  The quadrupole interaction at 111Cd impurity nuclei in the
intermediate-valence compound YbAl2 has been measured under pressure up to 80
kbar by the TDPAC spectroscopy. It was found that the quadrupole frequency nQ
measured on the 111Cd located at the Al sites in YbAl2, varies nonlinearly and
increases by almost four times with the pressure increase up to 80 kbar. A
linear correlation between the mean Yb valence, derived from Yb L3 OFY-XAS and
RXES measurements, and the electric field gradient (the quadrupole frequency
nQ=eQVzz/h) has been observed. The quadrupole frequencies on 111Cd in the
GdAl2, YbAl3, TmAl3 and CaAl2 compounds have been measured, also. The
possibility of determining the valence of Yb in the Yb compounds with p-metals
from the relation nQ (u(P)) = n2 + (n3 - n2) u(P) has been considered.
