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pondělí, 2. března 2020

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Synthesis, structure and physico-chemical properties of ACr2Se4

pondělí, 2. března, 10.30 » 12.00
Globální událost
SYNTHESIS, STRUCTURE AND PHYSICO-CHEMICAL PROPERTIES OF ACr2Se4 - SPINEL COMPOUNDS (A = Cu, Cd, Zn) DOPED WITH SELECTED ELEMENTS: p-, d- and f- electronic

Chromium spinels with general formula ACr2X4, (where A is a divalent cation: Cu, Cd, Hg, Mg, Fe or Zn, and X is a divalent anion: O, S, or Se, and Cr3+ ion is in the 3d3 configuration) belong to the group of compounds with many potential applications, especially for use in electronic and thermoelectric devices [1-3]. The compounds ACr2Se4 (A = Cd, Cu, Zn) belonging to the family of spinels, crystallize to a cubic structure (space group Fd-3m, No. 227). The value of lattice parameter is above 10Å and the value of the fractional coordinate u is about 0.250 Å. Selected spinels (CuCr2Se4, CdCr2Se4, ZnCr2Se4) have different physical properties. The CuCr2Se4 - compound is a ferromagnetic and has metallic conductivity (TC = 460K, ΘCW = 465K, CM = 2.50K / mol, μsat = 4.94μB), CdCr2Se4 is a ferromagnetic and p-type semiconductor (TC = 130 K, ΘCW = 200K, μsat = 5.30μB,

μeff = 5.49μB), while the spinel ZnCr2Se4 is a p-type semiconductor with a spiral magnetic structure (TN = 21K, ΘCW ~ 115K, CM = 3.54K /mol, μsat = 6.1μB, μeff = 5.90μB).

It is possible to improve the physico-chemical properties of the ACr2Se4 compounds using of some dopants. This effect depends on many factors. The most important of them are the size of the ion radius, ion placement in the spinel structure (tetra- or octahedral position), coordination number (CN) and type of chemical bond. The question is, how the introduction of third cation to the crystal lattice of ACr2Se4, influences on the crystal structure and physico-chemical properties of the parent compound.

In this lecture, the researches of physical and chemical properties of ACr2Se4 doped selected elements (Ni, Sn, Mn, Dy) will be presented. The seleno-spinels were synthesized by ceramic method (for polycrystalline samples) and by chemical vapour transport in order to obtain single crystals. The obtained samples were characterized using various method: X-Ray diffraction, SEM, SQUID, XPS, DSC/TG, XANES, NPD, Mössbauer spectroscopy. Depending on the substitution of one of the elements (magnetic or non-magnetic), a strong influence on the properties of the parent compound is observed, for example: 1) a spin-glass-like behavior in the ZnCr2Se4:Sn single crystals [4], 2) AFM order and the strong short-range FM interactions in the single crystals ZnCr2Se4:Dy was observed [5], 3) increase of FM interactions in the polycrystalline ZnCr2Se4:Mn [6], 4) weaker ferromagnetic interactions in the CdCr2Se4:Mn single crystals [7], 5) increase of AFM interactions in the CuCr2Se4:Ni single crystals [8].



References

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A31, prostřední spojovací chodba, 3. patro, budova A,