Synthesis of Crystalline Metastable Oxides
Our research in this area aims to elucidate and exploit the underlying factors that can govern the kinetic stabilization of semiconductor materials. Research thrusts specifically focus on metastable dielectric ceramics, such as that crystallize in a layered perovskite-
type structure, shown in the Figure (right). These materials have potential applications as new lead-free ferroelectrics and as small bandgap semiconductor materials. Research is directed toward the discovery of new pathways to increase their range of preparation and that can be experimentally achieved with the use of conditions that can, for example, drive product formation while controlling ion diffusion and phase segregation in order to inhibit decomposition. Structural characterization by X-ray and neutron scattering techniques is aimed at answering key questions regarding the formation and decomposition pathways of these materials. The extent and distribution of local and long-range structural disorder is probed at the precipices of energetically downhill decomposition pathways and the resulting new insights can help to push the limits of kinetic stabilization. Experimental efforts are complemented with quantification of thermodynamic relationships using materials informatics via open materials databases and density functional theory methods.
Funding Acknowledgment: National Science Foundation (#2004455)
Recent Publications:
a) Gabilondo, E.; O’Donnell, S.; Newell, R.; Broughton, R.; Mateus, M.; Jones, J.L.; Maggard, P.A. “Renaissance of Topotactic Ion-Exchange for Functional Solids with Close Packed Structures” Chem. Eur. J. 2022, 28, e202200479(1-6).
b) O’Donnell, S.; Smith, A.; Carbone, A.; Maggard, P.A. “Structure, Stability and Photocatalytic Activity of a Layered Perovskite Niobate after Flux-Mediated Sn(II) Exchange” Inorg. Chem. 2022, 61(9), 4062-4070.
c) Maggard, P.A. “Capturing Metastable Oxide Semiconductors for Applications in Solar Energy Conversion” Acc. Chem. Res. 2021, 54(16), 3160-3171.
d) Gabilondo, E.A.; O’Donnell, S.; Broughton, R.; Jones, J.L.; Maggard, P.A. “Synthesis and Stability of Sn(II)-Containing Perovskites: (Ba,SnII)HfO3 versus (Ba,SnII)SnO3” J. Solid St. Chem. 2021, 302, 122419(1-10).
Hybrid Semiconducting Photoelectrodes for Solar Energy Conversion to Liquid Fuels
Our efforts in this area focuses on the investigation of molecular catalyst-photoelectrode material systems that function at high solar-to-chemical conversion efficiencies and stabilities in aqueous solutions. Research efforts are aimed at unraveling the foundational relationships between the crystalline and electronic structures of carbon nitride and metal nitride semiconductor materials in order to achieve 
the requisite properties for optimized photoelectrochemical performance. Experimental efforts target semiconductor materials having small, tunable bandgaps (~1.9 eV to 2.5 eV), kinetic stability at their surfaces upon irradiation in aqueous solutions, and the attachment of molecular catalysts with high rates and product selectivity for the reduction of CO2 to liquid fuels. Tight control over reaction conditions is required to avoid the introduction of high concentrations of defects, such as anion vacancies, which are known to act as deep traps for electron-hole recombination. The utilization of flux-synthetic techniques also facilitates the growth of highly-faceted particles with specific exposed crystal facets and thus the preparation of textured polycrystalline material films. The electronic structures of the crystalline semiconductors are probed by density functional theory calculations to understand the nature of the underlying bandgap transitions, defect energies, and charge carrier mobilities.
Funding Acknowledgment: Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE; Department of Energy)
Recent Publications:
a) Pauly, M.; Kroger, J.; Duppel, V.; Murphey, C.; Cahoon, J.; Lotsch, B.V.; Maggard, P.A. “Unveiling the Complex Configurational Landscape of the Intralayer Cavities in a Crystalline Carbon Nitride” Chem. Sci. 2022, 13, 3187-3193.
b)Shang, B.; Zhao, F.; Choi, C.; Pauly, M.; Wu, Y.; Tao, Z.; Zhong, Y.; Harmon, N.; Maggard, P.A.; Lian, T.; Hazari, N.; Wang, H. “Monolayer Molecular Functionalization Enabled by Acid-Base Interaction for High Performance Photochemical CO2 Reduction” ACS Energy Lett. 2022, 7, 2265-2272.
c) Maggard, P.A. Ch. 2. Discovery and Development of Semiconductors for Photoelectrochemical Energy Conversion (Springer Handbook of Inorganic Photochemistry) Springer Nature, In Production, 2022.