Structure and properties of boron carbide with aluminum incorporation

B-C-Al ternary compounds were prepared by hot-pressing of the boron carbide (B4.3C) and Al powder at 1820°C and 45 MPa under argon atmosphere, with Al content in the range from 5 wt% to 20 wt%. X-ray diffraction analyses indicated that the main phase was B11C3Al with an enlarged boron carbide structure. Studies revealed the Al atoms located at the central sites of the chain units. With the increase of Al concentration the Al8B4C7 phase emerged. The thermoelectric properties of the samples were investigated as a function of temperature between 300 and 550 K. Al-containing boron carbide exhibited lower electric conductivities and thermal conductivities compared with that of the pure boron carbide. Proper amount of Al incorporation (5 wt%) resulted in remarkable increase of the Seebeck coefficient and an order of magnitude increase of the figure of merit Z compared to that of pure boron carbide was achieved at room temperature.