The HfV₂–HfV₂O₇ composite is proposed as a material with potentially temperature-independent thermophysical properties due to the combination of anomalously increasing thermoelastic constants of HfV₂ with the negative thermal expansion of HfV₂O₇. Based on literature data, the coexistence of both a near-zero temperature coefficient of elasticity and a coefficient of thermal expansion is suggested for a composite with a phase fraction of approximately 30 vol.% HfV₂ and 70 vol.% HfV₂O₇. To produce HfV₂–HfV₂O₇ composites, two synthesis pathways were investigated: (1) annealing of sputtered HfV₂ films in air to form HfV₂O₇ oxide on the surface and (2) sputtering of HfV₂O₇/HfV₂ bilayers. The high oxygen mobility in HfV₂ is suggested to inhibit the formation of crystalline HfV₂–HfV₂O₇ composites by annealing HfV₂ in air due to oxygen-incorporation-induced amorphization of HfV₂. Reducing the formation temperature of crystalline HfV₂O₇ from 550 °C, as obtained upon annealing, to 300 °C using reactive sputtering enables the synthesis of crystalline bilayered HfV₂–HfV₂O₇.

We describe the effect of the Fe layer thickness on the antiferromagnetic interlayer exchange coupling in ${[\mathrm{Fe}/\mathrm{MgO}]}_N$ superlattices. An increase in coupling strength with increasing Fe layer thickness is observed, which highlights the need for including the extension of both layers when discussing the interlayer exchange coupling in superlattices.

We report on the discovery of a boundary-induced body-centered tetragonal iron phase in thin films deposited on ${\mathrm{MgAl}}_2{\mathrm{O}}_4$ (001) substrates. We present evidence for this phase using detailed x-ray analysis and ab initio density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetization direction are observed, as compared with body-centered cubic iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultrathin iron layers.

We investigated the elastic properties of the HfV₂O₇ high-temperature phase, exhibiting negative thermal expansion, in a synergetic strategy of first-principle calculations and nanoindentation experiments performed on sputtered films. Self-consistent results were obtained for the measured elastic modulus (73 ± 14 GPa) and dispersion-corrected density functional theory calculations. The elastic properties of HfV₂O₇ are affected by long-range dispersion interaction, which may be induced by severe modification in the second-nearest neighbor O-O bond distance as obtained upon compression. HfV₂O₇ is composed of HfO₆, VO₄, and V₂O₇ building blocks, whereby the latter is characterized by an increasing V-O(-V) bond length upon compression.

Direct reduction of iron involves complex, multiscale phenomena, encompassing solid‐state phase transformations and gas transport through pores that must be accurately represented for predictive industrial implementation. Here, we present a thermodynamically sound pellet‐scale model that describes these mechanisms and can serve as a foundation for improving the understanding of pellet reduction kinetics in H₂/CO‐containing atmospheres. The model assumes that the gas phase remains in thermodynamic equilibrium instantly adjusting to any changes in composition. This reduces the number of fitting parameters drastically compared to other existing models, while maintaining a strict thermodynamic upper bound estimate. A driving force term is included in the reaction rate equation ensuring that the three iron oxide reduction steps and the formation of graphite and cementite in carbon‐containing gases occur only if they are thermodynamically possible. It is demonstrated that fitting kinetic parameters based on conversion degree data alone leads to overfitting. This is true both for existing models and the model introduced here, despite the fact that the latter contains fewer parameters. To overcome this overfitting problem, spatially resolved microstructural data at key reduction stages can be considered, as shown here for recently reported data for a pellet reduced in H₂ atmosphere.