Dependence on bulk density of the Relative Sensitivity Factor (RSF) of deuterium in spinel-structured oxides

To allow the analysis of hydrogen in nominally anhydrous spinel-structured oxides by ion microprobe, Relative Sensitivity Factors (RSFs), which are matrix-dependent, need to be determined. Spinel-structured oxides are characterized by a wide range of solid solution. For this work, we have selected 10 natural spinels, spanning the Mg-Al-Fe-Ti-Cr compositional space as well franklinite, gahnite and jakobsite, ranging in density from 3.76 to 5.20 g cm^-3. We have also included a natural ilmenite sample for comparison. Samples were implanted with a fixed dose of deuterium (1 × 10¹⁵ atoms cm^-2) at an ion energy of 40 keV. Subsequently, we performed depth profiling using a Cs⁺primary beam on the Cameca ims-6f ion microprobe at Hokkaido University, monitoring secondary ion counts of ²H^-and ¹⁸O^-, until the deuterium counts dropped below background levels. From the ion microprobe data, we calculated RSF values for ²H in an ¹⁸O matrix for spinel structured oxides. RSF values ranged from 7.48 × 10²¹ atoms cm^-3to 2.65 × 10²² atoms cm^-3. Ilmenite yielded an RSF value of 2.89 × 10²² atoms cm^-3. Repeat analysis of a chromite provided a standard error of the mean of 1.67 × 10²¹ atoms cm^-3. We show that for the spinel-structured oxides, RSF values correlate exponentially with the density of the spinel crystal. This indicates that the analysis of hydrogen in natural spinels may be achieved if the density of the oxide sample is known.