Analysis of the new ternary phase with C_(6)Cr_(23) structure in Mg-Co-B system by Rietveld method and physical properties of its Ni-substituting effect

A new ternary Mg_(1.4)Co_(21.6)B_(6) compound in the Mg-Co-B system was synthesized via a conventional solid-state reaction method and the effect of Ni-substitution on its crystal structure,thermal stability,solid solubility and physical properties were systematically investigated.The crystal structure of the Mg_(1.4)Co_(21.6)B_(6) compound was fully determined by the X-ray diffraction technique with Rietveld refinement method.It is found that Mg_(1.4)Co_(21.6)B_(6) crystallizes in the form of C_(6)Cr_(23) structure type(space group:Fm-3m(No.225),a=10.5617(2)A,Z=4).The results showed that the 4a sites have been occupied completely by Co atoms in present compound which with M_(2-x)Ni_(21+x)B_(6) form belonging to the W_(2)Cr_(21)C_(6)-type.When Mg_(1.4)Co_(21.6)B_(6) is repeatedly sintered at elevated temperatures,it becomes unstable and decomposes into Co3B and Mg.The lattice parameters of the Mg_(1.4)Co_(21.6)B_(6) solid solution alters dramtically with increasing Ni substitution,with no regular trend being observed.The electrical and magnetic performances of the 3.6Mg:3Co:17Ni:6B and 3.6Mg:3Co:18Ni:6B(nominal compositions)samples suggest that both samples are typical ferromagnetic materials.The temperature in the maximum drop of theρ(T)curve decreases as a function of the Ni content.Base on the correlation between the critical temperature and Ni content,a linear fitting equation is obtained and the critical temperature of Mg_(1.4)Co_(21.6)B_(6) calculated utilizing the linear fitting equation.The findings in this work may provide certain reference values for material science on electrical magnetic properties and other references for researching the material further.