Toru Matsuo

Electrical conductivity of a sintered pellet of octalithium zirconate

Abstract The conductivity of a sintered pellet of Li 8 ZrO 6 was measured in dry or wet argon atmosphere by the two-terminal technique with an AC Wheatstone bridge in the temperature range 350–1050 K. The temperature dependence of conductivity multiplied by temperature (σT) of Li 8 ZrO 6 in a dry environment had two transition points at 426 and 833 K. The activation energies of conductivity in high, middle and low temperature regions were 103.2, 52.1 and 37.4 kJ/mol, respectively. The activation energies of conductivity agreed well with those obtained by temperature dependence of spin-lattice relaxation time T 1 of 7 Li with pulsed nuclear magnetic resonance.

Conductivities of a sintered pellet and a single crystal of Li2O

Abstract The conductivities of a single crystal and a sintered pellet of Li 2 O were measured in argon atmosphere by the two-terminal technique with an ac Wheatstone bridge in the temperature range 300–1150°C. The conductivity of Li 2 O depended strongly on the concentration of the OH − impurity in the sample and the transition temperature T tr between the extrinsic and intrinsic regions increased with as increasing amount of OH − impurity in the sample. The activation energies of conductivity in the extrinsic and intrinsic regions were 0.4–0.5 eV and 1.2–1.3 eV, respectively.

Nuclear magnetic resonance investigations of lithium diffusion in Li2O, Li2SiO3 and LiAlO2

Spin–lattice relaxation rates of 7Li have been measured for Li2O, Li2SiO3 and LiAlO2 with pulsed nuclear magnetic resonance. Relaxation due to cation diffusion is observed with quadrupole and dipole interactions. Cation jump frequencies in the extrinsic region with apparent activation energies of ca. 0.4 eV for Li2O, 0.81 eV for Li2SiO3 and 0.77 eV for LiAlO2 are obtained. These activation energies are in good agreement with those of ionic conductivities in the extrinsic region.

Electric conduction of single crystal and glass of Li2B4O7

The dc and ac conductivity of single crystal and glass of Li2B4O7 have been measured at various temperatures. It has been shown that these materials are mixed conductors in which electronic and ionic conduction coexist. In the single crystals, both the electronic conduction and ionic conduction along the c axis are much smaller than that perpendicular to the c axis. The anisotropy in the electronic conduction is considered to be due to the conduction by the π electron of the BO3 layer located on the (001) crystallographic plane. The anisotropy in the ionic conduction is also considered to be due to the diffusion of Li ions and/or protons between the BO3 layers. The thermal activation energies of the electronic conduction were 0.65 eV for glass, 1.61 eV for the crystal parallel to the c axis, and 0.78 eV for the crystal perpendicular to the c axis. The activation energy of the ionic conduction was 0.46 eV for the crystal perpendicular to the c axis.

Nuclear Magnetic Resonance of 7Li in Li2B4O7 Single Crystal and Glass.

The spin lattice relaxation rates and the absorption line shapes of 7Li in both Li2B4O7 single-crystal and glass samples were measured from room temperature up to 900 K. At lower temperatures the dominant contribution to the relaxation rate was the spin-phonon interaction in both samples. For the single crystal the relaxation caused by the diffusion of Li ions became significant above 760 K, and the narrowing of the absorption line started at about 650 K. For glass the narrowing of the line started at room temperature and the effect of the diffusion of Li ions on the relaxation rate was dominant above 400 K. From these results the correlation time τ c of the fluctuating field at Li sites in the crystal and glass of Li2B4O7 was obtained.

Diffusion of Li ion in glassy Li2O·B2O3 system

Abstract The ionic migration in lithium borate glasses with various composition of molar ratio R ( R =0.15, 0.21, 0.33, 0.5, 0.7, 1 and 1.4) is studied by the conductivity and the nuclear magnetic resonance techniques. Four activation energies for Li ion migration characterizing these observed quantities, E σ determined from dc conductivity, E p from ac conductivity, E δω from motional narrowing phenomenon in nmr and E T 1 from spin lattice relaxation rate, are obtained. Relation between these energies is discussed. The prediction of the coupling model E σ E δω ∼ E T 1 does not hold. Applying a trapping model, the temperature and R dependence of ionic jump time are calculated and the results can explain successfully the experimentally determined ionic jump time τ nmr for the glasses with R >0.33. The model cannot be applied to the glasses ( R

Nuclear magnetic resonance of 7Li in LiB3O5 crystal and glass

The spin lattice relaxation rates and the absorption spectra of 7Li in both LiB3O5 crystal and glass samples were measured from room temperature up to 800 K. At low temperatures the dominant contribution to the relaxation rates was due to the spin–phonon interaction in both samples. For the crystal the relaxation caused by the diffusion of Li ions became significant above 580 K, and the narrowing of the absorption line started at about 540 K. For the glass the narrowing of the line started at room temperature and the effect of the diffusion of Li ions on the relaxation rate appeared above 400 K. From these results the correlation time τc of the fluctuating field at Li nuclei was obtained. Each value of the activation energy of τc deduced from the relaxation rate and the narrowing of the line, respectively, agreed well.

Nuclear magnetic resonance investigation of lithium diffusion in Li5AlO4

Nuclear magnetic relaxation rates of 7Li and conductivity in Li5AlO4 have been measured in the temperature range 20–700 °C. The spin–lattice relaxation rate T–11 for 7Li has a maximum in the plot of T–11 against temperature at ca. 600 °C. Quadrupole relaxation owing to vacancy diffusion was observed and a vacancy jump frequency of ν= 2.1 × 1011 exp (–0.60/kT) with an activation energy of 0.60 ± 0.03 eV was obtained. The activation energy of conductivity was 0.61 ± 0.03 eV, which was in good agreement with that obtained from T–11.

Nuclear Magnetic Resonance of 7Li in LiBO2 Crystal

The 7Li NMR spectra and spin lattice relaxation rates in crystalline LiBO2 sample were measured. The spectra exhibit a broad single line at low temperature and start to show a new narrow peak at the expense of the original peak as the temperature increases, i.e., in addition to a broad line, a narrow line is observed to grow as the temperature increases.

Nuclear spin relaxation in Li2BeF4

Nuclear spin lattice relaxation time T1 of 19F and 7Li in the solid and liquid phases of lithium tetrafluoroberyllate (Li2BeF4) were measured in the temperature range between 250 and 630 °C by means of pulse NMR technique. Nuclear magnetic resonance absorption spectra were also measured by use of a spectrometer. T1 of 19F and 7Li in the solid phase decreases exponentially as the temperature is increased. The temperature dependence of T1 of 7Li can be attributed to the diffusion of Li nuclei with an activation energy of 1.03 eV while T1 of 19F can be explained by the dipole interaction modulated by the diffusion of F ions with an activation energy of 1.23 eV. In the liquid phase T1 of 19F goes through a minimum at about 550 °C and is expressed as T1−1∝τ/(1+ω2τ2) in terms of a correlation time, τ. We obtained τ=5×10−16 exp (1.08/kT) s. It is suggested that the relaxation mechanism of 19F in the liquid phase is due to the dissociation of F ions from BeF4 complex ions and the long distance diffusion of the F ...