Structural Transitions of Silicate Nanocrystals in the Glass

The temperature dependences of resistivity and thermopower measurements reveal that nanocrystals of silicates in lead-silicate glass of various compositions undergo structural transitions in the temperature range of 800 – 1000 K. The diameter of these nanocrystals estimated from Scherrer’s formula is about 0.8 – 1.6 nm and each nanocrystal consists of 8 - 64 unit cells. Structure transitions are detected as sharply maxima of resistivity ρ and thermopower S at temperature T = 800 – 100 K. Lead-silicate glass was doped by RuO2 up to 16 weight% to facilitate the measurements of the ρ and the S. The doped lead-silicate glass has a metal-like behavior at the room temperature: the temperature dependences ρ(T) and S(T) are very slow, the value of the S is typical for metals (few and tens of μV/K). Beyond the maximum of the resistance (temperature T > 1000 K) doped lead-silicate glass turns into typical semiconductor having energy gap about 0.05 – 1.5 eV depending on the composition of the glass. Anomalous thermal expansion of the RuO2 relict crystals is detected at the temperatures of 800 – 1000 K as well.