Single crystals of KOH-doped ice Ih, transformed into the low-temperature ordered phase known as ice XI, have been studied by neutron diffraction. High-resolution measurements show a splitting of the 00l diffraction peaks into an ice XI and a residual ice Ih component, with about 37% transformation to ice XI. New diffraction peaks from the ice XI have been measured. These are consistent with a ferroelectrically ordered structure with space group Cmc2 1 .

A combination of X-ray techniques [diffraction and Zr K-edge absorption (EXAFS and XANES)] and multinuclear (1H, 13C, 17O) solid-state NMR spectroscopy is employed to follow in detail the structural development of nanocrystalline zirconia. 17O magic-angle spinning NMR spectroscopy of sol−gel produced undoped ZrO2 shows unequivocally that oxygen sites in the initial gel are monoclinic-like. This result is consistent with X-ray absorption measurements, which also suggest that the structures of the initial amorphous phases of doped and undoped samples produced by the hydroxide-precipitation and sol−gel methods are very similar. On crystallization, the local structure of the crystalline component is tetragonal, but a significant fraction of the sample remains disordered. Heating to higher temperatures results in conversion to monoclinic zirconia in undoped samples at room temperature. For sol−gel-produced ZrO2, 13C NMR shows that loss of all of the organic fragments occurs prior to crystallization. The 1H NMR experiments determined that the proton content remains significant until well above the crystallization temperature, so that the composition is not accurately described as ZrO2 until >500 °C.

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AbslraeL A neutron diffraction study has kea performed on AgBr at a series d temperalum from 293K U) 706K (melting point, T , = 701 K). including measuxmenls as close as 0.3f0.05' from T .. Analysis of the smciure lacion using the reverse Monte Carlo modelling technique indicates that the motion of the Ag+ ions about lheir mcksall lattice sites is anisolmpic, wilh incxasing Occupancy o f the (fit) tetrahedral interstitial site as the melting point is approached. It ir mncluded that the silver sub-lattice is undergoing a smnd-order transition to a fast-ion phase in which both tetrahedral and octahedral sites are occupied (posribly similar to the fast-ion lransition in the high p m u r e pcc phase of 4 1 ) although melting preMnu romplete fransition. mere is a clear discontinuity in Bragg scattering a1 T. , suggesting that the fintorda nature of the melting LTanSition is unaffected.