EPR and Ionic Thermocurrents Experiments on Cubic Solid Solutions Sr_1−xEu_xF_2+x

Abstract

In this paper we report about the results of EPR and ionic thermocurrents (ITC) experiments on cubic solid solutions of the type Sr_1−xEu_xF_2+x. A part of the Eu-ions is in the divalent state; these ions can be detected easily with EPR. From the EPR results we conclude that for 0≤x≤0.115 the long range order is still cubic and the lattice parameter does not vary appreciably. The interactions between distant Eu³⁺–F_i⁻ dipoles and the Eu²⁺ probes is estimated; from this we conclude that for x\gtrsim0.044 clustering of trivalent Eu-ions cannot be excluded.
The ITC results are in line with those obtained from EPR. In addition we note that for small values of x nearest neighbor (NN) Eu³⁺–F_i⁻ complexes are the dominant defects. For x>5.10⁻³ NNN dipoles are present also. Apart from the reorientation bands associated with the abovementioned defects we observe with ITC a depolarization peak, ascribed to space charge phenomena. The behavior of the dipole peaks and the space charge peak is discussed together with the conduction processes in concentrated solid solutions Sr_1−xEu_xF_2+x.