Phase composition control of biphasic tritium breeding ceramics

Abstract

This work introduces strategies for obtaining a convenient candidate for tritium breeder materials. Li_4+xSi_1-xCr_xO₄ (x = 0 and 0.1) has been successfully prepared using the sol-gel method. X-Ray diffraction, SEM, TEM, X-Ray Photoelectron Spectra (XPS), Raman spectra, Electronic Paramagnetic Resonance (EPR) and Electrochemical Impedance Spectroscopy (EIS) were undertaken. X-Ray diffraction revealed that this compound crystallizes in the monoclinic structure with P 1 21/m 1 space group. A secondary phase Li₂CO₃ was detected by means of the High score software. The difference of XRD intensity demonstrated that the chromium substitution on silicon position into lithium orthosilicate is possible. The porosity values of compound demonstrate that it is sufficient for the generation a tritium breeder. Using TEM, the particle size increases from 20.04 nm to 31.67 nm for x = 0 and 0.1 respectively. This increase has been accounted for in terms of the fact that the Cr³⁺ ions influence the morphology. XPS and Raman spectra indicated the presence of valence state of Cr₂O₃. The resonance g = 1.97 of Li_4.1Cr_0.1Si_0.9O₄ is assigned to the exchange coupled Cr³⁺-Cr³⁺ pairs. At room-temperature, Electrochemical impedance spectroscopy (EIS) was conducted in order to control the lithium diffusion coefficient (D_Li) as well as the Warburg coefficient (W). The increase of W from 86.761 Ω^0.5–87.328 Ω^0.5 and the growth of the lithium diffusion coefficient D_Li from 2.4710⁻⁸ cm²s⁻¹ to 8.4810⁻⁸ cm²s⁻¹ for x = 0 and 0.1, respectively, have been assigned to chromium (Cr) which can enhance the ionic conductivity. The latter is ascribed to the rise of porosity which in turn triggers the enhancement of the electrochemical kinetics.