  We performed an X-ray diffraction experiment while palladium bulk absorbed
and desorbed hydrogen to investigate the behavior of the crystalline lattice
during the phase transition between the $\alpha$ phase and $\beta$ phase. Fast
growth of $\beta$ phase was observed around x=0.1 and x=0.45 of PdH$_x$. In
addition, slight compression of the lattice at high hydrogen concentration and
increase in the lattice constant and the line width of the $\alpha$ phase after
a cycle of absorption and desorption of hydrogen was observed. These behavior
correlated with the change in the sample length, which may infer that the
change in shape was related to the phase transition.
