arXiv subjects

James M. Ball

Publications and source records attributed to James M. Ball.

4 recordsLinked to original sources

arXiv2026

Predictions from $s$-process AGB models of the isotopic variations of zirconium and neodymium for comparison to bulk meteorites

Bulk meteoritic data show isotopic variability of $slow$-neutron-capture ($s$-process) origin in a several elements heavier than Fe. One peculiar feature is that the lighter $s$-process elements (e.g., Zr and Mo) present larger anomalies than the heavier $s$-process elements (e.g., Nd and W). To address this observation, we compared Zr and Nd data to model predictions of the s-process abundances at the surface of low-mass asymptotic giant branch (AGB) stars of initial metallicity from solar to twice solar. We found that the relative magnitude of the isotopic variability between these two elements can be matched by models of AGB stars of super-solar metallicity. The match is favoured by stronger convective overshoot, leading to a deeper dredge-up of the H-rich envelope into the He-rich region, and/or a smaller (~ half than standard) mass of the region rich in the $^{13}$C nuclei that produce free neutrons via the $^{13}$C($α$,n)$^{16}$O reaction. We conclude that nucleosynthesis in AGB stars can match the difference in the magnitude of the bulk meteoritic variations in Zr and Nd, provided that super-solar metallicity stars are the original site of these signatures. The AGB stars that produced such variations could have belonged to the current population of old, super-solar metallicity stars seen in the galactic solar neighbourhood.

astro-ph.SR↗

arXiv2026

Stellar Interpretation of Meteoritic Data and PLotting for Everyone (SIMPLE): Isotope Mixing Lines for Six Sets of Core-Collapse Supernova Models

Bulk meteorites and their inclusions exhibit, for many chemical elements, isotopic variability produced by nucleosynthetic events in stars and supernovae before the formation of the Sun. While the exact astrophysical origins of these variations are still a matter of debate, their identification provides insights on the environment of the Sun's birth and the formation of the Solar System. Here we present a new Python tool called SIMPLE (Stellar Interpretation of Meteoritic Data and Plotting for Everyone) designed to compare the isotopic composition of the ejecta from core-collapse supernovae (CCSNe) with meteoritic data. In the present version, the SIMPLE toolkit includes a dataset of 18 CCSN models, from 6 different published sets, with initial masses of 15, 20, and 25 M$_{\odot}$ and solar metallicity. SIMPLE is designed to easily extract the isotopic abundances predicted by each CCSN model for any elements and post-process them into the format needed to compare to the meteoritic data, therefore, facilitating their interpretation. As an example of how to use SIMPLE, we analyze the composition of the Ni isotopes in the 18 models and confirm that bulk meteorite Ni anomalies are compatible with material from the innermost Si-rich region of CCSN ejecta. Designed as a collaborative platform, SIMPLE is open-source and welcomes community contributions to enhance its development and dissemination for stellar nucleosynthesis and meteoritic studies. Future enhancements include addition of more model predictions and inclusion of mixing between different layers of supernova ejecta.

astro-ph.SR↗

arXiv2024

A green solvent system for precursor phase-engineered sequential deposition of stable formamidinium lead triiodide for perovskite solar cells

Perovskite solar cells (PSCs) offer an efficient, inexpensive alternative to current photovoltaic technologies, with the potential for manufacture via high-throughput coating methods. However, challenges for commercial-scale solution-processing of metal-halide perovskites include the use of harmful solvents, the expense of maintaining controlled atmospheric conditions, and the inherent instabilities of PSCs under operation. Here, we address these challenges by introducing a high volatility, low toxicity, biorenewable solvent system to fabricate a range of 2D perovskites, which highly effective precursor phases for subsequent transformation to alpha-formamidinium lead triiodide (FAPbI3), fully processed under ambient conditions. PSCs utilising our FAPbI3 reproducibly show remarkable stability under illumination and elevated temperature (ISOS-L-2) and "damp heat" (ISOS-D-3) stressing, surpassing other state-of-the-art perovskite compositions. We determine that this enhancement is a consequence of the 2D precursor phase crystallisation route, which simultaneously avoids retention of residual low-volatility solvents (such as DMF and DMSO) and reduces the rate of degradation of FA+ in the material. Our findings highlight both the critical role of the initial crystallisation process in determining the operational stability of perovskite materials, and that neat FA+-based perovskites can be competitively stable despite the inherent metastability of the alpha-phase.

physics.app-ph↗

arXiv2018

Elucidating the long-range charge carrier mobility in metal halide perovskite thin films

Many optoelectronic properties have been reported for lead halide perovskite polycrystalline films. However, ambiguities in the evaluation of these properties remain, especially for long-range lateral charge transport, where ionic conduction can complicate interpretation of data. Here we demonstrate a new technique to measure the long-range charge carrier mobility in such materials. We combine quasi-steady-state photo-conductivity measurements (electrical probe) with photo-induced transmission and reflection measurements (optical probe) to simultaneously evaluate the conductivity and charge carrier density. With this knowledge we determine the lateral mobility to be ~ 2 cm2/Vs for CH3NH3PbI3 (MAPbI3) polycrystalline perovskite films prepared from the acetonitrile/methylamine solvent system. Furthermore, we present significant differences in long-range charge carrier mobilities, from 2.2 to 0.2 cm2/Vs, between films of contemporary perovskite compositions prepared via different fabrication processes, including solution and vapour phase deposition techniques. Arguably, our work provides the first accurate evaluation of the long-range lateral charge carrier mobility in lead halide perovskite films, with charge carrier density in the range typically achieved under photovoltaic operation.

cond-mat.mtrl-sci↗