Research Information System
PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, vol.198, no.2, pp.272-281, 2003 (SCI-Expanded)
Pulse-echo-overlap measurements of ultrasonic wave velocity have been used to determine the dependences of the elastic stiffness moduli of polycrystalline cementite (Fe3C) on temperature in the range 75295 K and hydrostatic pressure up to 0.1 GPa at room temperature. The longitudinal stiffness (C-L) and adiabatic bulk modulus (B-S) stiffen, while the shear stiffness (mu) and Young's modulus (E) soften with decreasing temperature. The ultrasonic velocities increase approximately linearly with pressure, much more steeply for the longitudinal than the shear mode. The values obtained at 295 K for the hydrostatic-pressure derivatives (partial derivativeC(L)/partial derivativeP)(P=0), (partial derivativemu/partial derivativeP)(P=0), and (partial derivativeB(S)/partial derivativeP)(P=0) of cementite are 7.9 +/- 1.7, 1.4 +/- 0.1 and 6.1 +/- 1.7, respectively: the zone-centre acoustic phonons stiffen under pressure. The longitudinal (gamma(L)), shear (gamma(S)) and mean (gamma(el)) acoustic-mode Gruneisen parameters of cementite are positive; gamma(S) is markedly smaller than gamma(L) indicating that the shear acoustic modes are less anharmonic than the longitudinal modes.