We report on a new class of ZnO/ZnS nanomaterials based on the wurtzite/sphalerite architecture with improved electronic properties. Semiconducting properties of pristine ZnO and ZnS compounds and mixed ZnO1−xSx nanomaterials have been investigated using ab initio methods. In particular, we present the results of our theoretical investigation on the electronic structure of the ZnO1−xSx (x = 0.20, 0.25, 0.33, 0.50, 0.60, 0.66, and 0.75) nanocrystalline polytypes (2H, 3C, 4H, 5H, 6H, 8H, 9R, 12R, and 15R) calculated using hybrid PBE0 and HSE06 functionals. The main observations are the possibility of alternative polytypic nanomaterials, the effects of structural features of such polytypic nanostructures on semiconducting properties of ZnO/ZnS nanomaterials, the ability to tune the band gap as a function of sulfur content, as well as the influence of the location of sulfur layers in the structure that can dramatically affect electronic properties. Our study opens new fields of ZnO/ZnS band gap engineering on a multi-scale level with possible applications in photovoltaics, light-emitting diodes, laser diodes, heterojunction solar cells, infrared detectors, thermoelectrics, or/and nanostructured ceramics.

A number of studies have indicated that the implementation of Si in CrN can significantly improve its performance as a protective coating. As has been shown, the Cr-Si-N coating is comprised of two phases, where nanocrystalline CrN is embedded in a Si3N4 amorphous matrix. However, these earlier experimental studies reported only Cr-Si-N in thin films. Here, we present the first investigation of possible bulk Cr-Si-N phases of composition Cr2SiN4. To identify the possible modifications, we performed global explorations of the energy landscape combined with data mining and the Primitive Cell approach for Atom Exchange (PCAE) method. After ab initio structural refinement, several promising low energy structure candidates were confirmed on both the GGA-PBE and the LDA-PZ levels of calculation. Global optimization yielded six energetically favorable structures and five modifications possible to be observed in extreme conditions. Data mining based searches produced nine candidates selected as the most relevant ones, with one of them representing the global minimum in the Cr2SiN4. Additionally, employing the Primitive Cell approach for Atom Exchange (PCAE) method, we found three more promising candidates in this system, two of which are monoclinic structures, which is in good agreement with results from the closely related Si3N4 system, where some novel monoclinic phases have been predicted in the past.

Dedicated to Professor Thomas Schleid on the occasion of his 65th birthdayScandium oxychloride (ScOCl) has recently become of interest as an advanced material with possible applications in solid oxide fuel cells, photocatalysis, and electronic devices, as are oxyhalides of various transition metals. In the present study, crystal structure prediction has been utilized to fully investigate the energy landscape of ScOCl. A multi-methodological approach has been used consisting of a combination of two search methods, where the final structure optimization has been performed on ab initio level using DFT-LDA and hybrid PBE0 functionals. The experimentally observed α-ScOCl phase has been found as well as several additional structure candidates at high pressures and/or temperatures. A successful synthesis of these novel ScOCl modifications would have the potential for extending the scientific, technological and industrial applications of ScOCl.

Crystal structure prediction has been performed via the global exploration of the energy landscape of lanthanum oxyiodide (LaOI), using simulated annealing and involving over one million local optimizations. Afterwards, the most promising structure candidates among the minima found were subjected to local optimizations on ab initio level. Density functional theory (DFT) calculations were performed, using the GGA‐PBE functional, together with the hybrid HSE06 exchange‐correlation functional. Seven most relevant low‐energy minima were found after the final ab initio relaxation. The global minimum found corresponds to the α‐LaOI tetragonal structure in agreement with previous experimental and theoretical reports. The prediction of the additional β‐, γ‐, δ‐, ϵ‐, ζ‐, and η‐LaOI modifications demonstrate the rich diversity of local cation‐anion coordinations and structure types ranging from cubic and tetragonal, over rhombohedral and orthorhombic to monoclinic symmetry. Moreover, there are many previous experimental reports on related structures in the lanthanide oxyfluorides, which might guide possible future syntheses of LaOI‐modifications. A successful synthesis of these novel LaOI materials could have multiple technological applications ranging from nano‐ and bio‐materials to medicine, solid oxide fuel cells and photocatalytic materials.

ZnO/ZnS core/shell nanostructures, which are studied for diverse possible applications, ranging from semiconductors, photovoltaics, and light-emitting diodes (LED), to solar cells, infrared detectors, and thermoelectrics, were synthesized and characterized by XRD, HR-(S)TEM, and analytical TEM (EDX and EELS). Moreover, band-gap measurements of the ZnO/ZnS core/shell nanostructures have been performed using UV/Vis DRS. The experimental results were combined with theoretical modeling of ZnO/ZnS (hetero)structures and band structure calculations for ZnO/ZnS systems, yielding more insights into the properties of the nanoparticles. The ab initio calculations were performed using hybrid PBE0 and HSE06 functionals. The synthesized and characterized ZnO/ZnS core/shell materials show a unique three-phase composition, where the ZnO phase is dominant in the core region and, interestingly, the auxiliary ZnS compound occurs in two phases as wurtzite and sphalerite in the shell region. Moreover, theoretical ab initio calculations show advanced semiconducting properties and possible band-gap tuning in such ZnO/ZnS structures.