Large Hysteresis Research Articles

High piezoelectricity and low strain hysteresis in PMN–PT-based piezoelectric ceramics

High piezoelectric properties and low strain hysteresis (<i>H</i>) are both equally necessary for practical applications in precisely controlled piezoelectric devices and systems. Unlike most of previous reports, where enhanced piezoelectric performance is typically accompanied by large hysteresis in lead-/lead-free-based ceramics, in this work, we report a reconstructed relaxor ferroelectric composition in 0.68Pb(Mg_1/3Nb_2/3)O₃–0.32PbTiO₃ (0.68PMN–0.32PT) ceramics through the introduction of (Bi_0.5Na_0.5)ZrO₃ (BNZ) to simultaneously achieve low strain hysteresis (~7.68%), superior piezoelectricity (~1040 pC·N⁻¹), and an electric field induced strain of 0.175%. Our work not only paves the way to simultaneously large piezoelectricity and negligible strain hysteresis in ceramic systems, but also lays the foundation for the further development of novel functional materials.

Total-Ionizing-Dose Effects and Low-Frequency Noise in N-Type Carbon Nanotube Field-Effect Transistors With HfO₂ Gate Dielectrics

Total ionizing dose (TID) irradiation and low-frequency noise characterization are performed on carbon nanotube field-effect transistors (CNTFETs). Large hysteresis due to high border-trap densities is observed in as-processed and irradiated devices. TID irradiation also leads to significant radiation-induced charge trapping in the surrounding dielectrics resulting in parametric degradation. Percolation-path switching, and border traps contribute to low-frequency noise, with a relatively more prominent role for border traps after irradiation than before irradiation. These results show that process improvements are required to optimize both the initial operating characteristics and the radiation response of CNTFETs.

Well-defined double hysteresis loop in NaNbO3 antiferroelectrics

Antiferroelectrics (AFEs) are promising candidates in energy-storage capacitors, electrocaloric solid-cooling, and displacement transducers. As an actively studied lead-free antiferroelectric (AFE) material, NaNbO3 has long suffered from its ferroelectric (FE)-like polarization-electric field (P-E) hysteresis loops with high remnant polarization and large hysteresis. Guided by theoretical calculations, a new strategy of reducing the oxygen octahedral tilting angle is proposed to stabilize the AFE P phase (Space group Pbma) of NaNbO3. To validate this, we judiciously introduced CaHfO3 with a low Goldschmidt tolerance factor and AgNbO3 with a low electronegativity difference into NaNbO3, the decreased cation displacements and [BO6] octahedral tilting angles were confirmed by Synchrotron X-ray powder diffraction and aberration-corrected scanning transmission electron microscopy. Of particular importance is that the 0.75NaNbO3−0.20AgNbO3−0.05CaHfO3 ceramic exhibits highly reversible phase transition between the AFE and FE states, showing well-defined double P-E loops and sprout-shaped strain-electric field curves with reduced hysteresis, low remnant polarization, high AFE-FE phase transition field, and zero negative strain. Our work provides a new strategy for designing NaNbO3-based AFE material with well-defined double P-E loops, which can also be extended to discover a variety of new lead-free AFEs.

Nanographene-Based Heterojunctions for High-Performance Organic Phototransistor Memory Devices.

Organic phototransistors can enable many important applications such as nonvolatile memory, artificial synapses, and photodetectors in next-generation optical communication and wearable electronics. However, it is still a challenge to achieve a big memory window (threshold voltage response ∆Vth ) for phototransistors. Here, a nanographene-based heterojunction phototransistor memory with large ∆Vth responses is reported. Exposure to low intensity light (25.7µWcm-2 ) for 1 s yields a memory window of 35V, and the threshold voltage shift is found to be larger than 140V under continuous light illumination. The device exhibits both good photosensitivity (3.6 × 105 ) and memory properties including long retention time (>1.5 × 105 s), large hysteresis (45.35V), and high endurance for voltage-erasing and light-programming. These findings demonstrate the high application potential of nanographenes in the field of optoelectronics. In addition, the working principle of these hybrid nanographene-organic structured heterojunction phototransistor memory devices is described which provides new insight into the design of high-performance organic phototransistor devices.

Reversible Thermal Hysteresis in Heating‐Cooling Cycles of Magnetic Susceptibility: A Fine Particle Effect of Magnetite

AbstractThermomagnetic curves of magnetic susceptibility (κ) are key to characterizing magnetic properties. We report hump‐shaped κ‐T curves of magnetite‐bearing basalt during heating‐cooling cycles to ∼340°C, with a large thermal hysteresis and similar starting and ending values, even in multiple repeated cycles, ruling out changes in magnetic mineralogy. Based on FORC diagrams and published results of engineered materials, we propose that thermal hysteresis arises from configurations of magnetic moments in clusters of single‐domain particles due to dipolar coupling, with different collective behavior during heating and cooling. This effect modifies the hump‐shaped thermal relaxation behavior of the individual nanoparticles. FORC and κ‐T results indicate an increase in effective particle sizes after 700°C‐heating. Our results are a warning against premature interpretation of a decreasing trend in κ‐T curves by maghemite inversion. Instead, fine particle behavior should be considered when a hump‐shaped κ‐T behavior is detected.

Thermal hysteretic behavior and negative magnetoresistance in the charge density wave material EuTe4

EuTe4 is a newly-discovered van der Waals material exhibiting a novel charge-density wave (CDW) with a large thermal hysteresis in the resistivity and CDW gap. In this work, we systematically study the electronic structure and transport properties of EuTe4 using high-resolution angle-resolved photoemission spectroscopy (ARPES), magnetoresistance measurements, and scanning tunneling microscopy (STM). We observe a CDW gap of about 200 meV at low temperatures that persists up to 400 K, suggesting that the CDW transition occurs at a much higher temperature. We observe a large thermal hysteretic behavior of the ARPES intensity near the Fermi level, consistent with the resistivity measurement. The hysteresis in the resistivity measurement does not change under a magnetic field up to 7 T, excluding the thermal magnetic hysteresis mechanism. Instead, the surface topography measured with STM shows surface domains with different CDW trimerization directions, which may be important for the thermal hysteretic behavior of EuTe4. Interestingly, we observe a large negative magnetoresistance at low temperatures that can be associated with the canting of magnetically ordered Eu spins. Our work shed light on the understanding of magnetic, transport, and electronic properties of EuTe4.

High electric field-induced ferroelectric loss of polymer/paraelectric barium titanate particle nanocomposites

Polymer nanodielectrics have manifested high energy densities for potential applications in film capacitors. However, ferroelectric-like large hysteresis is often observed in the bipolar polarization–electric field (P-E) loops, even though neither the polymer matrix nor the ceramic nanoparticle exhibits any intrinsic ferroelectricity. To understand this abnormal ferroelectric behavior, poly(vinyl pyrrolidone) (PVP)/60 nm BaTiO3 (BTO60) nanocomposite films were fabricated with uniform BTO60 nanoparticle dispersion. PVP was a linear dielectric polymer with an apparent dielectric constant of 6.8 and BTO60 was found to be paraelectric. When the volume fraction of BTO60 was above 30 vol%, broad ferroelectric P-E loops were yielded. Using a theoretical deconvolution of the broad P-E loops based on the Langevin-type function, three contributions were identified. First, deformational polarization generated the linear dielectric constant of nanocomposites, from which the linear dielectric constant of BTO60 nanoparticles was extracted using the Bruggeman mixing rule. Second, slim paraelectric P-E loops were obtained for the BTO60 nanoparticles. From the saturated polarization, the electric field-induced permanent dipole moment per unit cell was estimated to be 0.07–0.2 D at a poling field of 20–100 MV/m, which was significantly smaller than the dipole moment (5.3 D) of the tetragonal unit cell of BaTiO3, indicating the paraelectric nature of BTO60 nanoparticles. Third, strong particle–particle dipolar interactions induced transient ferroelectric domains among the high dielectric constant BTO60 nanoparticles, particularly when the poling electric field was high. The third contribution dominated the overall polarization process and thus accounted for the abnormal ferroelectric behavior for the linear dielectric polymer/paraelectric ceramic nanoparticle composites. The knowledge gained from this study will pave the way towards developing better strategies for polymer nanodielectrics in the applications of capacitive energy storage.

Reversible conversion–alloying of cobalt–bismuth oxide nanoneedles for long-life lithium storage anodes

Materials that undergo combined conversion and alloying reactions are promising as anodes for lithium storage application because they can accommodate multiple lithium ions. However, irreversible conversion reactions, large voltage hysteresis, poor rate capabilities, and low initial Coulombic efficiencies during continuous discharge–charge cycling make practical applications of conversion–alloying materials challenging. Herein, we present cobalt–bismuth oxide (CBO) nanoneedles, a new bimetallic material in which Li+-ion uptake proceeds stepwise, thus effectively suppressing volume expansion. During the initial lithiation stage, the CBO nanoneedles undergo a conversion reaction to form nanodomains of low-oxidation-state Coδ+ (δ ≤ 2) in a Li2O matrix. At the next potential platform, the Bi phase attracts Li+ ions via an alloying reaction, while the Coδ+/Li2O phase hinders excessive volume expansion. Consequently, the CBO electrode delivers a high reversible discharge capacity of 392 mAh g−1 at 50 mA g−1 for up to 100 cycles. Further, an ultrastable long-term capacity of 300 mAh g−1 at 250 mA g−1 is realized over 1000 cycles. The stepwise lithiation process decreases volume expansion significantly (by ∼10%), which leads to good cyclability. Owing to their ease of preparation and excellent performance characteristics, CBO nanoneedles are an attractive long-life anode material for lithium-ion batteries.

Site-specific atomic substitution in a giant magnetocaloric Fe2P -type system

Giant magnetocaloric (GMC) materials constitute a requirement for near room temperature magnetic refrigeration. (Fe,Mn)$_2$(P,Si) is a GMC compound with strong magnetoelastic coupling. The main hindrance towards application of this material is a comparably large temperature hysteresis, which can be reduced by metal site substitution with a nonmagnetic element. However, the (Fe,Mn)$_2$(P,Si) compound has two equally populated metal sites, the tetrahedrally coordinated $3f$ and the pyramidally coordinated $3g$ sites. The magnetic and magnetocaloric properties of such compounds are highly sensitive to the site specific occupancy of the magnetic atoms. Here we have attempted to study separately the effect of $3f$ and $3g$ site substitution with equal amounts of vanadium. Using formation energy calculations, the site preference of vanadium and its influence on the magnetic phase formation are described. A large difference in the isothermal entropy change (as high as 44\%) with substitution in the $3f$ and $3g$ sites is observed. The role of the lattice parameter change with temperature and the strength of the magnetoelastic coupling on the magnetic properties are highlighted.

Hydroxypropyl methyl cellulose reinforced conducting polymer hydrogels with ultra-stretchability and low hysteresis as highly sensitive strain sensors for wearable health monitoring

Conducting polymer hydrogels have emerged as promising materials to fabricate highly sensitive strain sensors. However, due to weak bindings between conducting polymer and gel network, they usually suffer from limited stretchability and large hysteresis, failing to achieve wide-range strain sensing. Herein, we combine hydroxypropyl methyl cellulose (HPMC), poly (3,4-ethylenedioxythiophene):poly (styrene sulfonic acid) (PEDOT: PSS) with chemically cross-linked polyacrylamide (PAM) to prepare a conducting polymer hydrogel for strain sensors. Owing to abundant hydrogen bonds between HPMC, PEDOT:PSS and PAM chains, this conducting polymer hydrogel exhibits high tensile strength (166 kPa), ultra-stretchability (>1600 %) and low hysteresis (<10 % at 1000 % cyclic tensile strain). The resultant hydrogel strain sensor shows ultra-high sensitivity, wide strain sensing ranges of 2–1600 %, and excellent durability and reproducibility. Finally, this strain sensor can be used as wearable sensor to monitor vigorous human movement and fine physiological activity, and services as bioelectrodes for electrocardiograph and electromyography monitoring. This work provides new horizons to design conducting polymer hydrogels for advanced sensing devices.

Crystal growth of CeMn0.85Sb2: Absence of magnetic order of Ce-sublattice

Single crystals of CeMn0.85Sb2 have been successfully synthesized by using the Bi as flux. Analysis of single crystal x-ray diffraction data confirms that CeMn0.85Sb2 crystallizes in the HfCuSi2-type structure with the space group P4/nmm (No. 129). In the case of H||c, CeMn0.85Sb2 displays a robust antiferromagnetic transition at ∼160 K for Mn-sublattice, and there is no sign of magnetic order regarding Ce-sublattice. In the case of H ⊥ c, the Mn-sublattice shows signs of magnetic order at 160 K and 116 K, indicating a possible spin reorientation. There is no sign of magnetic order for the Ce-sublattice either, but, alternating current magnetic susceptibility measurements reveal a spin glass state below 18 K in the case of H ⊥ c. Isothermal magnetization curves measured below magnetic order with H ⊥ c show saturation and even large hysteresis at 2 K, indicating the presence of a ferromagnetic component. In addition, a field-induced spin-flop transition is observed in the case of H ⊥ c, indicating a field-induced spin reorientation of Mn spins. Electrical resistivity measurements indicate a metallic nature for CeMn0.85Sb2 and large anisotropy which is consistent with its quasi-two-dimensional layered structure.

Ultrahigh electrostrain with excellent fatigue resistance in textured Nb 5+-doped (Bi 0.5Na 0.5)TiO 3-based piezoceramics

(Bi_0.5Na_0.5)TiO₃ (BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain (electrostrain) properties, but often suffer from large hysteresis and poor fatigue resistance, which strongly limit their applications. Here, &lt;00<i>l</i>&gt; textured Nb⁵⁺-doped 0.8(Bi_0.5Na_0.5)TiO₃–0.2(Bi_0.5K_0.5)TiO₃ (0.8BNT–0.2BKT) ceramics with a high degree of texturing (~80%) were prepared by the reactive template grain growth (RTGG) method using Bi₄Ti₃O₁₂ as a template. By the combination of donor doping in the B-site and the RTGG method, the electrostrain performance achieves a significant enhancement. A high electrostrain of 0.65% and a piezoelectric coefficient (<inline-formula> <math display="inline" id="MA1"><mrow><msubsup><mi>d</mi><mrow><mn>33</mn></mrow><mo>*</mo></msubsup></mrow></math></inline-formula>) of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained. No electrostrain performance degradation is observed after unipolar electric field loading of 10⁵ cycles, showing excellent fatigue endurance. These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.

Coupling between Charge Density Wave Ordering and Magnetism in Ho2Ir3Si5

Ho2Ir3Si5 belongs to the family of three-dimensional (3D) R2Ir3Si5 (R = Lu, Er, Ho) compounds that exhibit a first-order, charge-density-wave (CDW) phase transition, where there is a strong orthorhombic-to-triclinic distortion of the lattice accompanied by superlattice reflections. The analysis by single-crystal X-ray diffraction (SXRD) has revealed that the Ir–Ir zigzag chains along c are responsible for the CDW in all three compounds. The replacement of the rare earth element from nonmagnetic Lu to magnetic Er or Ho lowers TCDW, where TCDWLu = 200 K, TCDWEr = 150 K, and TCDWHo = 90 K. Out of the three compounds, Ho2Ir3Si5 is the only system where second-order superlattice reflections could be observed, indicative of an anharmonic shape of the modulation wave. The CDW transition is observed as anomalies in the temperature dependencies of the specific heat, electrical conductivity, and magnetic susceptibility, which includes a large hysteresis of 90 to 130 K for all measured properties, thus corroborating the SXRD measurements. Similar to previously reported Er2Ir3Si5, there appears to be a coupling between CDW and magnetism such that the Ho3+ magnetic moments are influenced by the CDW transition, even in the paramagnetic state. Moreover, earlier investigations on polycrystalline material revealed antiferromagnetic (AFM) ordering at TN = 5.1 K, whereas AFM order is suppressed and only the CDW is present down to at least 0.1 K in our highly ordered single crystal. First-principles calculations predict Ho2Ir3Si5 to be a metal with coexisting electron and hole pockets at the Fermi level. The Ho and Ir atoms have spherically symmetric metallic-type charge density distributions that are prone to CDW distortion. Phonon calculations affirm that the Ir atoms are primarily responsible for the CDW distortion, which is in agreement with the experiment.

Modulation of Local Charge Distribution Stabilized the Anionic Redox Process in Mn-Based P2-Type Layered Oxides.

An anionic redox reaction is an extraordinary method for obtaining high-energy-density cathode materials for sodium-ion batteries (SIBs). The commonly used inactive-element-doped strategies can effectively trigger the O redox activity in several layered cathode materials. However, the anionic redox reaction process is usually accompanied by unfavorable structural changes, large voltage hysteresis, and irreversible O2 loss, which hinders its practical application to a large extent. In the present work, we take the doping of Li elements into Mn-based oxide as an example and reveal the local charge trap around the Li dopant will severely impede O charge transfer upon cycling. To overcome this obstacle, additional Zn2+ codoping is introduced into the system. Theoretical and experimental studies show that Zn2+ doping can effectively release the charge around Li+ and homogeneously distribute it on Mn and O atoms, thus reducing the overoxidation of O and improving the stability of the structure. Furthermore, this change in the microstructure makes the phase transition more reversible. This study aimed to provide a theoretical framework for further improve the electrochemical performance of similar anionic redox systems and provide insights into the activation mechanism of the anionic redox reaction.

Improved capacitive energy storage in sodium niobate-based relaxor antiferroelectric ceramics

Ceramic-based dielectric capacitors have become an attractive issue due to their wide applications in current pulsed-/high-power electronic devices. Antiferroelectric ceramics generally exhibit ultrahigh energy density owing to their giant polarization activated by antiferroelectric–ferroelectric phase transition under a high electric field but suffer from large hysteresis, meanwhile giving rise to low efficiency. Herein, by introducing perovskite compound Sr(Fe0.5Ta0.5)O3 into an antiferroelectric NaNbO3 matrix, a stabilized antiferroelectric phase and an improved relaxor behavior are observed. That is, relaxor antiferroelectric ceramics are constructed. Accordingly, a double polarization–electric field (P–E) loop becomes slimmer with increasing incorporation of dopants, leading to an ultrahigh recoverable energy density of 11.5 J/cm3, an energy storage efficiency of 86.2%, outstanding frequency/cycling/thermal reliability, and charge–discharge properties in 0.90NaNbO3-0.10Sr(Fe0.5Ta0.5)O3 ceramics. This work reveals that inducing the relaxor behavior in antiferroelectric materials is an effective route to improve their capacitive energy storage.

Multifunctional Organohydrogel with Ultralow‐Hysteresis, Ultrafast‐Response, and Whole‐Strain‐Range Linearity for Self‐Powered Sensors

AbstractThe conductive hydrogels always suffered from high internal friction, large hysteresis, and low capability of accurately predicting physical deformation, which seriously restricted their application in smart wearable devices. To address these problems, solvent molecules are directionally inserted into the polymer molecule chains via bridge effect to effectively reduce the molecular internal friction. Moreover, swelling is also combined to eliminate the temporary entanglements in the hydrogel system. The cooperation between the bridge and swollen effect endows the prepared polyacrylamide (PAM)/laponite/H3BO3/ethylene glycol (Eg) organohydrogel (PLBOH) ultralow hysteresis (1.38%, ε = 100%), ultrafast response (≈10 ms), and high linearity in the whole‐strain‐range (R2 = 0.996) with a great sensitivity (GF = 2.68 at the strain range of 0–750%). Meanwhile, the prepared PL10B30OH exhibits long‐term stability, excellent stretchability, and low dissipated energy. Furthermore, the assembled triboelectric nanogenerator (TENG) displays an outstanding energy harvesting performance with an output voltage of 200 V with the size of 20 mm × 20 mm. The assembled strain sensors can monitor the small strain of facial expressions and large strain of human movements, indicating the tremendous applications in self‐powered intelligent and flexible wearable electronics under harsh environmental conditions.

Effects of Cr doping on the magnetic properties of one-dimensional spin chain system α–CoV2O6

This study investigates the structural and magnetic properties of α–CoV2O6 and Cr doped α–CoV2O6 samples synthesized using a wet chemical method. X-ray diffraction (XRD) measurements and analysis indicate that α–CoV2O6 forms in a monoclinic crystal structure, with lattice parameters a = 9.26 Å, b = 3.50 Å, c = 6.62 Å, β = 111.42°, and α = γ = 90°. The magnetic properties of the compounds were probed using a vibrating sample magnetometer (VSM), by measuring the temperature, T, field, μ0H, and time, t, dependence of magnetization, M. The compounds take on an antiferromagnetic (AFM) order at 0.1 T, with an enhancement of the magnetization below 6.5 K. Cr doping resulted in an enhancement of magnetization below TN. M(μ0H) isotherms show metamagnetic transitions with a 1/3 magnetization plateau for both samples. A large hysteresis is observed for fields less than 5 T and is attributed to frozen metastable, irreversible states. M(T) data at 2.5 T and 5 T shows that the metamagnetic transitions take both compounds from an AFM to an intermediate ferrimagnetic (FI) state and ferromagnetic (FM) state at high fields. No significant changes in TN were observed with Cr doping. Zero-field-cooled (ZFC) and field-cooled (FC) bifurcation was observed for fields between 1 T and 3 T, attributed to spin-glass-like freezing of the samples at TSG. The spin-glass behaviour of the samples was confirmed using the Gabay-Toulouse (G-T) line and M(t) curves.

Ultrahigh energy density and excellent discharge properties in Ce4+ and Ta5+ co-modified AgNbO3 relaxor antiferroelectric ceramics via multiple design strategies

Silver niobate (AgNbO3) has been recently regarded as one of the best candidates for developing high-performance dielectric capacitors on account of its large maximum polarization and near-zero remnant polarization, but its room-temperature ferrielectric (FIE) behavior and large electric hysteresis impede further improvement of energy storage properties. In order to solve this issue, herein, we design Ce4+ and Ta5+ co-modified (Ag0.96Ce0.01)(Nb1-xTax)O3 relaxor antiferroelectric (AFE) ceramics. The introduction of Ce4+ and Ta5+ decreases the tolerance factor, reduces the B-site cation polarizability, and enhances A- and B- site cation disorder, leading to suppressed FIE characteristic, improved AFE stability, and enhanced relaxor degree. Besides, the co-doping strategy causes the decrease of the grain size, and the experimental results and finite element simulations both indicate that this is fairly effect on the improvement of the breakdown strength. Consequently, an ultrahigh recoverable energy density of 7.37 J/cm3, which far exceeds those of the latest AgNbO3-based ceramics, and a large efficiency of 75.66% are simultaneously achieved in (Ag0.96Ce0.01)(Nb0.7Ta0.3)O3 ceramics. More encouragingly, the ceramic exhibits excellent actual discharge capacity with ultrafast discharge time of 23 ns and ultrahigh power density of 294.28 MW/cm3, which outperforms many recently reported lead-free dielectric ceramics, and the discharge properties are fairly stable during a wide temperature range of 20–180 °C. This work sheds light on designing and developing high-performance lead-free dielectric capacitors applicable in harsh environment.

Partially Reversible Anionic Redox for Lithium-Excess Cobalt Oxides with Cation-Disordered Rocksalt Structure

Li-excess electrode materials potentially boost the energy density of Li-ion batteries, but the origin of the instability of anionic redox in cation-disordered rocksalt material is still under debate. In this study, a binary system of Li3NbO4–CoO is targeted as electrode materials for lithium storage applications. In this binary system, stoichiometric LiCo2/3Nb1/3O2 crystallizes into a rocksalt-type structure with partial ordering of Nb ions. Upon increase of the Li3NbO4 fraction, cation ordering is lost, forming a cation-disordered rocksalt structure in Li-excess phases. Although Li-excess Li4/3Co2/9Nb4/9O2 delivers a large reversible capacity as electrode materials, inferior cyclability and large voltage hysteresis for charge/discharge curves are noted. Irreversible structural changes in electrochemical cycles are also evidenced from results of in situ XRD measurements, suggesting that anionic redox is destabilized for Li4/3Co2/9Nb4/9O2. X-ray absorption spectroscopy reveals that partial stabilization of ligand holes as observed in SrCoO3 is achieved for these oxides. Ligand holes are more effectively stabilized for Li7/6Co4/9Nb7/18O2 with less Li-excess and Co-rich composition. Through systematic study of the binary system of Li3NbO4–CoO with different chemical compositions, factors affecting reversibility and irreversibility of anionic redox are further discussed.

Dynamics of the freeze–thaw front of active layer on the Qinghai-Tibet Plateau

The seasonal dynamics of the freeze–thaw front during the freezing and thawing period strongly affect the hydrothermal processes in the active layer and the water-energy exchange processes between land and the atmosphere. Therefore, characterizing variation in the freeze–thaw front and its effect on the water and heat transfer mechanisms in the soil layer is important for enhancing our understanding of change in permafrost. In this study, we used data from field observations to analyze the freeze–thaw front dynamics during the freezing and thawing period in permafrost regions of the Qinghai-Tibet Plateau. The zero-curtain duration time was longer during the freezing period than during the thawing period at all sites. Changes in the freeze–thaw front were characterized by three distinct stages: the downward migration of the thaw front, zero curtain process at the bottom of the active layer, and the bidirectional freezing period. In addition, changes in the thaw front and soil moisture thaw period were consistent, but the freezing period of moisture showed large hysteresis compared with ground temperature. There was a power function and exponential relationship between the negative ground temperature and the unfrozen water content during warming and cooling processes, respectively. Linear and power relationships were observed between the net radiation accumulation and thawing front, and there was a power function relationship between the thawing front and soil heat flux. There was a quadratic polynomial relationship between the thawing front and thawing degree-days. The fitted relationships can better represent the dynamics of the freeze–thaw front during the freezing and thawing period. These findings aid our understanding of the hydrothermal characteristics of the active layers and will improve future permafrost simulation models.