Synthesis, Structures, Properties And Theoretical Studies Of Transition Metal Arsenide Zintl Phases

Pnictide-based transition metal Zintl phase compounds have a wide variety of structures, rich nature, which has been one of the hot points for research. Pnictides based Zintl compounds exhibit various structures:one-dimensional chains, two-dimensional layers, three-dimensional networks and Zero-dimensional clusters. These compounds include metallic compounds and semiconductors. The physical properties of them have been studied:superconductivity, magnetism, thermoelectricity, mixed valence and nonlinear optical properties, etc have been reported. Exploring new materials can not only enrich Zintl phases, adding new structure types, but also optimizing the performance of materials by doping. At present, some novel structural compounds have been excavated with extensive research on the Zintl phase compounds, which bring very interesting properties. We studied the Zintl phase compounds containg As, and have synthesized a number of arsenide Zintl compounds by adopting metal flux method, the crystal structures, physical properties and electronic structures are researched.Specific contents are as followed:1. Two new Zintl arsenic phases with novel structures, Sr2Cu3As3 å'Œ Eu2Cu3As3, have been synthesized by flux reactions with Pb as the flux. Their structures were identified by single-crystal X-ray diffraction. Both structures crystallize in the orthorhombic space of centrosymmetrical Cmcm (No.63, Z=2) with cell parameters of a= 4.2465(6)/4.1866(5) A, b= 17.604(3)/17.486(2) A and c= 4.2552(6)/4.2096(5) A for the Sr-and Eu-containing compounds, respectively. The two compounds are isostructural and have similar structures. Their anionic structures contain two anionic componets:Cu2-centred tetrahedral [CuAs4] and Cul-centred square triangles [CuAs3], which two bridged by As-As bonds, forming three-dimensional network structure. Interspersing among the space of these structures is formed by the cations. Magnetic property studies were examinated and the resulsts show long-range antiferromagnetic alignment, while the Curie-Weiss temperature is positive, proving the coexistence of ferromagnetic coupling and antiferromagnetic coupling of Eu-4/in the compound of Eu2Cu3As3, confirming the Eu2+ground state. Density functional calculations were performed based on the first principles density package LOMO proving that both compounds exhibit metallic behavior. From the COHP curve, we also know that the p-d mixing between Cu and As has an influence on the structure forming.2. A new quaternary Arsenic-containg Zintl phase, Ba2Mg3AgAs4, was discovered by the Sn-flux reaction. Its structure was determined by single-crystal X-ray diffraction. The compound adopt space groupI4/mmm (No.139), Z=2 with cell parameters a=4.2948 (10) A, c= 13.902 (6) A. This compound crystallizes in the 122 type ThCr2Si2 structure-type, in which Mg and Ag mixed on the site of 4d, and form tetradron with four As atoms. The edge-sharing Mg/Ag-centered tetrahedras are interconnected to form two dimensional anionic slabs separated by Ba cations along the c axle. Theory calculations on the electronic structures by Win2k confirm that Ba2Mg3AgAs4 is one electron-deficient metallic compound. We can get inspiration from the synthesis of the compounds, such as making use of isoelectronic substitution method to design new Zintl compounds on the basis of the CaAl2Si2 type.