On the relations between ISE and structure in some RE(Mg)SiAlO(N) glasses

International audienceSix oxide and oxynitride glasses were synthesized in the Y-Mg-Si-Al-O-N, Nd-Mg-Si-Al-O-N and La-Mg-Si-Al-O-N systems. As already known, nitrogen introduction increases the T(g), packing factor and mechanical properties of the glasses. Cationic substitution also has an influence on the glasses' behavior, particularly in terms of sensitivity to indentation load/size effect (ISE). The structure of the yttrium-containing glasses was investigated by mean of (27)Al and (29)Si MAS-NMR. Al is found to occur for 2/3 as a network former and for 1/3 as a modifier. The oxide glass mainly contains Q(2) and Q(3) silicate units and SiO(3)N and SiO(2)N(2) units are created when nitrogen is introduced into the glass network. The average number of rigid bonds per network former was calculated from the glasses' composition. A discrepancy between and the Raman spectra of the glasses suggests that parts of the magnesium behaves as a former in the network. seems to be a key parameter governing hardness and sensitivity to ISE and can be linked to normal/abnormal behavior of glasses regarding indentation

Changes in irradiated LnSiAlO(N) glasses at a microscopic scale

International audienceSix oxide and oxynitride glasses from three different M-Ln-Si-AI-O(-N) systems (where M is an alkaline-earth and Ln a rare earth) have been irradiated by Kr, Ni and S ions, with different energies varying from 350 to 700 MeV. Neither micro-bubble formation nor crystallisation are evidenced, but the irradiated glasses exhibit an anisotropic deformation under the ion beam. The main crack mode developed during scratching is shifted from radial for the pristine glasses to lateral for all the irradiated glasses. The hardness of each glass decreases when irradiated for all the incident ions used. This decrease appears to be in close relation with the electronic stopping power of the incident particle, and is associated with a change in the indentation mechanism (from normal to anomalous behaviour). The evolution of the scratches in the material depth confirms the change in deformation mechanism and the strong dependence between the hardness of the irradiated material and the electronic stopping power of the incident ion. Three phenomena can be the source of the changes in the properties: the creation of internal stresses during irradiation, the creation of point defects and the cross-linking of the silicate network. (c) 2006 Elsevier B.V. All rights reserved

Irradiation-induced changes in the local environment of Si and Al in LnSiAlON glasses as probed by Al-27 and Si-29 NMR

International audienceTwo compounds have been studied: an oxide glass from the Y-Si-Al-O system and an oxynitride glass from the Y-Si-Al-O-N system, both bombarded with Sn-ions (975 MeV, fluences ranging from 10(12) to 2.7 x 10(13) Sn/cm(2)). The changes in the environment of the silicon and the aluminium were investigated using NMR spectroscopy. Irradiation by Sn ions leads to a loss of nitrogen in the silicon and probably the aluminium environments. Part of the aluminium changes from a network former coordination to a network modifier coordination while the oxide silicate network exhibits a higher cross-linking due to an increase of the population of bridging oxygen. Part of the aluminium in five-fold coordination is formed at the expense of aluminium in six-fold coordination in the case of the oxynitride glass and the changes in the silicon environment occur at lower fluences than for the oxide glass. (c) 2006 Published by Elsevier B.V

Mechanical properties of sialon glass surface after swift heavy-ion bombardment

International audienceA Y-Mg-Si-Al-O-N glass was submitted to swift heavy-ion bombardment at GANIL (Caen, France) and the influence of irradiation on the mechanical properties was studied. The mechanical properties of the glass were characterized both before and after irradiation. Changes in hardness, elastic modulus and fracture toughness of the near-surface irradiated layer were determined using indentation techniques. SRIM calculations allowed to estimate the ions penetration range and the energy. deposition relative to electronic and nuclear interactions, which can be correlated to the experimental damaged depth. Meyer's hardness and Young's modulus decrease by about 30%, while fracture toughness is increased by more than 40%