Electrical conductivity, thermopower, and Hall effect of Ti 3 AlC 2 , Ti 4 AlN 3 , and Ti 3 SiC 2

In this paper we report on the thermopower and electrical conductivities of ${\mathrm{Ti}}_{4}{\mathrm{AlN}}_{2.9}$ and ${\mathrm{Ti}}_{3}{\mathrm{Al}}_{1.1}{\mathrm{C}}_{1.8}$ in the 300\char21{}850 K temperature range. We also measured the room temperature Hall effect in ${\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2},$ ${\mathrm{Ti}}_{4}{\mathrm{AlN}}_{2.9},$ and ${\mathrm{Ti}}_{3}{\mathrm{Al}}_{1.1}{\mathrm{C}}_{1.8}.$ Based on these results we conclude that holes are the majority carriers at room temperature in ${\mathrm{Ti}}_{3}{\mathrm{Al}}_{1.1}{\mathrm{C}}_{1.8}$ and ${\mathrm{Ti}}_{4}{\mathrm{AlN}}_{2.9}.$ At higher temperatures free electrons contribute to the transport properties. ${\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2}$ 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 ${\mathrm{Ti}}_{3}{\mathrm{SiC}}_{2}$ is due to the presence of a large concentration of charge carriers. The lower conductivity of ${\mathrm{Ti}}_{3}{\mathrm{Al}}_{1.1}{\mathrm{C}}_{1.8}$ is due to a dearth of charge carriers. The even lower conductivity of ${\mathrm{Ti}}_{4}{\mathrm{AlN}}_{2.9}$ is attributed to a reduced mobility, most probably due to vacancy scattering of the charge carriers.