New Arsenides with ThCr₂Si₂‐Type or Related Structures: The Compounds ARh₂As₂ (A: Eu, Sr, Ba) and BaZn₂As₂.

Abstract

ARh 2 As 2 (A: Eu, Sr, Ba) and BaZn 2 As 2 . -Single crystals of the title compounds are grown from the elements in a Pb or Pb/Bi flux at 1100 °C. EuRh2As2 and BaRh2As2 crystallize with the well-known ThCr2Si2 type structure (tetragonal, space group I4/mmm, Z = 2). Due to the rigid layers of RhAs4 tetrahedra and to the atomic size of Eu and Ba, the As-As distances between the layers are very long (2.97 and 3.66 Å, resp.). SrRh 2 As 2 is polymorphic and undergoes two phase transitions at about 190 and 282 °C. Main features of the three crystal structures are also layers of RhAs4 tetrahedra. At room temperature α-SrRh2As2 probably crystallizes with the BaNi2Si2-type (space group Cmcm, Z = 4), while β-SrRh2As2 (space group Fmmm, Z = 4) forms a new orthorhombically distorted variant of the ThCr2Si2-type. γ-SrRh2As2 crystallizes with the ThCr 2 Si 2 type structure. The same is true for the high temperature modification of BaZn2As2 (β-phase), whereas the already known α-BaZn2As2 phase exhibits the α-BaCu 2 S 2 type structure (space group Pnma, Z = 4) consisting of a three-dimensional-network of edge-and corner-sharing ZnAs4 tetrahedra wit Ba atoms in the voids of this network. -(HELLMANN, A.; LOEHKEN, A.; WURTH, A.; MEWIS*, A.; Z. Naturforsch., B: Chem. Sci. 62 (2007) 2, 155-161; Inst. Anorg. Chem. Strukturchem., Heinrich-Heine-Univ., D-40225 Duesseldorf, Germany; Ger., Abstr. Eng.) -Schramke 18-007

First-principles study on the electronic structures and magnetic properties of a diluted magnetic semiconductor Ba1−xKx(Zn1−yMny)2As2

“…1(a). The optimized lattice constants of a ¼ b ¼ 4.162 Å and c ¼ 13.451 Å are well consistent with the experimental value [19] of a ¼ b ¼ 4.167 Å and c ¼ 13.467 Å, respectively. Since the PBE-GGA usually underestimates the band gap of semiconductors, a hybrid functional of HSE06 [20] approach was used to get the accurate electronic structure of pure Ba(ZnAs) 2 compound, implemented by VASP2-WANNIER90 code [21].…”

Single-crystal growth and physical properties of the layered arsenideBaRh2As2

“…27 The elements were taken in the ratio Ba:Rh:As:Pb = 1.1 : 2 : 2.1 : 50, placed in an alumina crucible and then sealed in a quartz tube under vacuum (10 −3 mbar). The whole assembly was placed in a box furnace and heated to 1000…”

“…Our value of z = 0.3566 (3) is also in good agreement with z = 0.3569 (1) reported previously by the full single crystal refinement. 27 The single crystals of BaRh 2 As 2 have a high tendency to split/cleave into very thin plates perpendicular to the c-axis resulting in significant mosaicity/twinning. This resulted in some reflections to be broad/extended.…”

“…The initial cell parameters were taken as those previously reported for BaRh 2 As 2 (ThCr 2 Si 2 structure, Z = 2 formula units/unit cell, space group I4/mmm). 27 The final cell parameters and atomic positions were calculated from a set of 861 strong reflections with good profiles in the range 2θ = 6…”

“…27 The Ba and Eu compounds form in the ThCr 2 Si 2 type structure while the Sr compound forms in a different structure. The crystal structure of BaRh 2 As 2 is shown in Fig.…”