Fluctuation-induced broadening of Mn2+ EPR lines in the incommensurate phase of Rb2ZnCl4 crystals

The EPR spectra of Mn2+ ions in Rb2ZnCl4 crystals is investigated in the vi cinity of the transition from the paraelectric phase to an incommensurate m odulated phase. When these crystals are cooled below the transition tempera ture T-i=304 K, a splitting of the resonance lines is observed in the singu lar spectrum. A one-harmonic model is used to discuss the contributions tha t fluctuations in the amplitude and phase of the incommensurate displacemen t wave make to the local width of the singular spectra. It is shown that an omalies in the local width of the low-temperature singular peaks observed i n the vicinity of T-i are caused by amplitude fluctuations. (C) 1999 Americ an Institute of Physics. [S1063-7834(99)02809-9].