Ammonothermal synthesis is a method for synthesis and crystal growth suitable for a large range of chemically different materials, such as nitrides (e.g., GaN, AlN), amides (e.g., LiNH₂, Zn(NH₂)₂), imides (e.g., Th(NH)₂), ammoniates (e.g., Ga(NH₃)₃F₃, [Al(NH₃)₆]I₃ · NH₃) and non-nitrogen compounds like hydroxides, hydrogen sulfides and polychalcogenides (e.g., NaOH, LiHS, CaS, Cs₂Te₅). In particular, large scale production of high quality crystals is possible, due to comparatively simple scalability of the experimental set-up. The ammonothermal method is defined as employing a heterogeneous reaction in ammonia as one homogenous fluid close to or in supercritical state. Three types of milieus may be applied during ammonothermal synthesis: ammonobasic, ammononeutral or ammonoacidic, evoked by the used starting materials and mineralizers, strongly influencing the obtained products. There is little known about the dissolution and materials transport processes or the deposition mechanisms during ammonothermal crystal growth. However, the initial results indicate the possible nature of different intermediate species present in the respective milieus.

Polynator is a Python program capable of identifying coordination polyhedra, molecules and other shapes in crystal structures and evaluating their distortions. Distortions are quantified by fitting the vertices of a model to a selected set of atoms. In contrast to earlier programs, models can be deformable, which allows them to represent a point group or a range of shapes such as the set of all trigonal prisms, rather than a specific, rigid shape such as the equilateral trigonal prism. The program comes with a graphical user interface and is freely available. This paper discusses its working principle and illustrates a number of applications.

The combination of laser‐heated diamond anvil cells and synchrotron Mössbauer source spectroscopy were used to investigate high‐temperature high‐pressure chemical reactions of iron and iron nitride Fe₂N with nitrogen. At pressures between 10 and 45 GPa, significant magnetic hyperfine splitting indicated compound formation after annealing at 1300 K. Subsequent in situ X‐ray diffraction reveals a new modification of FeN with NiAs‐type crystal structure, as also rationalized by first‐principles total‐energy and chemical‐bonding studies.

Barium hexaferrite powder samples with grains in the μm-range were obtained from solid-state sintering, and crystals with sizes up to 5 mm grown from PbO, Na₂CO₃, and BaB₂O₄ fluxes, respectively. Carbonate and borate fluxes provide the largest and structurally best crystals at significantly lower growth temperatures of 1533 K compared to flux-free synthesis (1623 K). The maximum synthesis temperature can be further reduced by the application of PbO-containing fluxes (down to 1223 K upon use of 80 at % PbO), however, Pb-substituted crystals Ba_1–xPb_xFe₁₂O₁₉ with Pb contents in the range of 0.23(2) ≤ x ≤ 0.80(2) form, depending on growth temperature and flux PbO content. The degree of Pb-substitution has only a minor influence on unit cell and magnetic parameters, although the values for Curie temperature, saturation magnetization, as well as the coercivity of these samples are significantly reduced in comparison with those from samples obtained from the other fluxes. Due to the lowest level of impurities, the samples from carbonate flux show superior quality compared to materials obtained using other methods.

Research interest in inverse perovskite nitrides, since the early beginnings in the 1940s has considerably intensified in recent years. Within the last decades exploration lead to a wide variety of new compounds, compositions and structural arrangements. Electronic properties of the novel materials span from insulating and semiconducting via semimetallic and metallic, depending on element combination. Similarly, magnetic properties qualify for various applications, according to frequently high Curie temperatures and saturation magnetizations, together with development of delicate magnetic structures and often occurring metamagnetic transitions, to give only few examples. This minireview is intended to give an overview on formation of such metal‐rich compounds with focus on chemical systems and crystal chemistry.