Electron Paramagnetic Resonance of Cr³⁺ Ions in Antiferroelectric ADP Crystals

Abstract

The electron paramagnetic resonance absorption of Cr 3+ ions doped in ADP(NH 4 H 2 P0 4 ) single crystals was studied both in the paraelectric and the antiferroelectric phases. It is found that there is one kind of dominant Cr 3+ ion sites in the crystals in the para phase and that these sites are divided into two slightly different kinds of sites in the antiferro phase. From angular variation of the EPR spectrum, it is inferred that Cr 3+ ions of this sites take substitutionally the positions of NH 4 + ions and have two vacancies of neighboring protons so as to satisfy the charge compensation and the crystal symmetry. The spin Hamiltonian parameters are detarmined as g // = g ⊥ =1.98, | D |=0.100 cm -1 and | E |=0.022 cm -1 151°K. We could explain the line splitting of the EPR spectrum due to the two divided Cr 3+ ion sites, by using the twin structure model which consists of the right-hand a - b system and left-hand a - b system having the c -axis in common.