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Single-crystal X-ray diffraction with synchrotron radiation enabled the structure of microcrystalline SSZ-23 (see drawing on the right), the first zeolite with channels bounded by seven- and nine-membered rings, to be solved.

Powder neutron diffraction has been used to pinpoint the nature of the ferroelectricparaelectric phase transition in Bi 4 Ti 3 O 12 . Below T c (675 °C) the structure has been refined in orthorhombic space group B2cb [at 25 °C a ) 5.4444(1) Å, b ) 5.4086(1) Å, c ) 32.8425(6) Å; at 650 °C a ) 5.46183(5) Å, b ) 5.44843(5) Å, c ) 33.1742(3) Å]. At 800 °C the structure has been refined as tetragonal, I4/mmm a ) 3.86334(2) Å, c ) 33.2942( 2) Å. Bond valence sum analysis of the coordination environments around each metal site as a function of temperature clearly demonstrate that the driving force for the ferroelectric transformation is the requirement for Bi in the perovskite-like A sites to optimize its bonding to neighboring oxygen atoms.

We present the results of quantitative variable-temperature neutron powder diffraction experiments performed on the OSIRIS instrument at the ISIS facility on the pure silica zeolites chabazite and ITQ-4. Chabazite has been found to be one of the most strongly contracting materials known, with a linear expansion coefficient R v /3 varying from -0.5 × 10 -6 to -16.7 × 10 -6 K -1 over the temperature range 293-873 K. Full Rietveld refinement has been carried out using three different refinement strategies: free isotropic refinements, refinement using geometrical restraints, and a rigid body refinement. The free isotropic refinement was found to be the most successful. In agreement with previous studies on ZrW 2 O 8 and Sc 2 (WO 4 ) 3 type materials, we suggest that changes in Si-O-Si interpolyhedral bond angles are the driving force for the contraction mechanism. ITQ-4 has also been found to contract over the temperature range 95-510 K, with R v /3 varying from -2.2 × 10 -6 to -3.7 × 10 -6 K -1 over this range.