Covalency Parameters in MnSe and MnSe2

Covalency parameters have been deduced from neutron diffraction measurements on MnSe, Mg0.1Mn0.9Se, and MnSe2. The cubic phase of MnSe is contaminated at low temperatures with a hexagonal phase, and this leads to deduced covalency parameters for Mn2+(Aσ2 + 2Aπ2 + As2 = 6.2 ± 1.9%) of relatively low accuracy. More accurate values (Aσ2 + 2Aπ2 + As2 = 7.5 ± 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 α-MnS(Aσ2 + 2Aπ2 + As2 = 7.0%).