Symmetry and light stuffing of Ho2Ti2O7, Er2Ti2O7, and Yb2Ti2O7 characterized by synchrotron x-ray diffraction

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 nonstoichiometric 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 space group of the crystal structure of these rare earth titanate pyrochlores is Fd-3m, and that, thus, the (002) peak observed in the neutron scattering experiments has a nonstructural origin. The cell parameters and internal strain for lightly stuffed Ho2+xTi2-xO7 are also presented.