EPR study of the symmetry breaking effect in ferroelectric cesium dihydrogen phosphate doped with Cr5+ ions

Abstract

The (PO4)3− units in a CsH2PO4 (CDP) crystal were replaced in a small fraction of sites by (CrO4)3− groups and the EPR of the Cr5+ center was investigated. Splitting of the EPR line appears at T∗c=245 K, 91 K higher that the ferroelectric transition temperature Tc=154 K. The electronic wave function of Cr5+ (3d1) is identified as dx2−y2. The dx2−y2 function couples with the near protons and the reorientation of this unit in the two possible configurations occurs in the paraelectric phase and breaks the symmetry far above Tc. The observed correlation time 10−9 sec and associated activation energy ΔU=0.215 eV are discussed.