Linear and non-linear dielectric spectroscopy on ammonium doped Rochelle salt

In this work we present a thorough investigation of the mixed system of Rochelle salt doped with ammonium, with 0<=x<=1 for [Na(K{1-x}(NH4)x)C4H4O6 * 4H2O]. This interesting system is known to exhibit a rich phase diagram with a variety of polar and non-polar phases. However, most of the earlier investigations date back many decades and the experimental advances made since then should enable new insight into the physical nature of its phase diagram. We studied single crystals of 18 doping concentrations using linear and non-linear frequency-dependent dielectric response spectroscopy. In the low field measurements a variety of relaxation features are detected and analyzed in detail. The results for two concentrations of x=0 and x=0.15 are described qualitatively with a simple model. Possibly the most important outcome of the present work is the detection of a new electrically ordered phase for concentrations 0.18<x<0.89.