NMR-spectroscopic study of 207Pb\mathrm{^{207}Pb} in pure and barium diluted lead phosphate

31P and 207Pb MAS and static 207Pb NMR spectra of Pb3(PO4)2 and (Pb1−xBax)3(PO4)2 (x=0.08, 0.12) are analysed. The resonances stemming from different cation sites are correlated with the corresponding local symmetry and their oxygen neighbours. The coordination sphere of Pb(1) consists of 12 oxygen atoms and shows characteristics of a near-axial arrangement with a comparatively low anisotropy. The tenfold coordinated Pb(2) atoms are located in a more anisotropically-coordinated site. In Pb-diluted lead phosphate crystals the Pb(2) positions appear to be preferentially substituted by barium. There are indications that the cation distributions in the diluted samples are inhomogeneous. Furthermore, 31P MAS NMR experiments indicate a single phosphorus position

Precursors in lead phosphate-type ferroelastics: Diffuse X-ray scattering, group theory and modelling

A chain-adapted symmetry-mode analysis is presented for the symmetry change R 3 m > C12/c1 in ferroelastic lead phosphate. The primary and the secondary modes are derived for all relevant Wyckoff positions. The splitting schemes of the orbits and the patterns of the displacive modes are compatible with experimental diffraction studies performed in lead phosphate type crystals. The appearance of diffuse monoclinic X-ray diffraction signals above the ferroelastic transition point of lead phosphate is modelled using simple real structure simulations

Anti-phase boundaries and phase transitions in titanite; an X-ray diffraction study

X-ray diffraction rocking curves of titanite, CaTiSiO 5 , were measured using a novel high-resolution diffractometer. Three Bragg reflections were recorded as a function of temperature and their profiles analyzed in terms of a Gaussian Bragg peak and a diffuse scattering component with an overall Lorentzian shape. The temperature dependence of the Gaussian intensities of the rocking peaks of superstructure reflections, hkl with k+l odd, scale with the long-range order parameter as I infinity Q 2 infinity [T-T c ] (super 2beta ) , where beta = 0.14(1) is the effective order parameter exponent. The diffuse scattering intensity changes little with temperature at TT c with centers of their Lorentzian diffraction profiles shifted by Delta omega nearly equal 0.5 degrees with respect to the position of the equivalent Bragg peak. A second phase transition at 825 K is confirmed and the possibility of a third transition at approximately 1150 K is discussed

An AFM study on ferroelastic domains in lead phosphate, Pb3(PO4)2\mathrm{Pb_3(PO_4)_2}

The topography of the intersection of ferroelastic W domain walls with (100) surfaces of lead phosphate, , has been imaged with tapping mode atomic force microscopy (TMAFM). Spontaneous deformation of the ferrophase leads to a cleavage plane which forms a zig-zag profile along W domain walls. The predicted angle of between two adjacent domains on a (100) surface is confirmed by TMAFM observations. Surface deformation has no influence on this angle due to the dominance of the long-range spontaneous strain. Furthermore, W domains end as needle-like structures and TMAFM observations show that there is no detectable change in the local surface deformation in the vicinity of these needle tips

29Si\mathrm{^{29}Si} MAS NMR spectroscopy and synchrotron XRD study of metamict Cardiff titanite

Metamict titanite from the Cardiff uranium mine(M28696) in Ontario, Canada, has been analyzed using29Si magic angle spinning nuclear magnetic resonancespectroscopy (MAS NMR). A broad Gaussian shaped NMRsignal at –81 ppm occurs at room temperature resultingfrom the mainly locally ordered metamict structural state.NMR signals were obtained at room temperature andafter annealing at 600, 950, 1220 and 1470 K. Because ofincreasing crystallinity the full width at half maximum(FWHM) decreased from 24 ppm to 20 ppm, respectivelyusing a pseudo-Voigt fit. For comparison highly-crystallinetitanite from Rauris showed an NMR signal at –79.3 ppmwith FWHM of 4.1 ppm and an almost Lorentzian profilebecause of its good long range order. Integrating synchrotronX-ray diffraction (XRD) signals of Cardiff titaniteshow an increase of the crystallographic long range orderat annealing temperatures considerably lower than thelocal ordering seen by NMR