Vibrational Spectra,Force Constants,and Si-O Bond Character in Calcium Silicate Crystal Structure

Vibrational spectroscopic methods were used to study the Si-O bond character in silicates with different complex anions and crystal structures. The following calcium silicates were examined: Ca,(SiO₅), γ-Ca₂(SiO₄), β-Ca₂(SiO₄), Ca₃(Si₂O₇), Ca(SiO₃), and Ca(Si₃O₃). The band assignments in IR and Raman spectra of these compounds have been deduced mainly from ²⁸Si⁻³⁰Si and ⁴⁰Ca⁻⁴⁴Ca isotopic shifts. The GF matrix method and molecular approximation for force constant calculations in silicate anions were used. The Si-O bond parameters (bond order, charge distribution, and bond ionicity, etc.) were obtained from calculated force constants. The nature of Si-O bonds with respect to complex anion and crystal structure will be discussed.