ELECTRON LOCALIZATION AND METAL-NONMETAL TRANSITION IN FLUID KXKCL1-X- AN ELECTRON-SPIN-RESONANCE STUDY OF THE MAGNETIC-PROPERTIES WITH IN-SITU VARIATION OF S-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-10(-1))

We have measured the electron spin resonance (ESR) spectra of saltrich KxKCl1-x melts at temperatures near 800 degrees C and over a broad co mposition range, 10(-4) less than or equal to x less than or equal to 10(-1), approaching the metal-nonmetal (M-NM) transition in these solu tions. Emphasis has been given to a precise in situ variation of compo sition which has been achieved for the first time in a high temperatur e ESR experiment by Coulometric titration. The spectra are characteriz ed by a motional linewidth narrowing with a Lorentzian line shape. The ESR characteristics as determined from the Lorentz fits of the spectr a exhibit the following features as a function of x: In the nonmetalli c regime the g factor (g = 1.9938 +/- 0.0002) and the peak-to-peak hal fwidth (Delta B-PP = 0.2 mT) stay constant up to x similar to 0.05. Ab ove this composition a clear increase of Delta B-PP is observed indica ting the NM-M transition. The spin susceptibility kappa(s) has been de termined from the imaginary part of the Lorentz fits and has been cali brated against a sapphire signal measured simultaneously with the KxKC l1-x liquid samples. The spin susceptibility strongly deviates from si mple Curie behavior even at low x which gives evidence for spin paired states in the nonmetallic solutions. Above x similar to 0.05 kappa(s) rises steeply with x. The overall variation of kappa(s) with x is int erpreted by two limiting models: a thermodynamic defect model focusing on the particle character of localized paramagnetic and diamagnetic s tates for x less than or equal to 0.05, and a simple band model descri bing the strong increase of kappa(s) approaching the NM-M transition. Both approaches yield a satisfactory description of the observed varia tion of kappa(s). Further support of this interpretation is found in t he spin dynamics which are qualitatively discussed. (C) 1996 American Institute of Physics.