Electrical conductivity, thermopower, and hall effect of Ti3AIC2, Ti4AIN3, and Ti3SiC2

In this paper we report on the thermopower and electrical conductivities of Ti4AlN2.9 and Ti3Al1.1C1.8 in the 300-850 K temperature range. We also measured the room temperature Hall effect in Ti3SiC2 Ti4AlN2.9, and Ti3Al1.1C1.8. Based on these results we conclude that holes are the majority carriers at room temperature in Ti3Al1.1C1.8 and Ti4AlN2.9. At higher temperatures free electrons contribute to the transport properties. Ti3SiC2 is a mixed conductor wherein the concentrations and mobilities of the free electrons are, respectively, equal to those of the holes over an extended temperature range. The high conductivity of Ti3SiC2 is due to the presence of a large concentration of charge carriers. The lower conductivity of Ti3Al1.1C1.8 is due to a dearth of charge carriers. The even lower conductivity of Ti4AlN2.9 is attributed to a reduced mobility, most probably due to vacancy scattering of the charge carriers.