摘要
A series of new magnesium copper pnictide intermetallics,A_(2)Mg_(3)Cu_(9)Pn_(7)(A=Sr,Eu;Pn=P,As)and Eu_(5)Mg_(2.39)Cu_(16.61)As_(12),were synthesized through high temperature flux reactions.By the single-crystal X-ray diffraction technique,their structures were accurately determined.Sr_(2)Mg_(3)Cu_(9)P_(7),Eu_(2)Mg_(3)Cu_(9)P_(7),Sr_(2)Mg_(3)Cu_(9)As_(7)and Eu_(2)Mg_(3)Cu_(9)As_(7)crystallize in the Zr_(2)Fe_(12)P_(7)structure type(S.G.P6,no.174)with cell parameters:a=9.7736(19)/9.7417(7)/10.0550(10)Å/10.0410(8)Å,c=3.9280(16)/3.9008(5)/4.0544(9)/4.0364(6)Å,respectively,while Eu_(5)Mg_(2.39)Cu_(16.61)As_(12)adopts the Zr_(5)Co_(19)P_(12)structure type(S.G.P6¯2m,no.189)with cell parameters of a=13.2521(6)Åand c=4.0910(3)Å.These compounds can be viewed as an extensive branch of the ternary RE−M−Pn system(RE=rare-earth elements;M=transition metals;Pn=pnictogen)with the metal-to-nonmetal ratio being close or equal to 2:1.Interestingly,with the divalent alkaline-earth cations being introduced,these metal-rich phases exhibit electron deficiency according to the DFT calculations.Eu_(2)Mg_(3)Cu_(9)As_(7)is metallic based on the resistivity measurement,consistent with theoretical prediction,and the magnetic susceptibility data of Eu_(2)Mg_(3)Cu_(9)As_(7)confirmed the divalent oxidation state and weak ferromagnetic coupling for the europium cations.
基金
financial support from the National Natural Science Foundation of China(Grant No.51271098,51321091).
