  The crystal structure of Ca_{2-x}Sr_xRuO_4 with 0.2 < x < 1.0 has been
studied by diffraction techniques and by high resolution capacitance
dilatometry as a function of temperature and magnetic field. Upon cooling in
zero magnetic field below about 25 K the structure shrinks along the
c-direction and elongates in the a, b planes (0.2 < x < 1.0), whereas the
opposite occurs upon cooling at high-field (x = 0.2 and 0.5). These findings
indicate an orbital rearrangement driven by temperature and magnetic field,
which accompanies the metamagnetic transition in these compounds.
