High-temperature Capacitors Research Articles

Tailoring breakdown strength and energy-storage performance of silicon-integrated lead-free epitaxial BZT thin films through multi-element B-site substitutions

Developing high-temperature dielectric thin films with high-performance energy-storage properties for harsh environment applications has received increased attention. Herein, a multi-element co-doping strategy is proposed to enhance the breakdown strength and energy storage properties of lead-free BaTiO3-based thin films, which were deposited on silicon substrates using pulsed laser deposition. Due to the difference in ionic radii and valence states between the multi-dopants and host Ti-cations, the local lattice distortion and local charged defects are induced, which results in the reduction in the size of polar nanoregions (PNRs) and weakened coupling interactions between these PNRs, thus achieving stronger breakdown strength (EBD). Accordingly, owing to an enhanced EBD of 7.8 MV/cm and a delayed polarization saturation, a superior recoverable energy-storage density (Ur) of 140.8 J/cm3 along with an excellent energy efficiency (η) of 93.2 % were achieved at room temperature in the multi-element doped Ba(Zr0.2Ti0.2Mn0.2Nb0.2Sm0.2)O3 (BZTMNS) thin film. Moreover, the BZTMNS thin film also exhibits an excellent Ur of 102.6 J/cm3, a good η of 86.4 %, and a high EBD of 6.6 MV/cm at an operating temperature of 200 °C. Additionally, a small fluctuation of Ur (-6.1 %) and η (-11.7 %) values can also be observed in BZTMNS thin film in high cycling endurance, up to 1010 cycles, even when operated at an elevated temperature of 200 °C. These findings in the BZTMNS thin film demonstrate a feasible way to design high-temperature capacitors for modern electronic devices for hybrid vehicles and underground oil/gas explorations.

Remarkably boosted high-temperature energy storage of a polymer dielectric induced by polymethylsesquioxane microspheres.

Polymer dielectrics are the key materials in next-generation electrical power systems. However, they usually suffer from dramatic deterioration of capacitive performance at high temperatures. In this work, we demonstrate that polymethylsesquioxane (PMSQ) microspheres with a unique organic-inorganic hybrid structure can remarkably enhance the energy storage performance of a typical high-temperature dielectric polymer polyetherimide (PEI). Compared with traditional ceramic fillers, there exists -CH3 on the surface of PMSQ microspheres, which results in good compatibility between PMSQ and PEI. In addition, the PMSQ microspheres with excellent insulating properties can effectively block the charge transport, yielding significantly enhanced breakdown and energy storage performance. Consequently, the PEI based composite film with 5 wt% PMSQ microspheres exhibits ultrahigh energy storage densities of 12.83 J cm-3 and 9.40 J cm-3 with an efficiency (η) above 90% at 150 °C and 200 °C, respectively, which are 10.5 and 50.5 times those of the pure PEI film. This work demonstrates that microspheres with an organic-inorganic hybrid structure are excellent candidates for enhancing the high-temperature performance of polymer dielectrics, and these PMSQ/PEI composite films have huge potential for application in high-temperature film capacitors.

Effect of A/B sites co-doping on the structure, electric and dielectric properties of CaTiSiO5 ceramics

Dielectrics with high permittivity and temperature stability are important for the development of high-temperature multilayer ceramic capacitors (MLCCs). In this study, Ca[Formula: see text]NaxTi[Formula: see text]NbxSiO5 (abbreviated as CTS[Formula: see text]NN) ceramics were prepared by solid-phase reaction method. The introduction of NN weakens the long-range ordered displacement of Ti, leading to a significant increase in the dielectric temperature stability. The CTS−2%NN samples exhibit high permittivity (53) and TCC [Formula: see text] ppm/∘C in the range of [Formula: see text]C to 300∘C. The CTS-based ceramics behave high dielectric temperature stability. In addition, the bandgap of the CTS-based ceramics increased significantly, which is favorable for improving the breakdown strength of the material. For [Formula: see text]% samples, the breakdown strength reaches 621[Formula: see text]kV/cm. Thus, the designed CTS-based dielectrics are promising for high-temperature capacitors.

Mechanical properties and first-principle calculation investigation of ZrHfNbTa series refractory high entropy alloys prepared by a combined process

ABSTRACT Refractory high-entropy alloys (RHEAs) are widely used in aerospace engine, gas turbine high-temperature components, capacitors and catalysis. The study presents a combined process for preparing ZrHfNbTa series RHEAs. HEAs powders were prepared from metal oxide by molten salt electro-deoxidation process, and the bulk HEAs were prepared by vacuum hot-pressing sintering process. The study aimed to explore the alloying mechanism of mixed metal oxide in molten salt electro-deoxidation process to optimise the properties. The hardness and wear resistance of the bulk alloy were tested. The test results show that the hardness of ZrHfNbTa and VZrHfNbTa bulk RHEAs prepared by this process is 1251 and 1603 HV. According to the friction surface characterisation of bulk alloy, VZrHfNbTa HEA has better wear resistance than ZrHfNbTa. Based on the first-principle calculation results, the doping of V element produces a strong hybridisation of electron orbitals in RHEAs, which can effectively improve the mechanical properties of RHEAs.

Alicyclic Polyimide With Multiple Breakdown Self-Healing Based on Gas-Condensation Phase Validation for High Temperature Capacitive Energy Storage.

Polymer dielectrics with combined thermal stability and self-healing properties are specifically desired for high-temperature film capacitors. The high thermal stability of conventional polymers benefits from the abundance of aromatic rings in the molecule backbone, but the high carbon content sacrifices their self-healing properties. Here, analicyclic polyimide with a high glass transition temperature (256°C) and wide energy bandgap (4.58eV) is designed, which exhibits electric conductivity more than an order of magnitude lower than that of classical polyimide at high electric fields and high temperatures. As a result, alicyclic polyimide achieves a discharged energy density of 4.54 Jcm-3 and a charge-discharge efficiency of above 90% at 200°C, which is superior to existing dielectric polymers and composites. The alicyclic polyimide benefits from a low pyrolytic residual carbon rate, retaining 93% of the dielectric breakdown strength after four electrical breakdown cycles. Distinguishing from the current condensed-phase self-healing concept, for the first time, exploring the self-healing capability of high-temperature polyimide dielectric is presented based on dual self-healing mechanisms of gas-phase and condensed-phase. The high energy density at high temperatures and the superior self-healing capability of alicyclic polyimide further indicate the promise of polyimide dielectric film capacitors for extreme conditions.

Effect of strain gradient and interface engineering on the high-temperature energy storage capacitors

The miniaturization and high integration of electronic devices pose new requirements for the energy storage density and high-temperature performance of dielectric capacitors. For thin film materials, internal stress and the interface layer often show a significant impact on their energy storage performance. Therefore, the capacitors with different stress gradient sequences and different periods were designed by BaHf0.17Ti0.83O3 (BHTO17), BaHf0.25Ti0.75O3 (BHTO25), and BaHf0.32Ti0.68O3 (BHTO32) to investigate the effect of stress gradient and interface engineering on the energy storage characteristics. Dielectric thin film structures with upward gradient, downward gradient, and periodic upward gradient (4N) were constructed. The study found that the upward gradient structure had higher breakdown field strength than the downward gradient structure. This is because the upward gradient structure can effectively extend the ending electric field of the Ohmic conduction mechanism and delay the activation electric field of the F–N tunneling mechanism. The 4N structure had a slightly higher breakdown field strength (reaching 9.22 MV/cm) compared to the pure upward gradient structure. The 4N structure thin film also exhibited higher energy storage density (115.44 J/cm3) and wide temperature (−100 to 400 °C) characteristics. These findings provide important guidance and application value for improving the energy storage characteristics of dielectric capacitors at high temperatures through structural design.

Alter the charge transport orientation of aromatic polyimide by induction effect to achieve superior high-temperature capacitance performance

Aerospace, electric vehicles, and other particular application scenarios place higher demands on the applicable electric field and temperature of capacitors. Polyimide, as the most ideal and widely studied high-temperature capacitor dielectric material, has poor insulation performance under extreme conditions. The main reason is that many conjugated π-bonds on its aromatic rings provide channels for the movement of free electrons, this phenomenon is more intense in high-temperature and high-field environments, which accelerates the high-temperature performance degradation of polyimide. Herein, we propose a molecular structure strategy to design high-temperature capacitance performance polymer dielectrics based on the induction effect. Both the experimental and density functional theory calculation results indicate that the polar functional groups -CF3 and –OCH3 can lead to a strong induction effect, which changes the direction of electron transport on the aromatic ring, serve to weaken the free-sharing ability of electrons in the conjugated π bond, increases the energy levels of PI and induces the formation of local deep traps in the polymer films, which significantly restrains charge carrier transport, ultimately improves the high-temperature capacitance property for aromatic polyimide. The resultant polymer film exhibits an excellent discharged energy density (Ud) of 7.9 J/cm3 at 150 °C and 810.3 MV/m. Meanwhile, it maintains excellent stability at over 100,000 fatigue tests and 500 MV/m. Hopefully, it will provide theoretical and technical support for developing high-performance capacitors.

Structure and dielectric spectroscopy of double perovskite La2-xPrxCoFe1-yMnyO6 system

Double perovskites have shown promise in the development of spin polarized conduction and ferromag semiconductors. In this category of double perovskite, we report on the lanthanum ferrocobaltite, co-doped with Pr and Mn. The polycrystalline ceramics were analysed for its structural properties by using Rietveld refinement of X-ray diffraction (XRD) and Raman spectroscopy measurements. The pristine and co-doped samples possess monoclinic structure with P21/n space group. In the pristine compound Co and Fe octahedra are ordered periodically which later gets distorted upon cationic substitution. Scanning electron microscopy (SEM) and energy dispersive spectra (EDS) reveals the grain morphology and elemental analysis. The samples were investigated for their dc and ac electrical responses. The two-probe dc resistance was measured from room temperature RT to 575 K. Dielectric spectroscopy in the RT to 650 K temperature range was performed in the frequency range of 50 kHz to 5 MHz. We observed that introducing Pr at La-site and Mn at Fe site creates structural disorder and tilt in octahedra which results in decreasing the dielectric constant at RT but increases significantly at higher temperature with low dielectric loss. ac conductivity was found to increase with increasing temperature indicating the thermally governed hopping mechanism. All these features validate their potential applications as a high temperature capacitor and can be widely used in automotive and aerospace domains for the storage device application.

Broad temperature range with stable permittivity and low dielectric loss in (1–2x)Na0.5Bi0.5TiO3-xNaNbO3-xGdFeO3 system

High-temperature capacitors have garnered increasing attention in current research due to the inability of commercially available capacitors to meet the evolving industry demands. In this study, a Na0.5Bi0.5TiO3 based ternary system, denoted as [(1–2x)(Na0.5Bi0.5TiO3) -x(NaNbO3) -x(GdFeO3): x=0.01–0.09], was synthesised through solid-state reaction route. The influence of NaNbO3 and GdFeO3 on phase structure, dielectric, and ferroelectric properties are investigated. A fall of polar R3c phase % from X-ray refinement studies, diminishing macroscopic polarization, increasing breakdown strength, and flattening of temperature-dependent dielectric permittivity curves are perceived with the increase of substituent concentration. Temperature stable permittivity of (1–2x)(Na0.5Bi0.5TiO3) -x(NaNbO3) -x(GdFeO3) calculated ε'r/ε'r [250℃] at 1, 10, 100, 500 kHz with 10 % tolerance. Remarkably, (Δε′/ε′250°C ≤ ± 10 %) with x = 0.07 and 0.09 showed stable permittivity in the wide temperature range of (30°C to 600°C) at 500 kHz and a minimal dielectric loss (tan δ ≤ 0.01) measured at 250°C makes it a promising candidate for high-temperature dielectric capacitor applications.

Doublet doped titanate ferroelectric system for capacitors and NTC thermistor applications

A simple negative temperature coefficient (NTC) thermistor Ba0.85Sr0.15Ti0.85Zr0.15O3 system is elaborated using a conventional solid-state reaction route. The structural analysis confirms that the elaborated pseudo-cubic system, which is indexed in the P4mm space group, exhibits one single phase. The dielectric properties and the electrical resistivity data are investigated over a large temperature range from 413 K to 673 K. In this temperature interval, the Steinhart–Hart equations are employed to confirm that Ba0.85Sr0.15Ti0.85Zr0.15O3 is a promising system for sensor application. Accordingly, the thermistor constant (β=10154 K), the sensitivity factor (-5.5 %/K≤α≤-2 %/K), the activation energy (Ea=0.875 eV), and the stability factor (SF=2.27) parameters are calculated to approve that Ba0.85Sr0.15Ti0.85Zr0.15O3 exhibits an NTC-thermistor behavior. The temperature dependence of the electrical resistivity confirms that Ba0.85Sr0.15Ti0.85Zr0.15O3 reveals a semiconductor behavior. The dielectric investigation shows that Ba0.85Sr0.15Ti0.85Zr0.15O3 exhibits a motivating dielectric properties (elevated dielectric constant value (105<ε’<106) and low dielectric losses (mostly < 0.007) with almost frequency independence between 20 Hz to 500 kHz). The colossal dielectric response of Ba0.85Sr0.15Ti0.85Zr0.15O3 is attributed to the internal barrier layer capacitor (IBLC) and the surface barrier layer capacitor (SBLC) effects. Such response suggests the suitability of Ba0.85Sr0.15Ti0.85Zr0.15O3 ceramic for high temperature capacitor applications.

High-temperature high-performance capacitive energy storage in polymer nanocomposites enabled by nanostructured MgO fillers

High-temperature high-performance polymer dielectric capacitors are essential for cutting-edge electronics and high-power systems operated in harsh environment conditions. Herein, dielectric composites comprising polyetherimide (PEI) polymers and easily prepared magnesium oxide (MgO) nanoparticles are fabricated by tape casting to promote capacitive performance at high temperatures. Benefiting from high-insulation behavior and wide bandgap of the MgO nanoparticles, the designed PEI nanocomposites deliver the significantly suppressed leakage current density and prominent enhancement of the breakdown strength, especially under high temperatures, the rationality of which is further revealed by finite element simulations on high-field distribution and electrical tree evolution. Accordingly, the nanocomposites containing ultra-low loading volume (0.5 vol%) MgO nanoparticles endow a large discharged energy density (~ 6.60 J cm−3) at 150 °C, which is ahead of most investigated 0–3 dielectric nanocomposites with inorganic fillers. Moreover, the excellent fatigue resistance at 150 °C is simultaneously achieved. This study demonstrates a practical route to develop scalable high-temperature polymer nanocomposite dielectrics blended with inorganic nanoparticles with superior capacitive performance, thus accelerating the development of dielectric polymer capacitors.

Enhanced energy density in cellulose doped polyimide-based all organic composites for high temperature capacitor applications

Abstract The growing demand for electronic devices has induced a significant requirement for high energy density capacitors. In this investigation, we introduced small groups of cyanoethyl cellulose (CEC) into a polyimide (PI) substrate to create all organic CEC/PI composite films for high energy density capacitor applications. Due to the large dipole moment in C–CN dipoles in CEC groups, the dielectric constant of the CEC/PI-5 (5% CEC) composite increased by 26.3% to 4.31. Compared to the pristine PI film at room temperature, the breakdown field of the CEC/PI-0.5 increased by 4.7% from 502.29 to 526.1 MV m−1 and the energy storage density increased by 95% to 11.70 J cm−3. Furthermore, the CEC/PI-0.5 film exhibited an energy density of 6.39 J cm−3 with the breakdown field of 400 MV m−1 at 150 °C, which is 93.05% higher in energy densities than that of the pristine PI film. Furthermore, simulation results indicate that CEC groups can introduce deep traps in the CEC/PI composite, which can inhibit charge movement in the composite and increase the breakdown field of it. In this study, it was found that by adding small amount of CEC polar group in PI film, the high temperature energy density of CEC/PI composite materials was significantly improved. This study not only makes a significant contribution to the development of high-temperature energy-density capacitors, but also pave a way by using small molecule polar polymers to improve the energy density of dielectric materials at high temperature.

Cost-effective strategy for high-temperature energy storage performance of polyimide nanocomposite films

The performance of most polymer-based film capacitors deteriorates severely at high temperatures, while high Tg polymer capacitors, despite their good performance at high temperatures, but their performance still decays severely after prolonged operation at high temperature. This study involves the deposition of a wide bandgap SiO2 inorganic layer on both surfaces of polyimide (PI) films using electron beam thermal evaporation. The findings indicate a substantial enhancement in the breakdown field strength and energy storage density of the composite films at elevated temperature following the deposition of the SiO2 inorganic layer. Specifically, a 100-nm-thick inorganic layer resulted in a breakdown field strength of 459.65 MV m−1 and an energy storage density of 3.2 J cm−3 at 150 °C. Subsequently, the polyimide film coated with a 100 nm SiO2 inorganic layer was infused with small quantities of SrTiO3 nanoparticles, leading to a breakdown field strength of 504.08 MV m−1 and an energy storage density of 6.75 J cm−3 and maintained an efficiency of 90.9 %. These results surpass the performance of the majority of high-temperature polymer films reported to date, with the inorganic layer deposited via electron beam thermal evaporation matching that of the costly magnetron sputtering method. The study presents a cost-effective method suitable for large-scale industrial production, significantly enhancing the electrical performance of PI at elevated temperatures and offering an economical solution for the commercialization of poly composite-based high-temperature capacitors.

Crystal Structure Modification and Dielectric Properties of Sr- and La-Containing A2B2O7 Thin Films for High-Temperature Operational Film Capacitors.

In order to obtain thermally stable thin-film materials with high dielectric constant, A2B2O7 thin films (Sr2Ta2O7, Sr2Nb2O7, La2Zr2O7, and La2Ti2O7) containing Sr or La and their solid solutions were grown on Pt/Ti/SiO2/Si substrates by RF sputtering and their crystal structures and dielectric properties were investigated. The Sr2Ta2O7 and La2Ti2O7 films exhibit highly oriented crystal structures. By contrast, the Sr2Nb2O7 and La2Zr2O7 films exhibit polycrystalline structures. The leakage properties of the Sr-containing films are lower and more stable in the high-temperature region (up to 300 °C) than those of the La-containing films. Among the investigated films, the Sr2Ta2O7 film grown at 500 °C and annealed at 900 °C shows the most stable dielectric constant with respect to temperature in the temperature range from room temperature to 300 °C. In addition, the xSr2Ta2O7-(1-x)La2Ti2O7 solid solutions exhibit enhanced dielectric properties at x = 0.35. The dielectric constant is greater than 100, and its variation with temperature is less than 10%. The Sr-containing A2B2O7 ferroelectric thin films have potential applications as high-temperature film capacitors that can operate at temperatures as high as 300 °C.

Unveiling high resistivity mechanism in (0.8-x)BaTiO3-0.2BiScO3-x(Bi0.5Li0.5)TiO3 ceramics with good dielectric temperature-stability

Focusing on the high resistivity together with low intrinsic conduction in BaTiO3–BiMeO3 materials, it can contribute to the development of reliable high-temperature capacitor materials. In this work, x(Bi0·5Li0.5)TiO3-(0.8-x)BaTiO3-0.2BiScO3 (where x ranges from 0 to 0.2) ceramics were fabricated by a solid reaction method. The temperature stability of dielectric permittivity and resistance are improved significantly by the introduce of (Bi0·5Li0.5)TiO3 (referred to as BL) compared to BaTiO3–BiMeO3. The composition discrepancy due to chemical inhomogeneity can be determined by SEM and EDS mapping although XRD exhibit a single perovskite phase. The characteristics of distinct conductivity behaviors in micro-regions was measured by kelvin probe force microscopy (KPFM). The non-stoichiometry gives rise to two kinds of defects for charge compensation: an ionic compensation and oxygen-vacancy compensation in different grains. The increase of the hopping activation energy of charged carries enhances the high-temperature resistance of the system. The sample of x = 0.15 shows very good temperature stability of dielectric permittivity in the temperature range from 200 °C to 400 °C, and that of x = 0.1 exhibits the highest resistivity of 3.6 MΩ cm at 570 °C. The proposed method gives an efficient strategy for improving the dielectric temperature stability and insulation by the special defect compensation in the perovskite oxides.

Superior dielectric energy storage performance for high-temperature film capacitors through molecular structure design

Film capacitors based on polymer dielectrics face substantial challenges in meeting the requirements of developing harsh environment (≥150 °C) applications. Polyimides have garnered attention as promising dielectric materials for high-temperature film capacitors due to their exceptional heat resistance. However, conventional polyimides with narrow bandgaps suffer from significant conduction loss at high temperatures and high electric fields. Here, we design and synthesize a series of modified polyimides featuring different saturated alicyclic structures on their main chains. Among these, the HBPDA-BAPB polyimide exhibits a superior discharged energy density of 4.9 J/cm3 with a high efficiency exceeding 95 % at 150 °C, outperforming other reported dielectric polymers and composites. The mechanism is attributed to the incorporation of elongated noncoplanar dicyclohexyl units into the backbones, which significantly reduces molecular conjugation, enhances the bandgap and suppresses leakage current. Our findings demonstrate the potential of modified polyimides with alicyclic structures as high-temperature dielectric materials for practical applications.

High-temperature dielectric nanocomposite film of 2D Bi4Ti3O12/ABS with excellent energy storage performance

The utilization of high-temperature dielectrics in capacitive energy storage is of great significance in contemporary electronic systems. Nevertheless, the thermal stability of most emerging polymers exhibits a significant decline in their energy storage capacity as temperatures rise. In this study, a unique type of 2D Bi4Ti3O12 nanofillers was synthesized in order to improve the breakdown strength. A nanocomposite consisting of Bi4Ti3O12/poly(acrylonitrile-butadiene-styrene) (ABS) was synthesized with the aim of attaining enhanced dielectric characteristics and energy storage density under elevated temperatures. The Bi4Ti3O12/ABS nanocomposites exhibited notable temperature stability in relation to their dielectric and energy storage capabilities across a temperature range spanning from room temperature to 120 °C. Ultrahigh discharged energy density (Ue) of 12.44 J/cm3 for 3 wt%- Bi4Ti3O12/ABS nanocomposites and high efficiency of 87 % under 550 MV/m were achieved at room temperature. An excellent Ue of 9.12 J/cm3 and high efficiency of 86.2 % for 3 wt%- Bi4Ti3O12/ABS nanocomposites were also observed in 3 wt%- Bi4Ti3O12/ABS nanocomposites under 450 MV/m at 120 °C, which was 117 % and 114 % of ABS films. These capacitive performances could match or be higher than previously reported values for high-temperature capacitor applications.

Side-Chain-Type Polyimide-Cu Complexes with Suppressed Activation Energy of Relaxation for Advanced High-Temperature Capacitor

Side-Chain-Type Polyimide-Cu Complexes with Suppressed Activation Energy of Relaxation for Advanced High-Temperature Capacitor

High temperature electrical breakdown and energy storage performance improved by hindering molecular motion in polyetherimide nanocomposites

Polyetherimide (PEI) is widely used as a material for high temperature and high power energy storage capacitors in new energy vehicles and other fields. However, as the temperature increases, the electrical conductivity increases and the breakdown strength decreases, which greatly reduces the energy storage density of the capacitor and limits the application range. In order to clarify the influence mechanism of high temperature on the breakdown and energy storage performance of dielectrics, this paper established a charge capture and molecular displacement (CTMD) breakdown model based on the expansion motion of molecular segments to study the charge transport and molecular chain motion process of PEI nanocomposites (PNCs) at high temperature. The results show that at 100 °C, compared with pure PEI, the internal maximum molecular displacement of PEI PNCs with appropriate doping content (3 wt%) is reduced by 28.79 %, and the breakdown strength is increased by 11.20 %. Appropriate nano-doping can effectively increase the movement difficulty of molecular chains and reduce the activation volume that provides energy for charge transport. Thus, charge transport is inhibited, current density is reduced, and Joule heat accumulation is avoided. Finally, the high temperature breakdown and energy storage performance are improved.

Structural origins of dielectric anomalies in the filled tetragonal tungsten bronze Sr2NaNb5O15

The tetragonal tungsten bronze, Sr2NaNb5O15, shows promise for application in high-temperature high-efficiency capacitors vital for the sustainable energy revolution. Previously, the structural complexity of this and related materials has obscured the mechanisms underpinning two large anomalies in relative permittivity (εr) which give rise to their exceptionally broad dielectric response. Here, we comprehensively investigate the structural evolution from −173 to 627 °C, combining electron, X-ray and neutron diffraction, electron microscopy, and first principles electronic structure calculations to unambiguously identify the structural origins of both anomalies. The peak in εr at 305 °C is associated with a polar-nonpolar phase transition, wherein cations displace along the c axis. Guided by DFT, we identify a further transition upon cooling, associated with the second peak at −14 °C, linked to the softening of an in-plane polar distortion with a correlation length limited by ferroelastic nano-domains arising from rigid-unit-like tilting of NbO6 octahedra at high temperature, imparting relaxor-like behaviour. Thus, the two dielectric anomalies in Sr2NaNb5O15 are associated with two distinct crystallographic phase transitions and their interplay with a microstructure that arises from a third, non-polar structural distortion. Chemical control of these will enable development of tuneable materials with dielectric properties suitable for high-temperature energy storage applications.