[Paper Review] Composition induced diffused to relaxor ferroelectric phase transition in lead-free (1-x)(Li0.12Na0.88)NbO3-xBaTiO3 (0 to x to 0.40) ferroelectric ceramics

Supratim Mitra, Ajit R. Kulkarni|arXiv (Cornell University)|Dec 16, 2014

Ferroelectric and Piezoelectric Materials3 citations

TL;DR

This study investigates composition-driven phase transitions in lead-free (1-x)(Li0.12Na0.88)NbO3-xBaTiO3 ceramics (x = 0 to 0.40) using dielectric spectroscopy. It demonstrates a crossover from diffused ferroelectric phase transition (FE-DPT) to relaxor ferroelectric (RFE) behavior at x ≥ 0.225, attributed to evolving polar nanoregions (PNRs) with distinct relaxation dynamics and frequency-dependent dielectric maxima governed by the Vogel-Fulcher law.

ABSTRACT

(1-x)Li0.12Na0.88NbO3-xBaTiO3 (0 to x to 0.40) ferroelectric ceramics were prepared using conventional ceramics route and their phase transitional behavior is investigated by using dielectric spectroscopy. The temperature-dependent dielectric permittivity epsilon'(T) shows a diffused ferroelectric-paraelectric transition for all compositions. An acceptable and competent characterizing parameter (D) of diffused phase transition (DPT), defined by Uchino et al. [J Am Ceram Soc 2010;93:4011], was measured and validated. Interestingly, a crossover from diffused ferroelectric phase transition (FE-DPT) to relaxor ferroelectric (RFE) transition is found for the composition x greater than equal to 0.225. The FE-DPT is characterized by a frequency-independent temperature of dielectric maxima (Tm), while a RFE is found to have frequency-dependent Tm satisfying Vogel-Fulcher relation. The composition induced crossover is attributed to the dynamics of different PNR size and relaxation times that varies with different BaTiO3 content (x) leading to the appearance of a FE-DPT or RFE.

Motivation & Objective

• To understand the phase transition behavior in lead-free (1-x)(Li0.12Na0.88)NbO3-xBaTiO3 ceramics across varying BaTiO3 content.
• To identify the compositional threshold at which the ferroelectric phase transition shifts from diffused to relaxor character.
• To correlate dielectric response with the dynamics of polar nanoregions (PNRs) and their relaxation times.
• To validate the use of Uchino's diffuseness parameter (D) as a reliable metric for characterizing phase transition type.
• To determine whether the frequency dependence of dielectric maxima (Tm) follows the Vogel-Fulcher relation, indicating relaxor behavior.

Proposed method

• Synthesized (1-x)(Li0.12Na0.88)NbO3-xBaTiO3 ceramics via conventional solid-state ceramic processing for x = 0 to 0.40.
• Performed temperature-dependent dielectric permittivity (ε′(T)) measurements to analyze phase transition characteristics.
• Calculated the diffuseness parameter D using Uchino et al.'s formula to quantify the degree of diffuseness in the phase transition.
• Analyzed the frequency dependence of dielectric permittance maxima (Tm) to distinguish between FE-DPT (frequency-independent) and RFE (frequency-dependent) behavior.
• Fitted the frequency-dependent Tm data to the Vogel-Fulcher equation to confirm relaxor ferroelectric behavior.
• Correlated changes in PNR size and relaxation dynamics with increasing BaTiO3 content (x) to explain the transition mechanism.

Experimental results

Research questions

• RQ1 At what BaTiO3 composition (x) does the ferroelectric phase transition transition from diffused to relaxor character?
• RQ2 How does the frequency dependence of dielectric permittivity maxima (Tm) evolve with increasing x, and does it follow the Vogel-Fulcher law?
• RQ3 What is the role of polar nanoregions (PNRs) in mediating the transition from FE-DPT to RFE behavior?
• RQ4 How does the Uchino diffuseness parameter D vary with x, and is it a reliable indicator of the transition type?
• RQ5 What microstructural or dynamic factors underlie the observed shift in phase transition behavior with increasing BaTiO3 content?

Key findings

• A clear crossover from diffused ferroelectric phase transition (FE-DPT) to relaxor ferroelectric (RFE) behavior occurs at x ≥ 0.225.
• For x < 0.225, the dielectric permittivity maxima (Tm) are frequency-independent, confirming FE-DPT behavior.
• For x ≥ 0.225, Tm exhibits strong frequency dependence and fits the Vogel-Fulcher equation, confirming RFE character.
• The Uchino diffuseness parameter D increases with x, indicating enhanced diffuseness, peaking near x = 0.225 before stabilizing.
• The transition is attributed to evolving polar nanoregions (PNRs) with increasing BaTiO3 content, leading to broader distribution of relaxation times.
• The study validates the use of D as a reliable parameter for characterizing the degree of diffuseness in lead-free ferroelectric ceramics.