Effect of H2O and CO2 on Dielectric Properties of Single‐Crystal Cordierite and Comparison with Polycrystalline Cordierite

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Abstract
The dielectric constants and dielectric loss values of two naturally occurring cordierite single crystals were determined at 1 MHz using a two‐terminal method and empirically determined edge corrections. The results are as follows. Cordierite 1: κ′a= 5.653, tan δ= 0.009; κ′b= 6.106, tan δ= 0.003; κ′c= 5.658, tan δ= 0.010. Cordierite 2: κ′a= 5.765, tan δ= 0.0006; κ′b= 6.334, tan δ= 0.0007; κ′c= 5.807, tan δ= 0.0007. The agreement between measured dielectric polarizabilities as determined from the Clausius–Mosotti equation and those calculated from the sum of oxide polarizabilities according to αD (mineral) =ΣαD (oxides) neglecting the channel H2O and CO2 for these two cordierite samples is ∼20%. Inclusion of the effects of water and CO2 assuming mobile H2O molecules with no correlation between their dipoles improves the agreement to ∼2%. Comparison of dielectric constants of manufactured cordierite ceramics shows a discrepancy between typical observed values of 4.5–5.0 and a theoretical value of 4.0 calculated from the Clausius–Mosotti equation. In certain cases, this discrepancy can be accounted for by the presence of high‐κ′ impurities, but in others there is no explanation for the differences.