Electron paramagnetic resonance study of new paramagnetic centers in microcline-perthites from pegmatites

Abstract

Four new types of paramagnetic centers — NH⁺ ₃, N²⁻, Al-O⁻, E ₁ — have been detected in microcline perthites from pegmatites in the Ukrainian Shield. Values are tabulated for their g and A tensors and limits of thermal stability determined.

The NH⁺ ₃ center substitutes the K⁺ ion. It occurs naturally in potash feldspars but is intensified by gamma or X-ray irradiation. It is regarded as a radiational development of the more general NH⁺ ₄ ⇄ K⁺ isomorphism. It disappears after heating to temperatures higher than 470 K.

The N²⁻ center is an uncommon example of isomorphous substitution of a bridging oxygen, being located on a O _D(m) site between T ₂(o) and T ₁(m) silicon sites. It is stable to 820 K.

The hole center, Al-O⁻, has been detected on an O _A(l) oxygen shared by T ₁(o) and T ₁(m) tetrahedra. It is stable to 590 K.

The E ₁ center in these alkali feldspars is similar to the E ₁ center in quartz, being an electron trapped in an oxygen vacancy in the O _B (o) position. It is stable to 420 K.

The NH⁺ ₃, Al-O⁻ and E ₁ centers can be restored from temperatures above their stability limits by gamma radiation.

Concentration of centers varies from sample to sample depending on conditions of formation and subsequent history of the minerals.