Polarized electronic absorption spectra and Ni-Mg partitioning in olivines (Mg1-xNix)2[SiO4]
Hu, Xiaorui; Langer, Klaus; Boström, Dan
published: Mar 8, 1990
manuscript accepted: Oct 1, 1989
manuscript received: Apr 21, 1989
ArtNo. ESP147050201009, Price: 29.00 €
Abstract Polarized electronic absorption spectra of homogeneous olivine crystals, (Mg1-xNix)2[SiO4], grown at 1173K/1atm from Li2MoO4 flux with xNi = 1.00, 0.75, 0.31, 0.07, 0.04, as analysed by microprobe, were measured at room and liquid-nitrogen temperatures by microscope spectrometric techniques. Room-tempera- ture spectra were fitted to component bands by the least-squares method using the shapes of Gauss-Lorentzian product functions. The ten absorption bands observed could be assigned on the basis of their energy and relative intensity to spin-allowed and spin-forbidden transitions of Ni2+ in M1 and M2 sites. Crystal field parameters (in cm-1) are: 10DqNi(M1) = 9,500+461-xNi (r =0.837), 10DqNj(M2) 7,368 + 514-xNj (r = 0.918) ; CFSENi(Ml) = 11,384 + 574-xNi (r = 0.843), CFSENi(M2) = 8,828 + 631⋅xNi (r = 0.913) ; BNi(M1) = 882-127⋅xNi (r = -0.940), BNi(M2) = 950-92 xNi (r = -0.863). The fractional Ni2+-contents, Ni/(Ni + Mg), in M1 and M2 sites were calculated from the linear-absorption coefficient of the most intense Ni(M2) transition derived from 3A2(F) ⇒ 3T1(P) at 23,400-24,000 cmH (band b): xNi(M2)=αb/αb(x=1) and xNi(M1) = 2xNi-xNi(M2). The values obtained agree with those obtained by crystal structure refinements (Boström, 1987). This opens up the systematic determination by spectroscopic techniques of Ni-Mg partitioning as a function of temperature.