BaTiO 3 -xBaZrO 3 (BZT-x) solid solution represents the best-studied lead-free relaxor-ferroelectric (shortly relaxor) system with perspectives for piezoelectrics and electric field tunable microwave (MW) applications in a broad composition range. [1,2] Unlike usual lead-containing relaxors, they belong to isovalent solid solutions (Ti 4þ and Zr 4þ ions have the same valence) so that the quenched random electric fields, which play an important role in lead-containing relaxors, [3] are here not dominant. On increasing the Zr concentration x, it first undergoes the three first-order ferroelectric (FE) phase transitions (PTs) wellknown for barium titanate BaTiO 3 (BT), the best-known FE material. At T C % 400 K, BT undergoes predominantly displacive PT from the paraelectric cubic (C) perovskite structure to tetragonal (T) FE phase, near 270 K from T to orthorhombic (O) FE and near 180 K to rhombohedral (R) FE phase; for the general review and dielectric properties, see the studies by Lines and Petzelt [4,5] and references therein. For x % 0.11, the PTs merge into one diffuse FE transition and the behavior gradually changes into relaxor and finally dipolar glass one. BaZrO 3 (BZ) is a normal (slightly incipient FE) dielectric without any appreciable dielectric dispersion below the infrared (IR) phonon response. [6,7] Broadband dielectric spectroscopies up to terahertz (THz) and IR ranges are the most efficient experimental techniques for studying and understanding such rich properties. Namely, displacive proper FEs are characterized by an excitation whose frequency tends to zero on approaching the FE PT, socalled soft mode (SM), see the recent review [8] and references therein. Due to rather strong lattice anharmonicity (as is the case of BT), another overdamped excitation frequently appears below the SM frequency, so-called central mode (CM), which through mutual coupling takes over the SM softening close to T C . [8] Relaxor FEs (shortly relaxors) exhibit an additional relaxational (overdamped) excitation which appears below the SM-CM frequencies on cooling below so-called Burns temperature T B and characterizes the dynamics of the appearing polar nanoregions (PNRs), see the previous reviews [8,9] and references therein. This excitation softens typically from the MW range down to zero at so-called freezing temperature T f and creates the well-known frequency-dependent maximum T m > T f in the temperature dependence of the dielectric permittivity. Dipolar