In case of BaCr the as prepared glass was already in crystalline form and its TEC has low value of 6.8 × 10−6 K−1. However, after heat treatment for 10 h the crystallization of BaSi2O5 in the glass matrix increased the TEC value (7.6 × 10−6 K−1). With further increase in volume fraction of BaSi2O5 phase due to 100 h heat treatment the TEC value again increased to 8.1 × 10−6 K−1. In this sample, formation of BaSi2O5 phase might be having high TEC which leads to higher % change in TEC. It might also be attributed that crystalline phase (BaSi2O5) do not exhibit the intermediate cations which may be responsible for low change in TEC due to small ionic radii as compared to the Ba2+ (1.49 Å).
Table 2.