Electron spin resonance studies on locally additive low symmetry distortions in the mixed-crystal Sr 1 − xBa xF 2 system monitored with Eu 2+ dopants

Abstract

Local distortions in mixed crystals or solid solutions Sr 1 − x Ba x F 2 have been investigated by monitoring a doping Eu 2+ 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 SrF 2.