Publications

Data-driven Methods for the Study and Design of Alkali Superionic Conductors

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Our article on “Data-driven First Principles Methods for the Study and Design of Alkali Superionic Conductors” has been published in  Chemistry of Materials as part of an invited Methods and Protocols special topic. In this work, we provide a detailed exposition of the first principles techniques that can be used to design alkali superionic conductors, a topic of high current interest. Accompanying this article is a repository of well-documented Jupyter notebooks that allows any researcher to easily reproduce the analysis and apply the same techniques to other materials. The article is available online and the notebooks are available at the following Github repo.

Announcements

Crystalium released

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We have published the world’s largest database of surface energies and Wulff shapes, dubbed Crystalium. A collaborative effort between the Materials Virtual Lab and the Materials Project, this new open-source database can help researchers design new materials for technologies in which surfaces and interfaces play an important role, such as fuel cells, catalytic converters in cars, computer microchips, nanomaterials and solid-state batteries. You can read more about it in the UCSD press release on EurekAlert! This work is published in Scientific Data as an open-access article, and Richard Tran, one of our undergraduate volunteers, is the first author.

Publications

Sodium-Rich Anti-Perovskite Solid Electrolytes

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In this work published in the Journal of the Electrochemical Society, we studied the effect of cold-pressing and spark-plasma sintering (SPS) processing on the Na3OBr sodium-rich anti-perovskite solid electrolytes was studied. SPS was found to reduce the interfacial impedance by 3 orders of magnitude. The much lower conductivity of Na3OBr compared to the lithium analogue is attributed to the significantly higher defect formation energies. This work is led by the Laboratory of Energy Storage and Conversion of Prof Shirley Meng. Zhi Deng and Prof Ong are co-authors.

Publications

Uniform second Li ion intercalation in solid state ε-LiVOPO4

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In this follow-on work as part of the NECCESS EFRC, a combination of hard and soft x–ray photoelectron and absorption spectroscopy techniques to depth profile solid state synthesized LiVOPO4, a promising multi-electron electrode for rechargeable lithium-ion batteries. This work confirms that limited kinetics in the high voltage regime are responsible for the inability to fully intercalate 2 Li in this material. The evolution from LiVOPO4 to Li2VOPO4 via the intermediate phases as predicted in our previous work (“Thermodynamics, Kinetics and Structural Evolution of ε-LiVOPO4 over Multiple Lithium Intercalation”) is confirmed by O K–edge absorption spectroscopy and DFT calculations. Yuh-chieh Lin and Shyue Ping Ong are co-authors in this work.

Publications

Relationship between structural rigidity and quantum efficiency in phosphors for solid state lighting

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Our article on “An integrated first principles and experimental investigation of the relationship between structural rigidity and quantum efficiency in phosphors for solid state lighting” has just been published in the Journal of Luminescence. This work is a collaborative effort between the McKittrick and Ong groups, and Jungmin Ha and Zhenbin Wang are co-first authors. In this work, we test the hypothesis of whether high host structural rigidity results in phosphors with high quantum efficiency, and show using an integrated approach that combines DFT calculations and experimental studies that a high Debye temperature alone is not a sufficient condition for a high quantum efficiency.

Publications

Dopant segregation and embrittlement at Mo grain boundaries

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Richard Tran and Zihan Xu published their paper on “Computational study of metallic dopant segregation and embrittlement at Molybdenum grain boundaries” in Acta Materialia. Mo and its alloys are important refractory materials for high temperature applications, but suffer from low ductility. In this work, we investigated the segregation and strengthening effects of 29 metallic dopants using DFT and empirical continuum models. We show that dopant chemistry and site preference plays a significant role in segregation behavior and strengthening effects at the GBs that deviate from simple bond-breaking arguments. Ta, Re, Os and W are predicted to have a weak strengthening effect on Mo for the Σ5(310) tilt GB, and Mn, Fe, Co and Nb are predicted to have reasonable strengthening effects for the Σ5(100) twist GB. Check out the paper at our publications page.

Publications

Electronic structure descriptor for narrow-band red phosphors

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Congratulations to Zhenbin on his first paper “Electronic Structure Descriptor for Discovery of Narrow-Band Red-Emitting Phosphors” in Chemistry of Materials! Narrow-band red-emitting phosphors are a critical component in phosphor-converted light-emitting diodes for highly efficient illumination-grade lighting. In this work, we report the discovery of a quantitative descriptor for narrow-band Eu2+-activated emission identified through a comparison of the electronic structure of known narrow-band and broad-band phosphors. By incorporating this descriptor in a high throughput first principles screening of 2,259 nitride compounds, we identify five promising new nitride hosts for Eu2+-activated red-emitting phosphors that are predicted to exhibit good chemical stability, thermal quenching resistance and quantum efficiency, as well as narrow-band emission.

Publications

Insights into the Li7P3S11 superionic conductor

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Iek-Heng Chu just published a new article in ACS Applied Materials & Interfaces. This is a highly collaborative work involving the expertise of many MAVRL group members as well as the Meng group. In this work, we investigate the performance limits of Li7P3S11, a highly promising lithium superionic conductor solid electrolyte. We find that Li7P3S11 is metastable at 0 K but becomes stable at above 630 K (∼360°C) when vibrational entropy contributions are accounted for, in agreement with differential scanning calorimetry measurements. Both scanning electron microscopy and the calculated Wulff shape show that Li7P3S11 tends to form relatively isotropic crystals. In terms of electrochemical stability, first-principles calculations predict that, unlike the LiCoO2 cathode, the olivine LiFePO4 and spinel LiMn2O4 cathodes are likely to form stable passivation interfaces with the Li7P3S11 SCE. This finding underscores the importance of considering multicomponent integration in developing an all-solid-state architecture. We also find that the AIMD-predicted room-temperature Li+ conductivity of 57 mS/cm is much higher than the experimental values suggesting the potential for further optimization.