The electromechanical and structural properties of ½001Š and ½111Š-oriented PbðZn 1=3 Nb 2=3 ÞO 3 À6%PbTiO 3 (PZN À 6%PT) single crystals have been characterized using dielectric spectroscopy, x-ray diffraction, depolarization current, and piezoelectric techniques from 80 K to 300 K. Both unpoled and poled samples show a dielectric loss peak located in the range from 100 to 200 K. The poled samples show a change in the slope of the real part of the dielectric permittivity and a broad, frequency dependent peak in the imaginary part below 200 K. In the same temperature range, we observed a broadening of the Bragg peaks, fluctuations in the macroscopic polarization, and a change in the rate of decrease in the elastic compliance and the d 31 piezoelectric coefficient. These results were analyzed within the framework of three models proposed in the literature. This analysis argues that these observations originate from the freezing of the dynamics of the polar nanoregions (PNRs) at low temperature. This assumption implicates two important results; (i) the PNRs are embedded and persist within the ferroelectric, low-temperature phases, and (ii) they contribute to the large piezoelectric properties of the PZN À x%PT single crystals. These conclusions may be general to all ferroelectric relaxor systems. V C 2015 AIP Publishing LLC. [http://dx.