Low-temperature Phase Transition Research Articles

Two-Step Chemical Vapor Deposition for Fabrication of FAPbI3 Single-Crystal Microsheets with High Exciton Binding Energy.

Hybrid perovskites exhibit highly efficient optoelectronic properties and find widespread applications in areas such as solar cells, light-emitting diodes, photodetectors, and lasers. Here, we report the innovative synthesis of formamidinium lead iodide (FAPbI3) single-crystal microsheets via a two-step chemical vapor deposition (CVD) method. The microsheets exhibit hexagonal and trapezoidal shapes, with hexagonal FAPbI3 growing parallel to the substrate and trapezoidal FAPbI3 growing perpendicular to the substrate. The dominant role of single-exciton recombination in the photoluminescence (PL) of these microsheets is observed, especially pronounced at low temperatures, attributed to the relatively large exciton binding energies of the samples. Calculations reveal exciton binding energies as high as 110.8 meV for hexagonal and 133.3 meV for trapezoidal FAPbI3 single-crystal microsheets, attributed to reduced rotational freedom of the formamidinium (FA) ions. Further investigation into low-temperature phase transitions indicates lower transition temperatures (around 100 K) for these microsheets, suggesting reduced FA ion rotational freedom and consequently higher exciton binding energies.

The role of surface substitution in the atomic disorder-to-order phase transition in multi-component core-shell structures.

Intermetallic phases with atomic ordering are highly active and stable in catalysts. However, understanding the atomistic mechanisms of disorder-to-order phase transition, particularly in multi-component systems, remains challenging. Here, we investigate the atom diffusion and phase transition within Pd@Pt-Co cubic nanoparticles during annealing, using in-situ electron microscopy and ex-situ atomic resolution element analysis. We reveal that initial outward diffusing Pd partially substitutes Pt, forming a (Pt, Pd)-Co ternary system in the surface region, enabling the phase transition at a low temperature of 400 °C, followed by shape-preserved inward propagation of the ordered phase. At higher temperatures, excessive interdiffusion across the interface changes the stoichiometric ratio, diminishing the atomic ordering, leading to obvious change in morphology. Calculations indicate that the Pd-substitute in (Pt, Pd)-Co system leads to a significantly lower phase transition temperature compared to that of Pt-Co alloy and thus a lower activation energy for atomic diffusion. These insights into atomistic behavior are crucial for future design of multi-component systems.

LC3 cementitious binder incorporating microencapsulated phase change materials for self-defrosting traffic surfaces

Exposed surfaces of bridge decks, viaducts and pavements incur ice formation and accumulation of snow in cold seasons, which threatens traffic safety. Mitigating this problem using traditional methods such as deicing salts have caused ecosystem damage and inflicted substantial reinforcement corrosion and surface scaling to bridge decks and pavements, thus compromising their service life and causing colossal economic loss. This paper presents an alternative solution to overcome this problem through the development of a sustainable LC3 cementitious material incorporating micro-encapsulated phase change material (MEPCM) with low phase transition temperature to delay the surface temperature drop and mitigate snow accumulation and ice formation. MEPCM was incorporated in the cementitious matrix at 0 %, 10 % and 20 % by binder mass. Paste and mortar mixtures were prepared to investigate the microstructural, mechanical, physical, and thermal properties. Test results showed that incorporating MEPCM in the LC3 matrix achieved adequate compressive strength. Thermal simulations and visual observations conducted on mortar samples in the laboratory and outdoor exposure showed that MEPCM can effectively regulate the surface temperature of the LC3 matrix and mitigate temperature drops as well as snow accumulation. Analysis of temperature data in the 2023–2024 winter season of Hamilton, Ontario, Canada indicated that the MEPCM incorporated in mortar samples could effectively regulate 40 % of the total days considered and mitigate surface ice formation and snow accumulation, which provides both economic and environmental benefits.

Br-Induced Suppression of Low-Temperature Phase Transitions in Mixed-Cation Mixed-Halide Perovskites.

Mixed-cation mixed-halide lead perovskites have been shown to be excellent candidates for solar energy conversion. However, understanding the structural phases of these mixed-ion perovskites across a wide range of operating temperatures, including very low temperatures for space applications, is crucial. In this study, we investigated the structure of formamidinium-based Cs y FA1-y Pb(Br x I1-x )3 using low-temperature in situ synchrotron powder X-ray diffraction. Our findings revealed that substituting the I anion with Br in mixed-cation (Cs,FA) perovskites suppressed the phase transformation from tetragonal to orthorhombic at low temperatures. The addition of Br also prevented the formation of nonperovskite secondary phases. We gained fundamental insights into the structural behavior of these materials by creating a low-temperature phase diagram for the compositional set of mixed-cation mixed-halides. This understanding of the structural properties lays the groundwork for designing more robust and efficient energy materials capable of functioning under extreme temperature conditions, including space-based solar energy conversion.

Cause, Consequence, and Control of Ag Vacancies in BaAg2-xAs2.

The impact of transition metal (Ag) deficiencies on the structural and transport properties of ThCr2Si2-type arsenides are investigated. We experimentally confirm a partial occupancy of Ag in BaAg2-xAs2, which can be predictably controlled within 0.053(5) ≤ x ≤ 0.19(1) by varying the quenching temperature during the crystal growth. Density functional theory calculations reveal that substoichiometric concentrations of Ag lower the density of states at the Fermi level, providing an electronic cause for the tendency of Ag to form vacancies. This vacancy concentration is linked to a characteristic kink in electrical resistivity that can be substantially shifted from 22 to 125 K and is established as the metric of a low-temperature structural phase transition (SPT) in BaAg2-xAs2. Along with electrical resistivity, the Seebeck coefficient and heat capacity for selected BaAg2-xAs2 samples are presented, which also exhibit anomalies due to the SPT.

Phase behavior of aqueous two-phase systems formed with cholinium-based magnetic ionic liquids: Experimental insights and theoretical correlations

In this work, three cholinium-based MILs were synthesized, characterized and successfully applied to construct the magnetically responsive aqueous two-phase system (ATPs). This ATPs combined the advantages of ILs and magnetic responsiveness, and showed great potential in the field of extraction and separation. Phase behavior for the magnetic ionic liquid aqueous two-phase systems (MIL-ATPSs) containing [N 1 1n 2OH] [TEMPO-OSO3] + salts + water was investigated experimentally at different temperatures. Merchuk equation was adopted to fit the experimental binodal data with satisfactory correlation performances. The effects of the structure of MILs, temperature and types of salts on the phase behavior were evaluated. Investigation on the phase separation mechanism showed that the phase formation was affected by the structure and viscosity of MILs. The salting-out effect is recognized as the major force for phase separation, which is closely related to the Gibbs free energy of hydration (ΔhydG) and entropy of hydration (ΔhydS) of salts. In addition, a larger biphasic area was obtained by increasing the temperature, indicating the phase separation process was endothermic and entropically driven. The binodal curve at different temperature confirms that this MIL-ATPs has low critical solution temperature (LCST) phase transition behavior. All these experimentally measured data and the theoretical correlations can provide meaningful and valuable information that may promote further research and application.

Study on the influence of thermal properties of paraffin on flexible PTC materials

Abstract This paper experimentally studied paraffin’s influence on flexible PTC materials’ temperature resistance and flexibility. Their resistance-temperature characteristics are notably influenced by PA’s phase transition range thermal properties. Specifically, the Curie temperature is intricately linked and determined by the PA’s phase transition temperature. PA’s phase state and proportion in the composite directly impact PTC material flexibility significantly. Specifically, a lower PA phase transition temperature results in better flexibility of PTC materials at room temperature. Additionally, a lower PA content minimizes interference with the overall flexible mesh structure, further enhancing material flexibility. The PTC of this series of formulations showed good adaptive temperature control ability. The thermal control performance can be customized by adjusting the PA.

Vibrational, optical and elastic properties of Cs2AgBiX6 (X= Br, Cl) double perovskite materials: DFT, PL, Raman and Brillouin scattering studies

In this study, we explore the temperature-dependent Raman, photoluminescence (PL) and Brillouin spectroscopy, as well as Density Functional Theory (DFT) calculation results of Cs2AgBiBr6 and Cs2AgBiCl6 double perovskites. Single crystals of Cs2AgBiBr6 and Cs2AgBiCl6 were synthesized via a hydrothermal method. The lattice structure has been clearly defined, and the electronic band structures, validated by DFT calculations, are consistent with previously reported data. Optical properties calculated via DFT approach indicate superior energy storage capacity for Cs2AgBiBr6. Changes in optical properties at room temperature suggest potential suitability for specific applications, ranging from photovoltaics to lasers. Raman and Brillouin spectroscopy have revealed significant insights regarding the vibrational properties and atomic interactions within the materials, thereby contributing to a better understanding of the atomic interactions within the perovskite structures. Experimental data has highlighted anomalies in the Raman shifts, indicating the presence of a phase transition in Cs2AgBiBr6 at 115 K. However, no such phase transition was observed in Cs2AgBiCl6. This observation is further supported by Brillouin spectroscopy. PL measurements on Cs2AgBiBr6 revealed the presence of a low-temperature phase transition at 35 K. DFT calculations also provide detailed insights into the elastic properties of these perovskites, notably indicating superior mechanical strength for Cs2AgBiCl6. These findings will enhance the understanding of perovskite materials and expand their potential technological applications, especially in environments with varying thermal conditions

The Impact of Binary Salt Blends’ Composition on Their Thermophysical Properties for Innovative Heat Storage Materials

Heat storage is an emerging field of research, and, therefore, new materials with enhanced properties are being developed. Examples of phase change materials that provide high heat storage are inorganic salts and salt mixtures. They are commonly used for industrial applications due to their high operational temperature and latent heat. These parameters can be modified by combining different types of salts. This paper presents the experimental study of the impact of the composition of binary salts on their thermophysical properties. Unlike the literature data, this article provides a detailed analysis of the phase change process in both directions: solid–liquid and liquid–solid. The results indicate that the highest latent heat was observed for a 70% NaNO3 content in the NaNO3–KNO3 mixture. Therefore, when this salt is used for heat storage, the most favorable choice is a 70:30 ratio, which provides the highest heat storage density and the lowest phase transition temperature. In the case of the NaNO3–NaNO2 mixture, the highest value of latent heat occurs for a ratio of 80:20, resulting in phase transition temperatures of 267.0 °C for the solid–liquid transition, and 253.5 °C for the liquid–solid transition. For heat storage applications, it is recommended to use pure NaNO2 salt instead of the NaNO3–NaNO2 mixture.

Giant electro-optic response in transparent rhombohedral ferroelectric Sm-PIN-PMN-PT crystal based on domain engineering

The relaxor ferroelectric crystal Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), located near the morphotropic phase boundary (MPB), exhibits exceptionally high piezoelectric and electro-optic (EO) responses. Nevertheless, lower optical transparency and phase transition temperature of PMN-PT limit its optical applications. The ternary system Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) holds promise in addressing these challenges with a higher Curie temperature. Additionally, specific ferroelectric domain polarization techniques can eliminate domain scattering, substantially enhancing the transparency of the crystal. In this study, we explore the optical properties of Sm-doped PIN-PMN-PT. We achieve a 2R domain-engineered state by polarizing along the (110) direction of the crystal. The high transparency allows us to extract an effective EO coefficient of up to 431.5 pm/V from the Sm-PIN-PMN-PT crystal at the telecommunications wavelength. Second-harmonic generation (SHG) probing verified the domain-engineered state in Sm-PIN-PMN-PT. The temperature-dependent SHG reveals the ferroelectric phase transition process, laying the groundwork for studying the stability of the EO response. The Sm-PIN-PMN-PT crystal exhibits an exceptionally high EO coefficient, which is crucial for the development of enhanced EO devices with high integration and low driving voltages.

Low-temperature formation of Ti2AlN during post-deposition annealing of reactive multilayer systems

Mn+1AXn-phase Ti2AlN thin-films were synthesized using reactive sputtering-based methods involving the deposition of single-layer TiAlN, and Ti/AlN and TiN/TiAl multilayers of various modulation periods at ambient temperature and subsequent annealing at elevated temperatures. Ex situ and in situ x-ray diffraction measurements were used to characterize the Ti2AlN formation temperature and phase fraction. During annealing, Ti/AlN multilayers yielded Ti2AlN at a significantly lower in situ temperature of 650 °C compared to TiN/TiAl multilayers or single-layer TiAlN (750 °C). The results suggest a reactive multilayer mechanism whereby distinct Ti and AlN layers react readily to release exothermic energy resulting in lower phase transition temperatures compared to TiN and TiAl layers or mixed TiAlN. With a modulation period of 5 nm, however, Ti/AlN multilayers yielded Ti2AlN at a higher temperature of 750 °C, indicating a disruption of the reactive multilayer mechanism due to a higher fraction of low-enthalpy interfacial TiAlN within the film.

A sustainable high-performance bamboo fiber composite material for cryogenic engineering

Exploring the application and development of biomass materials in the field of special engineering in line with the principles of green development. This work investigates the mechanical and thermal properties response of bamboo scrimber (BS) with different densities and resin contents at room temperature and ultra-low temperatures (-196 °C). The results showed that ultra-low temperatures significantly enhanced the modulus of rupture (increase of 143.9 %), modulus of elasticity (125.0 %), compressive strength (150 %), and shear strength (165 %) of BS due to the cell shrinkage at low temperature and physical phase transition of internal water. The failure modes of BS at ultra-low temperatures transitioned from ductile to brittle, compared with that at room temperature. Furthermore, BS with lower-density exhibited better thermal insulation (thermal conductivity < 0.55 W/mK) and dimensional stability (CTE < 6 1/k−6). These findings established a research base for broadening the application areas of BS for cryogenic engineering applications.

A novel technology for lithium extraction through low-temperature synergistic roasting of α-spodumene with lepidolite

α-Spodumene and lepidolite have garnered significant attention because of the booming market of lithium (Li) salts. However, α-spodumene requires a high-temperature phase transition step at ≥1050 °C, and lepidolite needs a large amount of sulfate to extract Li. The economic and environmental benefits of these processes need to be improved. Herein, an innovative scheme, low-temperature synergistic roasting of α-spodumene with lepidolite, was proposed to efficiently extract Li. The conditions for phase transition roasting, acid baking, and water leaching were sequentially optimized. The mechanisms underlying the synchronous phase transition of α-spodumene and lepidolite were studied using various characterization methods. Results indicated that lepidolite lowers the transition temperature of spodumene from the α-phase to the β-phase by 150 °C. During the synergistic roasting, fluorine escapes from the lepidolite lattice and attacks SiO, AlO, and LiO bonds within the α-spodumene lattice. Under optimal conditions, 97.60 % of the Li was extracted, while the leaching ratios of Na, K, Al, and Si were only 50.96 %, 10.96 %, 5.75 %, and 0.30 %, respectively. Current scheme is a promising low-carbon technology that synchronously achieves the low-temperature phase transition of α-spodumene and additive-free Li extraction from lepidolite, offering superior economics, environmental benefits, and practicality compared with the existing methods.

Renewable synthesis of MoO3 nanosheets via low temperature phase transition for supercapacitor application

2D transition metal oxides have created revolution in the field of supercapacitors due to their fabulous electrochemical performance and stability. Molybdenum trioxides (MoO3) are one of the most prominent solid-state materials employed in energy storage applications. In this present work, we report a non-laborious physical vapor deposition (PVD) and ultrasonic extraction (USE) followed by vacuum assisted solvothermal treatment (VST) route (DEST), to produce 2D MoO3 nanosheets, without any complex equipment requirements. Phase transition in MoO3 is often achieved at very high temperatures by other reported works. But our well-thought-out, robust approach led to a phase transition from one phase to another phase, for e.g., hexagonal (h-MoO3) to orthorhombic (α-MoO3) structure at very low temperature (90 °C), using a green solvent (H2O) and renewable energy. This was achieved by implementing the concept of oxygen vacancy defects and solvolysis. The synthesized 2D nanomaterials were investigated for electrochemical performance as supercapacitor electrode materials. The α-MoO3 electrode material has shown supreme capacitance (256 Fg−1) than its counterpart h-MoO3 and mixed phases (h and α) of MoO3 (< 50 Fg−1). Thus, this work opens up a new possibility to synthesize electrocapacitive 2D MoO3 nanosheets in an eco-friendly and energy efficient way; hence can contribute in renewable circular economy.

Low temperature phase transitions in the visible and near-infrared (VNIR) reflectance spectra of (NH4)2HPO4 and (NH4)HSO4 salts

The detection of ammonium bearing crystalline solids in salt-water systems on icy bodies and solar system bodies could provide information about the ascent of these salts from a deep reservoir within the hydrosphere. Due to their chemical-physical properties, NH4+ compounds play a key role both in the internal dynamics of celestial bodies and in the potential habitability of ocean worlds. In this work we analysed the reflectance spectra of two synthetic NH4+ salts: ammonium hydrogen phosphate (NH4)2HPO4 and ammonium hydrogen sulphate (NH4)HSO4 in the 1–4.2 μm spectral range at low temperature, between 110 and 290 K. For (NH4)2HPO4 we also examined the effect of three different grain sizes (150–125 μm; 125–80 μm; 80–32 μm). The collected reflectance spectra show absorption features related to NH4+ group overtone and combination modes in the 1–2.5 μm range. In particular, the bands located at ∼1.09 μm (3ν3), ∼1.30 μm (2ν3 + ν4), ∼1.58 μm (2ν3), ∼2.02 μm (ν2 + v3) and ∼ 2.2 μm (v3 + v4) could be useful to discriminate these salts. The low temperature spectra, compared to those at ambient temperature, reveal finer structures, displaying sharper and narrower absorption bands. The selected NH4+-bearing salts are subjected to reversible low temperature phase transitions, which are revealed in the spectra by a progressive growth and shift of the bands toward shorter wavelengths with a drastic change of their depth. We performed laboratory measurements of ammonium (NH4+) compounds to address the limited data available expanding the existing database. The collected cryogenic spectra can be directly compared with remote sensing data from planetary missions of the upcoming decade such as NASA's Europa Clipper, and ESA's JUICE and the newly launched James Webb Space Telescope expanding the existing database of ammonium compounds at cryogenic temperature.

Effect of Process Parameters on Superelasticity of LPBF Ni-Rich Ni51.3Ti48.7 Shape Memory Alloy

Laser powder bed fusion (LPBF) presents both opportunities and challenges with regard to the customisation of NiTi alloy properties. This paper presents a systematic study of the influence of process parameters on the superelasticity of LPBF Ni-rich Ni51.3Ti48.7 shape memory alloy. The findings demonstrate that NiTi alloys produced through disparate process parameters exhibit disparate phase transformation behaviours and microstructures, which in turn result in varying degrees of superelasticity. At an energy density of 166.7 to 233.3 J/mm3, LPBFed Ni-rich Ni51.3Ti48.7 is predominantly in the martensite phase at room temperature due to the high phase transition temperature caused by a large amount of Ni evaporation loss, and exhibits almost no superelasticity. At an energy density of 66.7 to 116.7 J/mm3, LPBFed Ni-rich Ni51.3Ti48.7 has less Ni evaporation loss and lower phase transition temperature. It is primarily austenite phase at room temperature, and contains nano-precipitated phases internally, thereby exhibiting excellent superelasticity. The recovery rate is in excess of 5.5% at the initial compression (up to 5.7%) and in excess of 5.0% following ten cycles (up to 5.3%). Furthermore, the lower the energy density, the smaller the stress–strain hysteresis of LPBFed Ni-rich Ni51.3Ti48.7, with a variation range of 1.8–3.9 mJ/mm3.

A Multiferroic Spin-Crossover Molecular Crystal.

Spin-crossover (SCO) ferroelectrics with dual-function switches have attracted great attention for significant magnetoelectric application prospects. However, the multiferroic crystals with SCO features have rarely been reported. Herein, a molecular multiferroic Fe(II) crystalline complex [FeII(C8-F-pbh)2] (1-F, C8-F-pbh = (1Z,N'E)-3-F-4-(octyloxy)-N'-(pyridin-2-ylmethylene)-benzo-hydrazonate) showing the coexistence of ferroelectricity, ferroelasticity, and SCO behavior is presented for the first time. By H/F substitution, the low phase transition temperature (270K) of the non-fluorinated parent compound is significantly increased to 318K in 1-F, which exhibits a spatial symmetry breaking 222F2 type ferroelectric phase transition with clear room-temperature ferroelectricity. Besides, 1-F also displays a spin transition between high- and low-spin states, accompanied by the d-orbital breaking within the t2g 4eg 2 and t2g 6eg° configuration change of octahedrally coordinated FeII center. Moreover, the 222F2 type ferroelectric phase transition is also a ferroelastic one, verified by the ferroelectric domains reversal and the evolution of ferroelastic domains. To the knowledge, 1-F is the first multiferroic SCO molecular crystal. This unprecedented finding sheds light on the exploration of molecular multistability materials for future smart devices.

Impact of Lithium Sources on Growth Process and Structural Stability of Single‐Crystalline Li‐rich Layered Cathodes

Single‐crystalline (SC) Li‐rich layered oxides have garnered significant attention due to their inhibited lattice oxygen release and reduced crack formation compared with polycrystalline (PC) counterparts. However, it raises a crucial question regarding the selection of prevailing lithium sources—Li2CO3 and LiOH·H2O—for the solid‐state synthesis of SC cathodes, which critically impacts the technical route and future development of SC materials. Herein, a series of SC Li‐rich layered cathodes were synthesized using these two lithium sources. The SC materials prepared with LiOH·H2O (LRO−H) exhibited larger grain sizes compared with those using Li2CO3 (LRO−C). This can be attributed to the lower phase transition temperature of the precursor to spinel phase, which promotes further SC growth during solid‐state reactions. Furthermore, LRO−H demonstrated excellent electrochemical stability, whereas LRO−C exhibited superior initial capacities. To balance these attributes, a mixed lithium sources system (LRO−M) was proposed, showing superior Li+ diffusion kinetics and suppressed layered−to−spinel transformation, resulting in excellent rate performance and an extended battery lifespan. Altogether, these findings provide critical insights into the impact of lithium sources on the growth process, structural stability, and electrochemical properties of SC Li‐rich layered cathodes, guiding the synthesis and design of next‐generation cathode materials.

A light/thermal cascaded-driven equipment for machine recognition inspired by water lilies using as multifunctional soft actuator

Inspired by the natural stimulus–response of plants and animals, a range of soft equipment has been extensively developed and used in intelligent human–computer interaction, editable remote drives, and machine learning. Poly(N-isopropyl acrylamide) (PNIPAM) hydrogels have gained popularity thanks to their low phase transition temperature and excellent flexibility. However, the PNIPAM hydrogels suffer from poor mechanical properties, low electrical conductivity, and lack of self-responsiveness. Herein, a bilayer light/thermal cascaded-driven anisotropic poly acrylamide/poly(N-isopropylacrylamide-co-acrylamide)-polyvinyl alcohol-MXene (P/PP-M) actuator was prepared by a simple two-step polymerization method. The unique bionic light/thermal response mechanism enables rapid conversion of energy forms and the construction of remote editable actuators. Concretely, the mechanical properties of hydrogels (strain: 1014 %, stress: 94 KPa) have been greatly improved by copolymerizing MXene nanosheets and multiplex hydrogels through two-by-two interpenetrating molecular chains. MXene nanosheets formed dynamic networks conferring the hydrogel system with high conductivity and light/thermal conversion efficiency. The P/PP-M soft actuator features high sensitivity (Gauge factor = 3.62), fast response time (400 ms), and cycling durability (>500 cycles). Finally, the energy transfer mechanism from light to thermal energy to kinetic energy was corroborated by preparing a series of bionic equipment. Manual clips were prepared on this basis, which enables the transportation of objects and realizes the real-time reflection of the operating status of remotely driven soft manual clips through changes in electrical signals. Thus, the proposed efficient editable remote-driven machine recognition soft equipment provides new insights for developing intelligent flexible robots and wearable smart devices.

Enhanced visible transmittance with low phase transition temperature of VO2 enabled by W-Mg co-doping

Vanadium dioxide (VO2) is a promising thermochromic material for smart windows. However, the relatively high phase transition temperature (Tt) and low visible transmittance (Tlum) constrain its practical application. Cationic co-doping offers an effective strategy to optimize the optical switching properties near room temperature. In this line, herein, the W-Mg co-doped VO2 films were synthesized by a solution and annealing method from W-Mg co-doped ammonium citrato-oxovanadate (IV). The synergistic effect of W-Mg co-doping improves the performance of VO2 films with Tt of 42.6 °C, Tlum of 59.0 % and solar energy modulation of 12.8 %. By changing the amounts of Mg, the W-Mg co-doped VO2 film maintains the low Tt of W-VO2 film and meanwhile possesses higher Tlum, which is attributed to the band gap structure change induced by the W-Mg co-doping. The excellent optical, thermochromic and thermal insulation performances confirm that our research could provide guidance for advancing the application of VO2 in smart window fields.