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In oxide materials, an increase in oxygen vacancy concentration often results in lattice expansion, a phenomenon known as chemical expansion that can introduce detrimental stresses and lead to potential device failure. One factor often implicated in the chemical expansion of materials is the degree of localization of the multivalent cation electronic states. When an oxygen is removed from the lattice and a vacancy forms, it is believed that the two released electrons reduce multivalent cations and expand the lattice, with more localized cation states resulting in larger expansion. In this work, we computationally and experimentally studied the chemical expansion of two Pr-based perovskites that exhibit ultra-low chemical expansion, PrGa 1− x Mg x O 3− δ and BaPr 1− x Y x O 3− δ , and their parent compounds PrGaO 3− δ and BaPrO 3− δ . Using density functional theory, the degree of localization of the Pr-4f electrons was varied by adjusting the Hubbard U parameter. We find that the relationship between Pr-4f electron localization and chemical expansion exhibits more complexity than previously established. This relationship depends on the nature of the states filled by the two electrons, which may not necessarily involve the reduction of Pr. F ′-center defects can form if the reduction of Pr is unfavorable, leading to smaller chemical expansions. If hole states are present in the material, the states filled by the electrons can be Pr-4f and/or O-2p hole states depending on the degree of Pr-4f localization. The O-2p holes are more delocalized than the Pr-4f holes, resulting in smaller chemical expansions when the O-2p holes are filled. X-ray photoelectron spectroscopy reveals low concentrations of Pr 4+ in PrGa 0.9 Mg 0.1 O 3− δ and BaPr 0.9 Y 0.1 O 3− δ , supporting the possible role of O-2p holes in the low chemical expansions exhibited by these materials. This work highlights the non-trivial effects of electron localization on chemical expansion, particularly when hole states are present, pointing to design strategies to tune the chemical expansion of materials. 

Computational methods have become increasingly used in both academia and industry. At the University of Illinois Urbana Champaign, the Department of Materials Science and Engineering (MSE), as part of a university-funded educational innovation program, has integrated computation throughout its undergraduate courses since 2014. Within this curriculum, students are asked to solve practical problems related to their coursework using computational tools in all required courses and some electives. Partly in response to feedback from students, we have expanded our current curriculum to include more computational modules. A computational module was added to the freshman Introduction to Materials Science and Engineering class; thus, students will be expected to use computational tools from their first year onwards. In this paper, we survey students who are currently taking courses with integrated computation to explore the effects of gradually introducing students to programming as well as both macro- and micro-scale simulations over multiple years. We investigate the improving confidence level of students, their attitude towards computational tools, and their satisfaction with our curriculum reform. We also updated our survey to be more detailed and consistent between classes to aid in further improvements of our MSE curriculum.