Electrical Phase Transition Research Articles

Peculiarities of Electrical Switching and Phase Transition Dynamics in Bismuth-Infused Se–Te Chalcogenide Glasses: From Bulk to Thin Film Devices

Peculiarities of Electrical Switching and Phase Transition Dynamics in Bismuth-Infused Se–Te Chalcogenide Glasses: From Bulk to Thin Film Devices

Pressure-Induced Changes in the Crystal Structure and Electrical Conductivity of GeV4S8.

Lacunar spinels, represented by AM4X8 compounds (A = Ga or Ge; M = V, Mo, Nb, or Ta; X = S or Se), form a unique group of ternary chalcogenide compounds. Among them, GeV4S8 has garnered significant attention due to its distinctive electrical and magnetic properties. While previous research efforts have primarily focused on studying how this material behaves under cooling conditions, pressure is another factor that determines the state and characteristics of solid matter. In this study, we employed a diamond anvil cell in conjunction with high-energy synchrotron X-ray diffraction, Raman spectroscopy, four-point probes, and theoretical computation to thoroughly investigate this material. We found that the structural transformation from cubic to orthorhombic was initiated at 34 GPa and completed at 54 GPa. Through data fitting of volume vs pressure, we determined the bulk moduli to be 105 ± 4 GPa for the cubic phase and 111 ± 12 GPa for the orthorhombic phase. Concurrently, electrical resistance measurements indicated a semiconductor-to-nonmetallic conductor transition at ∼15 GPa. Moreover, we experimentally assessed the band gaps at different pressures to validate the occurrence of the electrical phase transition. We infer that the electrical phase transition correlates with the valence electrons in the V4 cluster rather than the crystal structure transformation. Furthermore, the computational results, electronic density of states, and band structure verified the experimental observation and facilitated the understanding of the mechanism governing the electrical phase transition in GeV4S8.

Redox Gating for Colossal Carrier Modulation and Unique Phase Control.

Redox gating, a novel approach distinct from conventional electrolyte gating, combines reversible redox functionalities with common ionic electrolyte moieties to engineer charge transport, enabling power-efficient electronic phase control. This study achieves a colossal sheet carrier density modulation beyond 1016 cm-2, sustainable over thousands of cycles, all within the sub-volt regime for functional oxide thin films. The key advantage of this method lies in the controlled injection of a large quantity of carriers from the electrolyte into the channel material without the deleterious effects associated with traditional electrolyte gating processes such as the production of ionic defects or intercalated species. The redox gating approach offers a simple and practical means of decoupling electrical and structural phase transitions, enabling the isostructural metal-insulator transition and improved device endurance. The versatility of redox gating extends across multiple materials, irrespective of their crystallinity, crystallographic orientation, or carrier type (n- or p-type). This inclusivity encompasses functional heterostructures and low-dimensional quantum materials composed of sustainable elements, highlighting the broad applicability and potential of the technique in electronic devices.

Phase Transition Engineering of Vanadium Dioxide Induced by Oxygen Vacancies

A reconfigurable optical functional system is a pioneering and comprehensive approach for portable future flexible electronics, irrespective of traditional silicon-based technology. VO2 shows tremendous temperature-dependent structural and electrical phase transitions as a complex correlated metal oxide, presenting it as a potential candidate for bolometers, thermal camouflage, and optoelectronics applications. However, the structural stability and high transition temperature restrict room-temperature applications. The present study reports the oxygen vacancies-assisted phase transition engineering in the VO2/muscovite heterostructure. The ion bombardment alters the oxygen stoichiometry of VO2/muscovite thin film at room temperature. A significant decrease in lattice constant has been observed during the transition of the insulating M1 (monoclinic) phase into the metallic R (tetragonal) phase, which was confirmed through high-resolution XRD. The change in oxygen vacancy concentration determined using X-ray photoelectron spectroscopy (XPS) actively suppressed and stabilized the epitaxial thin film of VO2 near room temperature. We investigated whether applying increasing power-mediated ion bombardment for a few minutes affects the oxygen vacancy formation on the VO2/muscovite film’s surface. Consequently, a change in KPFM and 4 orders of magnitude change in resistance of VO2 thin film have been observed. This report reveals the fundamental understanding of controlling the MIT in epitaxial VO2 thin film via facile and clean phase transition engineering techniques for advanced flexible electronic devices.

Electrical energy harvesting by connected form stable phase change material composites

Over the years, thermoelectric energy harvesting has been becoming a topic of intensive research and thermoelectric power generator has been utilized in various energy harvesting applications. However, a thermoelectric device is required to harvest energy, which has relatively low efficiency and high cost. To overcome such a common problem, the objective of this study is to generate electrical energy without using thermoelectric devices. To this end, an advanced energy harvester composed of two different phase change material composites was explored. It was hypothesized that based on the well-known Seebeck effect, stable electrical energy output would be feasible without a thermoelectric device, by directly connecting two types of phase change materials with different electrical conductivities and different phase transition temperatures. In this study, polydimethylsiloxane open-cell foam embedded with single walled carbon nanotubes was prepared and utilized as a supporting material to fabricate form stable phase change material composites. Two types of polydimethylsiloxane open-cell foams were prepared by embedding single walled carbon nanotubes, which had a weight fraction of 0.33 % and 0.1 %, respectively, leading to different electrical conductivities. The different electrical conductivities of the supporting foams are vital to cause electron motion. Two types of phase change materials with different phase change temperatures were selected as working materials by filling them into the polydimethylsiloxane open-cell foams. Based on the test results, it is found that direct connection of 1-tetradecanol and polyethylene glycol composites can produce stable electrical voltage and current under different thermal energy inputs: through the change of external temperature from 25 °C to 80 °C, through the light-on/-off process, and through heat flow treatment. The maximum output voltage was up to 1.18 mV with a 50 % energy harvesting efficiency and the harvesting time was maintained for 50 min. To confirm the temperature profiles of the phase change material composites, numerical simulation was conducted and the thermal properties during the phase transition process were estimated, with good agreement. This research would create a new concept of thermoelectric energy harvesting for further development in practical applications.

Buffer electrode layers tuned electrical properties, fatigue behavior and phase transition of KNN-based lead-free ferroelectric films

Herein, the impact of conductive buffer electrode layers (p- or n-type) on the electrical properties and fatigue behavior of KNN-based ferroelectric films are investigated.

Stress induced effects on piezoelectric polycrystalline potassium sodium niobate thin films

This work reports a systematical study highlighting the impact of substrate induced stress as a key parameter for the electrical performance and phase transition temperatures of (K,Na)NbO3 polycrystalline thin films.

The mechanism behind SnO metallization under high pressure

SnO is known to undergo metallization at ∼ 5 GPa while retaining its tetragonal symmetry. However, the mechanism of this metallization remains speculative. We present a combined experimental and computational study including pressure-dependent infrared spectroscopy, resistivity, and neutron powder diffraction measurements. We show that, while the excess charge mobility increases with pressure, the lattice distortion, in terms of the z-position of Sn, is reduced. Both processes follow a similar trend that consists of two stages, a moderate increment up to ∼ 3 GPa followed by a rapid increase at higher pressure. This behavior is discussed in terms of polaron delocalization. The pressure-induced delocalization is dictated by the electron–phonon coupling and related local anisotropic lattice distortion at the polaron site. We show that these polaronic states are stable at 0 GPa with a binding energy of ∼ 0.35 eV. Upon increasing the pressure, the polaron binding energy is reduced with the electron–phonon coupling strength of Γ and M modes, enabling the electrical phase transition to occur at ∼ 3.8 GPa. Further compression increases the total electron–phonon coupling strength up to a maximum at 10 GPa, which is a strong evidence of dome-shaped superconductivity transition with Tc = 1.67 K.

Electrical property and phase transition analysis of KNN-based lead-free ferroelectric films

The electrical properties, phase construction, thermal stability and phase transition behavior are investigated in 0.95(K0.49Na0.49Li0.02)(Ta0.2Nb0.8)O3–0.05BaZrO3 with 2 wt% MnO2 (KNNLT-BZM) lead-free epitaxial ferroelectric film on LaNiO3 (LNO)-coated SrTiO3 (STO) (001) substrate. The x-ray diffraction results show that a mixed orthorhombic (O) and tetragonal (T) phase is obtained in KNNLT-BZM film. The MnO2 doping can effectively suppress its leakage current, which greatly improves the electrical performance featured by a lower leakage value of 8 × 10–11 A cm−2, a twice remnant polarization of 44.7 μC cm−2, and frequency-dependent ferroelectricity between 50 Hz and 10 kHz. Strikingly, the KNNLT-BZM film maintained ferroelectric nature up to 200 °C, and exhibit a phase transition from O + T mixed phase to T phase (T Mix-T) at 300 °C with a high Curie temperature above 440 °C. These results suggest great application potentials of KNN-based films in lead-free micro-electronic devices.

Direct comparison of the electrical, optical, and structural phase transitions of VO2 on ZnO nanostructures

We examined the temperature-dependent electrical, optical, and structural properties of VO2 on ZnO nanorods with different lengths in the temperature range from 30 to 100 °C. ZnO nanorods with a uniform length were grown on Al2O3 substrates using a metal organic chemical vapor deposition, and subsequently, VO2 was ex-situ deposited on ZnO nanorods/Al2O3 templates using a sputtering deposition. The optical properties of the VO2/ZnO nanorods were measured simultaneously with direct current (DC) resistance using the reflectivity of an infrared (IR) laser beam with a wavelength of 790 nm. The local structural properties around V atoms of VO2/ZnO nanorods were simultaneously measured with the DC resistance using x-ray absorption fine structure at the V K edge. Direct comparison of the temperature-dependent resistance, IR reflectivity, and local structure reveals that an optical phase transition first occurs, a structural phase transition follows, and an insulator-to-metal transition finally appears during heating.

Gate-voltage-induced reversible electrical phase transitions in Mo0.67W0.33Se2 devices.

Tunable electrical phase transitions based on the structural and quantum-state phase transitions in two-dimensional transition-metal dichalcogenides have attracted attention in both semiconducting electronics and quantum electronics applications. Here, we report gate-voltage-induced reversible electrical phase transitions in Mo0.67W0.33Se2 (MoWSe) field-effect transistors prepared on SiO2/Si substrates. In gate-induced depletion regions of the 2H phase, an electrical current resumes flow at 150 K < T < 200 K with decreasing T irrespective of the layer number (n) for MoWSe when n < 20. The newly appearing electron-doped-type conducting channel again enters the 2H-phase region when the back-gate voltage increases, accompanied by the negative differential transconductance for four-layer and monolayer devices or by a deflection point in the transfer curves for a multilayer device. The thermal activation energies of the new conducting and 2H-phase branches differ by one order of magnitude at the same gate voltage for both the four-layer and monolayer cases, indicating that the electrical band at the Fermi level was modified. The hysteresis measurements for the gate voltage were performed with a five-layer device, which confirms the reversible electrical transition behavior. The possible origins of the nucleated conducting phase in the depletion region of the 2H phase of MoWSe are discussed.

Effect of implantation of nitrogen ions into VO2 thin films

Modifications in the structural and electronic properties of VO2 films induced by N+ ion implantation were investigated. VO2 films prepared by radio frequency (RF) magnetron sputtering deposition on quartz substrate were subjected to the N+ ion beam with 55 keV at different fluences (1 × 1015 and 1 × 1016 ions/cm2). Compared with the pristine VO2 film (Tc ∼ 342 K), structural and electrical phase transition temperatures were shifted around room temperature in the N+ ion implanted sample (fluence = 1 × 1015 ions/cm2). Furthermore, a higher fluence of N+ ions (fluence = 1 × 1016 ions/cm2) had significantly modified the crystalline structure of VO2 thin film, and a metallic behaviour was clearly noticed in the entire temperature range between 240 K and 373 K under this study. N+ ion implantation effectively induces the changes in the electronic structure of VO2 thin films, which are further confirmed by the X-ray absorption spectroscopy (XAS) measurements.

Indium-contacted van der Waals gap tunneling spectroscopy for van der Waals layered materials

The electrical phase transition in van der Waals (vdW) layered materials such as transition-metal dichalcogenides and Bi2Sr2CaCu2O8+x (Bi-2212) high-temperature superconductor has been explored using various techniques, including scanning tunneling and photoemission spectroscopies, and measurements of electrical resistance as a function of temperature. In this study, we develop one useful method to elucidate the electrical phases in vdW layered materials: indium (In)-contacted vdW tunneling spectroscopy for 1T-TaS2, Bi-2212 and 2H-MoS2. We utilized the vdW gap formed at an In/vdW material interface as a tunnel barrier for tunneling spectroscopy. For strongly correlated electron systems such as 1T-TaS2 and Bi-2212, pronounced gap features corresponding to the Mott and superconducting gaps were respectively observed at T = 4 K. We observed a gate dependence of the amplitude of the superconducting gap, which has potential applications in a gate-tunable superconducting device with a SiO2/Si substrate. For In/10 nm-thick 2H-MoS2 devices, differential conductance shoulders at bias voltages of approximately ± 0.45 V were observed, which were attributed to the semiconducting gap. These results show that In-contacted vdW gap tunneling spectroscopy in a fashion of field-effect transistor provides feasible and reliable ways to investigate electronic structures of vdW materials.

Effect of vanadium thickness and deposition temperature on VO2 synthesis using atmospheric pressure thermal oxidation

Vanadium dioxide (VO2) is a phase transition material that undergoes a reversible insulator-metal phase transition at ~ 68 ˚C. Atmospheric pressure thermal oxidation (APTO) of vanadium (V) is a simple VO2 synthesis method in which V thin film is oxidized in open air. For an optimum oxidation duration, VO2 films are obtained with good phase transition properties. We recently reported a modified APTO process using a step temperature profile for oxidation (Thin Solid Films 706, 138003 (2020)). We demonstrated an ultra-low thermal budget synthesis of VO2 thin films with good electrical and optical phase transition properties. For a 130 nm room-temperature RF sputtered V thin film, an optimum oxidation duration of ~ 30 s was obtained. In this work, we study how the starting V film thickness and deposition temperature affects the optimum oxidation duration. V thin films of varying thickness (15-212 nm) and 120 nm thick V films with varying deposition temperature (~27-450 ˚C) are prepared using RF magnetron sputtering. These films are oxidized for different oxidation durations and characterized using Raman and four-probe measurements to find the optimum oxidation duration for each deposition condition. We find that the optimum oxidation duration increases with the increase in V film thickness and V deposition temperature. We model the effect of V film thickness and deposition temperature on the optimal oxidation time using a parabolic law which can be used to obtain the optimal oxidation times for intermediate V thicknesses/deposition temperatures.

Numerical Study on Resistance Change Characteristics of Phase Change Materials

Phase change materials are a type of emerging materials whose states will change under certain conditions, which then lead to changes in resistance. To study the characteristics of the phase change materials, a numerical simulation model of the resistive change unit based on the finite element method and the classic nucleation/growth theory is established, while the partial differential equations of electricity and heat conduction and the discrete formula of the finite element are also derived. According to the phase transition process of phase change materials, a crystalline‐amorphous simulation model is also proposed in this paper to simulate the electrical and thermal properties and phase transition process of the resistive change unit. Simulations of the resistance change unit under single pulses with different amplitudes and widths as well as the simulations under continuous pulses are conducted in this paper. These results verify the characteristics of resistance change and can provide references for selecting the parameters of the resistance change units.

Fundamental Experiment on Invisible Crack Detection of Concrete Covered with Fiber Reinforced Polymer (FRP) through Electrical Impedance Variations and Phase Transition

Fundamental Experiment on Invisible Crack Detection of Concrete Covered with Fiber Reinforced Polymer (FRP) through Electrical Impedance Variations and Phase Transition

Vibrational Analysis and Electrical Conduction Mechanism Investigations ofOrder Disorder Phase Transitions in [N(C3H7)4]2ZnBr4Compound

Vibrational Analysis and Electrical Conduction Mechanism Investigations ofOrder Disorder Phase Transitions in [N(C3H7)4]2ZnBr4Compound

Effects of oxygen partial pressure on the electrical properties and phase transitions in (Ba,Ca)(Ti,Zr)O3 ceramics

To enhance the piezoelectric responses, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics were fabricated by a sol–gel method in various sintering atmospheres. The effects of oxygen partial pressure on the microstructure and electrical properties of BCZT ceramics were systematically investigated. The samples sintered in air, O2 and N2 are the coexistence of the orthorhombic (O)-tetragonal (T) phase at room temperature. The phase transition temperature of the O–T phase of BCZT samples sintered in air, O2 and N2 is gradually closer to room temperature. The results of EDS, XPS and the activation energy confirm the significant effect of oxygen sintering atmosphere. BCZT samples sintered in oxygen atmosphere show excellent ferroelectricity (2Pr = 31.62 μC/cm2, 2EC = 3.46 kV/cm) and significantly enhanced piezoelectricity (d33 = 604.3 pC/N, d 33 * = 647.5 pm/V and kp = 58%), resulting from the minimum oxygen vacancy, the phase transition temperature of O–T closer to room temperature and dense microstructure. These results demonstrate that adjusting oxygen partial pressure in sintering is an effective way to enhance the piezoelectric responses of BCZT ceramics.

Low temperature fabrication of high-performance VO2 film via embedding low vanadium buffer layer

Vanadium dioxide (VO2), which can initiate an automatic reversible metal-to-insulator transition (MIT) from tetragonal to monoclinic structure at the transition temperature (Tc) of 68 °C, is a promising candidate to realize electronic devices due to its dramatic changes in electrical resistivity through MIT. Moreover, the application of VO2 on modulation devices requires a narrow hysteresis width associated with a significant change in its electronic properties, which is quite challenging in VO2 films fabricated by magnetron sputtering, besides, the high preparation temperature around 400 °C also hinders the further industrial production of VO2 films. In this paper, by adding a simple and easy-to-obtain low-valence vanadium buffer layer between the substrate and the VO2 layer, high performance VO2 films with electrical phase transition close to four orders of magnitude and loop width less than 5 °C are obtained. Meanwhile, the annealing temperature of the fabricating process is decreased to only 320 °C, which is 80 °C lower than the ordinary preparation temperature and significantly reducing energy consumption and manufacturing difficulty. Such enhanced performance will benefit the publicity and application for VO2-based modulation devices.

Tuning Phase Transitions in Metal Oxides by Hydrogen Doping: A First-Principles Study.

Optimizing physical or chemical properties via electronic phase transitions is important for developing high-performance semiconductor materials. Using first-principles calculations, we established hydrogen doping (H-doping) as an alternative strategy for modulating phase transitions in metal oxide semiconductors. We found that H-doping can induce an insulator-to-metal phase transition in rutile TiO2 or wurtzite ZnO, a metal-to-insulator phase transition in rutile VO2, and sequential insulator-metal-insulator phase transitions in SnO2. H-doping not only creates defect-induced states inside the original bandgap but also induces new occupancy patterns in conduction band edge states. A linear relationship between occupation of the conduction band edge and H-doping concentration was found, offering the possibility of precisely tuning the material's free-carrier concentration, electrical conductance, and photoabsorption ability. We envision that this work will provide a promising way to tune electrical phase transitions in metal oxides.