Mitigating Crystallographic Orientation Effect in SIMS: In-Depth Characterization of Rutile (TiO2) Oxygen Isotopes

Abstract

Rutile (TiO2) is a multifunctional material of interest in both materials science and geoscience due to its applications in electrochemical energy storage and its uses as a geochemical indicator. However, accurate in situ oxygen isotope analysis in rutile has been limited due to methodological challenges, particularly the crystallographic orientation effect (COE). This study presents an in-depth characterization (IDC) strategy to mitigate the COE and retrieve reliable δ18O values from rutile. Three rutile samples were characterized using Raman spectroscopy and electron probe microanalysis (EPMA). Bulk oxygen isotopes and in situ oxygen isotope distributions from the surface phase to the bulk phase were analyzed using isotope ratio mass spectrometry (IRMS) and secondary ion mass spectrometry (SIMS), respectively. The results demonstrate that oxygen isotope precision improves to ∼0.5‰ (2SD) in the bulk phase, where the COE diminishes via SIMS. This technique enables high-precision in situ isotopic analysis of rutile and potentially other oxide minerals, such as magnetite and hematite. The approach is reproducible, correction-free, and applicable for studies in geothermometry, provenance, and defect-related processes in functional materials.