Composition dependence of low-frequency excitations in lithium silicophosphate glasses by nuclear magnetic resonance and electrical conductivity

Abstract

Low-frequency excitations ͑LFE's͒ of disorder modes were investigated in (1ϪxϪy)SiO 2 •yP 2 O 5 •xLi 2 O glasses by means of 7 Li and 31 P nuclear-spin relaxation ͑NSR͒ and ac conductivity experiments conducted at various frequencies between about 2 and 300 K. By varying the composition we were able to observe three different kinds of low-frequency excitations ranging between about 10 4 and 10 9 s Ϫ1 ; the first one was detected by NSR as well as by conductivity. The NSR data can be linked to the conductivity data by the fluctuationdissipation theorem indicating a common physical origin of the underlying relaxation process. This LFE is shown to be due to charge fluctuations related to the Li ϩ ions. The other two LFE's are observed only by NSR and not by conductivity indicating that they are mainly caused by magnetic fluctuations due to movements of the nuclear spins. 31 P NSR detected both contributions resulting in two separate NSR rate maxima at about 10 and 50 K, respectively, while 7 Li NSR shows just the 10 K maximum. Further, both contributions depend strongly on the content of phosphorous. We suppose that the corresponding LFE's are caused by fluctuations of phosphate units forming two different types of disorder configurations in the glassy network. All the data can be interpreted consistently in the framework of the asymmetric double-well-potential approach using just one set of parameters.

Lithium dynamics in the fast ionic conductorLi0.18La0.61TiO3probed byRivera1, Sanz2 2004Phys. Rev. B290171View full textAdd to dashboardCite

“…Kanert et al observed a similar, very slow, variation of SLR times at low temperatures in glassy ionic conductors, and they assigned it to relaxation processes produced via low frequency excitations inherent to glasses. 19,36,37 However, the frequency dependence predicted by their model, −p with an exponent 0.5Ͻ p Ͻ 1, is slower than the one observed in LLTO, 1 Ͻ p Ͻ 1.5 (Fig. 5).…”

Effect of devitrification on the ionic diffusion of Li-disilicate

“…From our previous studies of Li-ion transport in glasses, it is well established that the observed 7 Li NSR rate, T À1 1 , at temperatures >300 K arises from the diusive motion of Li while at temperatures <300 K the relaxation is due to localized low-frequency¯uctuations [11,13,18]. The¯uctu-ation-dissipation theorem implies that the ionic ac conductivity r ac is proportional to T À1 1 aT if the ionic jump rate is less than the frequency used in either measurement.…”

“…Then, a mean NSR rate was obtained from the data. Details of the NMR experiments are presented elsewhere [13]. One should Fig.…”

Effect of devitrification on ion motion in lithium-disilicate glass

“…Details of the high-temperature NMR probe head and the sample size used in the experiments are published elsewhere [13,14]. One should generally note that unlike conductivity experiments, the NMR technique requires neither a well-defined shape of the samples nor any sample electrodes, i.e.…”