Conductivity Of Glass-ceramics Research Articles

Thermal Conductivity of Li2O·Al2O3·nSiO2 Glass‐Ceramics between 5 and 100 K

The thermal conductivity of Li2O·Al2O3·nSiO2 glass‐ceramics is studied for n= 4, 6, 8, 10 between 5 and 100 K. A monotonic increase in conductivity is observed for all samples. This behavior is different from that of glassy counterparts which exhibit a plateau in thermal conductivity between 10 and 20 K. It is also observed that while the conductivity of glass‐ceramics is lower than that of glasses at low temperatures, the situation is reversed at higher temperatures. A crossover occurs around 40 K for all studied samples. The glass‐ceramic behavior is interpreted in the light of the acoustic mismatch theory of Little. At low temperatures, the thermal boundary resistance that exists at the crystalline‐amorphous mismatch is high and the thermal conductivity is low. At higher temperatures, the boundary resistance is very small and the high conductivity is mainly due to the crystalline region within the amorphous structure.

Electrical Conductivity of Crystallized Glasses of the System Na<sub>2</sub>O-V<sub>2</sub>O<sub>5</sub>-P<sub>2</sub>O<sub>5</sub> Containing Vanadium Bronze Crystals

In order to obtain highly conductive glass-ceramics containing vanadium bronze, MxV2O5 (M=alkali metal, etc), which is known to have high electronic conductivity, Na2O-V2O5-P2O5 glasses were heat treated to perform crystallization. The dc conductivities of the glasses containing 60 to 77mol% V2O5, in which [Na2O]/[V2O5] molar ratio was 1/6 to 1/3, were about 10-4 to 10-2ohm-1cm-1 at 150°C, and the activation energies were about 0.4eV. Exothermal peaks accompanied by weight losses were observed by TG-DTA in the temperature range from 250° to 300°C. Broad peaks of β-NaxV2O5 were observed by X-ray diffraction after 2 to 5 h-heat treatment at 260° to 300°C. Glass blocks and disks of glass powders were heat-treated in two steps, at 300°C for 2h and at 500°C for 1 to 4h in air. After the heat treatment at 500°C, sharp diffraction peaks of β-NaxV2O5 developed. The dc conductivity of the crystallized glasses was more than 3 orders of magnitude higher than that of as-cast glasses. The activation energy decreased to less than 0.1eV, similar to that of vanadium bronze. The microstructure of the crystallized glasses was observed by SEM and optical microscopy.