Abstract
Relaxors are complex materials with unusual properties that have been puzzling the scientific community since their discovery. The main characteristic of relaxors, that is, their dielectric relaxation, remains unclear and is still under debate. The difficulty to conduct measurements at frequencies ranging from ≃1 GHz to ≃1 THz and the challenge of developing models to capture their complex dynamical responses are among the reasons for such a situation. Here, we report first-principles-based molecular dynamic simulations of lead-free Ba(Zr0.5Ti0.5)O3, which allows us to obtain its subterahertz dynamics. This approach reproduces the striking characteristics of relaxors including the dielectric relaxation, the constant-loss behaviour, the diffuse maximum in the temperature dependence of susceptibility, the substantial widening of dielectric spectrum on cooling and the resulting Vogel–Fulcher law. The simulations further relate such features to the decomposed dielectric responses, each associated with its own polarization mechanism, therefore, enhancing the current understanding of relaxor behaviour.
Highlights
Relaxors are complex materials with unusual properties that have been puzzling the scientific community since their discovery
We report first-principles-derived simulations in BZT that reproduce the main characteristics of relaxor ferroelectrics, that is the frequency dependence of the real and imaginary parts of the dielectric response versus temperature
Analysis of these simulated results reveals that the relaxation-type polarization processes dominate in the dielectric response of disordered BZT for all temperatures, which contrasts with lead-based perovskite relaxors in which the response is purely of phonon nature for T4TB and the relaxation only appears below TB
Summary
Relaxors are complex materials with unusual properties that have been puzzling the scientific community since their discovery. A commonly proposed explanation is that it arises from the motion of polar nanoregions (PNRs), which appear on cooling at the so-called Burns temperature, TB (refs 3–5) Such a widely accepted mechanism has been recently challenged in (lead-based) relaxors on the ground of analysis of measured structural data[6,7,8] (note that the controversy extends to atomistic simulations, since some computational works did report the existence of PNRs in relaxor ferroelectrics[4,9,10] while others did not[11,12,13]). Note that BZT is chosen here because BaTiO3-based relaxors proved both experimentally[5,17] and theoretically[4,18,19,20] to exhibit PNRs and because some experimental data on BZT (to test the predictions against) are available at some terahertz and subterahertz frequencies
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