Hydrothermal Crystal Growth of Rare Earth Tin CubicPyrochlores, RE 2 Sn 2 O 7 (RE = La–Lu): Site Ordered, Low Defect SingleCrystals

A hydrothermal route to single crystals of rare earth stannates RE2Sn2O7 (RE = La-Lu) in the cubic pyrochlore structure is reported. Growth reactions were performed in aqueous fluids at 700 degrees C and 200 MPa with CsF mineralizers in concentrations ranging from 0 to 30 M, with 20 M CsF providing the most consistent results. Single crystals of the entire range of lanthanides were grown and characterized by single crystal X-ray diffraction and found to be isostructural in the Fd (3) over barm space group. The unit cell sizes range from 10.7106(16) A for La2Sn2O7 to 10.3005(9) angstrom for Lu2Sn2O7. Both the unit cell size and RE-O distances are found to be essentially linear with respect to the ionic radius of the rare earth ion. The high quality diffraction data strongly suggests that there is very little site disorder or lattice defects in the sample. Of particular interest is the synthesis and single crystal growth of Ce2Sn2O7, which represents one of the few f(1) pyrochlore samples. Specific heat measurements were obtained down to 50 mK on both Yb2Sn2O7 and Ce2Sn2O7, with the Yb material displaying a single sharp peak at 138 mK suggesting that the sample does not contain any site disorder or "lattice stuffing". The Ce analog shows only a broad featureless transition below 100 mK, with this lack of long-range magnetic order consistent with quantum spin liquid behavior.