Synthesis of amorphic and hexagonal boron nitride via high temperature treatment of NH3BH3 and Li(BH3NH2BH2NH2BH3).

Thermal decomposition of NH3BH3 and Li(BH3NH2BH2NH2BH3) was investigated at temperatures up to 1000 °C under various conditions with an inert atmosphere. It was found that complete dehydrogenation of ammonia borane towards amorphous boron nitride (a-BN) occurs at 850 °C when using monel reactors or at 1000 °C with the hot isostatic pressing method (HIP), which is significantly lower than was earlier reported. Li(BH3NH2BH2NH2BH3) was found to decompose towards hexagonal boron nitride (h-BN) at 1000 °C with the HIP method but at 850 °C in monel reactors towards a mixture of a-BN and h-BN. The findings are confirmed by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM).

Unexpected Coexisting Solid Solutions in the Quasi-Binary Ag(II) F2 /Cu(II) F2 Phase Diagram.

High-temperature solid-state reaction between orthorhombic AgF2 and monoclinic CuF2 (y=0.15, 0.3, 0.4, 0.5) in a fluorine atmosphere resulted in coexisting solid solutions of Cu-poor orthorhombic and Cu-rich monoclinic phases with stoichiometry Ag1-x Cux F2 . Based on X-ray powder diffraction analyses, the mutual solubility in the orthorhombic phase (AgF2 : Cu) appears to be at an upper limit of Cu concentration of 30 mol % (Ag0.7 Cu0.3 F2 ), while the monoclinic phase (CuF2 : Ag) can form a nearly stoichiometric Cu : Ag=1 : 1 solid solution (Cu0.56 Ag0.44 F2 ), preserving the CuF2 crystal structure. Experimental data and DFT calculations showed that AgF2 : Cu and CuF2 : Ag solid solutions deviate from the classical Vegard's law. Magnetic measurements of Ag1-x Cux F2 showed that the Néel temperature (TN ) decreases with increasing Cu content in both phases. Likewise, theoretical DFT+U calculations for Ag1-x Cux F2 showed that the progressive substitution of Ag by Cu decreases the magnetic interaction strength |J2D | in both structures. Electrical conductivity measurements of Ag0.85 Cu0.15 F2 showed a modest increase in specific ionic conductivity (3.71 ⋅ 10-13 ±2.6 ⋅ 10-15  S/cm) as compared to pure AgF2 (1.85 ⋅ 10-13± 1.2 ⋅ 10-15  S/cm), indicating the formation of a vacancy- or F adatom-free metal difluoride sample.