85 research outputs found
On hydrogen bond correlations at high pressures
In situ high pressure neutron diffraction measured lengths of O H and H O
pairs in hydrogen bonds in substances are shown to follow the correlation
between them established from 0.1 MPa data on different chemical compounds. In
particular, the conclusion by Nelmes et al that their high pressure data on ice
VIII differ from it is not supported. For compounds in which the O H stretching
frequencies red shift under pressure, it is shown that wherever structural data
is available, they follow the stretching frequency versus H O (or O O) distance
correlation. For compounds displaying blue shifts with pressure an analogy
appears to exist with improper hydrogen bonds.Comment: 12 pages,4 figure
Elastic relaxation behavior, magnetoelastic coupling, and order-disorder processes in multiferroic metal-organic frameworks
Pyrosmalite-(Fe), Fe8Si6O15(OH,Cl)10
Pyrosmalite-(Fe), ideally FeII
8Si6O15(OH,Cl)10 [refined composition in this study: Fe8Si6O15(OH0.814Cl0.186)10·0.45H2O, octairon(II) hexasilicate deca(chloride/hydroxide) 0.45-hydrate], is a phyllosilicate mineral and a member of the pyrosmalite series (Fe,Mn)8Si6O15(OH,Cl)10, which includes pyrosmalite-(Mn), as well as friedelite and mcgillite, two polytypes of pyrosmalite-(Mn). This study presents the first structure determination of pyrosmalite-(Fe) based on single-crystal X-ray diffraction data from a natural sample from Burguillos del Cerro, Badajos, Spain. Pyrosmalite-(Fe) is isotypic with pyrosmalite-(Mn) and its structure is characterized by a stacking of brucite-type layers of FeO6-octahedra alternating with sheets of SiO4 tetrahedra along [001]. These sheets consist of 12-, six- and four-membered rings of tetrahedra in a 1:2:3 ratio. In contrast to previous studies on pyrosmalite-(Mn), which all assumed that Cl and one of the four OH-groups occupy the same site, our data on pyrosmalite-(Fe) revealed a split-site structure model with Cl and OH occupying distinct sites. Furthermore, our study appears to suggest the presence of disordered structural water in pyrosmalite-(Fe), consistent with infrared spectroscopic data measured from the same sample. Weak hydrogen bonding between the ordered OH-groups that are part of the brucite-type layers and the terminal silicate O atoms is present
OH-defects in multiple-doped orthoenstatite at 4–8 GPa: filling the gap between pure and natural systems
High-Temperature Hydroxylation and Surface Corrosion of 2/1-Mullite Single Crystals in Water Vapor Environments
Crossover from classical to 3d-Ising critical behaviour near the antiferrodistortive phase transition of lawsonite
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