Axis Dependent Transport Properties of Single Crystal Re₄Si₇

We measured the thermoelectric transport properties of Re₄Si₇ along different axis and prove Re₄Si₇ to have axis dependent carrier polarity. In the cryostat measurement, we observe electrical conductivity and thermopower both increasing with temperature. In-plane Hall effects shows the crystals we obtained has a carrier density around 2*10¹⁹/cm³, while the Hall coefficient in-plane and cross-plane have opposite signs. Thermal conductivity measurement shows an isotropic lattice thermal and Nernst measurement shows a small Nernst coefficient and eliminates the possibility of two carrier system. High temperature thermoelectric properties measurement shows the resistivity keeps decreasing at high temperature. The thermopower of the cross-plane direction reaches 300 µV/K and turns flat at high temperature, which may come from a thermal smearing effect. With an estimate of the thermal conductivity, we propose a promising ZT over unity for future optimization.