasses.