Daniel Jezierski

We investigate the electronic structure of AgF 2 , AgFBF 4 , AgF, and Ag 2 O using x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) at the Ag L 3 edge. XAS results were compared with density functional theory computations of the spectra, allowing an identification of main features and an assessment of the theoretical approximations. Our RIXS measurements reveal that AgF 2 exhibits charge-transfer (CT) excitations and d d excitations, analogous to those observed in La 2 CuO 4 . We propose to use the ratio of d d to CT spectral weight as a measure of the covalence of the compounds and provide explicit equations for the weights as a function of the scattering geometry for crystals and powders. The measurements at the metal site L 3 edge and previous measurement in the ligand K edge reveal a striking similarity between the fluoride and cuprate materials, with fluorides somewhat more covalent than cuprates. These findings support the hypothesis that silver fluorides are an excellent platform to mimic the physics of cuprates, providing a promising avenue for exploring high- T c superconductivity and exotic magnetism in quasi-two-dimensional ( AgF 2 ) and quasi-one-dimensional ( AgFBF 4 ) materials.

Based on theoretical calculations, we introduce a new Ag ^II Ag ^III F ₅ monoclinic polymorph with a rare high-spin Ag ^III . It owes its stability to strong quasi-two dimensional antiferromagnetic interactions.

Based on theoretical calculations, we introduce a new AgIIAgIIIF5 monoclinic polymorph with a rare high spin AgIII. Our analysis of the experimental xray diffraction data available in the literature reveals that this polymorph was likely prepared in the past in a mixture with the triclinic form of the same compound. Theoretical calculations reproduce very well the lattice parameters of both forms. Calculations suggest that under ambient conditions, the monoclinic form is the more energetically stable phase of Ag2F5. We predict a strong one-dimensional antiferromagnetic superexchange between silver cations of different valences with superexchange constant of minus 207 meV (hybrid functional result). The polymorph with high spin AgIII owes its stability over the one with low spin AgIII, to these magnetic interactions.

A new family of intergrowth structures containing strongly correlated antiferromagnetic layers of AgF₂ is introduced. Charge reservoir layers allow to control the strain and magnetic properties, rendering them superior to oxocuprates(ii).

EIS study on the ionic conductivity of Li(BH₃NH₂BH₂NH₂BH₃) shows a decent value of 4.0 × 10⁻⁶ S cm⁻¹ at 65 °C in stark contrast to the previous study. This value is superior to that of the low-temperature form of LiBH₄.

We reinvestigated ionic conductivity of lithium ions for Li(BH3NH2BH2NH2BH3), an ammonia borane derivative. The observed conductivity (4.0x10–6 S/cm at 65°C) was found to be over four orders of magnitude higher than the value reported previously at 70oC for this compound. Since very slow thermal decomposition of Li(BH3NH2BH2NH2BH3) progresses already below 100°C, the previous results reported for 70–130°C most likely correspond to decomposed samples. The activation energy for lithium conductivity of polycrystalline layered Li(BH3NH2BH2NH2BH3) (57 kJ/mol) resembles that for powdered Li3N (59 kJ/mol) suggesting similar mechanism of lithium diffusion in both materials.

One-step pyrolytic synthesis of high quality a-BN and h-BN from ammonia borane at 850 °C and Li(BH₃NH₂BH₂NH₂BH₃) at 1000 °C/1000 bar, respectively.

As Ag ²⁺ is such a powerful oxidizer, not many open-shell transition metal cations can resist its neighborhood. Here we introduce AgCoF ₅ , a rare representative of the transition metal–Ag ²⁺ fluoride family.