ELECTRON-SPIN-RESONANCE STUDIES ON LOCALLY ADDITIVE LOW-SYMMETRY DISTORTIONS IN THE MIXED-CRYSTAL SR1-XBAXF2 SYSTEM MONITORED WITH EU2+ DOPANTS

Local distortions in mixed crystals or solid solutions Sr1-xBaxF2 have been investigated by monitoring a doping Eu2+ ion by means of electron spin resonance measurement. With increasing mixture ratios x near 0, the resolved hyperfine linewidths broaden in sequence from larger \M\ spin magnetic quantum numbers to smaller values for the M-->M-1 transition. This tendency also holds on decreasing the mixture ratio x near 1. As a source of these characteristic broadening effects, distortion compensation for lattice misfit has been considered to be made at local sites in the mixed crystal by adding the second-order low symmetry crystal fields of B-2(0) followed by B-2(2). It was found that the observed line broadening effects would be reasonable if the sum of the B-2(0) term and the second-order contribution term of B-2(2) was distributed over the region from -2.75 to 1.75 G, in which it corresponded to the displacements of fluorine ions to be detectable with the high sensitivity below 0.4% of the lattice parameter of SrF2.