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The crystal structure of albite from Stintino, Sardinia, Italy, was refined at different degrees of disorder to determine the (Si-Al) order-disorder process. Eight X-ray structure refinements were performed on single-crystal data collected at room temperature, after heating at 1050-1090 [degrees] C for 3 to 12 days. Average long-range order coefficients S between 0.93 and 0.24 were obtained for different samples. The results indicate that in the (Si-Al) disordering process Al enriches the T1m site more than T2o and T2m sites. This trend continues until both T1o and T1m are occupied by 30% of Al, and T2o and T2m by 20% of Al. No evidence of complete disorder in T1 and T2 sites has been experimentally found to date. The (Si-A1) disordering process induces a clockwise rotation of the four-membered rings of tetrahedra parallel to the (100) plane. An inverse linear relationship between the isotropic equivalent displacement parameter of the Na atom, [B.sub.eq](Na), and S is interpreted as positional disorder of Na. The variations in the Na-O bond lengths with increasing disorder are explained by the related variations in the bond strengths of tetrahedral cations.

The continuous structural transformation of tetragonal analcime ([Na.sub.15.87][Al.sub.15.20][Si.sub.32.64] [O.sub.96].16.3[H.sub.2]O) upon dehydration was studied, using Rietveld structure analysis of temperature-resolved powder diffraction data collected using synchrotron radiation. The variation of the a-c axis length difference and normalized intensity of the (200) reflection as a function of temperature suggest that tetragonal analcime evolves toward a cubic structure at high temperature. The removal of water was accompanied by a spreading of the initial Na sites into many positions bonded to the framework O atoms. The migration of [H.sub.2]O molecules through the [111] channels during dehydration caused the six-member ring apertures to open as widely as possible: this was accompanied by a twisting of the tetragonal prism, constituting the analcime framework, which led to an opposite tilting of tetrahedra connecting the prisms. These modifications induced by water diffusion are not energetically favored because they would increase the elastic energy of the system, and require a substantial thermal activation energy. The analcime framework reached a maximum distortion at about 650 K, the temperature of complete water loss, then underwent a relaxation process during which the T-O-T angles were restored to the starting value. The relative variation of cell volume associated with the opening of wide six-member ring channels during water migration, and then due to the framework relaxation process after complete dehydration, provides an explanation of the 'negative thermal expansion' (i.e., volume contraction) effect in dehydrated analcime, which is complementary to that based on the Rigid Unit Modes theory.

The continuous structural transformation of the natural zeolite stilbite ([Na.sub.3.62][K.sub.0.44][Ba.sub.0.03][Ca.sub.6.32][Sr.sub.0.28] [Mg.sub.0.04][[[Fe.sup.3+].su b.0.01][Al.sub.17.33][Si.sub.54.64][O.sub.144]][center dot]60[H.sub.2]O) upon dehydration has been studied using Rietveld structure analysis of temperature-resolved powder diffraction data collected with synchrotron radiation. In the initial stage of heating, the monoclinic F2/m stilbite structure (the so-called A phase) behaves as a noncollapsible framework, featuring only a slight framework distortion and a slight cell-volume contraction. At about 420 K, a first-order phase transition occurs changing the symmetry to an orthorhombic Amma phase, whose framework is collapsible and shows a large cell-volume contraction with temperature. The cell contraction is related to the process of T-O-T bond breaking and leads to a high-temperature stilbite phase with the same Aroma space group and a collapsed structure similar to the previously described B phase in stellerite and barrerite. The structural refinement indicates that the dynamics of bond breaking is related to the shift of the Ca cations in the channels to achieve optimal coordination after the release of the [H.sub.2]O molecules. Refined statistical occupancies of the tetrahedral atoms involved in the bond-breaking process (T1 and T1P) are consistent with a random rupture and re-formation of the T-O-T bonds. This is the first experimental study of the dynamic bond breaking of T-O-T bonds in a framework structure.

Single-crystal X-ray diffraction and microprobe examination provide insights into the crystal chemistry of 1M phlogopite. Selective partitioning of high-change cations in the cis M2 regions is evident from the geometric and chemical characteristics of the octahedral designs. Elevation in high-change cation content is accompanied by distinct responses of the pair of octahedral regions.

An in situ X-ray synchrotron powder diffraction augmented with Fourier transform (FT) IR analysis is used to study the thermally induced processes of CoAPO-34, an aluminophosphate molecular sieve with chabasite-type structure. The results show that the bridged Co(super 2+)-O(H)-P hydroxyls are present after morpholine removal.

The in situ time-resolved analysis of Co-exchanged synthetic ferrierite is performed in the range 53-810 degree C by Rietveld refinements of powder diffraction data. It is reported that five cation sites are localized above 500 degree C.