Thermal expansion of the hexagonal (4H) polytype of SiC

Thermal expansion of the hexagonal (4H) polytype of SiC was measured from 20 to 1000 °C by the x-ray diffraction technique. The principal axial coefficients of thermal expansion are expressed by the second-order polynomials: α11=3.21×10−6+3.56×10−9T−1.62×10−12T2, and α33=3.09×10−6+2.63×10−9T−1.08×10−12T2 (°C−1). The α11 is larger than the α33 over the entire temperature range, yielding a thermal expansion anisotropy ‘‘A’’ of 0.04 at room temperature which increases to 0.11 at 1000 °C. The thermal expansion of the (4H) structure is compared with previously published results for the cubic (3C) and the hexagonal (6H) SiC polytypes.