Enhanced Energy-Storage Performance of an All-Inorganic, Antiferroelectric, Thin-Film via Orientation Adjustments

An all-inorganic Pb0.99Nb0.02(Zr0.85Sn0.13Ti0.02)0.98O3 (PNZST) antiferroelectric (AFE) thin film was designed to enhance its energy-storage performance by adjusting its orientation. Using a radio frequency (RF) magnetron sputtering technology, 450-nm-PNZST AFE films with (111), (110), and (100) crystal orientations were successfully prepared. All the films showed a dense microstructure and the highly preferred orientations were determined by the orientation of the bottom electrodes. Moreover, the preferred orientation of the AFE thin film had a great influence on the dielectric and energy-storage properties. Meanwhile, the energy storage density of the PNZST AFE thin film with the (100) orientation reached 33.7 J cm−3, which was 43 % higher than that of PNZST AFE thin film with a (111) orientation. All of these results shed light on how the energy-storage performance of PNZST AFE thin films can be enhanced and optimized by adjusting its orientation. This offers a new strategy and innovation, which opens up a route to practical applications in micro-energy-storage systems.


I. INTRODUCTION
With the rapid development of intelligent systems, people tend to live more portable, convenient, and intelligent lifestyles. With the development of these lifestyles, flexible, portable and efficient electronic products and capacitors have attracted more and more attention from researchers, companies and other people. Generally, the energy storage density, charging and discharging speed, service life, and service safety are the main criteria used to measure whether a capacitor has efficient energy storage performance [1]- [3]. The material consisting of an array of ordered electric dipoles with opposite directions of adjacent dipoles is called antiferroelectric (AFE). The antiparallel dipole of the compound is forced to become parallel under the action of an electric field (E), corresponding to an electrically induced phase transition (i.e., antiferroelectric-ferroelectric, AFE-FE) [4]. It is worth mentioning that in 1951, PbZrO 3

(PZ) was identified as an
The associate editor coordinating the review of this manuscript and approving it for publication was Guijun Li . resistance and excellent energy storage density in a medium working voltage environment.
In recent years, some researchers have begun to study the substrate control and growth parameters of some thin-film materials, to improve their performance in specific fields. However, more studies have focused on the effects of strain on the AFE-FE phase transition and related changes in polarization. For example, some researchers have studied the effect of different preferences on PbZrO 3 thin-film energy storage, but they focused on the strain rather than the effect of preference on the AFE thin film itself. Furthermore, few people have deliberately controlled the bias and polarization switching characteristics. It was necessary and meaningful to further study and explore the influence of the orientation on the properties of the thin film [21]. Through the above research, it is found that the influence of optimization orientation on AFE thin films has important scientific value. Xu et al. [22] studied the Pb 0.99 Nb 0.02 (Zr 0.85 Sn 0.13 Ti 0.02 ) 0.98 O 3 , who believed that the strain could not significantly change the competition between AFE and FE.
Therefore, in this study, the different orientations of Pb 0.99 Nb 0.02 (Zr 0.85 Sn 0.13 Ti 0.02 ) 0.98 O 3 (abbreviation as PNZST) AFE films were prepared with a thickness of 450 nm. The purpose of this work was to examine the effects of different orientations on the dielectric and energy storage properties of the PNZST films.

II. EXPERIMENTAL PROCEDURES A. PREPARATION OF PNZST CERAMIC TARGET
PNZST ceramic target with the composition of Pb 0.99 Nb 0.02 (Zr 0.85 Sn 0.13 Ti 0.02 ) 0.98 O 3 was prepared using a conventional method. First, the stoichiometric amounts of Pb 3 O 4 , Nb 2 O 5 , ZrO 2 , SnO 2 , and TiO 2 powders were fully mixed with alcohol and ball milled for 24 hours before drying. An excess 15 mol% lead was added to the raw material to compensate the volatilization of lead during high temperature sintering. The mixed precursors were calcined at an optimized temperature of 900 • C for 2 h. After that, the calcined powder is re-ground and mixed with polyvinyl alcohol and pressed into a disk 60 mm in diameter and 3.5 mm in thickness. Finally, the target material was put into a high-temperature sintering furnace and calcined at 1150 • C for 2 hours.

B. THIN FILMS DEPOSITION
LaNiO 3 (LNO) is commonly used as a base electrode in film preparation, has excellent electrical conductivity, and is the only preferably oriented ABO 3 structure buffer for AFE film deposition [23]- [29]. In this work, LNO layers (250 nm) with either (100)-preferred and (110)-preferred orientations were deposited on Pt (111)/TiO 2 /SiO 2 /Si via radio frequency (RF) magnetron sputtering method, respectively, as the bottom electrode. Both two kinds of orientations LNO films were prepared using commercial ceramic LNO targets under the conditions of Ar and O 2 mixed atmosphere with the same power of 40 W and the same argon gas pressure of 1 Pa.The difference is that the sputtering temperature of (100)-preferred LNO films is 550 • C and that of (100)-preferred is 200 • C. Hence, the three bottom electrodes with different orientations in this article were LNO (100)/Pt (111)/TiO 2 /SiO 2 /Si (abbreviated as LNO (100)), LNO (110)/Pt (111)/TiO 2 /SiO 2 /Si (abbreviated as LNO (110)), and Pt (111)/TiO 2 /SiO 2 /Si (abbreviated as Pt (111)).
Then, PNZST AFE films were deposited from the sintered PNZST ceramic target at room temperature by RF magnetron sputtering. PNZST films were deposited on the bottom electrode with three different preferred orientation obtained above, and PNZST films corresponding to the preferred orientation with (100), (110) and (111) were obtained, respectively. The deposition parameters of all the PNZST AFE films such as sputtering time, sputtering power, sputtering pressure and sputtering atmosphere of PNZST films were optimized to obtain the required film thickness and significant energy storage performance. Ar pressure is 1 Pa and RF power is 100 W. Finally, the PNZST film was heat-treated and rapid heat treatment (RTA) was performed at 700 • C for 30 minutes. For convenience of description, the PNZST thin film with the (100)-preferred deposited on LNO (100)/Pt (111)/TiO 2 /SiO 2 /Si were abbreviated as PNZST (100). The PNZST thin film with the (110)-preferred deposited on LNO (110)/Pt (111)/TiO 2 /SiO 2 /Si were abbreviated as PNZST (110). And the PNZST thin film with the (111)-preferred deposited on Pt (111)/TiO 2 /SiO 2 /Si were abbreviated as PNZST (111).
To measure the electrical properties, a gold pad with a diameter of 0.2mm was applied to the surface as the top electrode by direct current (DC) sputtering. The design schematic diagram of the PNZST target material preparation, the PNZST thin film preparation by RF magnetron sputtering, and the PNZST thin-film annealing treatment by RTA as well as the coated gold pads are shown in Figures 1(a)-(d), respectively. Figure 1(e) gives the schematic diagram of the completed sample to be tested.

C. CHARACTERIZATION AND MEASUREMENTS
The crystal structures of the PNZST films were studied by X-Ray Diffraction (XRD) Bruker D8 Advance Diffractometer, Germany. Surface microstructure and thickness were observed by a field-emissive scanning electron microscope (FE-SEM, ZEISS Supra 55, Germany). In this work, the frequency and DC E-dependent dielectric properties were measured using a computer-controlled Agilent E4980A LCR analyzer. An E-induced polarization (P-E) hysteresis ring with a ferroelectric tester (Radiant Technologies, Inc., Albuquerque, NM, USA) at 1 kHz and different temperatures is proposed in this article. Finally, the energy storage performance of the thin film was obtained according to the calculation of P-E.

III. RESULTS AND DISCUSSION
Three typical XRD patterns of the PNZST films grown on LNO (100), LNO (110), and Pt (111) substrates were depicted in the Figure 2. The film of PNZST (100), PNZST (110) VOLUME 8, 2020  and PNZST (111) showed good crystalline quality and pure perovskite phase. It should be noted that the lattice index of the diffraction peak in the XRD pattern of the thin film was given based on the pseudo-cubic (perovskite) structure rather than the orthogonal structure [30]. It was determined from the Figure 2 that the preferred orientation of PNZST AFE film depended on the orientation of the preferred orientation of the bottom electrode. PNZST (100) showed highly oriented (100) fiber textures, e.g., PNZST AFE films grown on an LNO (100) preferred orientation also have a (100) preferred orientation. This was because the LNO formed seed layers or templates with the same perovskite structure and small lattice mismatches, thus promoting the grain growth of the PNZST film in a similar manner (same as PNZST (110)) [31]. Similarly, PNZST AFE films grown on a Pt (111) orientation showed a (111) preferred orientation. This was because Ti diffused into the Pt layer to form a seed layer [22], thus promoting the heterogeneous nucleation and growth of the perovskite (111) plane and forming the PNZST (111) thin film. In addition, it can see from the XRD diagram of the Figure 2 that when the preferential orientation of PNZST films is (100), (110), (111), the peak angles 2θ corresponding to PNZST are 21.76 • , 21.70 • and 21.74 • , respectively. In general, the larger the 2θ , the smaller lattice parameters. In other words, the PNZST (100) films are subjected to smaller compressive stress, which may contribute to the recoverable energy storage density, to a certain extent [32], [33].
The surface topography of the PNZST (100)/(110)/(111) preferentially oriented thin films obtained by FE-SEM were shown in Figures 3(a)-(c). The thicknesses of the three typical films with different orientations that were measured by scanning electron microscopy were presented in the inset of Figures 3(a)-(c). The films with different orientations show different morphologies, among which the difference in grain size is the most noticeable. Generally, different orientations lead to different stresses on the thin films, such as lattice mismatch, thermal expansion, etc., resulting in different constrained states during the growth process of the thin films, and ultimately resulting in different morphologies of the thin films. It can be seen from Figure 3(a) that the surface morphology of PNZST (100) is dense and presents a columnar microstructure. Its grain size is about 700 nm. Although the PNZST (110) had a similar microstructure to the PNZST (100), its grain size was about 30 % smaller than the PNZST (100). Notably, the PNZST (111) showed almost equiaxial particle microstructure, and the average grain size was only a few tens of nanometers. The above results indicated local epitaxy existed between grains, and a layered structure was also observed on the cross-section of the thin film shown in Figure 3. As shown in Figure 3 inset, all of the films were around 450 nm thick. The FE-SEM schematic diagram of the sample test is shown in Figure 3(d). The reason for the effect of PNZST film orientation on the surface morphology of the film is not clear. However, according to our work, from our respects, PNZST (100) thin films have larger surface particles, which are likely to improve the energy storage performance of the films. This point has also been confirmed in the following work.
The frequency-dependent dielectric properties (dielectric constant ε r and the dielectric loss tangent Tan δ) of PNZST AFE films were shown in the Figure 4. Figure 4(a) shows the ε r and the Tan(δ) for all films, which ranged from 1 kHz-1 MHz at room temperature. From the figure 4(a), it can be seen that over the entire frequency range, the ε r of all samples changed very little or was negligible enough to be ignored. Having such a stable ε r is very important for dielectric capacitors that require a wide range of frequency response. When the test frequency was 1 MHz, the ε r of the PNZST (100), PNZST (110), and PNZST (111) were 258, 260, and 246, respectively. Among three samples, the PNZST (100) and PNZST (110) had a similar dielectric constant and both of them were higher than the PNZST (111) samples, which was attributed to their larger grain size [34]. Notably, the dielectric loss of these films was very low (below 0.1) due to their dense and uniform microstructures.
When assessing the dielectric properties of energy storage materials, the relationship between the ε r and frequency should not only be considered but also the relationship between the ε r and the electric field (E). Therefore, Figure 4 shows a plot of the E-dependent dielectric constants (ε r -E) of all the films. The testing temperature was room temperature and the test frequency was set to 100 kHz. Here, the test mode was: from E max to -E max , then -E max to E max , with a time interval of 0.5 s. As seen from the Figure 4(b), the temperature curves of all materials showed a typical dual butterfly state for the AFE materials, which corresponded to the conversion from the AFE phase to the FE phase. Generally speaking, the phase switching field can usually be judged by the peak value of the ε r -E curve. Because, when ε r will increase sharply during the AFE-FE transition, and it will decrese sharply when the curve reaches the saturation value. The peak value at this time is what we usually call the phase transition field. It was concluded that the forward phase switches (AFE-to-FE) field (E F ) of the PNZST (100), PNZST (110), and PNZST (111) samples were about 278, 244, and 211 kV cm −1 , while the reverse phase switches (FE-AFE) field (E A ) were about 178, 133, and 122 kV cm −1 . As a consequence, the different orientations not only resulted in the grain size of the films but also resulted in the phase transition field. The polarization extended and rotated along the main polarization direction during the phase transition, thus arranging itself in the direction of the application field [35]. The orthorhombic cell of the PNZST was a multiunit cell when the electric field was E 0 , which contained eight tetragonal structure protocells [36]. When the E is large enough, AFE switches to FE phase, resulting in the transformation of the antiparallel dipole along the <110> direction of the tetragonal primitive cell [28] into the antiparallel dipole along the <111> direction of rhombohedral [37]. To further understand the impact of the orientation, based on the models of other researchers, Figure 5 shows the schematic diagram of AFE and FE phase protocells. In particular, Figure 5(a) shows the unit cells of the PNZST under different E, which include the projection of the orthogonal unit cells of the PNZST on the ab plane. Figure 5 also schematically shows the Pb 2+ antiparallel displacement (at E 0 ) and the forced parallel displacement (at E with magnitudes greater than E F ). The square containing one Pb 2+ represents a tetragonal primitive cell (blue line) at E 0 and a rhombohedral (red line) at an electric field higher than E F . Figures 5(b)-(d) depict the (001) (similar to (100)), (110), and (111) orientations of the primitive cells in the AFE and FE phases, respectively. It was seen that when the AFE switched to FE, the polarization expanded and rotated along with the main polarization directions of <100> T (Tetragonal of 100) to <111> R (Rhombohedral of 111), <110> T (Tetragonal of 110) to <111> R , and <111> T (Tetragonal of 111) to <111> R , to be arranged in the direction of the external field. Also, the movement of the polarization direction was along a certain angle. From Figure 5, it was seen that there was a large difference regarding the angle between the preferred orientation and the <111> R . When it came to the angle between the preferred orientation and the <111> R , the sequence of decreasing E F was <100> T ><110> T > <111> T . That is to say, the PNZST AFE materials along the (100) direction had the largest critical phase switching fields and the materials along the (111) direction had the smallest critical phase switching fields [38]. Ge et al. found the similar result in their report on PbZrO 3 AFE films [39], and in lead-based AFE O films by Hao and Zhai [40] and Hao et al. [41].
Temperature of the energy storage materials usually changed in the process of use, so it was important to test the relationship between the dielectric properties and the temperature. Figure 6(a) gives the change in the ε r of the PNZST AFE thin films with temperature. The testing frequency was 100 kHz, and the heating rate was 3 • C min −1 . From Figure 6, it was seen that the curves of the phases from the AFE to the paraelectric (PE) showed a typical diffusion phase transition, and the peak of the dielectric constant appeared, indicating that the dielectric properties had good temperature stability. The AFE-PE phase transition temperatures were 193 • C, 194 • C, and 182 • C for the PNZST (100), PNZST (110), and PNZST (111), respectively. The differences in the Curie temperatures of the films were mainly affected by the strain, which was caused by the substrate constraint and the annealing process [42], [43]. Also, to give a more detailed description, Figure 6(b) gives prominence to the temperature dependence of the ε r for the film of PNZST (111). It was found that there was a step in the curve of PNZST (111) between room temperature and 150 • C (T f ), which could have been effetted by the phase transition from the AFE O to the tetragonal antiferroelectric (AFE T ). This was also confirmed by the P-E loops measured at different temperatures, as picked in Figure 6(b). This has also been demonstrated in other AFE O ceramic materials [44]. Figure 7(a) showed the P-E of the PNZST AFE films. The test conditions at room temperature were as follows: the testing frequency was 1 kHz, and the testing E was 2133 kV cm −1 . Generally, the way to enhance the energy storage density of a material is to enhance its polarization value or increase its breakdown strength (BDS). The energy storage density was calculated by the formulae: where W tot is the total energy density, W rec is the recoverable energy density (the shaded area in the first quadrant represents the W rec ), E is the applied electric field, P is the polarization, P max is the maximum polarization, and P r is the remnant polarization. For AFE materials, in addition to the polarization and breakdown field strength acting on the W rec , the E F also had a significant effect on the W rec . Also, the higher P max meant that the orientation of the membrane was closer to the pole vector of the E F phase, resulting in a lower transition field. From Figure 7, it was seen that the values of the P max were 71.8, 70.0, and 57.1 µC cm −2 for the PNZST (100), PNZST (110), and PNZST (111), respectively. Generally, the relationships of E F and E A with thermal stress vary substantially as the orientations of films change. From the P-E loops measured at 533 kV cm −1 (inset of Figure 7(a)), the E F and E A values that were obtained for PNZST (100), PNZST (110), and PNZST (111) were 290, 260, 237 kV cm −1 and 115, 108, 40 kV cm −1 , respectively. It was clear that both the PNZST (100) and PNZST (110) not only possessed a higher P max but also a larger E F than the PNZST (111). It is observed that the E F for PNZST (100) has a 53 kV cm −1 increase than that for PNZST (111). The increase of switching field implies the difference of free energies between two phases is enlarged, and the AFE phase becomes more stable for PNZST (100) and PNZST (110). The differences in the values of P max were mainly due to the changes in the alignment of the principal polarization axes during phase transitions [35] and the average grain size. The similar works were also reported in other lead-based AFE films deposited on LaNiO 3 bottom electrodes [39].
Generally, the polarization is maximized when the electric field is in the direction of the main polarization axis.
However, in this work, since the average grain size for PNZST (111) was so small compared to the other two samples, only one value of 57.1 µC cm −2 for the P max was obtained. For the other two samples, the values of the P max were very close, which were due to similar grain sizes. It was expected that the PNZST (100) and PNZST (110) would exhibit higher energy density as compared to the PNZST (111), which meant that the preferred orientation of (100)/(110) enhanced the energy density of the PNZST films. For example, W at 2133 kV cm −1 was 27.5 J cm −3 for both the PNZST (100) and PNZST (110) and was 16.6 J cm −3 for PNZST (111). This corresponded to a 67 % increase. In this work, the phase switching field value derived from the P-E curve was slightly different from that derived from the ε r -E curves. They had higher values during the AFE-to-FE phase transition, while they had lower values during the FE-to-AFE phase transition. It should be noted that the test conditions of these two methods were different. The P-E curve was measured by a triangle wave, and the ε r -E curve was measured by the DC offset plus the weak AC wave.
To show the influence of the BDS on the W rec , Figure 7(b) illustrates the room temperature E-dependence of W rec and the energy-storage efficiency (η) of all three samples, which measured from 267 kV cm −1 to their BDS. With the increase of the E, the W rec of the samples linearly increased and showed an interrupt jump where the phase transition occurred. Moreover, the values of W rec at their corresponding BDS were 33.7, 27.5, and 23.5 J cm −3 for the PNZST (100), PNZST (110), and PNZST (111), respectively. The PNZST (100) and PNZST (110) possessed both higher E F and higher P max than the PNZST (111), and as expected, they obtained higher W rec . Also, the PNZST (100) exhibited higher energy density compared to PNZST (110), which was attributed to the higher BDS of the PNZST (100) over the PNZST (110). It was seen that the average grain size of the PNZST (100) was larger than that of the PNZST (110), which meant the PNZST (100) had a small boundary layer, leading to a higher BDS. The PNZST (100) showed the largest value of W rec among the three samples. It is worth noting that when the preferred orientation of the PNZST film is (100), the maximum peak angle 2θ is 21.76 • , as can be seen from the X-ray diffraction pattern of Figure 2. In general, the larger the 2θ , the smaller the lattice parameters. And the change of lattice parameters will further result in energy storage density to some extent, which is similar to that reported by Ge et al. [39]. In practical applications, apart from the higher W rec values, a larger η was also desired. The η was calculated by the following formula [45]: The η of the samples decreased significantly at the point where the phase transition occurred. Meanwhile, with the increase of the electric field above E F , the η value of each sample did change very little. For example, the value of η for the PNZST (100) gradually decreased from 58 % to 56 % with a change from 444 kV cm −1 to 2488 kV cm −1 .
The W rec and BDS in this study were compared with promising energy storage materials which were recently reported on [46]- [55], as shown in Figure 7(c). The high BDS (>3000 kV cm −1 ) enabled the dielectric material to have high energy storage performance, but such a high working electric field means strict requirements on the reliability of capacitors. This high electric field can be very inconvenient, such as in some microelectronics. Therefore, the development of dielectric capacitors in these practical applications has been greatly limited. The overall energy storage performance of PNZST AFE films is not outstanding without considering its BDS. However, within the same electric field range, the PNZST thin film had higher energy storage performance than most organic/inorganic materials. It was seen that the W rec of a low BDS (3000 kV cm −1 ) dielectric capacitor was usually lower than 25 J cm −3 . However, the PNZST film studied here showed a medium W rec (33.7 J cm −3 ) accompanied by a medium BDS (about 2488 kV cm −1 ), which meant that high energy storage performance was achieved at a relatively low voltage.
Thermal stability is critical for energy storage materials. Figure 8(a) shows the E F , E A , and the hysteresis switch E = E F -E A (inset of Figure 8(a)), which were obtained from the P-E loops measured at the different temperatures of 20, 40, 60, 80, 100, 120, and 140 • C. The values of E F and E A for the PNZST (100) were larger than that of the other two samples in the measurement range. From the inset in Figure 8(a), it was seen that the difference in orientation also resulted in a difference in E for the AFE films with the same composition. The values of E for the PNZST (100) and PNZST (110) were smaller than that of the PNZST (111) for that temperature. Also, the E of the PNZST (100) reached the smallest value above 100 • C, which indicated that the (100) orientation not only increased the value of E A , but it also reduced the hysteresis switch E. The W rec and the η were investigated in detail (Figure 8(b)) and were measured at 889 kV cm −1 in the temperature range of 20 to 220 • C. The results indicated good temperature stability for the given energy storage performance. The W rec values of the PNZST (100) and PNZST (110) slightly decreased with the temperature increase, but the W rec values of the PNZST (111) showed a slight increase. Also, the η values for the samples showed an increasing tendency. This phenomenon was mainly caused by the change in the saturation polarization, the forward switching field (E F ), and the backward field (E A ) as the operating temperature increased, as shown in the inset of Figure 8(b). All of the PNZST thin films achieved a prominent enhancement of W rec .

IV. CONCLUSION
In conclusion, a series of 450 nm Pb 0.99 Nb 0.02 (Zr 0.85 Sn 0.13 Ti 0.02 ) 0.98 O 3 (PNZST) AFE thin films with different preferred orientations were fabricated via RF magnetron sputtering technique. The preferred orientation of the film had a great influence on the dielectric properties and the energy storage performance of the films. The PNZST (100) film possessed the largest E F of 278 kV cm −1 due to the largest angle between the principal polarization directions of <100> T and <111> R . A large recoverable energy density of 33.7 J cm −3 was gained for the PNZST (100) at its critical breakdown field, which was 43 % higher than that of the PNZST (111) at 23.5 J cm −3 . Moreover, all the PNZST films exhibited a temperature dependence for energy storage performance, where the PNZST (100) possessed the smallest E above 100 • C. These properties indicated that changing the preferred orientation of the film was beneficial to obtain a high E F and energy storage density. Also, with a high energystorage density, the (100) oriented PNZST AFE thin films also had a strong potential application in energy storage.
XIAOLIN WANG received the M.S. degree from the Inner Mongolia University of Science and Technology, Baotou, China, in 2015. She is currently pursuing the Ph.D. degree in biomedical engineering with the Beijing Institute of Technology. Her research interests include radiation biology, cytobiology, and energy storage behaviors based on nanofilms.
ZHENQI JIANG was born in Wuxi, Jiangsu, China, in 1993. He received the B.S. degree in polymer materials and engineering from Changzhou University, in 2015, and the Ph.D. degree in material physics and chemistry from the University of Chinese Academy of Sciences, in 2020. He is currently pursuing the Ph.D. degree with the Beijing Institute of Technology under the advisor of Prof. Tang. His research interests include the synthesis of nanomaterials and its application in biomedicine, energy, absorption, and so on. He has published more than 20 peer-reviewed research articles in Nano Today, Biomaterials, and so on.
XIAOJUN CHEN received the M.S. degree in signal and information processing from Chongqing University, Chongqing, China, in 2014. She is currently pursuing the Ph.D. degree in biomedical engineering with the Beijing Institute of Technology, Beijing, China. Her research interests include biomedical image processing and biomedical signal processing. Her awards and honors include the Scholarship of the Beijing Institute of Technology and the Scholarship of Chongqing University.
XIAO HAN received the M.S. degree from Georgetown University, USA. She is currently pursuing the Ph.D. degree in biomedical engineering with the Beijing Institute of Technology, Beijing, China. Her research interests include signal regulation mechanism and application of magnetic particle imaging based on magnetic nanoparticle.
XIHONG HAO received the Ph.D. degree from Tongji University, Shanghai, China, in 2008. He is currently a Professor with the Inner Mongolia University of Science and Technology, Baotou, China. His research programs are centered on energy storage behaviors, electrocaloric effects, and energy harvesting performances of ferroelectric and antiferroelectric materials.
XIAOYING TANG received the Ph.D. degree from the Beijing Institute of Technology, Beijing, China. She is currently a Professor with the Beijing Institute of Technology. Her research programs are centered on biomedical image processing, biomedical signal processing, and key technology of MRI equipment.