Microstructure and thermophysical properties of NiTiZr phase change alloys for downhole tool heat storage

1.   Introduction

With the development and exploitation of oil and gas fields gradually moving deeper, and the depletion of shallow oil and gas fields in the ground, oil companies are gradually shifting their focus to the exploration and exploitation of ultra-deep wells. However, ultra-deep well surveys are constrained by various factors such as high temperature and pressure ^[1,2], complex formations, ultra-long wellbores, corrosion ^[3,4], and higher demands on downhole tool performance. The logging instrument is an indispensable tool for the oil and gas resources industry to obtain downhole information by measuring downhole temperature, pressure, porosity, and other parameters to determine the location of the oil field and reserves; however, it often faces problems such as heat leakage from the external high-temperature environment and defects in the internal self-heating of the electronic devices, resulting in the temperature of the electronics in the logging instrument to exceed the design temperature rapidly and failing to work ^[5].

Downhole tools usually use solid-liquid phase change materials (SL-PCM) for temporary thermal storage ^[6,7], which effectively extends the uptime of downhole electronics ^[8], but SL-PCM has the disadvantages of low thermal storage density, phase separation, and low heat absorption rate ^[9], which largely limits the temperature control effect of the thermal management system of logging instrument; this greatly limits the temperature control effect of the thermal management system of the logging instrument; Song et al. used graphite to reduce the supercooling of MgCl₂·6H₂O from 40.6 to 29.4 ℃, while the thermal conductivity was significantly improved ^[10]; Li et al. successfully solved the supercooling and phase separation problems of CaCl₂·6H₂O-MgCl₂·6H₂O eutectic salt by adjusting the ratios of the nucleating agent and the thickening agent ^[11]; and Wu et al. prepared Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O stoichiometric composite phase change materials using porous SiO₂ and expanded graphite ^[12,13], which effectively solved the phenomena of overcooling and phase segregation of phase change materials. However, SL-PCM has serious defects such as liquid leakage and easy reacts with containers when in the liquid state; thus, SL-PCM must be encapsulated when in use, which inevitably leads to a reduction in the volumetric storage capacity of the system and an increase in the production cost ^[14].

The solid-solid phase change materials (SS-PCM) have the advantages of high heat storage density, simple heat storage structure, high reliability, no power drive, and are not affected by other factors, which are particularly suitable for temperature control in high-temperature fields such as aerospace and petroleum industries ^[15,16]. Fukahori et al. found that compared with the conventional molten-salt phase change materials ^[17], Al-Si alloys have a higher heat storage capacity and a higher thermal conductivity, which is more suitable for high-temperature superconducting heat storage materials; Shharar D et al. found that NiTi can be used as a high power material substitute for 1-octadecanoic without sacrificing the bulk heat capacity ^[18]; and Kato1 et al. investigated the latent heat values of Ni-Ti alloys with different compositions and found that the latent heat values of Ni-Ti alloys are greater than those of other SMAs and can reach 35 J/g ^[19]. However, the isotonic ratio of the Ni-Ti alloys has phase transition temperatures below 100 ℃ and cannot be applied in high-temperature environments ^[20,21]. Li et al. developed ultra-high performance high-temperature Ni-Mn-Ti PCMs using a martensitic phase transition strategy ^[22]. The latent heat of Ni-Mn-Ti SS-PCMs was in the range of 43–65 J/g. Hite et al. utilized a shape memory alloy Ni-Ti-Hf as a solid-solid phase transition material since Ni_50.3Ti_29.7Hf₂₀ exhibits a high enthalpy of transformation of 32.5 J/g and a thermal conductivity of 11.19 Wm⁻¹K^{−1 [23]}. Nevertheless, the phase transition temperatures of these ternary alloys are too high to be suitable as heat storage materials for downhole high-temperature environments. It is well known that adding an appropriate amount of Zr element to the Ni-Ti alloy can significantly improve the mechanical properties and martensitic phase transition temperature. The Ni-Ti-Zr ternary alloy not only has a lower cost but also has the advantages of high thermal conductivity and no risk of leakage as a phase change material, which makes it an ideal thermal energy storage material. Moreover, solid-solid phase change materials are relatively lacking in downhole applications; thus, it is of great significance to utilize the Ni-Ti-Zr ternary alloy as a solid-solid phase change material for the thermal control of downhole tools.

We focus on the high-temperature environment of the downhole, Zr as a substitute of Ti element, designing an Ni_49.5Ti_50.5−xZr_x (x = 8, 10, 12, 15 at.%) alloy, and exploring new thermal storage materials for downhole tools. We also investigate the effect of different Zr content on the thermophysical properties and microstructure of the material. Finally, we use the thermophysical properties of alloys after multiple alternations of hot and cold environments to verify the thermal cycling stability of materials.

2.   Materials and methods

2.1.   Material preparation

Ni_49.5Ti_50.5−xZr_x (x = 8, 10, 12, 15 at.%) alloy button ingots were fabricated by arc melting under argon protection using high purity Ni (99.99%), Ti (99.98%) and Zr (99.99%) elements as raw materials. To ensure homogeneity of the material composition, the ingots were repeatedly melted at least six times. The button ingots were then sealed into quartz tubes filled with argon gas and homogenized at 1223 K for 2 h, followed by water cooling. Samples of different sizes were cut from the ingots by electro-discharge machining for various experimental measurements.

2.2.   Microstructure characterization

X-ray diffraction patterns (XRD) were obtained utilizing a Rigaku diffractometer (D8 Advance), equipped with Cu-Kα radiation, to analyze the phase compositions of the investigated alloys. The chemical composition from selected sample areas was analyzed with an EDS detector. Scanning electron microscopy (SEM, Zeiss Gemini 360) was used to analyze the surface features. The SEM samples were incrementally ground using SiC papers (400–3000 grit) to obtain a scratch-free surface before ultrasonic cleaning with acetone and ethanol for 10 min and drying with cold air, which was then chemically etched with Kroll's reagent (5 mL of HF, 25 mL of HNO₃, and 50 mL of H₂O).

2.3.   Thermophysical property analysis

2.3.1.   Density measurements and ethics approval of research

The densities of samples with different compositions were measured using the Archimedes' method. The samples of size 10 × 10 × 1.5 mm³ were first weighed in air (denoted as w_a) and then immersed in water and weighed again (denoted as w_s). The density (ρ) of the measured samples was determined by ρ = ρ_ww_a/(w_a − w_s), where ρ_w is the density of water.

2.3.2.   Measurement of phase transition temperatures and thermophysical parameters

The phase transition temperature and the enthalpy change of the phase transition were determined by differential scanning calorimetry measurements (DSC25) at a heating/cooling rate of 20 ℃min⁻¹ over a temperature range of −40 to 450 ℃. The specific heat capacity was measured by the modulated DSC technique, utilizing sapphire with a well-known specific heat capacity as a standard sample. The thermal cycling stability of Ni_49.5Ti_38.5Zr₁₂ PCM was examined by DSC measurements during 100 cycles of heating and cooling between −40 and 130 ℃ at 10 ℃ min⁻¹.

2.3.3.   Thermal conductivity and mechanical behavior measurement

Thermal diffusivity was measured using the laser flash method (NETZSCH, LFA467). Square samples with dimensions of 10 × 10 × 1.5 mm³ were used. Measurements were carried out at several temperatures during the heating for the phase change to occur. The thermal conductivity k was obtained by k = Cp·ρ·α, where Cp, ρ, and α are the specific heat capacity, density, and thermal diffusivity. The specimen was measured by an HV-50A hardness tester with a load of 100 N and a retention time of 15 s.

3.   Results and discussion

3.1.   Microscopic morphology analysis

Figure 1a–d shows the scanning electron microscopy images of Ti-Ni-Zr alloys with different Zr contents. The smooth (Ti, Zr)Ni matrix and austenite phase can be seen in all the images, in addition to some Ti₂Ni-type phases. With the increase of Zr content, the Ti₂Ni-type phases gradually decrease, and the Ti₂Ni-type phase around the second phase gradually turns into a gray color ^[24]. The gray zone should originate from the amplitude-modulated decomposition of the single-phase solid solution at high temperatures during cooling and the corresponding consists of the elements Ti, Ni, and Zr. From the EDS results in Table 1, the gray zone may be (Ti, Zr)₂Ni. On the other hand, with the increase of Zr content, the austenite phase is gradually connected into flakes from a single vesicle, and the (Ti, Zr)₂Ni phase is mostly distributed in the grain boundaries or within the grains. This is mainly due to the displacement of small-sized Ti atoms by large-sized Zr atoms, creating vacancy defects and causing redistribution of Zr and Ti atoms in the B2 phase, which in turn leads to distortion of the lattice, and the small vesicular matrix phase is squeezed and connected into sheets.

Figure 1.  The SEM diagram for different materials. (a) Ni_49.5Ti_42.5Zr₈; (b) Ni_49.5Ti_40.5Zr₁₀; (c) Ni_49.5Ti_38.5Zr₁₂; and (d) Ni_49.5Ti_35.5Zr₁₅.

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Table 1.  Chemical composition results of Ni-Ti-Zr alloys with different Zr contents.

Zr content (at.%)	P1 zone (matrix phase) (at.%)				P2 zone (gray zone) (at.%)
	Ni	Ti	Zr	Ti + Zr/Ni	Ni	Ti	Zr	Ti + Zr/Ni
8	49.81	42.52	7.67	1.0076	30.52	65.72	3.76	2.2765
10	49.62	40.66	9.72	1.0153	34.67	56.61	8.72	1.8843
12	49.71	38.23	12.06	1.0117	33.59	52.34	14.07	1.9771
15	49.69	35.53	14.78	1.0125	30.88	49.79	19.33	2.2383

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Figure 2 shows the XRD patterns of Ni_49.5Ti_50.5−xZr_x alloys (x = 8, 10, 12, 15 at.%) at room temperature. It can be seen that all the alloys have a (Ti, Zr)₂Ni phase and austenite B2 and martensite B19' phases, with the observed diffraction peaks of the Ni-Ti binary alloys exhibiting a high degree of similarity to the aforementioned position. The crystal surface indices corresponding to the main diffraction peak of XRD are (210), (220), (020), and (132) crystal planes, respectively. When the Zr content is 8% and 10%, the Ni atoms preferentially bind with the Ti atoms to form the Ti₂Ni phase. With the addition of the Zr element, the Ni-Ti lattice is distorted ^[25], and when the Zr content exceeds 12%, the residual Ni atoms diffuse into the TiNi matrix to form a Ni-rich region, which combines with Zr atoms to form the NiZr phase ^[26]. This promotes the formation of the B2 phase and the Ti₂Ni phase, and the Ti₂Ni phase gradually becomes the (Ti, Zr)₂Ni phase, and the diffraction peak is shifted to the left. Furthermore, the (Ti, Zr)₂Ni and Ti₂Ni phases are body-centered cubic (BCC) lattice structures, and the NiZr phase is a face-centered cubic (FCC) lattice structure.

Figure 2.  XRD patterns of Ni_49.5Ti_50.5−xZr_x (x = 8, 10, 12, 15 at.%).

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3.2.   Temperature and enthalpy of phase change

The differential scanning calorimetry (DSC) curves of Ni_49.5Ti_50.5−xZr_x (x = 8, 10, 12, 15 at.%) are shown in Figure 3a. It can be seen that all materials have heat absorption peaks during the temperature rise and exothermic peaks during the temperature reduction, corresponding to the reversible phase transformation processes of the low-temperature martensitic phase and the high-temperature austenitic phase ^[22]. With the increase of the Zr content, the heat absorption peaks of these solid-solid phase transition alloys shift to the right, which implies an increase in the onset temperature of the phase transformation. When the Zr content is in the range of 8%–10%, the phase transformation onset temperatures are increased slightly, and when the Zr content is 10%–15%, the phase transition onset temperature increases significantly. Based on the results of DSC, the onset and end temperatures of the forward and reverse phase transitions of these PCMs (M_s, M_f, A_s, and A_f) are determined using the tangent method; the results are shown in Figure 3b. The A_s for x = 8 is 11 ℃ and that for x = 15 is 144 ℃. This shows that the phase transition temperature is increased by about 20 ℃ for each 1% increase in Zr content, indicating that the replacement of Ti by Zr can increase the phase transition temperature of the alloy ^[27,28].

Figure 3.  Thermal parametric results of Ni_49.5Ti_50.5-xZr_x (x = 8, 10, 12, 15 at.%) SS-PCMs. (a) DSC curves. (b) Forward (M_s and M_f) and reverse (A_s and A_f) phase transition temperatures versus Ti content x curves. (c) Curves of average valence electron number e/a and average valence electron concentration Cv with Ti content x. (d) Curves of phase transition enthalpy with Ti content x.

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Figure 3c shows the variation curves of average valence electron number e/a and average valence electron concentration C_v with Zr content. The average valence electron number (e_v/a) and the average valence electron concentration (C_v) can be expressed using Eqs 1 and 2, respectively: f_Ni, f_Ti, and f_Zr represent the atomic fraction of the Ni, Ti, and Zr atoms in the Ni-Ti-Zr alloy; e_v^Ni, e_v^Ti and e_v^Zr represent the valence electron number of Zr atoms of Ti atoms of Ni, respectively; Z^Ni, Z^Ti and Z^Zr represent the atomic number of the Ni, Ti, and Zr atoms, respectively. With the increase of Zr content, the average valence electron number e/a of each alloy does not change, but the average valence electron concentration C_v of the alloys gradually decreases. This is mainly due to Ti and Zr belonging to the same family, with the same number of outermost electrons and different atomic numbers, which lead to an increase in the phase transition temperature.

The enthalpy changes (which equals the latent heat L) associated with the forward and reverse phase transitions, denoted as ΔH_M and ΔH_A, respectively, are obtained by integrating the areas of the exothermic and absorptive peaks on the DSC curves (Figure 3a), and the results are shown in Figure 3d. It is seen that the enthalpy change value increases gently with the increase of Zr content x when the Zr content is 8% to 10%. When the Zr content exceeds 12%, the enthalpy change value grows more rapidly, up to about 30 J g⁻¹, which shows a more favorable performance.

3.3.   Density

Figure 4 shows the density as a function of Zr content x. It can be seen that the density of the alloys increases linearly with increasing Zr content x. The density of all compositions ranges from 6.55–6.78g·cm⁻³ due to the replacement of the low-density Ti (4.54 g·cm⁻³) by the high-density Zr (6.49g·cm⁻³). The densities of these metallic SS-PCMs have much higher densities than the organic, inorganic, and hydrated salt PCMs (typically 0.10–2.50 g·cm⁻³). In addition, the red dashed line shows a linear regression model of the trend of the density fitted with the Zr content, which is given by the following equation: ρ = 0.03356 × Zr + 6.26159, where ρ is density in g/cm³ and Zr is hafnium content in at.%. Due to the small variation of the Zr content, there is some error between the measured density values and the calculated prediction from the fitted curve.

Figure 4.  Density as a function of Zr content x for the Ni_49.5Ti_50.5-xZr_x (x = 8, 10, 12, 15 at.%) SS-PCMs.

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3.4.   Specific heat capacity and thermal conductivity

Figure 5a–d shows the curves of specific heat capacity C_p and thermal conductivity k versus temperature T for different materials. From the left axis, it can be seen that for different material compositions, the C_p versus temperature T curves exhibit similar shapes. When the phase transformation occurs, the C_p rises with the temperature up to the peak temperature, and when it exceeds the peak temperature, the C_p starts to show a downward trend, which is the same as that exhibited by the DSC images of each material. The C_p value rapid increase is due to the increase in the enthalpy of the phase transition during the reverse martensitic phase transformation, so the specific heat capacity C_p in the range of the phase transformation does not represent the true C_p value ^[29]. After the completion of the phase transformation, the C_p value of each material is almost the same at high versus low temperatures, which is 0.49–0.52 Jg⁻¹K⁻¹. This overall trend is consistent with the specific heat capacity trend in NiTi SMA ^[30], which suggests that the C_p values may be independent of the composition of the high and low temperature phases.

Figure 5.  Variation curves of specific heat capacity C_p and thermal conductivity k with temperature for different materials. (a) Ni_49.5Ti_42.5Zr₈. (b) Ni_49.5Ti_40.5Zr₁₀. (c) Ni_49.5Ti_38.5Zr₁₂. (d) Ni_49.5Ti_35.5Zr₁₅.

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As seen from the right axis of Figure 5a–d, the thermal conductivity k exhibits the same trend as the specific heat capacity C_p at different temperatures. Before the phase transition occurs, the thermal conductivity k is about 8–10 W m⁻¹K⁻¹ at low temperatures, whereas during heating to undergo the phase transition, k exhibits a linear increase with increasing temperature. This could be due to the increase in electronic thermal conductivity due to the change in carrier mobility during the phase transition ^[31]. After the completion of the phase transition, it decreases slightly as the temperature increases, and the value of k at high temperatures is about 12 W m⁻¹K⁻¹, which is much higher than that of the thermal conductivity of the conventional organic materials (commonly 0.1–2.0 W m⁻¹K⁻¹). From Table 2, it can be seen that the thermal conductivity of the Ni-Ti-Zr alloy is higher compared to traditional organic paraffin. The reason for this is that the molecular interactions in paraffin are relatively weak, and the molecular chains are long, leading to a lower efficiency in heat transfer. The high thermal conductivity of the Ni-Ti-Zr alloy can be attributed to the following reasons: The Ti₂Ni phase in the alloy has a BCC lattice structure, which is relatively dense. Moreover, heat transfer primarily relies on lattice vibrations. The (Ti, Zr)₂Ni phase has a FCC lattice structure, which has a higher thermal conductivity. This lattice structure is less sparse than the Ti₂Ni phase, which facilitates better heat transfer. According to the XRD pattern, the increase in Zr content promotes the formation of the (Ti, Zr)₂Ni phase, thereby enhancing heat transfer. As a result, the thermal conductivity K of the alloy increases progressively. As the temperature increases, the lattice vibrations in the (Ti, Zr)₂Ni phase are more strongly excited by heat, increasing the lattice vibrations and further improving the thermal conductivity of the alloy.

Table 2.  Thermophysical parameters of heat storage materials.

Title	Density/g·cm−3	Specific heat capacity/J g−1 K−1	Thermal conductivity/W m−1K−1	Latent heat/J g−1
organic paraffin	0.82	2.011	0.15	210
Ni49.5Ti42.5Zr8	6.55	0.492	13.80	12.6
Ni49.5Ti40.5Zr10	6.58	0.443	10.59	17.8
Ni49.5Ti38.5Zr12	6.65	0.431	15.65	28.3
Ni49.5Ti35.5Zr15	6.78	0.423	20.17	30.2

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We compare this with the commonly used thermal storage material (organic paraffin) to investigate the feasibility of Ni-Ti-Zr alloy as a heat storage material for downhole tools. The thermophysical parameters of paraffin and the alloy are shown in Table 2. It can be seen that the latent heat value of the paraffin is higher than that of the Ni-Ti-Zr alloy, but the Ni-Ti-Zr alloy has a high density, and more heat is stored under the same mass, which is favorable for use in a limited space and is expected to be used for downhole heat storage tools. Moreover, the high thermal conductivity of the Ni-Ti-Zr alloy indicates that the heat is transferred faster inside the alloy. The quality factor (FOM) as a quantifiable measure of PCM performance is usually given by the Eq 3:

where k, ρ, and L are the thermal conductivity, density, and latent heat of phase transition, respectively ^[32,33]. Calculating the FOM values of Ni-Ti-Zr alloys with different compositions according to Eq 3 gives a quality factor of up to 4129.93 × 10⁶ J²K⁻¹s⁻¹m⁻⁴, which is much higher than existing organic paraffins. This provides a theoretical basis for thermal energy storage in metal-solid-solid phase-change materials.

3.5.   Thermal cycle analysis and mechanical properties

The thermal cycling stability of the thermophysical properties of PCMs is critical for their practical thermal storage applications when working in downhole high-temperature environments ^[34]. The thermal cycling stability of Ni_49.5Ti_38.5Zr₁₂ SS-PCM is investigated by measuring the DSC curves during 100 heating and cooling processes of the material. Figure 6a shows the results of Ni_49.5Ti_38.5Zr₁₂ SS-PCM after 100 rapid heating and cooling cycles at 10 ℃min⁻¹. It can be seen that the peak of DSC gradually shifts to the left with the increase in the number of thermal cycles and stabilizes after several thermal cycles in which the reverse phase transition temperatures (A_s and A_f) slightly decrease during the thermal cycles; the forward phase transition temperatures (M_s and M_f) remain almost unchanged during the cycles. Its thermophysical parameters after multiple thermal cycles are shown in Figure 6b, where the enthalpy change values ΔH_M (for forward phase change) and ΔH_A (for reverse phase change) remain unchanged during multiple thermal cycles. Ni-Ti-Zr alloy heat is released during the transition to martensite, but when cooled by the reverse transition from martensite down to autensite, the heat is absorbed. In this process, the heat is caused by the internal phase transition of the alloy, which involves atomic rearrangement, structural change, lattice dislocation, and other processes that are symmetrical, resulting in roughly the same heat absorbed or released by each phase transition without the loss or increase of heat. Thus, the latent heat of the forward/reverse martensitic phase transition, in this study, is almost equivalent. This indicates the superior thermal cycling stability of Ni-Ti-Zr SS-PCM, making it a strong candidate for heat storage materials for downhole tools.

Figure 6.  Thermal cycling stability of phase transition and thermophysical properties. (a) DSC curves of Ni_49.5Ti_38.5Zr₁₂ SS-PCM during multiple thermal cycles across phase transition. (b) Variation of corresponding phase transition temperatures (M_s, M_f, A_s, and A_f) and enthalpy changes of phase transitions (ΔH_M and ΔH_A) of Ni_49.5Ti_38.5Zr₁₂ SS-PCM with the number of cycles.

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From Figure 7, the hardness of Ni-Ti-Zr alloy gradually increases in the process of 1 to 20 thermal cycles, which promotes the precipitation of the enhanced phase or the refinement of the grains. When the number of thermal cycles reaches 30 times, the precipitate may dissolve or redistribute, and the alloy shows a higher hardness. However, when the number of thermal cycles exceeds 30 times, the hardness of the alloy does not increase because the grain has reached a certain uniformity, and the precipitation reinforcement tends to balance. When the number of thermal cycles continues to increase, the hardness of the Ni-Ti-Zr alloy begins to decrease, possibly because the excessive thermal cycles lead to excessive dissolution of the precipitate or the formation of an unstable phase, which reduces the hardness of the alloy ^[35,36].

Figure 7.  Curve of the Ni_49.5Ti_38.5Zr₁₂ SS-PCM hardness with the number of cycles.

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4.   Conclusions

The thermophysical parameters of Ni_49.5Ti_50.5−xZr_x (x = 8, 10, 12, 15 at%) SS-PCMs were investigated due to the advantages of metallic phase change materials such as high thermal conductivity and density. The effect of different contents of Zr on their thermophysical parameters was analyzed, and our major conclusions are as follows:

1. The microscopic morphology reveals the presence of a (Ti, Zr)Ni matrix and a small amount of Ti₂Ni phase, and with the increase of Zr, the Ti₂Ni phase gradually becomes the (Ti, Zr)₂Ni phase. Moreover, the Zr content is in the range of 8%~15%, the enthalpy of the phase transition of the alloy with the increase in the Zr content of x increases, and when the Zr content is more than 12%, the enthalpy of phase transition can reach around 30Jg⁻¹. This is attributed to the fact that the addition of the Zr element induces distortion in the Ni-Ti lattice and hinders the martensitic transformation, thus promoting the increase of the enthalpy of phase transition.

2. Ni_49.5Ti_50.5−xZr_x SS-PCMs quality factor FOM have a maximum value of 4129.93 × 10⁶J²K⁻¹s⁻¹m⁻⁴, and the phase transition temperature of these SS-PCMs can be adjusted by controlling the elemental composition ratio. When the Zr content is 12%, the temperature range required for the phase transformation meets the requirements of downhole working conditions. After 100 rapid heating and cooling cycles, the phase transformation temperature of the material decreases slightly, but the enthalpy change value is almost unchanged, which indicates that the material has good thermal cycling stability.

3. Metal phase change materials for heat storage have no risk of leakage and exhibit better heat storage performance than conventional SL-PCMs, and Ni-Ti-Zr alloys offer a potential option as SS-PCMs for heat storage in downhole tools. The phase change material studied in this paper can be applied to the special thermos, mainly to absorb the heat generated by the electronic devices when the logging instrument works.

4. Thermal cycle times can increase the hardness of the alloy within a certain range. Thus, the Ni-Ti-Zr alloy has 30 thermal cycles with the highest hardness and the strongest deformation resistance. Therefore, this material is applied to the log instrument to withstand a large load and high underground pressure.

Use of AI tools declaration

The authors declare they have not used Artificial Intelligence (AI) tools in the creation of this article.

Funding

This work was supported by the National Natural Science Foundation of China (No. 52071261).

Acknowledgments

The authors are grateful for the financial support from the National Natural Science Foundation of China (No. 52071261).

Author contributions

Conceptualization: W.Q.; methodology: Q.Z.; validation: H.L. and G.L.; formal analysis: Q.Z.; investigation: Q.Z. and B.P.; resources: H.L.; data curation: Q.Z.; writing—original draft preparation: Q.Z. and H.L; writing—review and editing: Q.Z. and B.P.; visualization: H.L.; supervision: W.Q. and G.L. All authors have read and agreed to the published version of the manuscript.

Conflict of interest

The authors declare no conflict of interest.