Pulse-echo-overlap measurements of ultrasonic wave velocity have been used
to determine the elastic stiffness moduli and related elastic properties of
aluminum nitride (AlN) ceramic samples as functions of temperature in the
range 100-295 K and hydrostatic pressure up to 0.2 GPa at room temperature.
Aluminum nitride is an elastically stiff but light ceramic: at 295 K, the
longitudinal stiffness (C-L), shear stiffness (mu), adiabatic bulk modulus
(B-S), Young's modulus (E) and Poisson's ratio (sigma) are 373 GPa, 130 GPa
, 200 GPa, 320 GPa and 0.234, respectively. The temperature dependences of
C-L and B-S show normal behaviour and can be approximated by the convention
al model for vibrational anharmonicity. The results of measurements of the
effects of hydrostatic pressure on the ultrasonic wave velocity have been u
sed to determine the hydrostatic-pressure derivatives of elastic stiffnesse
s and the acoustic-mode Gruneisen parameters. The values determined at 295
K for the hydrostatic-pressure derivatives (partial derivativeC(L)/partial
derivativeP)(P=0), (partial derivative mu/partial derivativeP)(P=0) and (pa
rtial derivativeB(S)/partial derivativeP)(P=0) are 4.7 +/- 0.1, 0.22 +/- 0.
03 and 4.4 +/- 0.15, respectively. The adiabatic bulk modulus B-S and its h
ydrostatic-pressure derivative (partial derivativeB(S)/partial derivativeP)
(P=0) are in good agreement with the results of recent high pressure X-ray
diffraction measurements and theoretical calculations. The longitudinal (ga
mma (L)), shear (gamma (S)), and mean (gamma (el)) acoustic-mode Gruneisen
parameters of AlN are positive: the zone-centre acoustic phonons stiffen un
der pressure. The shear gamma (S) (=0.006) is much smaller than the longitu
dinal gamma (L) (=1.09) accounting for the low thermal Grneisen parameter g
amma (th) (=0.65) obtained for this ceramic: since the acoustic Debye tempe
rature Theta (D) (=980 +/- 5 K) is so high, the shear modes play an importa
nt role in acoustic phonon population at room temperature. Hence knowledge
of the elastic and nonlinear acoustic properties sheds light on the thermal
properties of ceramic AlN. (C) 2001 Kluwer Academic Publishers.