Nuclear magnetic resonance in molten In-InI3mixtures

Abstract

Nuclear-magnetic-resonance data are reported for molten ${\mathrm{In}}_{1-x}{\mathrm{I}}_x$ mixtures with compositions in the range $0<~x<~0.75$ and at temperatures ranging from the liquidus up to 600-1200°C, depending on composition. Mixtures in the range $0<x<\mathrm{}0.50\mathrm{}$ form two immiscible phases which are clearly indicated by distinct ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ resonance lines and which remain separated to temperatures in excess of 1000°C. Chemical shifts in single-phase mixtures ($x>~0.50$) exhibit a systematic increase with I content. The ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ spin-lattice relaxation rates ($\frac{1}{T_1}$) and inverse free-induction decay lifetimes ($\frac{1}{{T_2}^{*}}$) are attributed to at least two processes: quadrupolar relaxation via ionic and molecular motion and a strong scalar magnetic coupling to paramagnetic centers. The composition dependence of the quadrupolar process, also observed for ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$, shows that the degree of dissociation increases with decreasing I content. The behavior of the scalar magnetic process in phase-separated mixtures ($x<\mathrm{}0.50\mathrm{}$) supports the $F$-center model for dissolved In in InI. It is proposed that the scalar relaxation in single-phase mixtures ($x>~0.50$) results from short-lived fluctuations to the paramagnetic ${\mathrm{In}}^{2+}$ state by single-electron hopping. The theory of relaxation by magnetic scalar coupling is generalized to allow for the large hyperfine couplings present. The generalized theory is in agreement with the experimental results and permits estimates of the frequency of electron hopping and the lifetime of the ${\mathrm{In}}^{2+}$ state.