EPR study of copper ions in Li2Ge7O15 crystals

Abstract

The EPR spectra of Cu2+ ions (2 D 5/2) located at two structurally nonequivalent positions Cu1 and Cu2 in crystals of lithium heptagermanate Li2Ge7O15 are recorded. The angular dependences of the EPR spectrum are measured in the paraelectric phase of the Li2Ge7O15 compound (T = 300 K). The components of the g factor and the hyperfine interaction tensor A are determined, and the orientation of the magnetic axes with respect to the crystallographic basis is established. The EPR spectra are recorded in the temperature range in the vicinity of the temperature T C = 283 K of the transition from the paraelectric phase to the ferroelectric phase. The position symmetry of the Cu1 and Cu2 centers is determined at temperatures above and below the phase transition temperature T C . The localization of paramagnetic centers in the structure is discussed, An analysis of the results obtained demonstrates that the Cu1 and Cu2 centers in the Li2Ge7O15 crystal lattice replace lithium ions located at two structurally nonequivalent positions with the symmetries described at temperatures above T C by the triclinic C i and monoclinic C 2 point groups, respectively.