Low-temperature transport properties of nanolaminates Ti3AlC2 and Ti4AlN3

In this paper we report on the electronic and magnetotransport properties of two Ti-based ternaries, Ti 3 AlC 2 and Ti 4 AlN 3 . In order to determine the effective carrier concentrations and their mobilities, the Hall effect, electrical conductivity, thermoelectric power, magnetic susceptibility, and magnetoresistance were measured as a function of temperature between 4 and 300 K and at magnetic fields up to 9 T. For Ti 3 AlC 2 , the Hall voltage is a linear function of magnetic field at all temperatures. At the lowest temperatures, the Hall coefficient is small but positive; above 100 K it is negative and drops more or less linearly with temperature. The magnetoresistance of Ti 3 AlC 2 is dominated by a positive quadratic field dependence. The magnetic susceptibility is nearly constant but displays a weak maximum around the temperature at which the Hall effect changes sign (100 K). In contrast, the Seebeck coefficient remains positive up to 800 K, with a maximum at 700 K. The results were analyzed within a two-band framework assuming a temperature-independent charge-carrier density and a hole mobility that is slightly smaller than the electron mobility. The model quantitatively accounts for our observations. The resistivity, magnetoresistance, and Hall coefficient of Ti 4 AlN 3 , on the other hand, were successfully described within the single-band model, with holes as the dominant charge carriers. This was supported by measurements of the Seebeck coefficient, which is positive and peaks at 300 K. The magnetic susceptibility of Ti 4 AlN 3 is also quite temperature independent.