Synthesis, crystal structure, and thermoelectric properties of a new layered carbide (ZrC)₃[Al_3.56Si_0.44]C₃

A new quaternary layered carbide, (ZrC)₃[Al_3.56Si_0.44]C₃, has been synthesized and characterized by x-ray powder diffraction and thermopower and electrical conductivity measurements. The crystal structure was successfully determined using direct methods and further refined by the Rietveld method. The crystal is trigonal (space group R3m*, Z = 3) with lattice dimensions a = 0.331389(7), c = 4.90084(7) nm, and V = 0.46610(1) nm³. The final reliability indices calculated from the Rietveld refinement were R_wp = 9.53% (S = 1.70), R_p = 7.22%, R_B = 1.81%, and R_F = 0.94%. The crystal structure is composed of the NaCl-type [Zr₃C₄] slabs separated by the Al₄C₃-type [Al_0.89Si_0.11C] layers. This material had thermoelectric properties comparable to the layered carbides (ZrC)₂[Al_3.56Si_0.44]C₃ (Zr₂[Al_3.56Si_0.44]C₅), (ZrC)₂Al₃C₂, and (ZrC)₃Al₃C₂ in the temperature range of 373–1273 K, with the maximal power-factor value of 6.6 × 10⁻⁵ W m⁻¹K⁻² at 545 K. The two quaternary carbides have been found to form a homologous series with the general formula of (ZrC)_n[Al_3.56Si_0.44]C₃ (n = 2 and 3).