EPR study of the symmetry breaking effect in ferroelectric cesium dihydrogen phosphate doped with Cr 5+ ions

Abstract

The (PO 4) 3− units in a CsH 2PO 4 (CDP) crystal were replaced in a small fraction of sites by (CrO 4) 3− groups and the EPR of the Cr 5+ center was investigated. Splitting of the EPR line appears at T ∗ c=245 K, 91 K higher that the ferroelectric transition temperature T c=154 K. The electronic wave function of Cr 5+ (3d 1) is identified as d x2 −y2. The d x2 −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 T c. The observed correlation time 10 −9 sec and associated activation energy ΔU=0.215 eV are discussed.