THz spectrum and ionic polarizability of PbB<inf>4</inf>O<inf>7</inf> crystal

The terahertz refractive index n(nu) of lead tetraborate (PbB ₄ O ₇ ) crystal decreases due to vanish of the ionic polarizabilities in sequence of the Pb ²⁺ , O ^2- and B ³⁺ ions when the frequency increasing. The ionic polarizabilities are calculated by the Clausius-Mossotti relation, alphaPb is 0.428times10 ^-24 cm ³ and alpha _o is 0.049times10 ^-24 cm ³ respectively.