Studies of EPR theory and trigonal distortion of the [Cr(H2O)6]3+ cluster in ferroelectric guanidinium aluminum sulfate hexahydrate (GASH): Cr3+ system at different temperatures

For a d3 configuration ion, a theoretical method for studying the inter-relationships between electronic and molecular structure is investigated by diagonalizing the 120 × 120 complete energy matrices. The theoretical results show the following: (i) the local distortion structure for the Cr3+ occupying the Al3+ sites I and II exhibits an expansion distortion and the EPR parameters (D, g∥, g⊥) are in good agreement with the experimental results at different temperatures. (ii) The |D| values decrease with the increasing temperature. (iii) The sign of the zero-field splitting parameter D is negative for the two trigonal Cr3+ centers I and II in guanidinium aluminum sulfate hexahydrate (GASH) at 295.5, 78.45 and 1.61 K.