In most intermetallic europium compounds, the Eu atoms exhibit a divalent oxidation state with a high effective magnetic moment since Eu²⁺ is isoelectronic with Gd³⁺. Trivalent intermetallic Eu compounds, in contrast, are extremely scarce and under 20 examples are known to literature. This mini-review summarizes the known binary and ternary examples along with their crystal-chemical peculiarities as well as their magnetic and ¹⁵¹Eu Mössbauer spectroscopic behavior. Additionally, compounds that exhibit valence phase transitions are summarized.

The present review summarizes important aspects of the crystal chemistry of ytterbium-based intermetallic compounds along with a selection of their outstanding physical properties. These originate in many cases from the ytterbium valence. Different valence states are possible here, divalent (4f¹⁴), intermediate-valent, or trivalent (4f¹³) ytterbium, resulting in simple diamagnetic, Pauli or Curie-Weiss paramagnetic, or valence fluctuating behavior. Especially, some of the Yb³⁺ intermetallics have gained deep interest due to their Kondo or heavy Fermion ground states. We have summarized their property investigations using magnetic and transport measurements, specific heat data, NMR, ESR, and Mössbauer spectroscopy, elastic and inelastic neutron scattering, and XAS data as well as detailed thermoelectric measurements.

The REAl ₂ series was characterized by solid-state NMR and Raman experiments. The spectroscopic data was correlated to the XRD measurements and the DFT calculations, gaining an insight into bonding, charge distribution and the strain.

Partially or fully reduced transition metal oxides show extraordinary electronic and catalytic properties but are usually prepared by high temperature reduction reactions. This study reports the systematic investigation of the fast mechanochemical reduction of rutile‐type TiO₂ and H‐Nb₂O₅ to their partially reduced black counterparts applying NaH and LiH as reducing agents. Milling time and oxide to reducing agent ratio show a large influence on the final amount of reduced metal ions in the materials. For both oxides LiH shows a higher reducing potential than NaH. An intercalation of Li⁺ into the structure of the oxides was proven by PXRD and subsequent Rietveld refinements as well as ⁶Li solid‐state NMR spectroscopy. The products showed a decreased band gap and the presence of unpaired electrons as observed by EPR spectroscopy, proving the successful reduction of Ti⁴⁺ and Nb⁵⁺. Furthermore, the developed material exhibits a significantly enhanced photocatalytic performance towards the degradation of methylene blue compared to the pristine oxides. The presented method is a general, time efficient and simple method to obtain reduced transition metal oxides.