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Two series of Mn-substituted rare-earth zinc arsenides RE1-yMnxZn2-xAs2 (RE = Eu-Lu) and RE2-yMnxZn4-xAs4 (RE = La-Nd, Sm, Gd) were prepared by reaction of the elements at 750 °C. Both series are derived from ideal empirical formula REM2As2 (M = Mn, Zn) and adopt crystal structures related to the trigonal CaAl2Si2-type (space group P...m1) in which hexagonal nets of RE atoms and [M2As2] slabs built up of edge-sharing M-centered tetrahedra are alternately stacked along the c-direction. For compounds with divalent RE components (Eu, Yb), the fully stoichiometric and charge-balanced formula REM2As2 is obtained, with Mn and Zn atoms statistically disordered within the same tetrahedral site. For compounds with trivalent RE components, the RE sites become deficient, and the Mn atoms are segregated from the Zn atoms in separate tetrahedral sites. Within the series RE1-yMnxZn2-xAs2 (Gd-Tm, Lu), the parent CaAl2Si2-type structure is retained, and the Mn atoms are disordered within partially occupied interstitial sites above and below [Zn2-xAs2] slabs. Within the series RE2-yMnxZn4-xAs4 (RE = La-Nd, Sm, Gd), the c-axis becomes doubled as a result of partial ordering of Mn atoms between every other pair of [Zn2-xAs2] slabs. Attempts to synthesize Gd-containing solid solutions with the charge-balanced formula Gd0.67MnxZn2-xAs2 suggested that these phases could be formed with up to 50% Mn substitution. Band structure calculations reveal that a hypothetical superstructure model with the formula La1.33MnZn3As4 would have no gap at the Fermi level and that slightly lowering the electron count alleviates antibonding Mn-As interactions; a spin-polarized calculation predicts nearly ferromagnetic half-metallic behavior. X-ray photoelectron spectroscopy confirms the presence of divalent Mn in these compounds. [ABSTRACT FROM AUTHOR]

Four series of ternary rare-earth zinc arsenides have been prepared by reaction of the elements at 75°CC: RE4Zn2-x,As5 forming for RE = La--Nd, Smj and RE5Zn2-xAs7 RE65Snz_xAs7, RE7'Zsi1_xASfi forming for RE = Ce, Pr, Nd, Sm. They crystallize in trigonal structure types in space group P3ml with Z = I for RE4Xn2_xAss and RE7Zn2-x_,tAss, or space group Riml with Z = 3 for REs7si2_:iAs6 and -RE6Zn2-x_xAs7. Through the structural principle of intergrowing rocksalt-type [HEAs] slabs of variable thickness within a parent CaAl2Si2-type structure containing Zn-deficient [Zn2-x_;,As2] slabs built from edge-sharing Zn-centered tetrahedra, these ternary arsenides belong to a homologous series with the formulation REZn2-x_xAsz-n(REAs) (n = 3, 4, 5, 6). Quaternary derivatives Ce4(Mn,Zn)2_xAs5 and Ce6(Mn,Zn)2__:(As7 were also obtained in which Mn partially substitutes for Zn. Band structure calculations predict that the electronic properties can be gradually modified from semiconducting to semimetallic behavior as more [JREAS] slabs are introduced. [ABSTRACT FROM AUTHOR]

The new nonlinear optical (NLO) crystal BaGa4S7for the mid-infrared (IR) has been grown by a Bridgman-Stockbarger technique. Polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S as the initial materials by solid-state reactions. The ultraviolet (UV) and IR transmittance of the crystal was determined with polished crystal pieces. The UV and IR optical absorption edges were found to be at 350 nm and 13.7 μm, respectively. From optical measurements of second harmonic generation on powders, the NLO coefficient d33was determined to be 12.6 pm/V. The laser damage threshold of a single crystal reached about 1.2 J/cm2at 1.064 μm. The Vickers-hardness value of the crystal is 327.5 HV5, which is equivalent to Mohs’ hardness of about 5. [ABSTRACT FROM AUTHOR]