Relaxor ferroelectrics are materials which exhibit strong and frequency dependent peak in temperature dependent permittivity. It reminds frequency-dependent ferroelectric phase transition, although the systems remain paraelectric down to zero Kelvin. Since the solid solutions of relaxor ferroelectrics with ferroelectrics exhibit a giant piezoelectric response, these materials are intensively studied, because understanding the properties is promising for improvement of piezoelectric properties as well as for required replacement of lead-based piezoelectrics by the lead-free piezomaterials, which are more friendly to environment. Our broad-band dielectric spectroscopy is used for the description of the broad and strong dielectric relaxations in relaxors, which have origin in the dynamics of polar nanoregions. Moreover, recently our analysis of THz and IR spectra of lead-based relaxors using Bruggeman effective medium formula explained the Curie-Weiss behavior of the high-temperature permittivity and revealed a structural phase transition within polar nanodomains at temperatures T*=350-450 K (depending on the chemical composition), i.e. at temperatures well above the peak of low-frequency permittivity. We investigated lead-based relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3 (PMN), Pb(Mg1/3Ta2/3)O3 (PMT), (Pb1-xLax)Zr0.65Ti0.35O3 (PLZT), ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) but also lead-free relaxors Sr1-xBaxNb2O6 (SBN), (Na1/2Bi1/2)TiO3 (NBT), 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3, Ba(ZrxTi1-x)O3 (BZT) and others. These investigations require dielectric studies in the broad spectral range (including THz), detailed structural measurements (including diffuse X-ray and neutron scattering) and phonons studies not only using IR but also inelastic neutron and X-ray scattering. Therefore three groups from our Department (this group + THz + inelastic light- and neutron scattering groups) are involved in these studies. Synergy of this collaboration is very important.
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