  The Ho2Ti2O7, Er2Ti2O7 and Yb2Ti2O7 pyrochlores were studied by synchrotron
X-ray diffraction to determine whether the (002) peak, forbidden in the
pyrochlore space group Fd-3m but observed in single crystal neutron scattering
measurements, is present due to a deviation of their pyrochlore structure from
Fd-3m symmetry. Synchrotron diffraction measurements on precisely synthesized
stoichiometric and non-stoichiometric powders and a crushed floating zone
crystal of Ho2Ti2O7 revealed that the (002) reflection is absent in all cases
to a sensitivity of approximately one part in 30,000 of the strongest X-ray
diffraction peak. This indicates to high sensitivity that the structural space
group of these rare earth titanate pyrochlores is Fd-3m, and that thus the
(002) peak observed in the neutron scattering experiments has a non-structural
origin. The cell parameters and internal strain for lightly stuffed
Ho2+xTi2-xO7 are also presented.
