The study, published in the Journal of Materials Science by Shuai Zou, Xiaoyu Song, Yaohang Gu, Xiaoyan Zhang, and Xiwei Qi, centers on sodium niobate, NaNbO3, a perovskite ceramic that has emerged as one of the most promising lead-free candidates for dielectric energy storage. Sodium niobate is attractive for several reasons. It is environmentally benign, it exhibits antiferroelectric-like behavior in which neighboring electric dipoles point in opposite directions, and it can deliver high recoverable energy density with excellent charge-discharge performance. When an electric field is applied, those anti-aligned dipoles can be coerced into alignment, and when the field is removed they snap back, releasing stored energy quickly and with minimal loss. That snap-back is precisely what a pulsed power capacitor needs.

But sodium niobate has a stubborn weakness that has kept it out of real-world products: thermal instability. The material undergoes a series of structural phase transitions as temperature changes, and each transition shifts its dielectric response. In practical terms, the capacitance of pure NaNbO3 varies by more than 50 percent across the temperature window from minus 50 to plus 150 degrees Celsius, a swing far too large for commercial electronics, which typically demand that capacitance stay within 15 percent of its room-temperature value. A capacitor that drifts wildly as a device heats up or cools down cannot be trusted in an automotive engine bay, an aircraft avionics bay, or even a laptop that warms under load.

The team’s solution draws on one of the hottest ideas in modern materials science: high-entropy design. Rather than doping sodium niobate with a single additive, the researchers composited it with a five-component rare-earth modified bismuth ferrite, (Bi0.2La0.2Y0.2Dy0.2Tb0.2)FeO3, abbreviated BLYDTF. In this phase, five different cations share the same crystallographic site in nearly equal proportions, creating a chemically disordered lattice in which no single element dominates. High-entropy oxides of this kind were first demonstrated a decade ago, and they have since been shown to flatten temperature-dependent properties, because the disorder smears out the sharp phase transitions that plague conventional compounds. Bismuth ferrite itself brings a very high Curie temperature, meaning its ferroelectric ordering persists to extremely high temperatures, providing a thermally robust backbone for the composite.

The researchers synthesized a series of ceramics with the general formula (1-x)NaNbO3-xBLYDTF, where x ranged from 0 to 0.15, and systematically evaluated their energy storage behavior. The results were striking. The optimized composition achieved a recoverable energy density of approximately 4.1 joules per cubic centimeter at an electric field strength of 510 kilovolts per centimeter. To put that number in perspective, recoverable energy density is the figure of merit that determines how much usable energy a capacitor can deliver per charge cycle, and values above 4 joules per cubic centimeter in a lead-free bulk ceramic place this material firmly among the competitive candidates for next-generation pulsed power capacitors.

Speed matters just as much as capacity, and here the material truly shines. The researchers measured a discharge time constant, denoted t0.9, of only 40 nanoseconds, meaning the ceramic can release 90 percent of its stored energy in 40 billionths of a second. That kind of ultr fast discharge is essential for pulsed power applications such as electromagnetic launchers, high-power microwave sources, defibrillators, and precision laser systems, where energy must be dumped almost instantaneously. Slow capacitors simply cannot serve these roles, no matter how much energy they hold. The combination of high density and nanosecond-scale release in a lead-free, thermally stable package is what makes this work notable.

The temperature stability results are arguably the headline achievement. The temperature coefficient of capacitance, or TCC, quantifies how much capacitance drifts as temperature changes, and industrial specifications known as EIA codes define acceptable limits. The X7R designation, one of the most widely used standards in the capacitor industry, requires capacitance to remain within plus or minus 15 percent of its 25-degree-Celsius value across the range from minus 55 to plus 125 degrees Celsius. The composite ceramic developed by the team fully satisfies the X7R specification, a milestone that pure sodium niobate cannot approach. Meeting X7R means the material is no longer a laboratory curiosity but a genuine candidate for multilayer ceramic capacitor manufacturing, where X7R-class dielectrics dominate the mid-capacitance market.

Underlying these headline numbers is a subtle microstructural story. Introducing the high-entropy bismuth ferrite phase into the sodium niobate matrix disrupts the long-range antiferroelectric order of the host, breaking large domains into smaller polar regions and introducing local random fields that make the material behave more like a relaxor ferroelectric. Relaxors respond to electric fields with slim, low-loss hysteresis loops, which means less energy is wasted as heat during each charge-discharge cycle and more of the stored energy is actually recoverable. The chemical disorder also tends to improve breakdown strength, since randomly distributed local structures impede the growth of the conductive pathways that lead to catastrophic dielectric failure at high fields. The 510 kilovolts per centimeter field the material withstands reflects that improvement directly, because recoverable energy density scales with the square of breakdown field.

The broader significance of the work lies in its design philosophy. Instead of searching for a single magic composition, the team combined two complementary strategies: a lead-free antiferroelectric host with intrinsically high energy storage potential, and an entropy-stabilized partner phase that suppresses thermal drift while introducing beneficial polar disorder. This compositing approach, sometimes described as high-entropy modulation of a conventional ferroelectric, has gained momentum across the field, with recent studies in Science and Nature Materials reporting ultrahigh energy storage in entropy-engineered ceramic capacitors. The present work extends that strategy to the sodium niobate family specifically with an eye on industrial temperature standards, bridging the gap between record-setting laboratory results and the reliability requirements of commercial components.

Challenges remain before such ceramics reach production. Multilayer capacitor manufacturing requires co-firing the dielectric with inexpensive base-metal electrodes at controlled temperatures, and the long-term reliability, fatigue behavior, and scalability of high-entropy composites must be validated under industrial conditions. Nevertheless, the demonstration that a lead-free sodium niobate-based ceramic can simultaneously deliver roughly 4.1 joules per cubic centimeter of recoverable energy, 40-nanosecond discharge, and full X7R compliance marks a meaningful step toward capacitors that are simultaneously powerful, fast, tough, and free of toxic lead. As portable electronics proliferate and pulsed power systems multiply, materials like this one may quietly become the unsung workhorses of the electrified world.

Subject of Research: Lead-free NaNbO3-based high-entropy composite dielectric ceramics for temperature-stable capacitive energy storage

Article Title: Design of an X7R-type NaNbO3-based energy storage ceramic by compositing with (Bi0.2La0.2Y0.2Dy0.2Tb0.2)FeO3

Article References: Zou, S., Song, X., Gu, Y., Zhang, X., & Qi, X. (2026). Design of an X7R-type NaNbO3-based energy storage ceramic by compositing with (Bi0.2La0.2Y0.2Dy0.2Tb0.2)FeO3. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13641-8

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13641-8

Keywords: sodium niobate, NaNbO3, energy storage ceramics, dielectric capacitors, high-entropy materials, bismuth ferrite, X7R standard, lead-free perovskites, relaxor ferroelectrics, pulsed power, temperature stability, recoverable energy density

The material at the center of the study is a glass-ceramic based on the PSBNT system, a lead-containing niobate-titanate composition that crystallizes into what researchers call tetragonal tungsten bronze niobate, a crystal structure prized in dielectric applications. Glass-ceramics like this are made by preparing a glass, crystallizing it into a ceramic phase, and then sintering the resulting powder into a dense solid. The problem has always been that sintering these niobate-based powders requires high temperatures, and high temperatures bring unwanted consequences: exaggerated grain growth, evaporation of volatile components such as lead, and porosity that undermines both dielectric performance and electrical breakdown strength. The team, led by Yunhe Yi of Northeastern University in Shenyang together with colleagues from the GRINM Group, GRIMAT Engineering Institute, the General Research Institute for Nonferrous Metals, and the Shanghai Institute of Ceramics, attacked this problem with a sintering aid called PZABS glass, a low-melting additive designed to soften and flow well below the temperature at which the main ceramic phase would normally densify.

The manufacturing route is as important as the chemistry. Rather than pressing dry powder into pellets, the researchers used tape casting, a scalable industrial process in which the powder is mixed with solvents, binders, and plasticizers into a slurry and spread into thin, uniform sheets. Tape casting is the same technique used to fabricate multilayer ceramic capacitors, where hundreds of thin dielectric layers are stacked and co-fired together. That connection matters because any improvement demonstrated in a tape-cast system translates more directly to real capacitor manufacturing than results obtained on conventionally pressed bulk ceramics. Prior work in the field, including studies on binder burnout shrinkage and compaction in multilayer capacitor fabrication, has shown how sensitive the final microstructure is to the details of this processing chain, which is precisely why the authors chose to investigate densification behavior in a tape-cast format.

The central variable in the experiments was the amount of PZABS glass added to the PSBNT powder, and the results traced a classic goldilocks curve. With no additive or too little of it, the ceramic particles sintered sluggishly, leaving pores scattered through the microstructure. As the glass content rose, the liquid phase formed during firing filled the gaps between particles, lubricated their rearrangement, and accelerated mass transport, driving the density up and the porosity down. At an addition of just 2 weight percent PZABS, the glass-ceramic reached its best state: a density of approximately 4.84 grams per cubic centimeter and a porosity of only about 0.30 percent, remarkably low numbers for a sintered niobate glass-ceramic. The liquid glass essentially acted as a transient glue, wetting the particle surfaces and pulling the compact together before it crystallized or vaporized away.

But the story turns when the glass dose climbs further. At 6 weight percent PZABS and above, the researchers observed the precipitation of a secondary phase, lead niobate-titanate with the formula Pb2(Nb0.67Ti0.33)2O6.67, alongside the dominant tetragonal tungsten bronze phase and minor silica. Excess glass also worsened densification rather than helping it, a counterintuitive result that the authors attribute to the way too much liquid phase disrupts the sintering balance, promoting secondary crystallization and degrading the microstructural uniformity that dense ceramics require. In other words, the sintering aid is a tool with a narrow effective window: enough to flow and fill pores, but not so much that it changes the phase chemistry of the material. This densification-versus-phase-stability tradeoff is a recurring theme in glass-assisted sintering, and the study quantifies it cleanly for this system.

The dielectric measurements tell the practical story. The optimally doped 2 weight percent sample achieved a relative dielectric permittivity of about 949, a high value that reflects both the intrinsic polarizability of the tungsten bronze niobate crystals and the near-absence of porosity, since air-filled pores dilute permittivity and concentrate electric fields. Just as importantly for energy storage, the sample withstood a breakdown strength of roughly 220 kilovolts per centimeter. Breakdown strength is the ceiling on how much voltage a capacitor can take before it fails, and dense, pore-free microstructures are the key to raising it, because pores and defects act as failure initiation sites. Combining high permittivity with high breakdown strength is the central balancing act of dielectric energy storage research, since the stored energy density scales with the square of the breakdown field.

Those two quantities together delivered the headline numbers of the study: a maximum energy density of 1.03 joules per cubic centimeter and a recoverable energy density of 0.82 joules per cubic centimeter. The gap between the two reflects hysteresis losses in the ferroelectric response, energy that is dissipated as heat rather than returned during discharge, and minimizing that gap is what efficiency means in this context. The researchers also tracked how the additive changed the character of the polarization response. Increasing PZABS content enhanced the relaxor behavior of the glass-ceramic, with the diffuseness exponent gamma rising from 1.81 to 1.96. Relaxor ferroelectrics have smeared-out, frequency-dependent transitions and slim polarization loops, which generally means lower hysteresis loss and better energy-storage efficiency, so the shift toward stronger relaxor character is a meaningful microstructural lever, not just a curiosity.

Placed in context, the work connects to a broad and active effort across the ceramics community to use glass additives as sintering accelerants and property modifiers. Previous studies have employed calcium-aluminosilicate glasses in strontium barium niobate ceramics, phosphorus pentoxide doping to enhance densification of SrO-BaO-Nb2O5-SiO2 tungsten bronze glass-ceramics, and zinc-bismuth-silicate glasses in barium titanate systems, while low-temperature co-fired ceramic technology has long relied on glass phases to bond ceramic layers at reduced temperatures. What distinguishes the new study is the combination of a deliberately low-melting PZABS glass, a tape-casting route compatible with multilayer device fabrication, and a systematic mapping of how additive content controls the full chain from thermal behavior and phase evolution to microstructure and final dielectric and ferroelectric performance. The authors also situate their findings within recent work on defect engineering and crystallization control in glass-ceramics, where managing the defects formed during crystallization has emerged as a parallel strategy for boosting energy storage.

There are honest caveats. The material contains lead, which raises environmental and regulatory questions in commercial electronics, even as much of the field pushes toward lead-free alternatives such as sodium niobate and bismuth-based systems. And an energy density of about one joule per cubic centimeter, while respectable for a sintered glass-ceramic, remains below the targets for the most demanding pulsed-power applications, where researchers pursue several joules per cubic centimeter through strategies like configurational entropy tuning and viscous polymer processing. The value of this study lies less in a record number and more in the demonstration of a controllable, industrially relevant processing knob: a two-weight-percent glass addition that simultaneously maximizes density, preserves the desired crystal phase, and tunes the relaxor response. The work was supported by the Beijing Natural Science Foundation, and the corresponding authors are Qingmeng Zhang and Zheng Lu.

For engineers designing the next generation of capacitors, the message is that sintering aids deserve the same careful optimization as the ceramic chemistry itself. The difference between the best and worst formulations in this study was only a few weight percent of glass, yet it separated a dense, high-permittivity, high-breakdown material from a porous one littered with secondary phases. As demand grows for compact, efficient energy storage in electrified transport and renewable power systems, such processing-level insights, validated in tape-cast form factors that mirror real device fabrication, are exactly the kind of incremental but transferable knowledge that moves dielectric materials from laboratory promise toward manufacturing reality.

Subject of Research: Low-melting glass-assisted sintering of PSBNT niobate glass-ceramics for dielectric energy storage

Article Title: Low-melting glass-assisted sintering of PSBNT glass-ceramics: densification, microstructure evolution and dielectric properties

Article References: Yi, Y., Chen, J., Zhao, Y., Zhou, M., Zhang, Q., & Lu, Z. (2026). Low-melting glass-assisted sintering of PSBNT glass-ceramics: densification, microstructure evolution and dielectric properties. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13841-2

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13841-2

Keywords: glass-ceramics, sintering, tape casting, dielectric materials, energy storage, tungsten bronze, relaxor ferroelectrics, sintering aids, porosity, breakdown strength, capacitors, materials science

The electrocaloric effect, or ECE, is deceptively simple in principle. When an electric field is applied to a dielectric material, its internal polarization increases, which reduces the entropy of the dipoles that make up that polarization. Because the total entropy of the material must be conserved when the field is applied adiabatically, the temperature of the material rises. Remove the field and the temperature drops again. This reversible temperature change, typically a few degrees in favorable materials, forms the basis of an entirely solid-state refrigeration cycle. In the cycle described in the review, the material first absorbs heat from a load while cold, is isolated and heated by the field, dumps that heat to a sink, and then cools again when the field is removed. This Brayton-type cycle repeats continuously, with no moving fluids and no greenhouse gases.

The phenomenon itself is far from new. The concept dates to 1878, and Kobeco and Kurtschatov first quantified it experimentally in 1930 in Rochelle salt. For decades, however, the observed temperature changes hovered around one degree Celsius, far too small for practical refrigeration. Early research focused on lead-based ferroelectric compounds, which delivered the strongest responses, including a landmark 12-degree temperature change in thin films of lead zirconate titanate reported in 2006. But lead-based materials carry serious liabilities: they are toxic, thermally unstable under prolonged heating, difficult to fabricate into devices, expensive to produce, and prone to polarization fatigue. European hazardous substance regulations have effectively mandated a search for alternatives, and that search now defines the field.

The review, authored by Sana Ullah, Hassan Raza, Awais Akhtar, Guangping Zheng, and Abhijit Pramanick, systematically catalogs the lead-free families now under investigation, from bulk ceramics and single crystals to thin films, multilayer structures, and polymers. Among bulk ceramics, barium titanate stands out as the workhorse. Reported ECE strength reaches 0.48 kelvin centimeters per kilovolt, with a maximum temperature change of 4.8 degrees under a field of 10 kilovolts per centimeter at 136 degrees Celsius. Substituting strontium into barium titanate to form barium strontium titanate allows researchers to tune the Curie temperature and broaden the operating window, though excessive strontium content actually suppresses the electrocaloric response, a reminder that compositional engineering is a delicate balancing act.

Doping strategies have proven especially powerful. Manganese-doped barium strontium titanate ceramics fabricated by spark plasma sintering achieved an entropy change of 4.77 joules per kilogram-kelvin, roughly 45 percent higher than undoped equivalents, thanks to dramatically improved electrical resistivity. Bismuth sodium titanate based compositions offer a different route: in these materials, applied fields induce transitions between ferroelectric and antiferroelectric states, and the resulting structural rearrangements produce substantial cooling. Bismuth sodium titanate barium titanate ceramics delivered a 2.1-degree temperature change under 60 kilovolts per centimeter, while barium calcium zirconium titanate ceramics, notable for their slim hysteresis loops, showed consistent electrocaloric behavior across a remarkably wide temperature range from about 28 to 105 degrees Celsius.

The review also highlights exciting developments in low-dimensional and hybrid materials that suggest the field is expanding well beyond classical ceramics. The layered van der Waals ferroelectric copper indium phosphorus sulfide, CuInP2S6, exhibits an entropy change of about 5.8 joules per kilogram-kelvin and a 3.3-kelvin temperature change near 315 kelvin under modest fields, demonstrating that two-dimensional ferroelectrics can deliver meaningful electrocaloric effects at room temperature. Scanning electrocaloric thermometry has even resolved local cooling in atomically thin indium selenide crystals. Layered organic-inorganic hybrid perovskites, typically studied for optoelectronics, have joined the club: one lead-containing hybrid chloride compound showed an 11-kelvin electrocaloric temperature change near ambient conditions, opening a new design space where molecular and inorganic sublattices can be engineered independently.

Films and multilayer architectures represent the pragmatic path toward devices, because thin geometries tolerate electric fields hundreds of times stronger than bulk ceramics can survive. Thin films of barium titanate have reached electrocaloric changes of nearly 12 degrees, rivaling lead-based analogues. Strontium bismuth tantalate films, measured for the first time for giant ECE, delivered 4.93 degrees at 600 kilovolts per centimeter. Perhaps most striking, bilayer thin films combining barium zirconium titanate and bismuth sodium titanate barium titanate produced a temperature change of roughly 23 kelvin near room temperature under a moderate field, attributed to interface-charge engineering between the two layers. Multilayer stacks with internal electrodes push further still: barium titanate multilayers reached 4 degrees at 352 kilovolts per centimeter in direct measurements, exceeding thermodynamic predictions, while eco-friendly bilayer thick films of barium zirconium titanate stacked on barium tin titanate achieved about 5.2 kelvin with an entropy change of 6.9 joules per kilogram-kelvin near zero degrees Celsius.

Polymers occupy the opposite end of the flexibility spectrum and may prove equally transformative. Polyvinylidene fluoride based copolymers and terpolymers, including P(VDF-TrFE) and its chlorofluoroethylene-modified terpolymer, exhibit giant electrocaloric responses, with copolymer films reaching 35 degrees at 1800 kilovolts per centimeter near a first-order ferroelectric transition, and Langmuir-Blodgett grown films recording up to 21 degrees. Nanocomposites push performance further: adding boron nitride nanosheets and barium strontium titanate nanostructures to a terpolymer matrix produced a colossal 50.5-degree temperature change at 2500 kilovolts per centimeter, while two-dimensional graphitic carbon nitride fillers enabled strong negative electrocaloric effects useful for heating-to-cooling switching. The review cautions, however, that indirect ECE estimates via Maxwell relations can seriously mislead in relaxor polymers, where polar nanoregions and non-ergodic dynamics violate the equilibrium assumptions underlying the equations, sometimes understating the true response by large margins.

Complementing the experimental landscape, the review surveys the theoretical machinery now guiding design, including Landau-Ginzburg-Devonshire phenomenology, phase-field simulation, and first-principles molecular dynamics. These tools have explained how clamping, misfit strain, domain structure, and surface effects modulate electrocaloric response, predicted giant effects in ferroelectric nanotubes and tunnel junctions, and revealed the coexistence of positive and negative electrocaloric regimes within single materials. The remaining hurdles are sobering: most high-performance materials still require fields far above what consumer electronics can supply, cooling peaks occupy narrow temperature windows, and long-term reliability under cyclic operation remains unproven at scale. Yet the trajectory is unmistakable. With compositional engineering, defect control, and multilayer architectures steadily lowering the field thresholds, and multifunctional designs that couple cooling with energy storage now emerging, lead-free electrocaloric materials are moving from laboratory curiosities toward the practical, compact, and genuinely green cooling systems that a warming world urgently needs.

Subject of Research: The electrocaloric effect in lead-free ferroelectric materials for solid-state cooling applications

Article Title: A comprehensive review of the electrocaloric effect in lead free ferroelectrics for solid state cooling

Article References: Ullah, S., Raza, H., Akhtar, A., Zheng, G., & Pramanick, A. (2026). A comprehensive review of the electrocaloric effect in lead free ferroelectrics for solid state cooling. Discover Industrial Chemistry and Materials, 1(1), Article 2. https://doi.org/10.1007/s44508-026-00001-2

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00001-2

Keywords: electrocaloric effect, solid-state cooling, lead-free ferroelectrics, barium titanate, relaxor ferroelectrics, ferroelectric polymers, PVDF copolymers, multilayer ceramics, phase transitions, Maxwell relations, refrigerant-free refrigeration, energy efficiency