We have determined the structure and magnetic properties of flux-grown single crystals of the triple-layer ruthenate Sr 4 Ru 3 O 10 by x-ray diffraction and magnetic susceptibility measurements, respectively. The orthorhombic unit cell has Pbam space group symmetry and contains two crystallographically independent triple layers. The RuO 6 octahedra in the outer two layers of each triple layer are rotated by an average of 5.6°around the c axis, while the octahedra of the inner layers are rotated in the opposite sense by an average of 11.0°. The Curie temperature of these ferromagnetic crystals is T Curie ϭ105 K, with a saturated moment of 1.0 B /Ru 4ϩ ion. Thus Sr 4 Ru 3 O 10 is a layered ferromagnetic ruthenate in the Ruddlesden-Popper ͑R-P͒ series Sr nϩ1 Ru n O 3nϩ1 , which also includes the unconventional superconductor Sr 2 RuO 4 (nϭ1), the enhanced paramagnetic metal Sr 3 Ru 2 O 7 (nϭ2), and the pseudocubic ferromagnetic metal SrRuO 3 (nϭϱ).

No abstract

Compositional zoning in biotite-garnet pairs in metamorphic rocks from eastern Finland has been studied. The Mg profiles in the garnet side of biotite-garnet crystal pairs have been interpreted by means of Lasaga's theory (geospeedometry). However, the binary interdiffusion equations are first reformulated by starting from a ternary system and using the lattice fixed frame of reference. This frame of reference gives the fluxes directly by means of the numbers of diffusing ions, which helps to check the 1-dimensionality of the analysis assumed in Lasaga's theory. It is also shown that the recently argued effect of the third cation Ca is negligible in our samples. We were able to investigate satisfactory profiles in three samples from different areas. The values for the cooling rate are a few degrees per million years if the diffusion data obtained by Freer are adopted. The cooling rates are in agreement with recent estimates based on the K-Ar ages on biotite in the same areas.

No abstract

Rates of hydrolysis of some substituted 2-aryloxytetra hydrofurans have been measured in dilute aqueous acids. Rate-limiting carbon-oxygen bond cleavage, concerted in some sense with proton transfer to the oxygen atom, is suggested for the mechanism of the reaction. Structural effects of the substituents on the phenoxy group reveal, from the Hammett reaction constant, that protonation is relatively more advanced than carbon-oxygen bond cleavage in the transition state. The substituent constant for para-substituents which tend t o withdraw electrons b y resonance is suggested to be a linear combination of CT and 0-values, the combining factor being a Brsnsted-like coefficient a. Transition state acidities were calculated using the rate constants for oxonium ion catalysed and uncatalysed reactions. Comparison of this acidity with that of the phenol corresponding t o the leaving group in the reaction was suggested to give a Brsnsted-like coefficient as well. Both treatments gave similar values for the O! Coefficient.