Comprehensive analysis of structural, dielectric, magnetic properties in self-propagating high-temperature (SHS) prepared lead iron niobate

Abstract

Lead iron niobate, Pb(Fe_1/2Nb_1/2)O₃ (PFN), was synthesized via a self-propagating high-temperature synthesis (SHS) technique. The SHS process achieved pyrochlore-free monoclinic perovskite (space group Cm) at room temperature, transitioning to cubic symmetry (Pm3 m) above 380 °C, as confirmed by high-temperature XRD (HT-XRD). Lattice contraction with rising temperature revealed negative thermal expansion (NTE), driven by Pb²⁺ vibrational modes and octahedral tilting. Sintering at 800 °C (PFN-8-3) eliminated residual pyrochlore phases (Pb₂Fe₄Nb₄O₂₁) and enhanced relative density to 98 %, compared to 80 % for samples sintered at 700 °C (PFN-7-2). Dielectric studies identified a diffuse phase transition (DPT) near 105–115 °C, with permittivity reaching ∼18,600 (1 kHz) for PFN-8-3, attributed to grain densification and reduced porosity. Frequency-independent T_m and Debye-like relaxation confirmed non-relaxor behavior, linked to ordered Fe³⁺/Nb⁵⁺ B-site cation distribution. Electron density mapping via Fourier analysis highlighted Pb-dominated charge density (∼69 e/ų), with Fe/Nb contributions (∼29–32 e/ų), aligning with X-ray scattering trends. Magnetic hysteresis loops revealed weak room-temperature ferromagnetism, intensifying at higher sintering temperatures (coercivity ∼80 Oe, remnant magnetization ∼0.12 emu/g for PFN-8-3). The coexistence of ferroelectricity and ferromagnetism underscores PFN's potential in multifunctional devices, while the SHS route offers a rapid, energy-efficient pathway to phase-pure perovskites. This work bridges synthesis optimization, structural dynamics, and functional performance, advancing PFN's applicability in high-density capacitors, magnetoelectric sensors, and thermal management systems.