Field-induced Phase Transition Research Articles

Numerical simulation of electric field-induced phase transition evolution and boiling characteristics in the evaporative cooling medium C6F12O

Phase change cooling technology offers high cooling efficiency, safety, and reliability, representing a novel approach to achieving efficient heat dissipation for high-power and large-capacity electrical equipment. The formulation of the cooling medium is pivotal to phase change cooling technology. However, current media exhibit compatibility, stability, economy, and environmental friendliness deficiencies. Consideration could be given to implementing the C6F12O medium due to its superior overall performance and ability to meet the latent heat requirements in phase change cooling equipment. This paper employs a numerical simulation approach that combines the phase field method based on the Cahn-Hilliard equation with the theory of electrohydrodynamics. It investigates the impact of temperature, electric field intensity, and electric field direction on the evolution of bubble motion and the boiling state of the C6F12O medium, considering the interaction of electric-fluid-heat-phase fields. Numerical results indicate that the system undergoes initial nucleate boiling, nucleate boiling, and film boiling stages at T = 330–335 K, T = 335–350 K, and T ⩾ 355 K, respectively. The introduction of an appropriate electric field can enhance the motion evolution of C6F12O bubbles. However, attention must be paid to the formation of bubble channels under high field strength to prevent potential decreases in insulation performance. An inhomogeneous electric field in the vertical direction proves more effective in improving the bubble release rate compared to a uniform electric field. To some extent, an inhomogeneous electric field in the horizontal direction can prevent the mass accumulation of bubbles in regions of high field intensity. This research has the potential to offer theoretical guidance for the engineering application of the C6F12O phase change cooling medium.

Phenomenological analysis of positive and negative electrocaloric effects in Rochelle salt

Ferroelectrics exhibiting both positive and negative electrocaloric effects stand out as promising materials for achieving high-efficiency solid-state refrigeration. The phase transition is acknowledged as a crucial factor in designing such materials. This study investigates the electrocaloric behavior and its correlation with phase transitions in Rochelle salt single crystal using Landau thermodynamic theory. Analysis of free energy density, ferroelectric, and dielectric data uncovers a complex temperature-dependent phase transition sequence of paraelectric–ferroelectric–paraelectric. This imparts Rochelle salt single crystal with intriguing field-induced phase transition behaviors and electrocaloric responses. Pronounced positive and negative electrocaloric effects are, respectively, observed near the high-temperature and low-temperature Curie point. The opposite sign of entropy differences between the ferroelectric and the two paraelectric phases is identified as the origin of the difference in electrocaloric response. These findings not only enhance our understanding of the electrocaloric effect but also provide a design solution for materials with the coexistence of positive and negative electrocaloric effects.

Polarization fatigue mechanism of laminated hafnium zirconium oxide ferroelectric thin films

Laminated HfO2-based ferroelectric thin films (FE-HfO2) have offered unexpected opportunities to implement the high-density ferroelectric memory and on chip piezoelectric or pyroelectric devices. But the polarization fatigue performance is poor and the underlying mechanism is unknown. In this work, we comprehensively investigate the polarization fatigue behaviors of Hf0.5Zr0.5O2(HZO)/Al2O3/HZO laminated thin films. Several possible mechanisms for the fatigue performances are discussed in detail. On basis of the analysis of micro-structures and domain switching dynamics before and after fatigue, we confirm that domain wall pinning phenomenon exists in the fatigued laminated HZO, without field-induced phase transition as well as thickness and chemical properties changes of interfacial layers. Moreover, we discover by a pulse measurement method that domain wall pinning induced by the increase of Al2O3/HZO interface trap charge is responsible for the fatigue performances of the laminated films. This work will provide useful guidance for designing high-reliability laminated FE-HfO2, and contribute to understand the physical mechanisms of FE-HfO2.

An enhanced strain response in micrometer-thick BNT-ST thin films

Lead-free Bi0.5Na0.5TiO3-SrTiO3 (BNT-ST) thin films with various thicknesses were deposited on the Pt(111)/Ti/SiO2/Si(100) substrates employing a sol-gel technique with a two-step annealing process. Despite the variations in thickness, the films exhibited a consistent polycrystalline structure, evidenced by identical diffraction peaks, albeit with differences in intensity. An imprint became evident in micro-thick films, increasing with film thickness. Also, the emergence of self-polarization was observed in thicker films detected by piezoresponse force microscopy. Noteworthy is the pronounced influence of film thickness on strain response, with the 1.38 μm-thick films demonstrating a large strain of 1.18%. The outstanding strain response can be attributed to the notable contribution of electric field-induced phase transition and polarization dynamics. This work provides a promising potential application of micrometer-thick BNT-ST thin films in advanced actuator devices.

Achieving large negative electrocaloric effect in AgNbO3-based antiferroelectric ceramics based on dipole disordering

The electrocaloric effect (ECE) is considered as an environmentally friendly refrigeration technology, which can be used to replace vapor compression refrigeration. Lead-free antiferroelectric (AFE) ceramics are promising electrocaloric materials because of large saturation polarization and polarization change with temperature, which can generate large positive or negative ECE. In this work, the lead-free Ag(Nb1-0.8xHfx)O3 (x = 0, 0.001 and 0.003) AFE ceramics are fabricated through a conventional solid-state reaction method which shows a decreased the phase transition temperature of M1 - M2 toward room temperature (RT), and a large negative ECE (ΔT = −2.3 K under 130 kV cm−1) is obtained near the ambient temperature by using an indirect measurement in ANH0.001 AFE ceramic. The large negative ECE behavior is ascribed to dipole disordering (i.e. the anti-parallel dipoles are broken and gradually becomes disordered under an external electric field) resulting from the field-induced phase transition under a modest electric field. This work shows that AgNbO3-based AFE ceramics could be used in the refrigeration devices as an electrocaloric material.

Ultra-high strain in Bi0.5(Na0.41K0.09)TiO3 Pb-free piezoelectric ceramics modified by Sr(Hf0.5Sb0.4)O3

The lead-free piezoelectric ceramics used in piezoelectric actuators have attracted extensive attention owing to their substantial electric-field-induced strain. In this study, The (1-x)Bi0.5(Na0.41K0.09)TiO3-xSr(Hf0.5Sb0.4)O3 (BNKT-xSHS) piezoelectric ceramics were synthesized using the conventional solid-state reaction method. The impact of SHS substitution on the microstructure and electrical properties was systematically explored. Among them, the BNKT-0.015SHS sample, featuring ergodic relaxor states, demonstrates a high piezoelectric strain coefficient (d33*) of 785 p.m./V under a low electric field of 50 kV/cm(Strain = 0.392 %). It exhibits a repeatable strain value of 0.47 % under an 80 kV/cm electric field(d33* = 590 p.m./V). Moreover, the strain values remain around 0.4 % between room temperature and 100 °C, with variations within 90 %. The heightened repeatable strain response is considered to be linked to the electric field-induced reversible phase transition occurring within the ergodic relaxor state. The higher strain temperature stability is ascribed to the coexistence of quadrilateral polar nanoregions and rhombic polydomain nanoregions. This study provides an effective example for achieving significant strain responses, presenting a feasible candidate material for applications in piezoelectric actuators.

Magnetic field-induced phase transition in spinor exciton-polaritons condensate

We theoretically study the magnetic phase transition of condensed exciton-polariton microcavities in an applied magnetic field. When the magnetic field is strong, all polariton spins are polarized parallel to the magnetic field as usual. On the contrary, in the weak magnetic-field region, the polariton polarization degree is negative, namely, anti-parallel to the magnetic field. For a strong magnetic field, the magnetic phase of the polaritons arises and leads to a paramagnetic, while around a weak magnetic field, with zero exciton–photon detunings, and weak Rabi splitting the spin polarization of the polaritons leads to a diamagnetic. Thus, magneto-polariton phase transition polarization originates from the competition between the polariton Zeeman effect and polariton–polariton interactions. Moreover, the polariton polarization strongly depends on the exciton–photon detuning and Rabi splitting and has a large negative value as they are both small. At last, we compare our theoretical results with the experiments and find they match each other very well.

Electrocaloric effect with enhanced temperature stability in an interfacial polarization controlled ferroelectric laminated composite

Research on zero-emission lead-free ferroelectric materials is fascinating in the field of solid-state refrigeration due to the observed large electrocaloric phenomenon. However, one of the challenges involved is realizing a large adiabatic temperature change ( ΔT ) over a wide temperature span. Here, a laminated ferroelectric structure with layers, having successive phase transitions covering room temperature, is proposed to overcome this problem. BaTi1−x Sn x O3 with x = 0.08, 0.12, and 0.15 compositions exhibiting the required ferroelectric Curie temperatures was chosen for the component layers. The designed interfacial polarization engineered laminated structure with 0.15/0.08/0.12 compositional layers yielded a value of adiabatic temperature change ΔT max ⩾ 0.6 °C by an indirect method using Maxwell’s thermodynamic equations over a wide temperature span (30 °C–85 °C). The observed results are correlated to the interrelated cumulative effect of reduced interfacial polarization, homogeneous electric field distribution, field-induced phase transitions, and enhanced domain switching, which are the manifestation of the designed laminated geometry.

Magnetic field-induced narrow first-order and metamagnetic phase transitions of Nd5Ge3

We report on the magnetic behaviour of Nd5Ge3 by investigating through magnetization, neutron diffraction and muon spin relaxation measurements. Temperature dependent-magnetization, muon depolarization rate (λ), initial asymmetry (A0) and the stretched exponent (β) show a clear anomaly at the Néel temperature TN ∼ 54 K. However, the short-range correlated ferromagnetic interactions below TN are inferred from the diffuse scattering mechanism as revealed by zero-field neutron diffraction data. Narrow first order phase transition is due to the competing interaction of a high temperature weak-antiferromagnetic and low temperature glassy states. Magnetic field-induced reentrant spin glass state from a magnetic glass state is observed, before it transforms to a ferromagnetic state.

Achieving ultrahigh piezoactuation constant of 2240 pm/V and giant electrostrain of 1.12% simultaneously in BNT-based polycrystalline ceramics

Ultrahigh electrostrain (Sm) at low driving field in lead-free piezoceramics could alleviate key concerns by reducing energy consumption and the risk of electrical breakdown for advanced applications. However, the giant electrostrain always accompanied with an extremely large drive field is a long-standing conflict referred as the strain-electric field trade-off. Herein, we engineer a novel strategy of introducing the B-site unequal double doping cations (ZnSn0.5)4+ into (Bi0.5Na0.5)0.93Ba0.07TiO3 ceramic to generate the spontaneous phase transition from relaxor state to ferroelectric state, polar nanoregions PNRs and defect cluster. The giant strain of Sm= 1.12% is achieved by integrating the field-induced phase transition, morphotropic phase boundary MPB and the enhanced synergistic effect between the spontaneous polarization Ps and the defect cluster polarization Pd under a low electric field of 50 kV/cm, thus yielding extremely large piezoactuation constant d33 * =2240 pm/V in (Bi0.5Na0.5)0.93Ba0.07Ti0.97(ZnSn0.5)0.03O3 piezoceramics. This finding also demonstrates an unexpected new route to design novel ferroelectric materials via nonconventional mechanisms.

Drastic magnetic-field-induced chiral current order and emergent current-bond-field interplay in kagome metals.

In kagome metals, the chiral current order parameter [Formula: see text] with time-reversal-symmetry-breaking is the source of various exotic electronic states, while the method of controlling the current order and its interplay with the star-of-David bond order [Formula: see text] are still unsolved. Here, we reveal that tiny uniform orbital magnetization [Formula: see text] is induced by the chiral current order, and its magnitude is prominently enlarged under the presence of the bond order. Importantly, we derive the magnetic-field ([Formula: see text])-induced Ginzburg-Landau (GL) free energy expression [Formula: see text], which enables us to elucidate the field-induced current-bond phase transitions in kagome metals. The emergent current-bond-[Formula: see text] trilinear coupling term in the free energy, [Formula: see text], naturally explains the characteristic magnetic-field sensitive electronic states in kagome metals, such as the field-induced current order and the strong interplay between the bond and current orders. The GL coefficients of [Formula: see text] derived from the realistic multiorbital model are appropriate to explain various experiments. Furthermore, we discuss the field-induced loop current orders in the square lattice models that have been studied in cuprate superconductors.

Energy storage performance and piezoelectric response of silver niobate antiferroelectric thin film

AgNbO3-based antiferroelectric materials have attracted extensive attention in energy storage due to their double polarization-electric field hysteresis loops, but they always suffer from low breakdown strength (Eb). Films with few defects and small thickness exhibit high breakdown strength, which helps to improve energy storage performance. In the present work, an AgNbO3 film with a small thickness of ∼200 nm is prepared via pulsed laser deposition, which has a dense microstructure and a small average grain size of ∼34.5 nm. The AgNbO3 film displays an antiferroelectric nature, as confirmed by the double polarization-electric field hysteresis loops at room temperature. The room temperature phase structure of the AgNbO3 film determined by the dielectric behaviour is the antiferroelectric M2 phase. Due to the small thickness and fine grain size, a high Eb of 1200 kV/cm is obtained, which boosts a recoverable energy storage density (Wrec) of 9.3 J/cm3 and an energy efficiency (η) of 63.7 % in the AgNbO3 film. In addition, Wrec exhibits good temperature stability at 30–120 °C. The AgNbO3 film shows an obvious piezoelectric response after the electric field-induced antiferroelectric-ferroelectric phase transition as confirmed by piezoresponse force microscopy. These results provide guidance for the development of AgNbO3 antiferroelectric films and devices with good energy storage performance.

Unlocking the key mechanism behind field-induced ferroelectric phase transition in sodium niobate for energy storage systems

The intricate phase transition dynamics of NaNbO3 under the influence of an electric field has been explored, shedding light on the underlying mechanisms responsible for the irreversible transition from the antiferroelectric (AFE) to ferroelectric (FE) phases.

Magnetic Field-Induced Phase Transition and Weak Ferromagnetism in Nonsuperconducting Optimally Doped PrBCO Cuprate

Magnetic Field-Induced Phase Transition and Weak Ferromagnetism in Nonsuperconducting Optimally Doped PrBCO Cuprate

Magnetic Field-Induced Martensitic Phase Transition in Cr-Substituted Ni–Mn–Sb + B Shape Memory Alloys

Magnetic Field-Induced Martensitic Phase Transition in Cr-Substituted Ni–Mn–Sb + B Shape Memory Alloys

Phase stability and energy storage properties of polycrystalline antiferroelectric BaTiO3-substituted NaNbO3 thin films

Lead-free sodium niobate (NN) thin films with varying barium titanate (BT) content and 1 mol% manganese were deposited on platinized silicon substrates by chemical solution deposition. Microstructural analysis reveals a change in nucleation mechanism, and X-ray diffraction and Raman spectroscopy confirmed a composition-driven antiferroelectric (AFE) to ferroelectric (FE) phase transition at 0.01 < x < 0.03, providing a stability interval for the AFE phase despite increasing the tolerance factor. The thin films show well-shaped ferroelectric response under applied electric field, indicating an irreversible field-induced phase transition. The composition with 7 mol% BaTiO3 showed the most promising energy storage properties (Wrec ∼5.7 J/cm3 and 68% efficiency (η)), along with excellent thermal stability up to 120 °C and largely improved cyclic stability up to 5 * 106 bipolar cycles. These findings highlight the potential of NN-based thin films as lead-free candidates for energy storage, emphasizing the importance of stabilizing the AFE phase under electric fields for practical applications.

Field induced ferroelectric phase transition and dielectric spectrum behavior in PMN ceramics

The problem of field induced phase transition into the ferroelectric phase in relaxor ceramics and in particular in PMN ceramics was studied for many years, but the results are still controversial. The temperature and field dependences of PMN polycrystalline ceramics dielectric spectra have been studied. The transitions from the glass-like into the ferroelectric phase were found both in field cooling and zero field heating after field cooling regimes under the fields above 3 kV/cm. Electric field scans near the diffuse maximum of the dielectric permittivity demonstrated the shift of the loss maximum to the high frequency at increasing of applied electric field. The experimentally observed frequency-dependent sign of the C–V effect (the decrease (negative effect) or the increase (positive effect) of dielectric permittivity at increasing field) is due to spectra hardening. In contrast to single crystal, where the application of the electric field higher than 1.6 kV/cm in <111> direction induces phase transition into ferroelectric state, in polycrystalline ceramics no clear evidence of the phase transition from the paraelectric into the ferroelectric state up to 6 kV/cm neither at 242 K nor at 246 K was found. This difference between the single crystal and polycrystalline ceramics can be explained by very strong dependence of the threshold field from the field orientation at this transition. The influence of external field on low frequency relaxation process parameters for PMN single crystal and ceramics is compared.

Magnetic-field-induced transitions and the inverse magnetocaloric effect at liquid helium temperatures in the Mn1-xCoxNiGe system (0.15 ≤ x 

Magnetic field-induced phase transitions found in the Mn1-xCoxNiGe system (0.15 ≤ x < 0.8) at T = 5 K may differ in nature and magnitude of the saturation magnetization of the initial weakly magnetic phase. These differences also affect the phenomena accompanying the transitions, specifically, the inverse magnetocaloric effect (MCE). In the current work, the mechanisms of these phenomena are analyzed within the framework of the magnetostructural model, which takes into account the difference in the limiting values of the magnetic order parameters in competing orthorhombic and hexagonal crystal structures. As follows from the analysis performed, the features observed in Mn1-xCoxNiGe can be explained by the realization at low temperatures of a metastable orthorhombic crystal state in magnetically ordered phases with a stable high-temperature hexagonal crystal structure.

Magnetic field-induced phase transition in ilmenite-type CoVO3

The ilmenite-type CoVO3 undergoes an antiferromagnetic transition below 140 K, and the tetravalent vanadium ions form V–V dimers below 550 K. This paper presents the magnetic spin structure and the phase transition induced by a magnetic field in CoVO3. Neutron powder diffraction at 50 K reveals that the spins of Co2+ arrange in a zigzag order on the honeycomb lattice with no external magnetic field. This magnetic spin structure does not exhibit spontaneous magnetization, corroborating previous magnetic measurements. Magnetization measurements in a pulsed-magnetic field revealed a transition to a weak-ferromagnetic phase at 37 T (100 K) and above 50 T (4.2 K), with spontaneous magnetization approximating 0.3–0.5 μB/f.u. This phase transition could potentially be attributed to a transition to a canted antiferromagnetic phase, which is brought about by the reduction in structural symmetry due to magnetostriction.

Stress and electric field induced phase transitions for ultra high energy conversion in ferroelectrics

This work focuses on energy harvesting of ferroelectric relaxors PMN-25PT and PZN-8PT single crystals with high uniaxial stress and electric field. Ericsson cycle, which consists of applying and releasing electric field and stress at different steps of the cycle, has been used. A large energy density for PZN-8PT high as 410 mJ/cm3 was obtained. Different working temperatures were tested by experiment and modeled via Landau–Devonshire theory. Optimal working temperatures were identified for high level energy conversion and were successfully predicted by simulation. It appeared that the optimum working temperature was different from that optimizing the d33. Polarization mechanisms induced by these extreme conditions for energy harvesting are explained in the frame of experimental and modeling results. The results obtained at high stress levels tend to indicate that operating along the polarization direction yields the best results, which contradicts conclusions drawn in the case of domain engineered crystals.