On crystalfield parametrization in a uniformly strained crystal lattice
Abstract
The general consequences of uniform strain of a crystal lattice or coordination complex in phenomenological parametrization of the crystalfield potential are considered. The analysis is based on the threedimensional derivatives of intrinsic crystalfield parameters within the superposition model of the crystalfield potential. The problem of the lowest possible symmetry of a uniformly strained crystal is discussed. Some limitations of the admissible deformations arise from the invariance of symmetry planes and inversion centre with respect to uniform strains. For any uniform strain, the crystalfield potentials that are expressible by qeven terms only can never be reduced to potentials requiring qodd terms. Therefore, their maximal symmetry lowering must terminate at a monoclinic point symmetry group. However, for a general uniform strain, some real derivatives of parameters of orthorhombic character IIk2 for 2 k 6, apart from the axial ones B_{k0} for 1 ≤ k≤ 6, can always occur. As a consequence, the decrease in symmetry for point groups that are characterized by an oddfold axis (qodd) and lack of any symmetry plane is unrestricted down to the triclinic systems. However, some incomplete sets of crystalfield parameters compared with those predicted by group theory are needed. Uniform strains in crystals occur generally as a response to external stress used in pressure studies. The calculation method of the relative dimensionless changes of dB_{kq}/B_{kq} as a function of pressure using the stressstrain data (elastic stiffness moduli) is given. Such successful calculations for the Pr^{3+} : LiYF_{4} system based only on the crystallographic data and the t_{k} exponents (in the distance dependence of B_{kq}) are presented as an example. (
 Publication:

Physica Status Solidi B Basic Research
 Pub Date:
 October 2003
 DOI:
 10.1002/pssb.200301849
 Bibcode:
 2003PSSBR.239..316M
 Keywords:

 71.70.Ch