The specific heat of typical relaxors, $\mathrm{P}\mathrm{b}({\mathrm{M}\mathrm{g}}_{1/3}{\mathrm{N}\mathrm{b}}_{2/3}){\mathrm{O}}_3$ (PMN) and $\mathrm{P}\mathrm{b}({\mathrm{M}\mathrm{g}}_{1/3}{\mathrm{T}\mathrm{a}}_{2/3}){\mathrm{O}}_3$ (PMT), was measured by adiabatic and relaxation methods between 2 and 420 K. A broad anomaly was found in the specific heat curve over the wide temperature range between 150 and 500 K for PMN, and between 50 and 400 K for PMT, which provides evidence for the formation of ferroelectric nanoregions (FNR) in the paraelectric matrix. The entropy of the anomaly was estimated as $3.3\mathrm{J}{\mathrm{K}}^{-1}{\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$ and $2.9\mathrm{J}{\mathrm{K}}^{-1}{\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$ for PMN and PMT, respectively, which implies an order-disorder-type mechanism for the formation of FNR.

• Received 25 November 2002

DOI:https://doi.org/10.1103/PhysRevLett.90.205901