Lead-Free Dielectric Materials

Updated 22 October 2025

Lead-free dielectric materials are ceramics and thin films that exclude toxic lead, using benign substitutions to achieve desired electrical properties.
Compositional design through A- and B-site ion replacement and microstructure control via grain boundary engineering yield enhanced dielectric, piezoelectric, and energy storage performance.
Advanced processing methods like hydrothermal synthesis and surfactant-assisted techniques enable high permittivity, robust breakdown strength, and multifunctionality for next-generation devices.

Lead-free dielectric materials are ceramic or thin-film systems characterized by the absence of toxic lead compounds, typically replacing Pb-based perovskite structures with environmentally benign alternatives. Modern research has focused on designing these materials for optimized dielectric, ferroelectric, piezoelectric, energy-storage, and electrocaloric functionalities, leveraging structural phase transitions, compositional disorder, and grain boundary engineering. The development and deployment of such materials are motivated by both regulatory pressures on toxic elements and demand for high-performance components in advanced electronic, energy storage, sensor, and actuator applications.

1. Compositional Design and Phase Evolution

A central aspect of lead-free dielectrics is the strategic substitution of A- and B-site ions in the perovskite ABO₃ lattice. Typical systems include BaTiO₃ variants with isovalent and aliovalent substitutions: Ba₁₋ₓCaₓTi₁₋ₓZrₓO₃ (BCZT) (Hanani et al., 2018, Hanani et al., 2018, Hanani et al., 2019, Hanani et al., 2020, Mezzourh et al., 2020, Lakouader et al., 2022, Khardazi et al., 2023, Ihyadn et al., 21 May 2024), BaTiO₃–Bi(Mg₁/₂Zr₁/₂)O₃ (Anand et al., 2013), NaNbO₃-based systems with Li and BaTiO₃ doping (Mitra et al., 2013, Mitra et al., 2014, Mitra et al., 2014), NBT-based relaxors modified by K/La (Verma et al., 2018), CaMnO₃ (Samantaray et al., 2022), and thin films such as NaNbO₃–BaHfO₃ (Dong et al., 2021). Substitutions (e.g., Ba²⁺ by Ca²⁺, Ti⁴⁺ by Zr⁴⁺ or Sn⁴⁺) are selected to tune the tolerance factor and induce morphotropic phase boundaries (MPB), which typically mark compositional regions with coexisting polymorphs and enhanced dielectric/piezoelectric response.

The formation and control of MPB—orthorhombic-tetragonal in BCZT (Hanani et al., 2020, Mezzourh et al., 2020, Khardazi et al., 2023) or tetragonal-cubic in BaTiO₃–Bi(Mg₁/₂Zr₁/₂)O₃ (Anand et al., 2013)—are achieved via compositional fine-tuning. Structural disorder, as seen in highly substituted (Ba,Ca)TiO₃–Bi(Mg,W)O₃ (Schulz et al., 2021) and Ba₁₋ₓLaxTi₀.₈₉Sn₀.₁₁O₃ (Khardazi et al., 11 Mar 2025), further induces relaxor ferroelectricity, allowing broad, thermally stable dielectric peaks and diffuse phase transitions quantified by a diffuseness exponent γ or y (from a modified Curie–Weiss law).

2. Microstructure Control and Grain Boundary Engineering

The dielectric and energy storage properties are deeply influenced by the ceramic’s grain size, distribution, and density. Methods such as surfactant-assisted solvothermal processing (CTAB/SDS) (Hanani et al., 2018), low-temperature hydrothermal synthesis (Hanani et al., 2018, Hanani et al., 2020), and the addition of low-permittivity glasses (Ihyadn et al., 21 May 2024) are employed to reduce grain size, enhance density, and suppress porosity.

For example, BCZT ceramics processed hydrothermally at 160 °C reveal a bulk density of 5.62 g/cm³ (97.1% theoretical) and εᵣ ≈ 12,085 at 1 kHz with tan δ = 0.017 (Hanani et al., 2020). Surfactant addition produces bimodal grain size distributions that increase densification and dielectric constant, with measured εᵣ values up to 9646 (Hanani et al., 2018). Glass additives (e.g., BaO–Na₂O–Nb₂O₅–WO₃–P₂O₅) can reduce average grain size to ~1.25 µm, slim hysteresis loops, and significantly enhance breakdown strength and recoverable energy density (Ihyadn et al., 21 May 2024).

3. Dielectric and Ferroelectric Properties: Diffuse Transitions and Relaxor Behavior

Lead-free dielectrics typically exhibit either normal or diffuse ferroelectric–paraelectric transitions. Diffuse phase transitions, often arising from compositional disorder and ionic size mismatches, are quantified by the exponent y in the relationship 1/(ε′ – ε′ₘ) = C⁻¹ (T – Tₘ)ʸ (Mitra et al., 2013, Anand et al., 2013, Khardazi et al., 11 Mar 2025). Values of y ≈ 1 indicate classical ferroelectricity, and y → 2 signals relaxor behavior, with intermediate values for diffuse transitions (e.g., γ = 1.34–1.98 in hydrothermal BCZT (Hanani et al., 2020), γ ≈ 1.68 in BaTiO₃–Bi(Mg₁/₂Zr₁/₂)O₃ (Anand et al., 2013), and y = 1.94 in BLTSn2.5 (Khardazi et al., 11 Mar 2025)).

Relaxor systems such as (Ba₀.₆Bi₀.₂Li₀.₂)TiO₃ (Borkar et al., 2016) and hexavalent-modified (Ba,Ca)TiO₃–Bi(Mg,W)O₃ (Schulz et al., 2021) display broad, frequency-dependent dielectric peaks, slim P–E loops, and frequency shifts described by the Vogel–Fulcher relation. Dielectric permittivities in high-performance BCZT can reach 16,310 (Mezzourh et al., 2020), and BLTSn2.5 yields up to 158.8 mJ/cm³ of recoverable energy density (Khardazi et al., 11 Mar 2025).

4. Energy Storage and Breakdown Strength

Optimized lead-free dielectrics demonstrate high recoverable energy densities, energy storage efficiency, and breakdown strength, critical for capacitor and power-electronics deployment. Energy density W_rec is calculated as ∫₍P_r₎^P_max E dP, and efficiency as η = (W_rec / W_total) × 100% (Khardazi et al., 2023, Khardazi et al., 11 Mar 2025, Ihyadn et al., 21 May 2024, Dong et al., 2021). In BCZT with glass additive, W_rec reaches 0.52 J/cm³ at 135 kV/cm and η = 62.4% (Ihyadn et al., 21 May 2024). BLTSn2.5 achieves η = 82.73% (Khardazi et al., 11 Mar 2025). Thin films, such as NaNbO₃–BaHfO₃, reach 23.1 J/cm³ at 1100 kV/cm with η = 66.2% (Dong et al., 2021).

Breakdown strength improves via microstructure refinement and compositional tuning; addition of BaHfO₃ to NaNbO₃ thin films enhances E_b by more than fourfold compared to pristine NaNbO₃ (Dong et al., 2021).

5. Electrocaloric and Multifunctional Effects

Electrocaloric response, essential for solid-state cooling, is characterized by the adiabatic temperature change ΔT, calculated by ΔT = – (T/(ρ Cₚ)) ∫ (∂P/∂T)_E dE (Hanani et al., 2019, Smail et al., 2020, Lakouader et al., 2022). BCZT ceramics show electrocaloric responsivity ζ = 0.164–0.42 K·mm/kV (Hanani et al., 2019, Lakouader et al., 2022), refrigeration capacity RC = 4.59 J/kg, and coefficient of performance COP = 12.38 (Lakouader et al., 2022).

Advanced functionality includes light-sensitive relaxor dispersion in BBLT (Borkar et al., 2016), magnetodielectric coupling in CaMnO₃-modified NBT (Samantaray et al., 2022), and tunable dielectric response through polar nanoregions (PNRs) and chemical inhomogeneity. Magnetodielectric constants MD% reach –3.69% at 100 kHz for optimized NBT–CMO compositions (Samantaray et al., 2022), highlighting prospects for multifunctional devices.

6. Key Characterization and Theoretical Models

The evaluation of dielectric and ferroelectric properties employs techniques such as X-ray and synchrotron diffraction, Raman spectroscopy, electron microscopy, impedance spectroscopy, and P–E loop tracing. Modeling frameworks include the Curie–Weiss and modified Curie–Weiss laws for transition analysis, Jonscher’s universal law for ac conductivity (Mitra et al., 2014), and Landau–Ginzburg–Devonshire (LGD) theory for energy density and ECE predictions (Ihyadn et al., 21 May 2024, Lakouader et al., 2022), where free energy is expressed as F = ½ aP² + ¼ bP⁴ and E(P) = aP + bP³.

Parameter extraction, such as activation energies (0.45–2 eV for grain/grain-boundary conduction (Khardazi et al., 2023)), diffuseness exponent γ or y, piezoelectric constants (d₃₃), and EC coefficients, provides quantitative guidance for materials optimization.

7. Applications and Future Prospects

Lead-free dielectric ceramics and thin films are increasingly adopted in high-energy density capacitors, multilayer ceramic capacitors (MLCCs), electrocaloric refrigeration, piezoelectric resonators, power electronics, sensors, and actuators. Compositions exhibiting high permittivity, low dielectric loss, broad temperature stability, rapid charge-discharge behavior, and enhanced breakdown strength are favored for energy storage and conversion technologies (Dong et al., 2021, Khardazi et al., 2023, Ihyadn et al., 21 May 2024, Khardazi et al., 11 Mar 2025).

Continued research aims to further optimize microstructure, composition, and phase boundaries, engineer multifunctionality (magnetoelectric and optoelectric coupling), and improve integration with microelectronic architectures. The focus remains on achieving operational reliability in harsh environments (e.g., automotive, aerospace), scalability, lead elimination, and regulation compliance.

The transition from classical ferroelectric to relaxor dielectrics—induced by compositional disorder and nanostructuring—enables the development of tunable materials with superior energy storage, thermal stability, and environmental safety, supporting next-generation dielectric applications across multiple sectors.