X and Q band EPR studies of paramagnetic centres in natural and heated tourmaline

作者：Babinska Joanna; Dyrek Krystyna^*; Pieczka Adam; Sojka Zbigniew

来源：European Journal of Mineralogy, 2008, 20(2): 233-240.

DOI：10.1127/0935-1221/2008/0020-1790

• tourmaline
• EPR spectroscopy
• simulation
• thermal oxidation
• paramagnetic centres : Fe(2+), Fe(3+), Mn(2+), Mn(3+), Mn(4+), V(4+) ions

Various members of the tourmaline group (schorl, dravite, and elbaite) as well as the products of their gradual oxidation were investigated by EPR spectroscopy in X and Q bands at 293 K and 77 K. In the EPR spectra of the schorl and dravite samples the signals at g approximate to 2 and 4.3 were attributed to clustered and isolated Fe(3+) ions, respectively. The EPR spectra of Fe-poor elbaite are dominated by signals at g approximate to 2.5 and 3.5, assigned to Mn(2+) ions.
In the schorl and dravite samples, gradually annealed in air above 750 K, the total intensity of the EPR spectrum increased with increasing temperature, due to the oxidation of Fe(2+) (d(6)) to Fe(3+) (d(5)) ions. The Fe(3+) ion being a product of thermal oxidation initially occupies sites with g approximate to 4.3 and after heating at temperatures above 1070 K forms clusters with g approximate to 2.0.
In the Fe-poor elbaite the total intensity of the spectrum gradually decreased with the increasing oxidation temperature up to 1150 K, due to the transformation of paramagnetic Mn(2+) (d(5)) into Mn(3+) (d(4)) ions. Simultaneously, the signal of Fe(3+) at g approximate to 4.3 became more pronounced. At still higher temperatures (T > 1150 K) the intensity of the signal around g approximate to 2.0 increased indicating further oxidation of Mn(3+) to Mn(4+) (d(3)).

• 出版日期2008-4