INELASTIC NEUTRON SCATTERING ON SOLID ELECTROLYTE LiI-LiPO₃

The dynamic insight of a lithium phosphate, LiI-LiPO₃, glassy electrolyte was studied by using a time-of flight inelastic neutron spectrometer. By utilizing the multiple incident energies of the AMATERAS spectrometer at Japan Proton Accelerator Research Complex (J-PARC), Japan with a beam proton of 217 kW, various two-dimensional maps of dynamic structure factors, S(Q,E) with four incident neutrons energies, E_i ∼ 94, 23, 10 and 6 meV were simultaneously obtained. The elastic scattering S(Q,E=0) of LiPO₃ at E_i ∼ 94 meV shows a general characteristic of the structure factor of metaphosphate glasses. Below Q ∼ 10, there are four broad peaks centered around Q ∼ 1.8, 2.8, 5.5 and 8.2 and the rest is corresponding to P-O network as appears in other phosphate glasses. By using E_i ∼ 6 meV, with closer inspection on the first diffraction peak, it appears that the peak is rather flat, and constitutes from two peaks at around 1.1 and 1.8 but both merge into one plateau. However, the origin of this anomalous peak is not clear yet. The inelastic neutron scattering, S(Q,E) with constant-E shows dispersive behavior at higher Q and E. The so-called Boson Peak was clearly observed from the E-dependence of S(Q,E) with E_i ∼ 23 meV, and total integration over Q. The Boson Peak appears at the energies around 7 to 10 meV, and centered at E ∼ 6 meV. The Li-incorporation into the phosphate network reduces the connectivity of the system by breaking links between basic tetrahedra, thus local vibration will shifts the cooperative motions into higher energy range.