International
Tables for
Crystallography
Volume D
Physical properties of crystals
Edited by A. Authier

International Tables for Crystallography (2013). Vol. D, ch. 1.6, p. 157

## Section 1.6.3.3. The dielectric impermeability tensor

A. M. Glazera* and K. G. Coxb

aDepartment of Physics, University of Oxford, Parks Roads, Oxford OX1 3PU, England, and bDepartment of Earth Sciences, University of Oxford, Parks Roads, Oxford OX1 3PR, England
Correspondence e-mail:  glazer@physics.ox.ac.uk

#### 1.6.3.3. The dielectric impermeability tensor

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It has been seen how the refractive indices can be described in a crystal in terms of an ellipsoid, known as the indicatrix. Thus for orthogonal axes chosen to coincide with the ellipsoid axes, one can write where , and . One can write this equation alternatively as where the are the relative dielectric impermeabilities. For the indicatrix in any general orientation with respect to the coordinate axesThus the dielectric impermeability tensor is described by a second-rank tensor, related inversely to the dielectric tensor.