NEUTRON DIFFRACTION STUDIES OF LIQUID ALLOYS WITH CHEMICAL SHORT-RANGE ORDER UP TO TEMPERATURES OF 2000 K

摘要

Neutron diffraction measurements havebeen carried out on equiatomic liquid alloysexhibiting significant chemical short-range order,such as K-Pb, Cs-Pb, Na-Sn and Cs-Tl, over a widetemperature interval, ranging from 700 to 2000 K, andat pressures up to 150 bar. In the crystalline state,these are semiconducting or semimetallic compoundscontaining polyanions. The diffraction resultsindicate the survival of polyanions in the expandedliquid alloys, even up to high temperatures, as canbe inferred from the persistence of the peak of thestatic structure factor S(Q) at Q ? 1 A~(-1), whichis indicative of intermediate-range order. Withincreasing temperature and correspondinglydecreasing density, the position of this peak shiftstowards lower Q-values, its height decreases, and itswidth drastically increases. In several cases, atendency towards microphase separation is detected atthe highest temperatures. The experimental resultsand the corresponding real-space information arecompared 'with both the crystal structures in thesolid state and with the results of computer modellingstudies and with recent ab-initio molecular dynamics calculations.