Use the Clausius–Mossotti expression to estimate the dielectric permittivities of the cubic perovskites BaZrO₃ (a = 4.19 Å), KTaO₃ (a = 3.99 Å), and SrTiO₃ (a = 3.90 Å). Compare your estimates to the observed values in Table 8.1. How does the divergence between calculated and observed values correlate with the tendency for the octahedral cations to undergo SOJT distortions? What does this tell you about compositions for which the Clausius–Mossotti equation can reliably be used?

Table 8.1

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Substance Air Teflon C (diamond) Si NaF MgO SiO CaF2 Pbl HO Er 1.0006 2 6 12 5 10 4 7 21 80 Substance SnO ZrO TiO Perovskite dielectrics BaSnO3 BaZrO3 CaTiO3 SrTiO3 KTaO3 BazZnTaO9 Er 13 22 94 18 43 165 330 242 30