We investigate lattice ordering phenomena for the heterovalent ternaries that are based on the wurtzite lattice, under the constraint that the octet rule be preserved. We show that, with the single exception of a highly symmetric twinned structure, all allowed lattice orderings can be described by a pseudospin model corresponding to the two different stackings of ABAB rows of atoms in the basal plane that occur in the P na21 and P mc21 crystal structures. First-principles calculations show that the difference in the energies of formation between these two structures is 13±3 meV/fu (formula unit) for ZnSnN2 and is an order of magnitude larger for ZnGeN2, and that for both materials the P m31 structure, which contains only octet-rule-violating tetrahedra, has a significantly higher energy of formation and a signficantly lower band gap. We predict almost random stacking and wurtzite-like x-ray diffraction spectra in the case of ZnSnN2, consistent with reported measurements. The octet-rule-preserving model of disorder proposed here predicts a band gap that for ZnSnN2 is relatively insensitive to ordering, in contrast to the prevailing model, which invokes the random placement of atoms on the cation sublattice. The violations of the octet rule in the latter model lead to significant narrowing of the band gap. The Raman and photoluminescence spectra of ZnSnN2 are interpreted in light of the ordering model developed here. The observation that ZnGeN2 orders in the P na21 structure under appropriate growth conditions is consistent with the larger difference in the energies of formation of the P na21 and P mc21 structures for this material. The ordering model presented here has important implications for the optical, electronic and lattice properties of all wurtzite-based heterovalent ternaries.

A series of experiments was carried out to explore the conditions under which ZnSnN2 would form by vapor–liquid–solid synthesis from a Zn–Sn melt exposed to a nitrogen plasma. ZnSnN2 precipitated at melt temperatures between 455 and 560 °C for melt compositions between 1.5 and 15 at.% Zn. Sn3N4 formed for temperatures between 440 and 560 °C for melt compositions below 1 at.% Zn. Zn3N2 apparently grew only in the vapor phase, and only at melt temperatures between 409 and 463 °C. Each of the materials was identified by its characteristic Raman spectrum and by Auger chemical analysis. The composition profiles of the melts were modeled as a function of time using the measured temperature profiles. The results were compared with post‐growth measurements of the melt compositions. These comparisons support the visual observation that exposure of the melt to the nitrogen plasma suppressed Zn evaporation substantially even prior to the formation of a solid crust of precipitate. This work helps define the range of growth conditions available for synthesis of ZnSnN2 by this vapor–liquid–solid method. Material yielded as a function of synthesis temperature and the composition of the melt, measured post‐synthesis by EDS. The two ZnSnN2 samples labeled with asterisks were grown with a plasma power of 60 W. All others were grown using a plasma power of 240 W.

The use of magnetic resonance imaging (MRI) in healthcare and the emergence of radiology as a practice are both relatively new compared with the classical specialties in medicine. Having its naissance in the 1970s and later adoption in the 1980s, the use of MRI has grown exponentially, consequently engendering exciting new areas of research. One such development is the use of computational techniques to analyze MRI images much like the way a radiologist would. With the advent of affordable, powerful computing hardware and parallel developments in computer vision, MRI image analysis has also witnessed unprecedented growth. Due to the interdisciplinary and complex nature of this subfield, it is important to survey the current landscape and examine the current approaches for analysis and trend trends moving forward.