Application of the Onsager Principle to the Polar-axial Phenomena in Crystal Physics

An approach is proposed to the determination of nature of a tensor of any rank describing the linear relationship between an external impact on a crystal and the resulting effect. It is shown that, in addition to the Onsager principle, polar nature of the tensor takes place when the external impact on a crystal and the resulting effect are axial in nature and their ranks have values from zero to two, but so that the sum of their ranks is equal to the rank of the physical property described. Analytical expressions are obtained for the considered crystal physical properties both of polar and axial nature for various ranks and various natures of the external impact and the resulting effect. Their application was demonstrated both for the description of the already known properties of crystals, for prediction of new properties of the second and third ranks, and for the establishment of the conditions for their observation. It is concluded that the proposed expansion of the Onsager principle not only increases the number of phenomena covered by it, but also predicts new properties of polar or axial nature – gradient and divergence properties, if the impact on the crystal is inhomogeneous over its volume.