Recrystallization and structural recovery in α-decay damage in zircon samples have been studied using Raman spectroscopy. Fifteen zircon samples with different degrees of radiation damage have been thermally annealed between 600 K and 1800 K for up to 28 days and 8 hours. The experimental results from this study reveal that recrystallization in the damaged zircon samples is a multi-stage process that depends on the degree of initial damage of the samples. In partially damaged samples the lattice recovery of damaged crystalline ZrSiO 4 takes place at temperatures as low as about 700 K, as shown by a remarkable band-sharpening and a significant increase in the frequencies of ν 1 and ν 3 Si-O stretching vibrations together with the external band near 357 cm −1 with increasing temperature. A dramatic increase of Raman scattering intensity of ZrSiO 4 occurs in partially damaged samples near 1000 K due to a recrystallization process involving epitaxial growth. Heavily damaged samples tend to decompose into ZrO 2 and SiO 2 at high temperatures. Tetragonal ZrO 2 has been observed under annealing between 1125 K and about 1600 K in heavily damaged samples while monoclinic ZrO 2 appears above 1600 K. Weak signals from ZrSiO 4 were detected at 1125 K in highly metamict zircon although the main recrystallization appears to occur near 1500 K accompanied by a decrease of the volumes of ZrO 2 as well as SiO 2. This suggests that this recrystallization is associated with the reaction of ZrO 2 with SiO 2 to form ZrSiO 4. A possible intermediate phase has been observed, for the first time, by Raman spectroscopy in damaged zircons annealed at temperatures between 800 K and 1400 K. This phase is characterized by strong, broad Raman signals near 670, 798 and 1175 cm −1. Prolonged isothermal annealing at 1050 K results in a decrease of these characteristic bands and eventually the disappearance of this intermediate phase.

The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth. The samples, grown in the presence of varying amounts of Ag+ ions for scheduled irradiation times, have been characterized by ultraviolet−visible−near infrared (UV−vis−NIR) absorption spectroscopy, analytical transmission electron microscopy (ATEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and extended X-ray absorption fine structure (EXAFS) measurements. Moreover, the time evolution of size and shape distribution has been investigated by statistical analysis of the relevant TEM data. EXAFS measurements at the Ag K-edge have unambiguously disclosed the presence of Ag species in the final product, identifying their chemical state as well as the most probable lattice environment around them with a reasonably high level of confidence. The extensive sample knowledge gained by the combination of spectroscopic, structural, and morphological measurements has provided reliable information regarding the most relevant processes underlying the Ag+-assisted formation of Au NRs by the photochemical route. An induction period prior to occurrence of fast nanoparticle nucleation has been identified, which has been correlated to the slow accumulation of a critical concentration of Au(I)−surfactant species from reduction of their Au(III) parent precursors. The role played by Ag in directing Au growth toward the formation of NRs has been clarified through demonstration of preferential adsorption of zerovalent Ag species on {110} facets of the growing Au nanoparticles, which can be therefore responsible for restricting crystal development along the relevant crystallographic directions

[1] Using theoretical methods, we calculate the full elastic constant tensor and equation of state of antigorite up to 10 GPa, a pressure range that encompasses its experimentally observed stability field. At ambient conditions, the elastic constant tensor reveals significantly large acoustic anisotropy (38% in V P ; 35% in V S ) compared to the dominant mantle phase olivine. The shear anisotropy is enhanced upon compression. Upon compression, the full elastic constant tensor reveals anomaly at r ∼ 2.69 gm cm ). Our results on elasticity and anisotropy at conditions relevant to the mantle wedge indicates that a 10-20 km layer of antigorite might account for the observed shear polarization anisotropy with fast polarization parallel to the trench and associated large delay times of 1-2 sec observed in some subduction zone settings.Citation: Mookherjee, M., and G. C. Capitani (2011), Trench parallel anisotropy and large delay times: Elasticity and anisotropy of antigorite at high pressures, Geophys. Res. Lett., 38, L09315,

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