Pressure dependence of c-axis elastic parameters of oriented graphite

The elastic c-axis moduli C₃₃ and C₄₄ of compression-annealed pyrolytic graphite and their derivatives with hydrostatic pressure have been measured at room temperature over a pressure range from 1 to 7000 bars (700 MNm^?2) using an ultrasonic pulse-echo technique. The experiments were also made with material irradiated with fast neutrons. The pressure dependence of the c-axis compressibility of these materials was calculated from the experimental data, enabling pressure derivatives of the c-axis moduli to be also expressed as c-axis strain derivatives.