Chen Liquan

Studies on PAN-based lithium salt complex

A new type of polymer electrolyte, the PAN[poly(acrylonitrile)]-based lithium salt complex is studied. The conductivities from −15 to 55°C have been measured. At room temperature the conductivity can reach 9.12 × 10−4 S cm−1. The transference number has been determined to be 0.36 by a method combining an ac impedance study of lithium ions and dc polarization experiment. The compatibility with metallic lithium is proved to be rather good. The results of NMR investigation are presented and discussed by combining conductivity results. The activation energy at ca 298 K has been calculated to be 0.32 eV from NMR and 0.49 eV from conductivity data.

Ionic conductivity enhancement during pre-crystallization in amorphous lithium ionic conductor Li2B2O4

Abstract It is found from the temperature dependence of the ionic conductivity of amorphous Li2B2O4 that the ion transport process is rather complicated. At temperature below Tk (≈310°C), the ionic conductivity obeys an Arrhenius relation. Above the crystallization temperature Tc (≈410°C) ion transport is dominated by the process in the crystalline state. In between the ionic conductivity is anomalously enhanced. In this pre-crystallization range two distinguishable steps with a transition temperature at Tp (≈380°C) can be identified. At temperature between Tk and Tp, the conductivity increase is due to the redistribution of free volume. For temperature between Tp and Tc the specimen contains a small amount of crystallites but the crystallinity is less than 5%. The 7Li NMR spectra show that the line shape of partially crystallized amorphous material is quite similar to that of LiCl containing DSPP but in this case the second-phase particles are crystallites of the parent material.

Influence of DSPP on the properties of AgI

Abstract For this investigation AgI was used as a matrix and η-Al2O3(0.05 μm) or ∝-Fe2O3 (0.6 μm) were taken as dispersed second phase particles (DSPP). The conductivity in β phase was increased remarking by the addition of DSPP. The maximum increment appears at 40 m/o for η-Al2O3 and 30 m/o for ∝-Fe2O3. The conductivity of β-AgI(40 m/o η-Al2O3) is three orders of magnitude higher than that of pure β-AgI at room temperature. The activation energies are obviously decreased. The conductivity in ∝-AgI containing DSPP decreases and the activation energy increases. It is found that DSPP influences the phase transition, especially ∝ to β transition. As a result the ∝ to β phase transition temperature of AgI(50 m/o η-Al2O3) is about 17 °C lower than that of pure AgI. Mossbauer spectrum of AgI(∝-Fe2O3 covered with 57Fe) has been studied. It is suggested from the results that both bulk and interfacial effects exist in AgI (∝-Fe2O3).

Experimental study of the pre-crystallization process in the amorphous fast ionic conductor 0.60AgI0.25Ag2O0.15P2O5

Abstract Systematic investigations on the pre-crystallization process in the amorphous ionic conductor 0.60AgI0.25Ag 2 O0.15P 2 O 5 have been carried out by means of ultrasonic measurements, thermal analysis, electron microscopy (SEM and TEM) and ionic conductivity experiments. The temperature dependence of the longitudinal ultrasound attenuation and velocity showed anomalous attenuation peaks and sudden unusual relative sound velocity changes near 330 and 341 K, indicating that possible structural changes and softening of interatomic bonds occurred. These are consistent with the anomalous changes of ionic conductivity of the same samples. Thermal analysis revealed that such anomalous changes are directly related to the glass transition and the microcrystalline formation, respectively. Moreover, direct evidence for the processes of crystallizations above 344 K were given from our SEM and TEM study. Therefore, it is suggested that the observed anomalous enhancements near 326 and 344 K of ionic conductivity of this amorphous fast ionic conductor is related to the destruction of the amorphous structure and the crystallization of the amorphous state.

Investigation of new lithium ionic conductors Li+xV1−xSixO4

Abstract A continuous solid solution Li3+xV1−xSixO4 has been found at high temperature in the system Li4SiO4−Li3VO4. At room temperature the solid solution ranges fromx = 0.1 tox = 0.5. This solid solution is formed by stabilizing the high temperature ψII-phase of Li3VO4 which the addition of Li4SiO4. Of compositions studied, Li3.3V0.7Si0.3O4 has the highest conductivity, reaching 1×10-5 Ω-1 cm at room temperature and having an activation energy of 0.36 eV in the temperature range 42–192°C. The NMR linewidth of7Li in this material was measured at different temperatures. Motional narrowing has been observed near -20°C. It is suggested that Li+ ions are the mobile species. The high conductivity domains in the pseudo-ternary system Li4GeO4−Li4SiO4−Li3VO4 have been roughly determined.

Ultrasonic studies on high Tc superconductor YBa2Cu3O7-x

Ultrasonic attenuation and velocity measurements down to 77K were performed on high Tc superconductor Y-Ba-Cu-O samples with different sintering procedures. The change of sound velocity was found near Tc in two samples which have density of 94% of the theoretical density and excellent diamagnetism. In one of the samples an anomaly related to ultrasonic frequency was observed around Tc in the ultrasonic attenuation. Another sample also possesses an excellent diamagnetism, but no anomaly in ultrasonic attenuation was found near Tc. We did not observe anomaly in attenuation resulted from electron-phonon interaction in these two samples.

Electrical double layer capacitor by useing β″-Al2O3 containing fine carbon particles as electrolytes

Abstract The capacitors have been constructed by using (1−x) Na-β″Al2O3 +xC as solid electrolytes and carbon as electrodes, here x≦0.06, C=Carbon. The optimal DC parameters with static specific capacitance up to 4.39F/cm2, leakage current less than 2.62mA(after one minute), equivalent series resistance not more than 2.34KΩ and breakdown voltage not less than 10 voltage have been obtained. The characteristics of the electrolytes and the change in capacities with carbon content are presented. The action of the carbon as second phase has been exhibited.

Some recent studies on Rb4Cu16I7Cl13

Abstract The plot of conductivity versus inverse temperature shows two or three transition points at -25 °C and/or -52 °C and -108 °C, respectively. Heat capacity measurements indicate clearly three peaks at -27 °C, -52 °C and -107 °C. Thus it is probable that there are three transition points in Rb 4 Cu 16 I 7 Cl 13 . This is confirmed by positron annihilation experiment. The ionic conductances of both porous and dense specimens have been measured between -80 °C to +80 °C under hydrostatic pressure from 0.5 Kbar to 11.6 Kbar. A conductance maximum appears near 4–5 Kbar on conductance versus pressure curve for porous specimen, while the conductance decreases as the pressure increases for dense specimen. The activation volumes are 0.90 cm 3 /mol. and 1.55 cm 3 /mol. for∝-phase and for β-phase, respectively.

Insulator to superconductor transition of Pb doped 2201 single crystal in Bi-system by oxygen deficiency

Flux method was used to grow large 2201 single crystal in Bi-Sr-Cu oxide. The as-grown crystal was nonsuperconductor and showed semiconductivity in resistivity curve. After it was reduced in flowing N2 at 570°C and appropriate oxygen vacancies were induced, superconductivity with Tcon = 6K was obtained. The great influence of oxygen deficience on superconductivity is evident. Also, the incorporation of Pb adjusted the modulation pattern.

Acoustic Properties of High Tc Superconductor YBa2Cu3O7-x

Ultrasonic attenuation and velocity measurements down to 4.2 K were performed on high Tc superconductor Y–BaCu–O samples of different sintering procedures. Attenuation peaks appeared at different temperatures, probably being related to the sintering procedure. However, one peak in attenuation obeserved in both samples below Tc may be due to the glass behavior of the samples. The mean sound velocity, which is related to the Debye temperature and specific heat, has been calculated using the experimental data of longitudinal and transverse sound velocity. The slope of mean velocity vs temperature is changed near Tc.