Critical Insight into Pretransitional Behavior and Dielectric Tunability of Relaxor Ceramics

Abstract

This model discussion focuses on links between the unique properties of relaxor ceramics and the basics of Critical Phenomena Physics and Glass Transition Physics. It indicates the significance of uniaxiality for the appearance of mean-field type features near the paraelectric-to-ferroelectric phase transition. Pretransitional fluctuations, that are increasing up to the size of a grain and leading to inter-grain, random, local electric fields are responsible for relaxor ceramics characteristics. Their impact yields the pseudospinodal behavior associated with “weakly discontinuous” local phase transitions. The emerging model redefines the meaning of the Burns temperature and polar nanoregions (PNRs). It offers a coherent explanation of “dielectric constant” changes with the “diffused maximum” near the paraelectric-to-ferroelectric transition, the sensitivity to moderate electric fields (tunability), and the “glassy” dynamics. These considerations are challenged by the experimental results of complex dielectric permittivity studies in a Ba0.65Sr0.35TiO3 relaxor ceramic, covering ca. 250 K, from the paraelectric to the “deep” ferroelectric phase. The distortion-sensitive and derivative-based analysis in the paraelectric phase and the surrounding paraelectric-to-ferroelectric transition reveal a preference for the exponential scaling pattern for ε(T) changes. This may suggest that Griffith-phase behavior is associated with mean-field criticality disturbed by random local impacts. The preference for the universalistic “critical & activated” evolution of the primary relaxation time is shown for dynamics. The discussion is supplemented by a coupled energy loss analysis. The electric field-related tunability studies lead to scaling relationships describing their temperature changes.

Global population: from Super-Malthus behavior to Doomsday criticality

“…( 9 ) is worth stressing. It resembles the critical-like behavior in constrained system complex systems, for instance, in critical phenomena physics within the so-called Griffiths model 107 – 109 . For the parameters that can be derived from the results presented in Fig.…”

The Dominance of Pretransitional Effects in Liquid Crystal-Based Nanocolloids: Nematogenic 4-methoxybenzylidene-4′–butylaniline with Transverse Permanent Dipole Moment and BaTiO3 Nanoparticles

“…For instance, it occurs in the paraelectric phase, where order parameter changes (polarization) can be tested concerning the coupled field parameter (electric field in the given case). Such behavior is explained within the Clausius–Mossotti local field model, generally valid for systems composed of non-interacting and weakly interacting dipole moments, including their ‘immersion’ in a mean-field surrounding [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 ]. Experimental dielectric studies of liquids under nano-constraints showed that they can mimic the behavior under quasi-negative pressure conditions [ 77 , 78 , 79 , 80 ], i.e., the ‘rarefication’ (isotropic stretching), which has to weaken intermolecular and inter-dipolar interactions.…”

“…Such behavior is explained within the Clausius–Mossotti local field model, generally valid for systems composed of non-interacting and weakly interacting dipole moments, including their ‘immersion’ in a mean-field surrounding [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 ]. Experimental dielectric studies of liquids under nano-constraints showed that they can mimic the behavior under quasi-negative pressure conditions [ 77 , 78 , 79 , 80 ], i.e., the ‘rarefication’ (isotropic stretching), which has to weaken intermolecular and inter-dipolar interactions. Such nano-constrained conditions can be essential for quasi-liquid nano-layers in the solid-state pre-melting domain.…”

Global Population: from Super-Malthus behavior to Doomsday Criticality

“…It resembles the critical-like behavior in constrained system complex systems, for instance, considered in physics within the so-called Griffiths model. [107][108][109] For the parameters that can be derived from the results presented in Fig. 3, the following relation approximates global population changes in Industrial Revolutions period:…”