Structural Transitions of Silicate Nanocrystals in the Glass

Institute of Power Engineering and Automation, the Uzbek Academy of Sciences, 29 Do'rmon yo'li, Tashkent, 100125 Uzbekistan Abstract The temperature dependences of resistivity and thermopower measurements reveal that nanocrystals of sili- cates 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 (tem- perature T > 1000 K) doped lead-silicate glass turns into typical semiconductor having energy gap about 0.05 - 1.5 eV de- pending on the composition of the glass. Anomalous thermal expansion of the RuO2 relict crystals is detected at the tem- peratures of 800 - 1000 K as well.