  Structural phase transition accompanying with quadrupolar ordering in DyB4
with Shastry-Sutherland type geometrical frustration has been studied by X-ray
diffraction. Previous study [D. Okuyama et al.: J. Phys. Soc. Jpn. 74 (2005)
2434.] using resonant X-ray scattering revealed short-range ordering of the
Ozx-type quadrupolar moments and the c-plane component of the magnetic moments
in addition to long-range ordering of the c-axis component of the magnetic
moments. The present report focuses on the lattice distortion below the
quadrupolar ordering temperature at TN2=12.7 K. The (0 0 l=integer) fundamental
lattice reflection splits into four peaks along the h and k directions and the
(h=even 0 0) reflection becomes broad along the l direction. This indicates
that a structural transition from tetragonal to monoclinic takes place below
TN2 together with the ordering of the quadrupolar moments.
