Spatially resolved quantitative profiling of compositionally graded perovskite layers using laser ablation-inductively coupled plasma mass spectrometry

Abstract

Fuel cell cathodes can be constructed as a stack of perovskite layers whose composition gradually changes over a few hundreds of µm. They are prepared by sintering a mixture of two ceramic powders (Mn-perovskite and Co-perovskite), where the proportions of the mixture contributes to the chemical gradation. Laser ablation-ICP-MS permitted the determination of the proportions of Mn-perovskite and Co-perovskite, in several depth profiles. The set-up and the laser operating conditions were specifically optimised so that correct elemental concentration profiles could be acquired, without beam induced artefacts. Lateral resolution below 100 µm and a depth resolution of 0.1–0.2 µm were obtained. Quantification was carried out from the proportions of the mixture of perovskites and the elemental composition of the individual perovskites (i.e., a “weighted summation”). The composition of the powder was previously determined via digestion and ICP-MS. Comparison with semi-quantitative data from SEM-EDX showed that the developed method provided reliable responses. Analysis of the signal structure of the depth profiles was performed by means of signal convolution and numerical differentiation. The occurrence of differential bands in conjugate pairs could be assessed and used for a realistic description of the sample structure. The fluctuation of analyte concentrations at low level (<1 µm) suggests that further improvements in the sampling thickness might conflict with robust and powerful quantification. Therefore, the determined pulse-related depth resolution of 100–200 nm seems to be a good compromise between spatially resolved analysis and quantification capability. The rapidity, flexibility and detection power of LA-ICP-MS are advantages that integrate and extend the analytical capabilities of other well-established beam-assisted techniques (i.e., XPS, AES, SIMS, SNMS, GD-OES/MS, SEM-EDX) and permit critical control of the quality of the fabricated products.