This work reports on the solid state synthesis and structural and thermoelectrical characterization of hexaborides (CaB6, SrB6, BaB6, EuB6), diboride dicarbides (CeB2C2, LaB2C2), a carbaboride (NaB5C) and composites of boron carbide. The characterization was performed by X-ray diffraction methods and Rietveld refinements based on structure models from literature. Most of the compounds were densified by spark plasma sintering at 100 MPa. As high-temperature thermoelectric properties the Seebeck coefficients, electrical conductivities, thermal diffusivities and heat capacities were measured between room temperature and 1073 K. ZT values as high as 0.5 at 1273 K were obtained for n-type conducting EuB6. High-temperature X-ray diffraction also confirmed its thermal stability. The solid solutions CaxSr1-xB6, CaxBa1-xB6 and SrxBa1-xB6 (x = 0, 0.25, 0.5, 0.75, 1) are also n-type but did not show better ZT values for the ternary compounds compared to the binaries, but for CaB6 the values of the figure of merit (ca. 0.3 at 1073 K) were significantly increased (ca. 50 %) compared to earlier investigations which is attributed to the densification process. Sodium carbaboride, NaB5C, was found to be the first p-type thermoelectric material that crystallizes with the hexaboride-structure type. Seebeck coefficients of ca. 80 µV*K-1 were obtained. Cerium diboride dicarbide, CeB2C2, and lanthanum diboride dicarbide, LaB2C2, are metallic. Both compounds were used as model compounds to develop compacting strategies for such layered borides. Densities obtained at 50 MPa were determined to be higher than 90 %. A new synthesis route using single source precursors that contain boron and carbon was developed to open the access to new metal-doped boron carbides. It was possible to obtain boron carbide, but metal-doping could not be detected. Furthermore boron carbide/metal boride-composites were investigated concerning their high-temperature thermoelectric properties up to 1073 K. In some cases selected thermoelectric properties were optimized compared to boron carbide (example: Seebeck coefficients of ca. 240 µV*K-1 for a boron carbide/titanium diboride-composite), but such systems still remain to be optimized concerning their homogeneity and overall thermoelectric performance.