Vibronic amplification

Here = Kqq(0) is elastic constant of the tetragonal E vibrations in one octahedron. The coefficients q and p are well-known vibronic reduction factors [1,2,61]. As the vibronic coupling constant, V, increases, the reduction factors, q and p, approach their limiting values, q = and p = 0. Therefore, at strong vibronic coupling, the product qV in (38) increases linearly with V. Therefore, qV is known as the factor of vibronic amplification [1, 2, 61]. At the same time, the factor pV... 

It follows that by increasing the constant of vibronic coupling the relative contribution of Jahn-Teller nuclear vibrations to the effective quadrupole moment determining the birefringence is increasing. Therefore ( ",)(r, ft) [to be distinguished from the reduction parameters (r, /3)] can be called the parameter of vibronic amplification of the vibrational contributions to the quadrupole moment. 

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