Ferroelectric-like State Research Articles

Ferroelectric phase transitions in epitaxial antiferroelectric PbZrO3 thin films

The archetypical antiferroelectric, PbZrO3, is currently attracting a lot of interest, but no consensus can be clearly established on the nature of its ground state as well as on the influence of external stimuli over its physical properties. Here, the antiferroelectric state of 45-nm-thick epitaxial thin films of PbZrO3 is established by observing the characteristic structural periodicity of antiparallel dipoles at the atomic scale, combined with clear double hysteresis of the polarization-electric field response related to antiferroelectric–to–ferroelectric phase transitions. Surprisingly, while the antiferroelectric state is identified as the ground state, temperature-dependent measurements show that a transition to a ferroelectric-like state appears in a large temperature window (100 K). Atomistic simulations further confirm the existence, and provides the origin, of such ferroelectric state in the films. Electric-field-induced ferroelectric transitions are also detected by the divergence of the piezoresponse force microscopy response. Using this technique, we further reveal the signature of a ferroelectric ground state for 4-nm-thick PbZrO3 films. Compared with bulk crystals, these results suggest a more complex competition between ferroelectric and antiferroelectric phases in epitaxial thin films of PbZrO3.

Coexistence of Ferroelectriclike Polarization and Dirac-like Surface State in TaNiTe_{5}.

By combining angle-resolved photoemission spectroscopy, scanning tunneling microscopy, atomic force microscope based piezoresponse force microscopy and first-principles calculations, we have studied the low-energy band structure, atomic structure, and charge polarization on the surface of a topological semimetal candidate TaNiTe_{5}. Dirac-like surface states were observed on the (010) surface by angle-resolved photoemission spectroscopy, consistent with the first-principles calculations. On the other hand, piezoresponse force microscopy reveals a switchable ferroelectriclike polarization on the same surface. Wepropose that the noncentrosymmetric surface relaxation observed by scanning tunneling microscopy could be the origin of the observed ferroelectriclike state in this novel material. Our findings provide a new platform with the coexistence of a ferroelectriclike surface charge distribution and novel surface states.

Nature of polar state in 0.67BiFeO3–0.33BaTiO3

This study was conducted to understand the nature of the polar state in the morphotropic phase boundary composition 0.67BiFeO3–0.33BaTiO3 (0.67BF–0.33BT). Both the unpoled and poled specimens exhibit an average cubic structure. The poling induces a 0.14% increase in the lattice parameter. Macrodomains are absent both in the initial and polar state of 0.67BF–0.33BT. A typical relaxor-type dielectric anomaly was observed (Tf = ~ 627 K, TB = ~ 820 K). The remnant polarization (Pr), maximum value of electrostrain (Sm), and magnitude strain at Ec in the bipolar mode (Sneg) increase clearly during heating (Pr, ~ 40 µC/cm2; Sm, 0.191% under 40 kV/cm at 453 K). Unlike Bi0.5Na0.5TiO3-based nonergodic relaxors, the first-cycle bipolar electrostrain loops indicate that the minimum strain on the negative side of the bipolar strain curves is negative. Furthermore, the slopes of the relative permittivity versus log frequency plots in unpoled (− 21) and poled (− 23) specimens are similar. The transition between the relaxor state and ferroelectric-like state does not involve a clear dielectric anomaly even in the poled specimen.

Non-volatile electric control of spin-charge conversion in a SrTiO3 Rashba system.

After 50years of development, the technology of today's electronics is approaching its physical limits, with feature sizes smaller than 10nanometres. It is also becoming clear that the ever-increasing power consumption of information and communication systems1 needs to be contained. These two factors require the introduction of non-traditional materials and state variables. As recently highlighted2, the remanence associated with collective switching in ferroic systems is an appealing way to reduce power consumption. A promising approach is spintronics, which relies on ferromagnets to provide non-volatility and to generate and detect spin currents3. However, magnetization reversal by spin transfer torques4 is a power-consuming process. This is driving research on multiferroics to achieve low-power electric-field control of magnetization5, but practical materials are scarce and magnetoelectric switching remains difficult to control. Here we demonstrate an alternative strategy to achieve low-power spin detection, in a non-magnetic system. We harness the electric-field-induced ferroelectric-like state of strontium titanate (SrTiO3)6-9 to manipulate the spin-orbit properties10 of a two-dimensional electron gas11, and efficiently convert spin currents into positive or negative charge currents, depending on the polarization direction. This non-volatile effect opens the way to the electric-field control of spin currents and to ultralow-power spintronics, in which non-volatility would be provided by ferroelectricity rather than by ferromagnetism.

Ferroelectricity woos pairing

Ferroelectricity and superconductivity do not have much in common. Now, a superconducting and a ferroelectric-like state have been found to coexist in a doped perovskite oxide.

Interfacial charge-induced polarization switching in Al2O3/Pb(Zr,Ti)O3 bi-layer

Detailed polarization switching behavior of an Al2O3/Pb(Zr,Ti)O3 (AO/PZT) structure is examined by comparing the phenomenological thermodynamic model to the experimental polarization–voltage (P-V) results. Amorphous AO films with various thicknesses (2–10 nm) were deposited on the polycrystalline 150-nm-thick PZT film. The thermodynamic calculation showed that the transition from the ferroelectric-like state to the paraelectric-like state with increasing AO thickness occurs at ∼3 nm thickness. This paraelectric-like state should have exhibited a negative capacitance effect without permanent polarization switching if no other adverse effects are involved. However, experiments showed typical ferroelectric-like hysteresis loops where the coercive voltage increased with the increasing AO thickness, which could be explained by the carrier injection through the thin AO layer and trapping of the carriers at the AO/PZT interface. The fitting of the experimental P-V loops using the thermodynamic model considering the depolarization energy effect showed that trapped charge density was ∼±0.1 Cm−2 and critical electric field at the Pt electrode/AO interface, at which the carrier transport occurs, was ∼±10 MV/cm irrespective of the AO thickness. Energy band model at each electrostatic state along the P-V loop was provided to elucidate correlation between macroscopic polarization and internal charge state of the stacked films.

The study of the ferroelectric properties of lithium-titanium ferrite

Loop-shaped dependences of the electric polarization on the electric field strength (the dielectric hysteresis) are registered for the first time for polycrystalline Li-Ti ferrite. Temperature evolution of the hysteresis loop parameters is investigated for ferrite samples. A thermal Barkhausen effect is detected during heating and cooling of ferrite specimens prepolarized in an electric field. The results obtained can be interpreted from the viewpoint of the Maxwell-Wagner relaxation polarization or induced ferroelectric-like state in the electric ferrite subsystem.

Investigation into the special features of the dielectric and polarization properties of lithiumtitanium ferrite ceramics

Loop-shaped dependences of the electric polarization on the electric field strength (the dielectric hysteresis) are registered for the first time for polycrystalline Li–Ti ferrite. Temperature evolution of the hysteresis loop parameters is investigated for ferrite samples. The results obtained can be interpreted from the viewpoint of the Maxwell–Wagner relaxation polarization or induced ferroelectric-like state in the electric ferrite subsystem.

Ferroelectricity in Free Niobium Clusters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ferroelectricity in free niobium clusters.

Electric deflections of gas-phase, cryogenically cooled, neutral niobium clusters [NbN; number of atoms (N) = 2 to 150, temperature (T) = 20to 300kelvin], measured in molecular beams, show that cold clusters may attain an anomalous component with very large electric dipole moments. In contrast, room-temperature measurements show normal metallic polarizabilities. Characteristic energies kBTG(N) [Boltzmann constant kB times a transition temperature TG(N)] are identified, below which the ferroelectric-like state develops. Generally, TG decreases [110 > TG(N) > 10K] as N increases, with pronounced even-odd alternations for N > 38. This new state of metallic matter may be related to bulk superconductivity.

Specific heat studies for λ-(BEDT-TSF) 2FeCl 4

We have measured the specific heat on λ-(BEDT-TSF) 2FeCl 4 as a function of temperature by a thermal relaxation method to study the metal-to-insulator (MI) transition around 8 K and anomalous ferroelectric-like state revealed by microwave measurements for the metallic state. The specific heat exhibits a sharp peak due to the antiferromagnetic ordering at T MI =8.3 K . We have found a remarkable jump at 70 K labeled as T FM. Together with the ferroelectric-like response emerging around T FM, this result confirms thermodynamically a ferroelectric-like transition at T FM in the metallic states. Furthermore, the thermal conductance of the sample may exhibit an anomaly at T FM.

Anomalous Dielectric Response in the π–dCorrelated Metallic State of λ-(BEDT-TSF)2FeCl4

The temperature dependence of the microwave conductivity σ 1 and dielectric constant e 1 has been measured on λ-(BEDT-TSF) 2 FeCl 4 by a cavity perturbation method at 16.3 GHz, employing the TE 011 resonant mode. In spite of the highly metallic state above the metal-to-insulator (MI) transition at T MI = 8.3 K, a novel ferroelectric-like response is observed in e 1 c along c at high temperatures from T MI to T FM = 70 K, which is enhanced to the order of 10 3 just above T MI . Then a transition from a ferroelectric-like to paraelectric-like state with e 1 c ∼ 45 takes part in the MI transition. In contrast to the dc conductivity, σ 1 c becomes much more conductive as considered by a collective mode. The ferroelectric-like response is associated with the dynamical response of the charge degrees of freedom in the π electronic system. An absence of these dielectric and thermodynamical anomalies in the nonmagnetic Ga analogue indicates the importance of the π– d interaction for the ferroelectric-like state as...

The influence of fields on low-and infralow frequency dielectric response of barium doped PSN ferroelectric ceramics

The history effects on dielectric response in (Pb1−xBax)(Sc0.5Nb0.5)O3 ferroelectric ceramics are studied. A bias field applied to PSN at temperatures T>Tm induce transition from the superparaelectric to a ferroelectric-like phase. Transition from relaxor phase to ferroelectric phase occurs in PSN spontaneously at temperatures T<Tm. In the presence of Ba admixture (x=0.04) spontaneous transition to the ferroelectric phase is not observed, while under a strong electric field the transition from relaxor state to the ferroelectric-like state proceeds at T<Tm. The low-and infralow frequency dielectric response in systems with x≥0.06 measured at weak and strong fields is similar to that observed in dipole glasses.