Engineering topics

Tan, Yueze

Publications and source records attributed to Tan, Yueze.

5 records

DOE OSTI2024

Spontaneous Supercrystal Formation During a Strain‐Engineered Metal–Insulator Transition

Abstract Mott metal–insulator transitions possess electronic, magnetic, and structural degrees of freedom promising next‐generation energy‐efficient electronics. A previously unknown, hierarchically ordered, and anisotropic supercrystal state is reported and its intrinsic formation characterized in‐situ during a Mott transition in a Ca 2 RuO 4 thin film. Machine learning‐assisted X‐ray nanodiffraction together with cryogenic electron microscopy reveal multi‐scale periodic domain formation at and below the film transition temperature ( T Film ≈ 200–250 K) and a separate anisotropic spatial structure at and above T Film . Local resistivity measurements imply an intrinsic coupling of the supercrystal orientation to the material's anisotropic conductivity. These findings add a new degree of complexity to the physical understanding of Mott transitions, opening opportunities for designing materials with tunable electronic properties.

Gorobtsov, Oleg Yu.↗

DOE OSTI2024

Influence of oxygen vacancies on the domain wall stability in BiFeO 3

Oxygen vacancy is the most common type of point defects in functional oxides, and it is known to have profound influence on their properties. This is particularly true for ferroelectric oxides since their interaction with ferroelectric polarization often dictates the ferroelectric responses. Here, we study the influence of the concentration of oxygen vacancies on the stability of ferroelectric domain walls (DWs) in BiFeO 3 , a material with a relatively narrow bandgap among all perovskite oxides, which enables strong interactions among electronic charge carriers, oxygen vacancies, and ferroelectric domains. It is found that the electronic charge carriers in the absence of oxygen vacancies have essentially no influence on the spatial polarization distribution of the DWs due to their low concentrations. Upon increasing the concentration of oxygen vacancies, charge-neutral DWs with an originally symmetric polarization distribution symmetric around the center of the wall can develop a strong asymmetry of the polarization field, which is mediated by the electrostatic interaction between polarization and electrons from the ionization of oxygen vacancies. Strongly charged head-to-head DWs that are unstable without oxygen vacancies can be energetically stabilized in the off-stoichiometric BiFeO 3–δ with δ ~ 0.02 where ionization of oxygen vacancies provides sufficient free electrons to compensate the bound charge at the wall. Our results delineate the electrostatic coupling of the ionic defects and the associated free electronic charge carriers with the bound charge in the vicinity of neutral and charged DWs in perovskite ferroelectrics.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Controlled Nucleation and Stabilization of Ferroelectric Domain Wall Patterns in Epitaxial (110) Bismuth Ferrite Heterostructures

Ferroelectric domain walls, topological entities separating domains of uniform polarization, are promising candidates as active elements for nanoscale memories. In such applications, controlled nucleation and stabilization of domain walls are critical. In this work, using in situ transmission electron microscopy and phase-field simulations, a controlled nucleation of vertically oriented 109° domain walls in (110)-oriented BiFeO 3 (BFO) thin films is reported. In the switching experiment, reversed domains that are nucleated preferentially at the nanoscale edges of the “crest and sag” pattern-like electrode under external bias subsequently grow into a stable stripe configuration. In addition, when triangular pockets (with an in-plane polarization component) are present, these domain walls are pinned to form stable flux-closure domains. Phase field simulations show that i) field enhancement at the edges of the electrode causes site-specific domain nucleation, and ii) the local electrostatics at the domain walls drives the formation of flux closure domains, thus stabilizing the striped pattern, irrespective of the initial configuration. The results demonstrate how flux closure pinning can be exploited in conjunction with electrode patterning and substrate orientation to achieve a desired topological defect configuration. These insights constitute critical advancements in exploiting domain walls in next generation ferroelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Observation of Unconventional Dynamics of Domain Walls in Uniaxial Ferroelectric Lead Germanate

Application of scanning probe microscopy techniques such as piezoresponse force microscopy (PFM) opens the possibility to re-visit the ferroelectrics previously studied by the macroscopic electrical testing methods and establish a link between their local nanoscale characteristics and integral response. It is reported that the nanoscale PFM studies and phase-field modeling of the static and dynamic behavior of the domain structure in the well-known ferroelectric material lead germanate Pb 5 Ge 3 O 11 . Here, several unusual phenomena are revealed: 1) domain formation during the paraelectric-to-ferroelectric phase transition, which exhibits an atypical cooling rate dependence; 2) unexpected electrically induced formation of the oblate domains due to the preferential domain walls motion in the directions perpendicular to the polar axis, contrary to the typical domain growth behavior observed so far; 3) absence of the bound charges at the 180 degrees head-to-head (H-H) and tail-totail (T-T) domain walls, which typically exhibit a significant charge density in other ferroelectrics due to the polarization discontinuity. This strikingly different behavior is rationalized by the phase field modeling of the dynamics of uncharged H-H and T-T domain walls. The results provide a new insight into the emergent physics of the ferroelectric domain boundaries, revealing unusual properties not exhibited by conventional Ising-type walls.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Deterministic Ferroelastic Domain Switching Using Ferroelectric Bilayers

Composition gradients, or dissimilar ferroelectric bilayers, demonstrate colossal electromechanical figures of merit attributed to the motion of ferroelastic domain walls. Yet, mechanistic understanding of polarization switching pathways that drive ferroelastic switching in these systems remains elusive. Here, the crucial roles of strain and electrostatic boundary conditions in ferroelectric bilayer systems are revealed, which underpin their ferroelastic switching dynamics. Using in situ electrical biasing in the transmission electron microscope (TEM), the motion of ferroelastic domain walls is investigated in a tetragonal (T) Pb(Zr,Ti)O 3 (PZT)/rhombohedral (R) PZT epitaxial bilayer system. Atomic resolution electron microscopy, in tandem with phase field simulations, indicates that ferroelastic switching is triggered by predominant nucleation at the triple domain junctions located at the interface between the T/R layers. Furthermore, this interfacial nucleation leads to systematic reversable reorientation of ferroelastic domain walls. Finally, deterministic ferroelastic domain switching, driven by the interfacial strain and electrostatic boundary conditions in the ferroelectric bilayer, provides a viable pathway toward novel design of miniaturized energy-efficient electromechanical devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗