Neutron Powder Diffraction with ~(nat)Sm:Crystal Structures and Magnetism of a Binary Samarium Deuteride and a Ternary Samarium Magnesium Deuteride

摘要

Binary SmH3(trigonal,a=656.7(3),c=680.1(3)pm,p3c1,Z=6),ternary SmMg2H7(tetragonal,a=626.47(6),c=937.2(2)pm,p41212,Z=4)and the corresponding deuterides SmD3(a=653.9(1)m,c=676.7(2)pm)and SmMg2D7(a=624.10(1).c=934.81(2)pm)have been prepared by hydrogenation(deuteration)of ele mental samarium and the Laves phase SmMg2,respectively,and investigated by X-ray and neutron powder diffrac tion and SQUID and vibration magne-tometry.The problem of the enormous neutron absorption of the natural iso-topic mixture(~(nat)Sm)is circumvented by carefully choosing the neutron wavelength(approx=50 pm)and the use of double-walled cylindrical sample hold ers and a high-intensity neutron dif-fractometer(D4c at ILL).SmD3 crys tallises with a tysonite-type structure and has three independently ordered deuterium atom sites with trigonal-planar,trigonal-pyramidal and tetrahe-dral metal environments and Sm-D bond lengths in the range 220(1)-258(1)pm(average:235 pm).SmMg2D7 is a new deuteride that crys-allises with an LaMg2D7-type struc ture.It displays four fully occupied deuterium sites having triangular and tetrahedral metal environments and Sm-D bond lengths in the range227.6(5)-246.8(8)pm(average:239 pm).These are the first samarium-deuterium bond lengths to be reported.Both deuterides are paramagnetic down to 2K(SmD3:mu_(eff)=0.63(1)mu_B.theta_p approx=-4K;SmMg2D7:mu_(eff)=0.57(2)mu_B,theta_p approx=-4 K).Their crystal structures and chemical and physical properties sug gest mainly ionic bonding according to the limiting ionic formulae Sm~(3+)(H)3 and Sm~(3+)(Mg~(2+))2(H)7.