Effect of isovalent substitution on the crystal structure and properties of two-slab indates BaLa2−xSmxIn2O7

Exploring the effect of isomorphic substitution of atoms on crystal structure and features of oxide compounds is one of the main tasks of modern materials science. This paper deals with the La/Sm isovalent substitution in a two-slab perovskite-like BaLa2In2O7 structure and its effect on the structural features and magnetic properties of BaLa2−xSmxIn2O7 indates synthesized. A complete characterization including data of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), structural calculations (Rietveld method), second optical harmonic generation of the laser radiation, calculations of valence bond sums (VBS), and magnetic susceptibility data of phases obtained is presented. The existence region of BaLa2−xSmxIn2O7 solid solutions with a two-slab perovskite-like structure (0 ≤ x ≤ 1.8) was established, and their coordinate parameters were refined. The character of barium and RE atoms distribution in BaLa2−xSmxIn2O7 structure has determined, and the correlation between substitution degree of lanthanum atoms and the length of Ln–O2 interblock distance has revealed. The magnetic properties of BaLa2−xSmxIn2O7 were considered in terms of the crystal field effect.

New n-type Zintl Phases for Thermoelectrics: Discovery, Structural Characterization and Band Engineering of the Compounds A2CdP2 (A = Sr, Ba, Eu)

Zintl phases, owing to their complex crystal structures and intricate chemical bonding, have recently been recognized as promising candidates for thermoelectric (TE) applications. Band engineering, including band convergence has been shown to be an effective way to enhance the thermoelectric performance of such materials. In this work, a series of emerging TE materials, the isostructural Zintl phases with the general formula <i>A</i>₂CdP₂ (<i>A</i> = Sr, Ba, Eu) are presented for the first time. Their structures, established from single-crystal X-ray diffraction methods, show them to crystallize with the orthorhombic Yb₂CdSb₂ structure type, with first-principles calculations on phase stability confirming that Ba₂CdP₂ and Sr₂CdP₂ are thermodynamically stable. Computationally, it was found that both Ba₂CdP₂ and Sr₂CdP₂ have the potential to exhibit high <i>n</i>-type TE performance (0.6 and 0.7 relative to the <i>n</i>-type PbTe, a reference TE material). To optimize the TE performance, band engineering strategies, including isovalent substitution and cation mutations, were investigated. From the band engineering of Ba₂CdP₂ via isovalent substitution of Sr on a single Ba site, leading to the quaternary composition SrBaCdP₂, it can be suggested that increasing the conduction band valley degeneracy is an effective way to improve the <i>n</i>-type TE performance by three-fold. Moreover, first-principles defect calculations reveal that both Ba₂CdP₂ and SrBaCdP₂ are <i>n</i>-type dopable, adding these compounds to a small list of rare <i>n</i>-type dopable Zintl phases. The band engineering strategies used in this work are equally applicable to other TE materials, either for optimization of existing TE materials or designing new materials with desired properties.

New n-type Zintl Phases for Thermoelectrics: Discovery, Structural Characterization and Band Engineering of the Compounds A2CdP2 (A = Sr, Ba, Eu)

Zintl phases, owing to their complex crystal structures and intricate chemical bonding, have recently been recognized as promising candidates for thermoelectric (TE) applications. Band engineering, including band convergence has been shown to be an effective way to enhance the thermoelectric performance of such materials. In this work, a series of emerging TE materials, the isostructural Zintl phases with the general formula <i>A</i>₂CdP₂ (<i>A</i> = Sr, Ba, Eu) are presented for the first time. Their structures, established from single-crystal X-ray diffraction methods, show them to crystallize with the orthorhombic Yb₂CdSb₂ structure type, with first-principles calculations on phase stability confirming that Ba₂CdP₂ and Sr₂CdP₂ are thermodynamically stable. Computationally, it was found that both Ba₂CdP₂ and Sr₂CdP₂ have the potential to exhibit high <i>n</i>-type TE performance (0.6 and 0.7 relative to the <i>n</i>-type PbTe, a reference TE material). To optimize the TE performance, band engineering strategies, including isovalent substitution and cation mutations, were investigated. From the band engineering of Ba₂CdP₂ via isovalent substitution of Sr on a single Ba site, leading to the quaternary composition SrBaCdP₂, it can be suggested that increasing the conduction band valley degeneracy is an effective way to improve the <i>n</i>-type TE performance by three-fold. Moreover, first-principles defect calculations reveal that both Ba₂CdP₂ and SrBaCdP₂ are <i>n</i>-type dopable, adding these compounds to a small list of rare <i>n</i>-type dopable Zintl phases. The band engineering strategies used in this work are equally applicable to other TE materials, either for optimization of existing TE materials or designing new materials with desired properties.

Bandgap bowing in a zero-dimensional hybrid halide perovskite derivative: spin–orbit coupling versus lattice strain

The bandgap bowing phenomenon has been observed in lead-free MA3Sb2I9 perovskite upon isovalent substitution by bismuth (Bi3+).

Preparation and luminescent properties of zinc sulfoselenide thin films

The preparation of zinc sulfoselenide heterolayers is considered. The possibility of obtaining a hexagonal modification of the crystal lattice by the method of isovalent substitution was shown. The λ-modulated optical reflection was studied and the parameters of the energy structure of α-ZnSe, α-ZnS, α-ZnS0.45Se0.55 were determined. It has been established that the obtained heterolayers are characterized by intense photoluminescence with a quantum yield η = 8–12% in the blue-violet region. It is formed by constituent bands, the nature of which is determined by the annihilation of bound excitons and interband transitions of free charge carriers. It is shown that the selection of temperature regimes allows obtaining radiation with ħωm maxima in the violet 2.80 eV, blue 2.70 eV and green 2.45 eV spectral regions. It is determined by the generation-recombination transitions involving donor and acceptor states formed by intrinsic point defects of the crystalline lattice , і Zni, respectively. The models of radiative recombination are discussed.