Infrared absorption spectroscopy of hydrogen and deuterium in CaO and SrO crystals
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R. Gonzalez3' Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (Received 4 January 1988; accepted 29 September 1988)
Infrared absorption spectra have been used to characterize OH" and OD~ ions at the surface and the bulk of undoped CaO, lithium doped CaO, and SrO crystals. Diffusion of deuterons from D2O vapor into these crystals was performed at elevated temperatures. Diffusion coefficients were obtained to be £>(CaO) = 3 x 1(T6 cm2/sec at 1773 K and D(SrO) = 4 x 10~7 cm2/sec at 1523 K. For the doped CaO crystal with lithium concentration of 310 ppm, the diffusion coefficient was measured to be £>(CaO: Li) = 4 x 10~7 cm2/sec at 1473 K and the activation energy in the Arrhenius equation was estimated to be 1.7 eV.
I. INTRODUCTION In the last two decades, hydrogen impurities have been studied in different oxide materials.1"10 Hydrogen is important because it is present in most as-grown crystals and can affect the usefulness of the materials for technology." 12 Hydrogen and its isotopes, deuterium and tritium, generally diffuse much more slowly in oxides than through metals. On one hand, some metals are suitable for hydrogen-storage purposes. On the other hand, the usefulness of ceramics lies precisely in low-hydrogen permeation. Diffusion coefficients and activation energies for protons and deuterons at elevated temperatures have been measured previously in TiO 2 , MgO, LiNbO 3 , and amorphous cordierite using infrared absorption measurements. 47 ' 810 A fundamental understanding of the basic mechanisms for hydrogen diffusion in oxides, however, will require the examination of many different classes of material. In the alkaline-earth oxides, the complex infrared spectrum is related to the many possible configurations of hydroxyl ions in the lattice. In an oxide matrix the protons normally occupy cation sites and give rise to OH~ ions. In addition, the infrared spectra of oxides containing hydrogen and its isotopic deuterium provide a simple method to estimate the relative concentration of OH~ or OD~ ions. Since these crystals are hygroscopic, attention was focused on hydroxyl bands on the surface, as well as in the bulk material, and on the temperature which hydrogen diffused in and out the crystal. The present study focused on the characterization of OH" and OD~ bands in CaO, Li doped
" Permanent address: Departmento de Fisica del Estado Solido, Facultad de Ciencias Fisicas, Universidad Complutense, 28040 Madrid, Spain 224
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CaO(CaO:Li), and SrO crystals and on the diffusion of deuterons into these oxides. II. EXPERIMENTAL PROCEDURES AND ANALYSES The single crystals of CaO, CaO:Li, and SrO used in the present study were grown by the arc-fusion method at the Oak Ridge National Laboratory13 and cleaved along [100] direction. The starting materials were reagent grade CaCO3 and SrCO3 powder from the Mallinckrodt Chemical Company. The dopant material for CaO:Li was approximately 5% of Li2CO3 mixed intimately with CaCO3 powder
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