Mixed modifier effect in lithium‐calcium borosilicate glasses

The mixed modifier effect ( MME ) in the lithium‐calcium borosilicate glasses, which have a composition of 0.4[(1− x )Li 2 O– x CaO ]–0.6[(1− y )B 2 O 3 – y SiO 2 ] with x in the range of 0~1 and y in the range of 0.33~0.83, is investigated. The MME manifests itself as a positive deviation from linearity in the activation energy of electrical conductivity (Ea σ ) and as a negative deviation from linearity in the fraction of four‐coordinated boron ( N 4 ), glass transition temperature ( T g ), dilatometric softening temperature ( T d ), Vickers microhardness (H v ), dielectric constant (ε), and dielectric loss (tanδ). Moreover, the deviation, which exhibits a maximum at [CaO]/([CaO]+[Li 2 O])=0.5, is enhanced with increasing [SiO 2 ]/[B 2 O 3 ] ratio in the glass network. The observed MME in T g , T d , and H v are attributed to the bond weakening in the network; however, the MME in ε, tanδ, and Ea σ are caused by the obstruction of modifier transport in the glass network.