Influence of temperature and external electric field on the EPR spectra of Cr3 ion in NaH3(SeO3)2 (STHS) crystals

The influence of the temperature and external electric field on the EPR spectra of Cr3+ ion in the improper ferroelectric-ferroelastic NaH3(SeO3)2 (STHS) has been investigated.The Cr3 + ion in STHS occupies the site Na+ ion, its coordination environment consists of 6 oxygens of neighbouring SeO3 groups.Non-local charge compensation of the excess charge +2 of Cr3+ ion might be secured by two proton vacancies. The number of paramagnetic complexes of Cr3+ ion in STHS can be explained in the “off-center” model of position of Cr3 + ion in oxygen octahedron and influence of the internal electric fields from vacancies. The activation energy of displacement between complexes IA ⊼ IB and IIA ⊼ IIB type has been determined. In the triclinic β-phase which has two components of spontaneous polarization Psx and Psy the influence of the external electric field Ex and Ey on the intensity of EPR lines has been examined thus allowing for elucidation of changes in geometry and reconstruction of domain structure of this complicated bi-axial improper ferroelectric-ferroelastic.