One of the general features of ferroelectric systems is a complex nature of polarization reversal, which involves domain nucleation and motion of domain walls. Here, time‐resolved nanoscale domain ...imaging is applied in conjunction with the integral switching current measurements to investigate the mechanism of polarization reversal in yttrium‐doped HfO2 (Y:HfO2)—currently one of the most actively studied ferroelectric systems. More specifically, the effect of film microstructure on the nucleation process is investigated by performing a comparative study of the polarization switching behavior in the epitaxial and polycrystalline Y:HfO2 thin film capacitors. It is found that although the epitaxial Y:HfO2 capacitors tend to switch slower than their polycrystalline counterparts, they exhibit a significantly higher nucleation density and rate, suggesting that this is a rate‐limiting mechanism. In addition, it is observed that under the external fields approaching the activation field value, the switching kinetics can be described equally well by the nucleation limited switching and the Kolmogorov‐Avrami‐Ishibashi models for both types of capacitors. This signifies convergence of two different mechanisms implying that the polarization reversal proceeds via a homogeneous nucleation process unaffected by the film microstructure, which can be considered as approaching the intrinsic switching limit.
Snapshots of instantaneous domain patterns arising during polarization reversal in polycrystalline and epitaxial Y:HfO2 capacitors obtained by stroboscopic piezoresponse force microscopy. Convergence of Kolmogorov‐Avrami‐Ishibashi and nucleation limited switching models at high fields close to the thermodynamic activation value suggests a homogeneous nucleation process unaffected by film microstructure, which can be considered as approaching the intrinsic switching limit.
Materials with tunable thermal properties enable on-demand control of temperature and heat flow, which is an integral component in the development of solid-state refrigeration, energy scavenging, and ...thermal circuits. Although gap-based and liquid-based thermal switches that work on the basis of mechanical movements have been an effective approach to control the flow of heat in the devices, their complex mechanisms impose considerable costs in latency, expense, and power consumption. As a consequence, materials that have multiple solid-state phases with distinct thermal properties are appealing for thermal management due to their simplicity, fast switching, and compactness. Thus, an ideal thermal switch should operate near or above room temperature, have a simple trigger mechanism, and offer a quick and large on/off switching ratio. In this study, we experimentally demonstrate that manipulating phonon scattering rates can switch the thermal conductivity of antiferroelectric PbZrO
bidirectionally by -10% and +25% upon applying electrical and thermal excitation, respectively. Our approach takes advantage of two separate phase transformations in PbZrO
that alter the phonon scattering rate in different manners. In this study, we demonstrate that PbZrO
can serve as a fast (<1 second), repeatable, simple trigger, and reliable thermal switch with a net switching ratio of nearly 38% from ~1.20 to ~1.65 W m
K
.
Preparation of orthorhombic Y-doped TaON film Mimura, Takanori; Shimizu, Takao; Funakubo, Hiroshi
Journal of the Ceramic Society of Japan,
07/2022, Letnik:
130, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Y-doped TaON films were grown on (001)YSZ and (012)Al2O3 substrates by radio frequency (RF) magnetron reactive sputtering deposition from Ta metal target and Y metal chips under the mixture gases of ...N2, O2 and Ar gases. Films with various Y content were prepared by changing area ratio of Y/(Y + Ta) of the target. The pure monoclinic phase was obtained for TaON films on both substrates by controlling the partial pressure of N2 and O2 gasses. Crystal structure changed from the monoclinic phase to the orthorhombic one with the lattice parameters of a = 0.518 nm, b = 0.488 nm, and c = 0.504 nm with the increase in Y content in the films. Our results reveal that TaON could be used as a novel mother fluorite-like monoclinic structure to prepare orthorhombic phase.
The ferroelectric phase transformation from the tetragonal phase to the orthorhombic phase, induced by an electric field, is demonstrated in a 5%YO1.5‐doped Hf0.5Zr0.5O2 epitaxial film which is grown ...on Sn‐doped In2O3‐covered (111) yttria‐stabilized zirconia by the pulsed laser deposition method at room temperature and subsequent heat treatment. Although X‐ray diffraction shows the film to consist of a paraelectric tetragonal phase after the heat treatment, polarization–electric field (P–E) measurements reveal a hysteresis loop attributed to the ferroelectricity. To clarify the discrepancy between the crystal structure and electric characteristics, the crystal structure after electric field loading is determined by scanning transmission electron microscopy and synchrotron X‐ray diffraction measurements. Both structural characterizations clearly reveal that the application of an electric field promotes the phase transition from the paraelectric tetragonal phase to the ferroelectric orthorhombic phase. This ferroelectric transition is irreversible, as the ferroelectric phase remains after the removal of the electric field. These results facilitate the elucidation of the mechanism by which ferroelectricity is displayed in HfO2‐based fluorite ferroelectric materials and imply unimportance of the orthorhombic phase for as‐prepared films.
The phase transition in ferroelectric Y‐doped Hf0.5Zr0.5O2 epitaxial thin film induced by an electric field is demonstrated, which triggers the emergence of ferroelectric characteristics from the nonpolar tetragonal phase to the polar orthorhombic phase. This ferroelectricity induced by the electric‐field‐induced phase transition is quite an important mechanism by which ferroelectricity is exhibited in flurorite‐oxides ferroelectrics.
The crystal structure and ferroelectric properties of 12- to 18 nm-thick epitaxial YO1.5-HfO2 films with 5–9% YO1.5 on (111)ITO//(111)YSZ substrates are investigated to clarify the formation ...mechanism of the ferroelectric phase. The ferroelectric orthorhombic phase can be obtained by transformation from the higher symmetric tetragonal phase by surmounting a relatively low energy barrier. The orthorhombic phase is obtained for 6% and 7% YO1.5-doped HfO2 films by heat treatment at 1000 °C. Although the 5% YO1.5-doped HfO2 film heat-treated at 1000 °C is in a monoclinic phase, the orthorhombic phase was increased by heat treatment at 1200 °C because the high temperature promotes the phase transition from the monoclinic phase in as-deposited films to the tetragonal phase. The 8% and 9% YO1.5-doped HfO2 films have a tetragonal structure without the transition to the orthorhombic phase. Nevertheless, the 8% YO1.5-doped HfO2 film exhibits ferroelectricity by polarization-electric field hysteresis measurement. A microarea X-ray diffraction study reveals that the electric-field-induced phase transition can take place in an 8% YO1.5-doped HfO2 film. The comprehensive study of high-temperature X-ray diffraction measurements implies that the tetragonal phase in 8% YO1.5-doped HfO2 is a supercooled state. Therefore, external stimulation, such as application of an electric field, induces the transition from the tetragonal to the orthorhombic phase. The supercooled tetragonal phase can also be reduced by a slower cooling rate. These results reveal that the formed phase in YO1.5-doped HfO2 epitaxial film is not governed by the simple difference in the formation energy; rather, the kinetics is more important for obtaining the ferroelectric orthorhombic phase.
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