Piezoelectric properties and elastic constants of 4H and 6H SiC at temperatures 4–320 K

4H and 6H silicon carbide (SiC) crystals are piezoelectric and can be excited to resonant vibrations with quality factors up to Q≊100 000 and an electromechanical coupling factor of k31≊0.03 for 6H material. The resonance frequencies are used for the determination of elastic constants from 4 to 320 K. One finds a Poisson’s ratio σ=0.212 and low-temperature values s11=2.035×10−12 m2/N and c33=55.12×1010 N/m2 for 6H, s11=2.114×10−12 m2/N, and c33=60.52×1010 N/m2 for 4H crystals. All elastic constants show a nonmonotonic dependence from the temperature at about 50 K.