  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.
