Covalency Parameters in MnSe and MnSe2

Abstract

Covalency parameters have been deduced from neutron diffraction measurements on MnSe, Mg_0.1Mn_0.9Se, and MnSe₂. The cubic phase of MnSe is contaminated at low temperatures with a hexagonal phase, and this leads to deduced covalency parameters for ${\mathrm{Mn}}^{\text{2+}}{\mathrm{(A}}_{\sigma }^2{\text{\hspace{0.17em}+\hspace{0.17em}2A}}_{\pi }^2{\mathrm{\hspace{0.17em}+\hspace{0.17em}A}}_s^2\text{\hspace{0.17em}=\hspace{0.17em}6.2\hspace{0.17em}±\hspace{0.17em}1.9\%)}$ of relatively low accuracy. More accurate values ${\mathrm{(A}}_{\sigma }^2{\text{\hspace{0.17em}+\hspace{0.17em}2A}}_{\pi }^2{\mathrm{\hspace{0.17em}+\hspace{0.17em}A}}_s^2\text{\hspace{0.17em}=\hspace{0.17em}7.5\hspace{0.17em}±\hspace{0.17em}0.3\%)}$ have been obtained from the magnesium‐doped compound which remains cubic down to 4.2°K. The measured covalency parameter sum for MnSe₂ is 7.8 ± 1.1% indicating that the Se–Se bond has little effect on the total covalency. Covalency in the manganese selenides is seen to be similar to that in $\mathrm{\alpha ‐}\mathrm{MnS}{\mathrm{(A}}_{\sigma }^2{\text{\hspace{0.17em}+\hspace{0.17em}2A}}_{\pi }^2{\mathrm{\hspace{0.17em}+\hspace{0.17em}A}}_s^2\text{\hspace{0.17em}=\hspace{0.17em}7.0\%)}$ .