NMR study of electron localization in some alkali-antimony alloys

Abstract

²³Na NMR shift and relaxation data are reported for liquid Na_1−xSb_x alloys over the concentration range 0<x_Sb<0·55 at temperatures up to 940°C. These results are compared with previous measurements for ¹³³Cs in the Cs-Sb alloys over a similar concentration range. A metal-non-metal transition near the M₃Sb composition is indicated by a strong concentration dependence of shift and relaxation rate. The NMR data are consistent with localization by non-degenerate states, possibly arising from s-p type bonding. In the semiconducting transport regime near the MSb compound the electron correlation times deduced from the relaxation rates are longer in caesium alloys than in sodium alloys, indicating stronger localization in the former system. A strong temperature dependence for the shift is found in Sb-rich Na-Sb alloys.