INELASTIC-NEUTRON-SCATTERING STUDIES ON GLASSY AND LIQUID CA0.4K0.6(NO3)(1.4)

Triple-axis inelastic-neutron-scattering measurements have been carrie d out on the ionic glass material Ca0.4K0.6(NO3)(1.4). Our measurement s of the temperature dependence of the position of the main elastic di ffraction peak in the liquid give a linear coefficient of thermal expa nsion of (2.3+/-0.2)x10(-4), which is markedly greater than the value of 1.2x10(-4) from density measurements. This shows that the expansion is accompanied by structural rearrangements. The Debye-Waller factor, as determined from the temperature dependence of the intensity of the main elastic diffraction peak, shows an anomaly at the calorimetric g lass transition temperature, T-g = 335 K, but the anomaly at the criti cal temperature T-c predicted by mode-coupling theory is not seen. In contrast, the change in the effective root-mean-square displacement, [ r(2)](eff)(T)-[r(2)](eff)(300) deduced from the Q dependence of the te mperature variation of the quasielastic scattering over a wide range o f wave vector Q from 2 to 4 Angstrom(-1), shows a break of slope at a temperature that can be identified as T-c, but there is no anomaly at T-g. Our results give T-c = 368 +/- 5 K. The inelastic scattering for constant Q scans at frequencies nu = omega/2 pi less than or equal to 0.5 THz deviates from harmonic-phonon-like behavior at temperatures ab ove T-g. This can be identified as a fast relaxation or beta process, as predicted by mode-coupling theory. Such a deviation is not observed at higher frequencies. In the present work, we establish the Q and nu dependences of the beta process.