Changes in the crystal structure and the lattice constants of powdered
crystalline V2O5 after absorption of hydrogen were measured, as a fun
ction of the concentration, by X-ray diffractometry. The diffraction s
pectra obtained showed that three kinds of phases, alpha (x < 0.4 in H
xV2O5), beta (co-existing with either terminal phase in the range of 0
.4 less-than-or-equal-to x < 3.2) and gamma (3.2 less-than-or-equal-to
x less-than-or-equal-to 3.9), appear up to x = 3.9, which was found t
o be the upper limit of the absorption at 70-degrees-C under a hydroge
n pressure of 5 M Pa. The crystal system of the three phases was deter
mined to be orthorhombic, although the lattice constants differed. The
diffraction lines were broadened, and the background of the X-ray spe
ctra grew with hydrogenation, especially in the gamma-region, which in
dicates the growth of the lattice distortion and a quasi-amorphous sta
te. The occupation of hydrogen atoms in each phase is discussed on the
basis of the experimental results.