Superparaelectric phase in the ensemble of noninteracting ferroelectric nanoparticles

A. N. Morozovska

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Physical Review B - Maryland, USA: American Physical Society (APS), 2008, #78


We predict the conditions of superparaelectric phase appearance in the ensemble of noninteracting spherical ferroelectric nanoparticles. The superparaelectricity in the ensemble of nanoparticles was defined by analogy with superparamagnetism, obtained earlier in small nanoparticles made of magnetic material. Calculations of correlation radius, energetic barriers of polarization reorientation, and polarization response to external electric field, performed within Landau-Ginzburg phenomenological approach for perovskites Pb(Zr,Ti)O3, BiFeO3, uniaxial ferroelectrics Rochelle salt, and triglycine sulfate, proved that under the favorable conditions ensemble of noninteracting nanoparticles possesses superparaelectric features. The main favorable conditions for the superparaelectricity observation in ferroelectric nanoparticles are the radius smaller than the correlation radius, surface screening of depolarization field, small Curie-Weiss constant, and high nonlinear coefficients, which guarantee that the barrier of the particle polarization orientation will be smaller than the thermal energy and the particle is single domain. The theoretical forecast is waiting for experimental revealing.