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Unveiling unusual coloration in amorphous phosphate pigments: a study inspired by the mineral Brazilianite
(2026-12-01)
Onoda, Hiroaki
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Higuchi, Kanata
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Charoonsuk, Thitirat
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Pulphol, Phieraya
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Muanglhua, Rangson
Brazilianite, with the formula NaAl<inf>3</inf>(PO<inf>4</inf>)<inf>2</inf>(OH)<inf>4</inf>, exhibits an intriguing pale yellow to green coloration, a phenomenon not readily explained by the absence of conventional d-block chromophoric metal ions. This study investigates the synthesis of amorphous phosphate-based pigments compositionally analogous to Brazilianite, aiming to replicate and understand the origin of its distinctive coloration through controlled precursor stoichiometry and thermal processing. Sodium, aluminum, and phosphate precursors were precisely mixed and thermally treated. X-ray diffraction (XRD) confirmed the predominantly amorphous nature of the synthesized materials, irrespective of achieving long-range crystalline order analogous to mineral Brazilianite. Despite this, samples processed at intermediate temperatures (e.g., 300–400 °C) exhibited a consistent yellowish hue. This non-conventional coloration, attributed to intrinsic electronic or structural features within the amorphous phosphate network rather than traditional chromophores, represents a significant scientific innovation. This coloration was found to be intrinsically linked to the phosphate network itself. Stability assessments in acidic (0.1 wt% H<inf>2</inf>SO<inf>4</inf>) and basic (0.1 wt% NaOH) environments revealed significant vulnerability, attributed to the facile dissolution of sodium and aluminum phosphate species. Notably, the yellowish coloration persisted across various Na/Al/P compositional ratios, even with systematic variations in aluminum or sodium content. This strongly suggests that the observed color is not critically dependent on a precise Na: Al stoichiometry but is fundamentally governed by the local electronic structure within the phosphate network, potentially involving defect centers or specific P-O-Al/Na linkages. These findings offer valuable insights into designing novel, non-toxic, color-stable pigments where coloration arises from mechanisms beyond traditional transition metal ion incorporation, highlighting the potential role of controlled disorder in phosphate-based materials for sustainable applications.
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Process-structure-property relationships in low-temperature microwave dielectric ceramics: from glass-assisted sintering to cold sintering for 5G/6G devices
(2026-12-01)
Pulphol, Phieraya
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Tang, Ying
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Fang, Liang
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Vittayakorn, Wanwilai
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Sukkha, Usa
With the rapid advancement of wireless communication from 5G to 6G, a pressing need has emerged for microwave dielectric ceramics with excellent performance at reduced processing temperatures, compatible with low-temperature co-fired ceramic technology. This review traces historical milestones and highlights modern design strategies for achieving optimum dielectric constant, ultra-low dielectric loss, and near-zero temperature coefficient of resonant frequency. Special emphasis is placed on recent advances in low-temperature densification routes, including sintering aids, intrinsically low-sintering-temperature ceramic families, and novel techniques like the cold sintering process. This review provides a critical analysis of the performance trade-offs inherent to each strategy, addressing the persistent challenges in achieving ultra-low loss. Furthermore, we highlight the paradigm shift toward a holistic, multifunctional design imperative for 6G systems. Finally, the transformative potential of cross-disciplinary approaches, particularly AI-assisted discovery, and computational modeling, is discussed as a key enabler for accelerating the design of next-generation, high-performance, and sustainable LTCC-compatible materials.
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Immobilized microalgae-driven triboelectric nanogenerators for sustainable bioelectricity production
(2026-12-01)
Kaja, Kushal Ruthvik
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Janpum, Chalampol
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Komkhum, Tanakit
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Hajra, Sugato
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Vivekananthan, Venkateswaran
Triboelectric nanogenerators (TENG) are emerging as promising solutions for decentralised energy generation due to the growing need for sustainable power sources. These devices convert wasted mechanical energy into electricity under ambient conditions, offering advantages such as eco-friendly operation, material versatility, and effective energy scavenging. Despite these benefits, their relatively low electrical output compared to conventional sources like batteries and fuel cells remains a limitation. Microalgae have attracted attention for their ability to produce bioelectricity through photosynthesis and respiration while simultaneously capturing carbon dioxide. Immobilising microalgal cells on conductive substrates improves electron transfer and metabolic activity. In this context, living Chlorella vulgaris TISTR 8580 with varied cell densities was immobilised on aluminium electrodes and incorporated into a TENG platform to explore energy harvesting from solid-solid and solid-liquid interactions. The highest output of 110 V and 330 nA was generated, confirming the microalgae as a promising tribolayer and extending the conventional triboelectric series. However, sustaining cell viability over extended periods remains a challenge, highlighting the need for optimised light and nutrient conditions in future developments.
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Enhanced densification and thermoelectric properties of Ca3Co4O9 ceramics fabricated by solid-state combustion and hot-pressing
(2026-11-15)
Thatawong, Bhoowadol
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Sriondee, Manlika
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Chongsatan, Wistsarut
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Palaporn, Dulyawich
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Pinitsoontorn, Supree
The Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> powders were synthesized by the solid-state combustion method and then calcined at 775-875 °C for 6 h. The combination of combustion-derived fine powders and hot pressing was adopted to improve the densification and thermoelectric (TE) performance of Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> ceramics. Dense Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> ceramics were subsequently fabricated by hot-pressing to investigate the influence of hot-pressing temperature (800-950 °C, 2 h) on phase formation, microstructure, electrical, and TE properties. The Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> powder was obtained after calcination at 800 °C for 6 h and exhibited an average particle size of 0.55 μm. XRD analysis confirmed that Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> was the predominant phase in all hot-pressed samples. XPS analysis further confirmed the presence of oxygen vacancy (V<inf>O</inf>++)-related defects and mixed-valence cobalt species. FESEM observations revealed a dense microstructure composed of plate-like grains with an average grain size ranging from 0.61 to 0.96 μm. The bulk density ranged from 4.31 to 4.46 g/cm3, indicating dense ceramics. The electrical resistivity (ρ) decreased with increasing measured temperature for all samples. Among all samples, the ceramic hot-pressed at 900 °C exhibited the lowest ρ at 600 °C. The Seebeck coefficient (S) significantly increased from 150 μV/K to 223 μV/K, while the thermal conductivity (κ) decreased with increasing temperature. Due to the favorable combination of low ρ and high S, the sample hot-pressed at 900 °C achieved the highest power factor (PF) and a maximum dimensionless figure of merit (ZT) of 0.17 at 600 °C.
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Integration of CCTAO/PDMS composite films into proximity capacitive sensor devices
(2026-12-01)
Bongkarn, Theerachai
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Panpho, Phakakorn
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Charoonsuk, Thitirat
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Vittayakorn, Naratip
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Pakawanit, Phakkhananan
Flexible capacitive proximity sensors are promising for contactless sensing applications, but their performance is strongly influenced by the dielectric properties and microstructure of the sensing layer. In this work, CaCu<inf>3</inf>Ti<inf>4-x</inf>A<inf>x</inf>O<inf>12</inf>/polydimethylsiloxane (CCTAO/PDMS, A = Nd3+ or Gd3+) composite films were developed as flexible dielectric layers for interdigitated capacitive proximity sensors. Nd- and Gd-doped CCTO ceramics were synthesized by a solid-state reaction method and incorporated into a PDMS matrix at different filler loadings. Structural analysis confirmed that the CCTAO ceramics retained the cubic CCTO phase after rare-earth substitution, while the composite films preserved the characteristic amorphous structure of PDMS with embedded ceramic fillers. The FESEM, EDS mapping and X-ray tomographic microscopy analyses showed that the CCTNdO/PDMS composite had a more uniform distribution of ceramic particles than the CCTO/PDMS system. The dielectric measurements demonstrated the improvement in the dielectric constant of the PDMS-based composites upon CCTNdO incorporation and also indicated that the composites did not exhibit any significant changes in their dielectric properties across the range of frequencies examined. The CCTNdO/PDMS films were found to show the negative capacitance response as a function of distance due to the electric-field shunting mechanism when used in an interdigitated capacitor sensor. The sensor with composition 10 wt% CCTNdO/PDMS had excellent performance with a maximum normalized capacitance change equal to −8.70%, which corresponds to a proximity sensitivity of around 0.42%/mm and an effective sensing range of around 20 mm. It is concluded that the optimization of the loading of the rare-earth material in a flexible PDMS matrix is an effective approach to achieve a compromise between the dielectric enhancement of the sensor and the dispersion of the filler and fringing-field interaction in the contactless capacitive proximity sensor.
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The opposing effect of gamma irradiation on proton and sodium ion conduction in Na2Ti3O7 and its defective analog
(2026-10-01)
Maluangnont, Tosapol
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Chaithaweep, Kanokwan
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Sangtawesin, Tanagorn
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Vittayakorn, Naratip
It is known that γ-irradiation of Na<inf>2</inf>Ti<inf>3</inf>O<inf>7</inf> induces Na + ion deintercalation, oxygen-vacancy formation, and proton/water incorporation, yielding the defective phase Na<inf>2- x </inf>H<inf>0.5 x </inf>Ti<inf>3</inf>O<inf>7-0.5 x </inf>(OH)<inf>0.5 x </inf> with multiple charge carriers. Although Na<inf>2</inf>Ti<inf>3</inf>O<inf>7</inf> is a well-studied ion conductor, charge-transport details in its γ-irradiated analogs remain limited. Here, we report their AC conductivity and dielectric properties under a temperature cycle (RT→350 °C→RT). Proton conduction dominates at ambient temperature but diminishes upon heating. This produces a dehydration-driven increase of resistivity known as the apparent Positive Temperature Coefficient of Resistivity (PTCR) effect, consistent with the Heywang model recently applied to water-adsorbing ceramics. Proton conductivity increases with γ-irradiation dose up to 200 kGy, then decreases at 400 kGy due to excessive structural disorder. At high temperatures, Na+ ion conduction prevails and follows Arrhenius behavior, with activation energy decreasing with dose. This discrepancy might be understood considering that Na+ ion conduction is governed primarily by its concentration rather than mobility; excessive doses lower activation energy but deplete Na+ ions and decrease conductivity. Dielectric-loss fitting using Jonscher's universal dielectric response (UDR) indicates that proton-transport pathways are sensitive to thermal history, whereas Na+ ion conduction exhibits low-frequency dispersion (LFD) across all conditions.
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Fabrication of BNBT-BS ceramics via a solid-state combustion approach for BNBT-BS/PDMS composite films in hybrid PENG/TENG applications
(2026-10-01)
Luangpangai, Anupong
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Apirattanon, Nattapong
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Yimsabai, Sununta
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Sumang, Rattiphorn
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Rittidech, Aurawan
Synthesis of (1-x)Bi<inf>0.47</inf>Na<inf>0.47</inf>Ba<inf>0.06</inf>TiO<inf>3</inf>-xBaSnO<inf>3</inf> ceramics (BNBT-xBS, where 0 ≤ x ≤ 0.05) was accomplished via a solid-state combustion approach. The influence of BaSnO<inf>3</inf> concentration on the phase structure, microstructure, dielectric, ferroelectric and strain properties was thoroughly examined. All specimens exhibited the coexistence of rhombohedral and tetragonal phases within a pure perovskite structure. The composition with x = 0.01 demonstrated optimal electrical properties, achieving a dielectric constant (ɛ<inf>m</inf>) of 6199, a maximum polarization (P<inf>max</inf>) of 41.86 μC/cm2, a maximum strain (S<inf>max</inf>) of 0.34% and a normalized strain (d<inf>33</inf>*) of 489 pm/V. The ceramic powder of BNBT-0.01BS was incorporated into a PDMS matrix at concentrations ranging from 0 to 30 wt%. The hybrid PENG/TENG devices achieved their largest electrical output at a BNBT-0.01BS loading of 20 wt%, recording a voltage of 92 V and a current of 0.50 μA. This work outlines a fabrication and development method for composite films with BNBT-0.01BS with PDMS polymers for high-efficiency nanogenerators, playing an important role in improving future energy harvesting technologies.
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Kinetic analysis of liquid–solid contact electrification: Using adsorption models as mechanistic probes for hybrid EDL behavior
(2026-08-01)
Chaithaweep, Kanokwan
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Pharino, Utchawadee
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Pongampai, Satana
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Sriphan, Saichon
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Charoonsuk, Thitirat
Liquid–solid interfaces are central to technologies ranging from energy storage to triboelectric nanogenerators (TENGs). Whereas classical electric double layer (EDL) theory describes these interfaces mainly in terms of electrostatic ion adsorption, hybrid EDL concepts suggest that interfacial electron transfer may also contribute importantly to charge generation. However, the hybrid EDL model has so far been discussed primarily at a qualitative level or through complex theoretical and computational treatments, and a simple, experimentally accessible macroscopic kinetic handle that can discriminate, in operando, between adsorption‑dominated and ET‑influenced regimes remains lacking. By analyzing high-resolution charging dynamics over systematically varied H₂SO₄ and HNO₃ concentrations, a clear concentration-dependent kinetic transition is identified. At low ionic strengths, the charging process is described more effectively by pseudo-second-order (PSO) kinetics, consistent with a reaction-influenced interfacial step, whereas at higher concentrations the system becomes pseudo-first-order (PFO) dominated, consistent with transport- and ion-screening-controlled behavior. Although previous studies have provided compelling theoretical and spectroscopic evidence that interfacial electron transfer contributes to liquid–solid contact electrification in TENGs, these mechanisms have rarely been examined through such simple macroscopic kinetic formalisms. In this work, classical adsorption kinetic models are used as operational probes for distinguishing electron-transfer-influenced regimes from ion-transport-dominated regimes at PTFE/liquid interfaces. The PSO-to-PFO crossover reported here is interpreted within the hybrid EDL framework as a kinetic marker of a transition from an electron-transfer-influenced charging regime at low concentration to an ion-transport- and screening-dominated regime at high concentration, thereby demonstrating how adsorption kinetics can serve as a practical diagnostic language for liquid–solid triboelectric systems.
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Interfacial field-driven self-poling in a lead-free P(VDF–TrFE)/BCZT nanogenerator: achieving high-performance energy harvesting via percolation-optimized dielectric coupling
(2026-07-23)
Ukasi, Sirinya
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Triputtikun, Jakkrit
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Sae-tang, Chanachot
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Sumang, Rattiphorn
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Panpho, Phakakorn
Achieving spontaneous dipole alignment without external poling remains a grand challenge in developing high-performance ferroelectric nanogenerators. This work reports a self-poling mechanism driven by engineered interfacial fields at the polymer–ceramic junction. By embedding lead-free Ba<inf>0.85</inf>Ca<inf>0.15</inf>Zr<inf>0.1</inf>Ti<inf>0.9</inf>O<inf>3</inf> (BCZT) crystals into a P(VDF–TrFE) matrix, we create strong localized electric fields that promote unidirectional dipole orientation, thereby eliminating the need for conventional electrical poling procedures. The resulting hybrid piezo-triboelectric nanogenerator (H-PTENG), optimized at a 1 wt% BCZT loading, exhibits remarkable energy-harvesting performance with a high open-circuit voltage (∼173.4 V), short-circuit current (∼5.23 µA), and power density (∼182 µW cm−2), outperforming most lead-free counterparts. This dielectric percolation-like optimum maximizes the dielectric–ferroelectric coupling mediated by Maxwell–Wagner–Sillars interfacial polarization, simultaneously enhancing piezoelectric and triboelectric outputs while preserving low dielectric loss. The device also demonstrates robust mechanical durability (>10 000 bending cycles) and retains usable output under varying humidity and temperature conditions, although its performance is reduced at ultra-high relative humidity due to water-induced charge dissipation. Its real-world applicability is confirmed by directly powering commercial electronics, including 82 LEDs, a digital wristwatch, an electronic scoreboard, and a Bluetooth-enabled humidity–temperature sensor. Collectively, this work establishes a scalable, lead-free, and poling-free design paradigm based on interfacial field engineering for next-generation flexible, self-powered electronic systems.
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The Y3+ Donor-Doped CCTO (Ca0.95Y0.05Cu3Ti4O12) Dielectric Fillers for Electrical Output Enhancement of Flexible Triboelectric Nanogenerator
(2026-06-03)
Saichompoo, Kittipan
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Rattanawongwiboon, Thitirat
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Kingkam, Wilasinee
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Pakawanit, Phakkhananan
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Sukkha, Usa
The escalating wearable electronic devices with their flexible energy sources demand has rendered the imperative scientific challenge on the development of materials for the flexible triboelectric nanogenerators (F-TENG), one of advanced energy harvesting systems. Dielectric material optimization, the Y3+ donor-doped calcium copper titanate based on exactly stoichiometric Ca<inf>0.95</inf>Y<inf>0.05</inf>Cu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf> (CCTYO), serves as a critical pathway in this work for achieving enhanced F-TENG via compositing with the polydimethylsiloxane (PDMS) polymer. The enhancement of electrical output has garnered substantial interest owing to its increased relative permittivity ((Formula presented.)). The influence of the loaded CCTYO amounts on structure, morphologies, dielectric properties, and electrical output, including open-circuit voltage (V<inf>OC</inf>), short-circuit current (I<inf>SC</inf>) and power density for PDMS/CCTYO composites is investigated. As compared with loading undoped CCTO, the additional Y3+ can improve higher F-TENG output by increasing the (Formula presented.) along with maintaining the loss tangent (tan δ < 0.02) at optimized condition. The appropriate amounts of CCTYO 0.75 wt% make the PDMS/CCTYO F-TENG to achieve V<inf>OC</inf> of ∼76.4 V (8.5 V/cm2) and I<inf>SC</inf> of ∼130.0 μA (14.4 μA/cm2), which were higher than pristine PDMS for 2.7 and 4.3 times. The power density of 53 µW/cm2 is 8.9 times higher than that of 6.3 µW/cm2 from the pristine PDMS. This study also provides a COMSOL multiphysics simulation, bridging laboratory experiments, for quantifying the triboelectric capability of dielectric materials.

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