Radiation ordering in quenched alloy sobserved “in situ” in the high voltage microscope

Different alloys with a face centered cubic disordered structure have been electron irradiated in the quenched or short range order state under direct observation in a high voltage electron microscope. Ordering due to 1 MeV irradiation has been observed in Au₄Mn, Ni₄Mo and Cu₃Pd. Care has been taken to avoid ordering due to the thermal effect of the electron beam. It has been demonstated that although similar states of order can be achieved by thermal and irradiation ordering, the path followed can be different however.     

Forthcoming events 2001

Abstract

The magneto-optical spectra of the R₁ and R₂ lines of Cr³⁺ ions in alexandrite have been measured under hydrostatic pressures and magnetic fields up to 6 GPa and 15 T, respectively. The spins of the excited states, ²E, have the Heisenberg-type characters at atmospheric pressure, though the g-values are anisotropic with the values between 1.3 and 2.0. The g-values for the direction parallel to the α-axis remain unchanged with increasing pressure, while for the directions normal to the α-axis they are reduced appreciably. The fine structure parameters of spins in the ground state, ⁴A₂, exhibit quite a similar behavior. The R₁-R₂ splitting is reduced also by pressure. These properties are the evidences that the spins of the ²E states become of the king-type under pressures above about 15 GPa. The mechanism of such the change of spin character is discussed quantitatively on the basis of a crystal field model.     

Radiation-Induced Paramagnetic Centers in the Glasses Of CaO-Ga2O3-GeO2 System

The X-band (v ? 9.4 GHz) ESR spectra of the UV-, X-, and γ-irradiated glasses of CaO-Ga₂O₃-GeO₂ system with compositions similar to Ca₃Ga₂Ge₃O₁₂, Ca₃Ga₂Ge₄O₁₄, and Ca₃Ga₂O₆ crystals have been investigated at 300 and 77 K. It was shown that X- and γ-irradiation of the Ge-contained glasses induce simultaneously electron and hole paramagnetic centers, stable at room temperature. The UV-irradiation of Ge-contained glasses leads to the generation of stable centers of electron type, whereas the X- and γ-irradiation of glasses with Ca₃Ga₂O₆ composition induces stable hole centers, exclusively. The electron centers are assigned to E′ (Ge) centers with different local environments. ESR spectrum of hole centers is ascribed to O^? centers, localized on non-bridging oxygen of the glass network. The E′ (Ge) and O^? centers show high thermal stability in the CaO-Ga₂O₃-GeO₂ glass network. The obtained ESR spectra are described by spin Hamiltonian with g-factor of axial and rhombic symmetry for the E′ (Ge) and O^? centers, respectively. The nature, electron structure and some formation peculiarities of the radiation defects in CaO-Ga₂O₃-GeO₂ glasses are discussed in comparison with other glasses as well as Ca₃Ga₂Ge₃O₁₂ and Ca₃Ga₂Ge₄O₁₄ crystals.