Dominant Polarization Research Articles

Spatially-varied crustal deformation indicating seismicity at faults intersection in the SE margin of the Tibetan Plateau: Evidence of S-wave splitting from microseismic identification

The Sanjiang Lateral Collision Zone (SLCZ) in the SE margin of the Tibetan Plateau is a special area where several strike-slip faults intersect, resulting in strong deformation and frequent earthquakes. We employ seismic waveforms recorded by a dense temporary broadband array (SJ array) and regional permanent stations to construct more complete microseismic catalogs by the microseismic identification in the SLCZ. New microseismic catalogs effectively increase the number of small earthquakes, revealing the details of the fault structures and providing many more records for S-wave splitting (SWS) analysis. It provides with an uncommon opportunity to detect the detailed upper crustal anisotropy in the fault intersection zone of SLCZ and to dissect the influence of faults, such as the Lijiang-Xiaojinhe fault and Red river fault, on crustal deformation. The spatial distribution of SWS parameters suggests multiple disturbance mechanisms to the upper crustal anisotropy in the study zone. Spatial distribution of dual dominant polarization directions of fast S waves near the block boundary faults uncovers the stress-focus range. Strong deformation from SWS data indicates frequent local seismicity. It reveals the spatial upper crustal deformation indicated by SWS parameters is closely related to not only stress, fault and local structure, but also local seismicity.

Polarity transitions of narrow bipolar events in thundercloud tops reaching the lower stratosphere

Blue corona discharges are often generated in thunderclouds penetrating into the stratosphere and are the optical manifestation of narrow bipolar events (NBEs) observed in radio signals. While their production appears to depend on convection, the cause and nature of such discharges are not well known. Here we show the observations by a lightning detection array of unusual amounts of 982 NBEs during a tropical storm on the coastline of China. NBEs of negative polarity are predominantly observed at the cloud top reaching the stratosphere, and positive NBEs are primarily at lower altitudes. We find that the dominant polarity changes with the typical time of development of thunderstorm cells, suggesting that the polarity depends on the phase of the storm cells. Furthermore, we find that the lightning jump of negative NBEs is associated with above-anvil cirrus plumes of ice crystals and water vapor in the lower stratosphere. We propose that variations in updrafts induce changes in the altitude and charge concentrations of the cloud layers, which lead to the polarity transition. Our results have implications for studies of the chemical perturbations of greenhouse gas concentrations by corona discharges at the tropopause.

Thermal behavior of LiFePO4 battery at faster C-rates and lower ambient temperatures

Extensive focus is needed on the thermal safety of lithium-ion batteries at extreme operating conditions to prevent fire incidents. To accurately investigate the thermal behavior, this study employs a robust electrochemical-thermal model (P2D-T). The model incorporates temperature and concentration-dependent electrochemical parameters translating into an accurate prediction of temporal-spatial temperature variations, heat generation terms and shift in controlling mechanisms. The model has been validated with experimental data (18650 LiFePO4) and computed for a discharge rate of 1 C to 5 C and ambient temperature of 258.15 K to 328.15 K. Results reveal that at normal ambient temperature, the cell temperature gradient rises with the discharge rate (∆T5c2.3=∆T3c1.6=∆T1C). Since, the discharge is electronic conductivity controlled (σs <<σl), spatial non-uniform heat generation peaks form at the positive electrode. The dominant polarization heat (47% contribution, affected by overpotential and local current density) rises, complementing ohmic heat (27% contribution affected by transport resistance), while reversible reaction heat shifts to exothermic near the end of each discharge, contributing to the overall rise in cell temperature. At extreme conditions such as the discharge rate of 5 C and ambient temperature below 263.15 K (-10°C), the cell revealed a critical shift in heat generation mechanisms. Ohmic heat generation starts dominating (31% contribution) where ion transfer limitations (electrolyte diffusivity controlled) lead to non-uniform heat generation at the negative electrode rendering unsafe heat distribution with underutilization of energy (drops by 1.9 Wh/kg).

X-ray polarization in magnetar atmospheres – effects of mode conversion

ABSTRACT Magnetars, the most strongly magnetized neutron stars, are among the most promising targets for X-ray polarimetry. Imaging X-ray Polarimetry Explorer (IXPE), the first satellite devoted to exploring the sky in polarized X-rays, has observed four magnetars to date. A proper interpretation of IXPE results requires the development of new atmospheric models that can take into proper account the effects of the magnetized vacuum on par with those of the plasma. Here we investigate the effects of mode conversion at the vacuum resonance on the polarization properties of magnetar emission by computing plane-parallel atmospheric models under varying conditions of magnetic field strength/orientation, effective temperature, and allowing for either complete or partial adiabatic mode conversion. Complete mode conversion results in a switch of the dominant polarization mode, from the extraordinary (X) to the ordinary (O) one, below an energy that decreases with increasing magnetic field strength, occurring at $\approx 0.5\, \mathrm{keV}$ for a magnetic field strength of $B=10^{14}\, \mathrm{G}$. Partial adiabatic mode conversion results in a reduced polarization degree when compared with a standard plasma atmosphere. No dominant mode switch occurs for $B=10^{14}\, \mathrm{G}$, while there are two switches for lower fields of $B=3\times 10^{13}\, \mathrm{G}$. Finally, by incorporating our models in a ray-tracing code, we computed the expected polarization signal at infinity for different emitting regions on the star surface and for different viewing geometries. The observability of quantum electrodynamics signatures with IXPE and with future soft X-ray polarimeters as Rocket Experiment Demonstration of a Soft X-ray Polarimeter is discussed.

Structure characteristics and microwave/terahertz dielectric response of low-permittivity (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr3(MoO4)9 high-entropy ceramics

Microwave dielectric ceramics play a vital role in wireless communication systems. However, it is a great challenge to obtain ideal performances of single-phase ceramics. In this work, (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr3(MoO4)9 (abbreviated as L5ZMO) high-entropy ceramics were successfully prepared by the solid-state reaction method, the pure trigonal L5ZMO structure can be synthesized in the mixture calcined at 700 °C. Rietveld refinement based on XRD data reveals that lattice parameters of L5ZMO ceramics are affected by the radius of the five rare earth elements, which indicates that the rare earth elements have been solubilized and randomly distributed in the Ln-site. The relative density illustrates a strong dependence on sintering temperature, which gradually increases with increasing sintering temperature. Based on the analysis of bond characteristics, the Mo–O bond exhibits a vital effect on the dielectric properties of L5ZMO ceramics. Besides, the infrared reflection spectrum and terahertz time-domain spectroscopy analysis show that ionic polarization is the dominant polarization in the microwave/terahertz bands. Meanwhile, the tan δ can be further reduced by optimizing process parameters. Notably, the L5ZMO high-entropy ceramics sintered at 750 °C exhibit outstanding dielectric properties of εr = 10.46, Q·f = 59,713 GHz, and τf = −21.94 ppm/°C, indicating that the high-entropy design optimizes τf (−38.8 ppm/°C) of the simple La2Zr3(MoO4)9 ceramics. The attempt provides theoretical guidance for the application of high-entropy design concepts in microwave/terahertz bands.

Paleomagnetic study of Late-Carboniferous-Permian rocks from the Cadí Basin (Eastern Pyrenees): Tectonic implications

We have carried out a detailed paleomagnetic study of volcanic rocks (18 sites) and red beds (10 sites) from the Late-Carboniferous-Permian series of the Cadí Basin (Eastern Pyrenees). The study provides reliable Late Carboniferous-Permian paleomagnetic directions, in an area where paleomagnetic studies are scarce. The main characteristic component in both rock types shows a SSE direction with a shallow inclination and a dominant reverse polarity. The magnetic carriers, both in the volcanic rocks and the red beds, are magnetite and hematite. The main component is interpreted as a primary magnetization of Permian age in the red beds; in the Late Carboniferous volcanic rocks, the main component likely represents primary magnetization or early remagnetization. These results are consistent with the poles for the Iberian plate during the Permian and indicate an absence of regional vertical axis rotations for the Orri nappe, in whose hanging wall the Cadí Basin was transported southwards during the Pyrenean orogeny.

Mapping of stress and structure controlled upper crustal anisotropy in Kumaon-Gharwal Himalaya

Shear wave splitting analysis of local earthquakes provides valuable insights into the structure and stress controlled upper crustal anisotropy signatures. We examine these signatures at the Kumaon-Garhwal Himalaya and provides an excellent example of anisotropic crustal structure in the ongoing continent-continent collision settings between Indian and the Eurasian plates. A total of 256 local earthquakes were selected for the analysis (1.0 ≤ M ≤ 5.4) between January 2017 and February 2021, recorded at a dense network of 51 broadband stations. The result indicates the observed crustal anisotropy is parallel to stress-aligned micro-cracks far from the major Himalayan fault zones and structure parallel near the fault zones. The dominant fast polarization directions (FPD) in the Inner Lesser Himalaya (ILH) and Higher Himalaya, are consistent with the maximum compressive horizontal stress directions (SHmax), essentially influenced by the local stress field. Whereas in the Outer Lesser Himalaya (OLH) and Sub Himalaya, fast directions are sub-parallel to the structural trends, suggesting that the anisotropy is associated with the shear fabric from recent deformation episodes related to structural induced anisotropy. The computed normalized delay times show a mean value of 1 ms/km, within the OLH and Sub-Himalaya, while in ILH and Higher Himalaya, this value increases up to 5.3 ms/km. The associated crack densities are 0.0038 and 0.0207, with shear wave velocity anisotropy of 0.38% and 2.07% respectively. Significant scatter within the depth range of 10–15 km is observed in normalized delay times, suggesting the source of anisotropy within the upper crust.

Exploratory study of macrophage polarization and spatial distribution in colorectal cancer liver metastasis: a pilot study.

The liver is the most typical site of metastatic disease for patients with colorectal cancer (CRC), and up to half the patients with CRC will develop colorectal liver metastasis (CLM). Studying the tumor microenvironment, particularly macrophages and their spatial distribution, can give us critical insight into treatment. Ten CLMs (five treatment-naïve and five post-neoadjuvant chemotherapy) were stained with multiplex immunofluorescence panels against cytokeratins, CD68, Arg1, CD206, CD86, CD163, PD-L1, and MRP8-14. Densities of cell phenotypes and their spatial distribution in the tumor center and the normal liver-tumor interface were correlated with clinicopathological variables. M2 macrophages were the predominant subtype in both the tumor center and the periphery, with a relatively higher density at the periphery. The larger tumors, more than 3.9cm, were associated with higher densities of total CD68+ macrophages and CD68+CD163+ CD206neg and CD68+CD206+ CD163neg M2 macrophage subtypes. Total macrophages in the tumor periphery demonstrated significantly greater proximity to malignant cells than did those in the tumor center (p=0.0371). The presence of higher than median CD68+MRP8-14+CD86neg M1 macrophages in the tumor center was associated with poor overall survival (median 2.34 years) compared to cases with lower than median M1 macrophages at the tumor center (median 6.41 years) in univariate analysis. The dominant polarization of the M2 macrophage subtype could drive new therapeutic approaches in CLM patients.

Ketogenic diet: Assessing YouTube video information using quality, reliability, and text analytics methods.

Patients and the general audience refer social media platforms, such as YouTube, to learn and apply contemporary dietary methods. It is difficult for users to analyze the correctness and quality of information available on open platforms. Using scientific evaluation, this study assessed the quality, reliability, and content of YouTube videos on ketogenic diet (KD). Three experienced medical practitioners reviewed and evaluated 95 videos. The quality and reliability of the videos were assessed using the quality criteria for consumer health information and the global quality scale (GQS). Topic modeling and sentiment analysis were employed to determine the dominant themes and polarity of the information. Three types of publishers (doctors, educational institutions, and influencers) were identified for the study. The mean length of videos posted by doctors was high at 42.24 min. The reliability and quality scores ranging from 0 (low) to 5 (high) had an average of 3.08 ± 1.14 and 3.18 ± 1.18, respectively, for sampled videos. One-way analysis of variance reveals significant differences in DISCERN and GQS scores among doctors, educational institutions, and influencers. Topic discovery identified four themes: keto versus glucose, diabetes, KD food, and major chronic diseases. Sentiment analysis reveals positive content polarity, some content shared by doctors had a neutral sentiment. Content creators should augment the content by citing medical information and terminology. Viewers relied more on doctors for information related to KD. The aesthetic quality is high for all types of publishers. Publishers could focus on the discovered themes to create more content. Publishers should produce high-quality videos by improving esthetics (to increase engagement), and reliable medical information (to increase impact).

Cathode Kinetics Evaluation in Lean-Electrolyte Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries afford great promise on achieving practical high energy density beyond lithium-ion batteries. Lean-electrolyte conditions constitute the prerequisite for achieving high-energy-density Li-S batteries but inevitably deteriorates battery performances, especially the sulfur cathode kinetics. Herein, the polarizations of the sulfur cathode are systematically decoupled to identify the key kinetic limiting factor in lean-electrolyte Li-S batteries. Concretely, an electrochemical impedance spectroscopy combined galvanostatic intermittent titration technique method is developed to decouple the cathodic polarizations into activation, concentration, and ohmic parts. Therein, activation polarization during lithium sulfide nucleation emerges as the dominant polarization as the electrolyte-to-sulfur ratio (E/S ratio) decreases, and the sluggish interfacial charge transfer kinetics is identified as the main reason for degraded cell performances under lean-electrolyte conditions. Accordingly, a lithium bis(fluorosulfonyl)imide electrolyte is proposed to decrease activation polarization, and Li-S batteries adopting this electrolyte provide a discharge capacity of 985 mAh g-1 under a low E/S ratio of 4 μL mg-1 at 0.2 C. This work identifies the key kinetic limiting factor of lean-electrolyte Li-S batteries and provides guidance on designing rational promotion strategies to achieve advanced Li-S batteries.

Seismic Anisotropy in the upper crust beneath the Sanjiang lateral collision zone in the southeastern margin of the Tibetan Plateau revealed by S wave splitting from a temporary array

The Sanjiang lateral collision zone is a key region to understand the Tibetan Plateau’s tectonic structure and the Tethys-Himalayan’s tectonic evolution. Complex tectonic structures, intense crustal deformation, frequent seismicity, and abundant metal deposits are all present. With the seismic data recorded by a temporary array (SJ-Array) and permanent stations (Nov. 2018 ~ Dec. 2020), this paper adopts the S wave splitting technique to obtain the essential properties of upper crustal anisotropy. In the interested area, it is shown that the dominant polarization of the fast S wave is NNW, with a mean polarization direction of 167.9°. In addition, the study area can be divided into three subzones from the west to the east: A, B, and C, according to the various mean polarizations varying from NNW, NS to NNE. The mean normalized time delay between the two split S waves is 4.0 ms/km, and the range of time delay is from 2.0 to 6.3 ms/km. The largest time delay is located at the east side of the western boundary of the Sichuan-Yunnan rhombus block. Furthermore, there is a strip area of strong anisotropy stretching along the western segment of the Lijiang-Xiaojinhe fault. These all demonstrate the local tectonic differences and indicate that the crustal structure may be strongly controlled by the fault and block boundary strike.

Upper crust anisotropy of the 2020 Jiashi MS 6.4 earthquake

The 2020 Jiashi MS 6.4 earthquake occurred north of the 1997–1998 Jiashi earthquake swarm. Because of its complex tectonic environment and frequent strong earthquake occurrence, scholars have paid extensive attention to this area. To study the upper crustal anisotropy in the source area, we applied microseismic event detection and shear-wave splitting techniques to the seismic data recorded by five stations around the epicenter. First, the earthquake catalog of the Jiashi MS 6.4 earthquake sequence was rebuilt using the “Match &amp;amp; Locate” method. A total of 9,695 earthquake events were obtained, and the number of newly detected earthquakes was approximately 7.3 times the number in the officially released catalog. The newly identified microseismic data greatly increased the number of effective records and improved the reliability of the results. We analyzed shear-wave splitting according to the updated catalog. The results showed that the dominant polarizations of the fast shear waves were in NW or NNW at the stations BPM, XKR, L6505, and L6513, consistent with the stress near the source area. There are also blind faults with an NNW direction in the strike distributing en echelon and parallel to the main stress direction in the Jiashi seismic area. Thus, the fast shear-wave polarization of the four stations may also reflect the strike of multiple buried NNW faults in the study area. The fast shear-wave polarization of station HLJ, located at the Halajun Basin, was E–W, with the overall trend of the Kalpin thrust nappe structure. However, this station didn’t show the same NW or NNW fast-wave direction as the four stations previously mentioned. This finding may indicate that the NW-trending buried faults in the Jiashi seismic area have a limited size in both the length and the depth, only reaching northward near the second row of the Kapingtag nappe structure. The temporal trend of the delay time at station HLJ showed that a stress-release process occurred before the MS 6.4 earthquake and that stress-release occurred again after the mainshock. At station XKR, the delay time rapidly increased and then fell in the early period after the MS 6.4 earthquake, indicating that stress accumulated rapidly after the main earthquake but was released during the aftershock sequence. This study provides novel insights into the complex structural characteristics and seismogenic environment in the Jiashi area.

Diabetic macrophage small extracellular vesicles-associated miR-503/IGF1R axis regulates endothelial cell function and affects wound healing.

Diabetic foot ulcer (DFU) is a break in the skin of the foot caused by diabetes. It is one of the most serious and debilitating complications of diabetes. The previous study suggested that dominant M1 polarization during DFU could be the leading reason behind impaired wound healing. This study concluded that macrophage M1 polarization predominates in DFU skin tissue. iNOS was increased in HG-induced M1-polarized macrophages; conversely, Arg-1 was decreased. Macrophage pellets after HG stimulation can impair endothelial cell (EC) function by inhibiting cell viability, tube formation and cell migration, indicating M1 macrophage-derived small extracellular vesicles (sEVs) -mediated HUVEC dysfunction. sEVs miR-503 was significantly upregulated in response to HG stimulation, but inhibition of miR-503 in HG-stimulated macrophages attenuated M1 macrophage-induced HUVEC dysfunction. ACO1 interacted with miR-503 and mediated the miR-503 package into sEVs. Under HG stimulation, sEVs miR-503 taken in by HUVECs targeted IGF1R in HUVECs and inhibited IGF1R expression. In HUVECs, miR-503 inhibition improved HG-caused HUVEC dysfunction, whereas IGF1R knockdown aggravated HUVEC dysfunction; IGF1R knockdown partially attenuated miR-503 inhibition effects on HUVECs. In the skin wound model in control or STZ-induced diabetic mice, miR-503-inhibited sEVs improved, whereas IGF1R knockdown further hindered wound healing. Therefore, it can be inferred from the results that the M1 macrophage-derived sEVs miR-503 targets IGF1R in HUVECs, inhibits IGF1R expression, leads to HUVEC dysfunction, and impedes wound healing in diabetic patients, while packaging miR-503 as an M1 macrophage-derived sEVs may be mediated by ACO1.

Down-regulated GAS6 impairs synovial macrophage efferocytosis and promotes obesity-associated osteoarthritis.

Obesity has always been considered a significant risk factor in osteoarthritis (OA) progression, but the underlying mechanism of obesity-related inflammation in OA synovitis remains unclear. The present study found that synovial macrophages infiltrated and polarized in the obesity microenvironment and identified the essential role of M1 macrophages in impaired macrophage efferocytosis using pathology analysis of obesity-associated OA. The present study revealed that obese OA patients and Apoe-/- mice showed a more pronounced synovitis and enhanced macrophage infiltration in synovial tissue, accompanied by dominant M1 macrophage polarization. Obese OA mice had a more severe cartilage destruction and increased levels of synovial apoptotic cells (ACs) than OA mice in the control group. Enhanced M1-polarized macrophages in obese synovium decreased growth arrest-specific 6 (GAS6) secretion, resulting in impaired macrophage efferocytosis in synovial ACs. Intracellular contents released by accumulated ACs further triggered an immune response and lead to a release of inflammatory factors, such as TNF-α, IL-1β, and IL-6, which induce chondrocyte homeostasis dysfunction in obese OA patients. Intra-articular injection of GAS6 restored the phagocytic capacity of macrophages, reduced the accumulation of local ACs, and decreased the levels of TUNEL and Caspase-3 positive cells, preserving cartilage thickness and preventing the progression of obesity-associated OA. Therefore, targeting macrophage-associated efferocytosis or intra-articular injection of GAS6 is a potential therapeutic strategy for obesity-associated OA.

Prevention of mania in a primigravida at ultra-high risk of postpartum recurrence.

Prevention of mania in a primigravida at ultra-high risk of postpartum recurrence.

Ultra-high-resolution observations of persistent null-point reconnection in the solar corona

Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ultraviolet observations of persistent null-point reconnection in the corona at a scale of about 390 km over one hour observations of the Extreme-Ultraviolet Imager on board Solar Orbiter spacecraft. The observations show formation of a null-point configuration above a minor positive polarity embedded within a region of dominant negative polarity near a sunspot. The gentle phase of the persistent null-point reconnection is evidenced by sustained point-like high-temperature plasma (about 10 MK) near the null-point and constant outflow blobs not only along the outer spine but also along the fan surface. The blobs appear at a higher frequency than previously observed with an average velocity of about 80 km s−1 and life-times of about 40 s. The null-point reconnection also occurs explosively but only for 4 minutes, its coupling with a mini-filament eruption generates a spiral jet. These results suggest that magnetic reconnection, at previously unresolved scales, proceeds continually in a gentle and/or explosive way to persistently transfer mass and energy to the overlying corona.

Synthesis, magnetic, AC conductivity and dielectric properties of hematite nanocrystallites

We are reporting the synthesis along with magnetic, ac conductivity and dielectric properties of hematite nanocrystallites. The prepared Fe2O3 is crystallizing in corundum structure which belongs to the rhombohedron system with the space group R3-c. The magnetization data shows a typical Morin transition, TN = 265 K for 110 nm crystallites, whereas this transition is decreasing with decrease in crystallite size, TN = 252 K for 33 nm. The value of magnetization is increased with increasing crystallite size. The enhanced dielectric permittivity and ac conductivity were observed in higher hematite crystallite size. The overall dielectric response has revealed conduction mechanism is due to the extrinsic contribution from the dominant Maxwell-Wagner polarization.

Determining the preferable polarization loss for magnetoelectric microwave absorbers by strategy of controllably regulating defects

Regulating the inner defects could lead to transformation of the prominent dielectric loss for the microwave absorbers, which is a necessary foundation to explore the preference type of dielectric loss mechanism. Herein, in this work, selective molar ratios of melamine/cetyl trimethyl ammonium bromide (CTAB) precursors were designed to construct the Fe/C/N based hybrid materials. The results demonstrate that the dominated polarization loss can be obtained with the high molar ratio of melamine/CTAB due to the improved level of defects density such as point defects, heterointerface distortion, etc. Differently, it is easy to obtain the conductive carbon phase and high crystallinity degree of Fe3C with a low melamine/CTAB molar ratio, achieving significantly conductive loss. Finally, the Fe/C/N hybrid with dominant polarization loss harvests a broad bandwidth of 6.2 GHz at 1.7 mm, verifying the superiority of polarization loss for enhancing electromagnetic absorption performance. Furthermore, simulation results prove that this composite possesses the desirable radar cross section (RCS) reduction and electromagnetic protection for the human head, indicating the potential applications in both military and civilian fields.

Shear wave splitting analysis of local earthquakes from dense arrays in Shimian, Sichuan

The Shimian area of Sichuan sits at the junction of the Bayan Har block, Sichuan-Yunnan rhombic block, and Yangtze block, where several faults intersect. This region features intense tectonic activity and frequent earthquakes. In this study, we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region. We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area. Although some stations returned a polarization direction of NNW-SSE, a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area. The polarization directions of the fast shear wave were highly consistent throughout the study area. This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults. The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures. The mean delay time between fast and slow shear waves was 3.83 ms/km, slightly greater than the values obtained in other regions of Sichuan. This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.

Resistive-like Behavior of Ferroelectric p–n Bilayer Structures Based on Epitaxial Pb(Zr0.2Ti0.8)O3 Thin Films

The p–n junctions are the building blocks of nowadays electronic devices. The n- or p-type conductivity is obtained in classic semiconductors, like Si, by doping with atoms acting as donors or acceptors, respectively. Doping was used in ferroelectrics to influence the transition temperature, magnitude of some physical properties, but not necessarily conduction type. Therefore, comprehensive studies to obtain true ferroelectric p–n junctions by controlled doping are missing. Recently, it has been shown that Pb(Zr0.2Ti0.8)O3 films doped with ≈1% atomic Nb (n-type doping) or Fe (p-type doping) have different orientations of polarization in the as-grown state. Knowing that polarization orientation depends on doping type, the next step is to build ferroelectric p–n homojunctions and to study their properties in relation to ferroelectric polarization. p–n and n–p structures were grown for this purpose by successive deposition of Nb-doped and Fe-doped Pb(Zr,Ti)O3 layers with different thicknesses. We find that these p–n homojunctions are ferroelectric, but the magnitude of the polarization and coercive field, as well as the dominant polarization orientation in the as-grown state, depend on the conduction type of the first grown layer. The I–V characteristics are quasi-linear, although the interfaces with the electrodes behaves as Schottky contacts. The resistance extracted from the I–V characteristics displays an exponential dependence on temperature, with an activation energy in the range of 0.14–0.17 eV. These results are explained assuming that the total current in the junction is the total of electron and hole injections at the electrode interfaces. It is shown that for relatively low doping concentrations, the current density contains a dominant term with a linear voltage dependence and an exponential temperature dependence, as observed experimentally, and a secondary (correction) term that is dependent on the free carrier density and can induce non-linear voltage dependence when this density is significant.