Research · Hodges Group — Solid State Chemistry at Penn State

Our research group seeks new synthetic tools for building inorganic solids with challenging combinations of elements. This leads us into less explored regions of the periodic table and composition space where few or no compounds exist. These are fertile areas for exploratory efforts, but demand creative strategies for directing atoms with disparate reactivities into well-defined structures. The reward is new materials with unusual bonding, and structural building blocks that assemble into phases with exotic properties.

What we work on

Anion ordering in mixed-chalcogen solids

Although chalcogens tend to form solid solutions in simple crystals, ordering does occur in structures with more than one anion site. Order-disorder phenomena affect their properties in numerous ways, but often go unnoticed and are poorly understood. The research team is seeking to establish a deeper understanding of the fundamental mechanisms that define atomic-scale ordering in chalcogenides and other extended solids. Our interdisciplinary approach, which unifies experiment and theory, is establishing chemical models for predicting local and long-range ordering phenomena.

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Oxychalcogenides by design

Heteroanionic solids offer unique levers for tuning structures and properties, but accessing multianion phase space remains challenging because of mismatches in anion reactivity. We have discovered a new family of A₂Hf₃Q₆O oxychalcogenides, the first reported in the A–Hf–Q–O quaternary space. To gain control over the heteroanion stoichiometry, we react pre-synthesized HfQ₂ with A₂CO₃, which releases A₂O intermediates at high temperature that react with the binary precursors. Conceptually, rows of bridging O atoms are inserted into the layered TMD sheets, breaking the octahedral connectivity and partitioning the layers into nanometer-wide 1D [Hf₃Q₆] ribbons. The materials are direct-gap semiconductors with band gaps from 1.8 to 2.6 eV and giant emission anisotropy.

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Porous oxides for selective oxidation

MoV-based oxides with the M₁ phase are an important family of catalysts for oxidative dehydrogenation of light alkanes. M₁ materials are typically synthesized from complex precursors using multi-step protocols that include high-temperature annealing to induce crystallization. We have described a single-step hydrothermal synthesis of phase-pure MoV_0.3Bi_0.05Ox, a Bi-containing M₁ analogue that is inaccessible by conventional methods. The approach reacts simple oxide precursors in the presence of carboxylic acids and ethylene glycol to give the M₁ product in high yield. The protocol offers a scalable alternative to traditional M₁ syntheses, and we are adapting this chemistry to other synthetically challenging mixed-metal oxide systems.

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