Electret formation in transition metal oxides by electrochemical amorphization

Zhang

Advanced Optical Materials

et al. 2021

Electric-field-induced topotactic phase transitions have recently gained increased attention. [7][8][9][10] Such transitions involve reversible changes of the crystal structure driven by controllable stoichiometric changes in a material, for example, those involving oxygen vacancies in SrCoO 3−δ , [11][12][13] Sr(Fe,Co)O 3−δ , and SrFeO 3−δ each having different crystalline phases with varied oxidation states. [3,7,8,[13][14][15] In recent years, such TMOs, especially those with perovskite (PV) structure, have been shown to possess a wide range of chemical and physical properties, and associated functionality. [2,10,14,16] This occurs instinctively out of the fact that the two sub-lattices in the PV structure can be independently adjusted through chemical substitutions, which leads to substantial changes in functional returns. The optical properties in some systems are normally set as O 2p to the transition metal in 3d electronic transitions. [9,17] This aspect becomes important when topotactic transitions involve reversible changes of oxygen content because of a strongly variable hybridization of the Fe 3d and O 2p states, which lead to a transfer of electron density from the O 2p to the Fe 3d band and vice versa, involving significant changes in optical properties of the material. Based on this literature, our research is now starting to discover the optical responses in some of the PVs that can be adjusted by external fields.In this study, we show that inorganic SrCo 0.66 Fe 0.34 O 3−δ (SCFO) layers possess a strong electrochromic effect, that arises from a different principle mechanism compared to the conventional one described in the beginning for prototypical WO 3 , that is, a topotactic transition of the material, which completely and reversibly changes the crystal structure, reminiscent of prominent electrochromism because of the melting oxygen-vacancy order in other PVs. [18] A combination of optical techniques in association with high-resolution measurements such as scanning probe microscopy is used to investigate associated electrochromic properties, including coloration efficiency in the visible and near infrared range, which compare very well to commercially used WO 3 systems. Results and Discussion Optical Images and Crystallographic CharacterizationSCFO films with an 80 nm thick were epitaxially grown on lanthanum aluminate (LAO) substrates with and without thermal Topotactic transitions, that is, reversible crystal structure changes due to controllable stoichiometry of material, offer substantial potential to control a wide variety of functionality in transition metal oxides, especially in systems with high ionic mobility and correlated electrons. Here the authors report on topotactic electrochromism with prominent coloration efficiency in SrCo 0.66 Fe 0.34 O 3−δ associated with changes of electrical conductivity and electronic structure of the material. Changes in electron correlation lead to significant coloration and light absorption, which provides a general approach for utilizing topotactic t...

Section: Electrically Induced Topotactic and Electrochromic Transitionsupporting

confidence: 59%

Topotactic Electrochromism for Efficient Coloration Applications

Zhang

Advanced Optical Materials

et al. 2021

“…We chose TPU and PLA because they are both biocompatible with the human body. [ 25,26 ] Also, they are, respectively, on the negative and positive sides of the triboelectric series, [ 27 ] which is an important factor for increasing the triboelectrification. The human lumbar spine has low‐frequency vibrations normally within a range of 1–8 Hz.…”

Section: Resultsmentioning

confidence: 99%

Patient‐Specific Self‐Powered Metamaterial Implants for Detecting Bone Healing Progress

Barri

Zhang

Swink

et al. 2022

Adv Funct Materials

There is an unmet need for developing a new class of smart medical implants with novel properties and advanced functionalities. Here, the concept of “self‐aware implants” is proposed to enable the creation of a new generation of multifunctional metamaterial implantable devices capable of responding to their environment, empowering themselves, and self‐monitoring their condition. These functionalities are achieved via integrating nano energy harvesting and mechanical metamaterial design paradigms. Various aspects of the proposed concept are highlighted by developing proof‐of‐concept interbody spinal fusion cage implants with self‐sensing, self‐powering, and mechanical tunability features. Bench‐top testing is performed using synthetic biomimetic and human cadaver spine models to evaluate the electrical and mechanical performance of the developed patient‐specific metamaterial implants. The results show that the self‐aware cage implants can diagnose bone healing process using the voltage signals generated internally through their built‐in contact‐electrification mechanisms. The voltage and current generated by the implants under the axial compression forces of the spine models reach 9.2 V and 4.9 nA, respectively. The metamaterial implants can serve as triboelectric nanogenerators to empower low‐power electronics. The capacity of the proposed technology to revolutionize the landscape of implantable devices and to achieve better surgical outcomes is further discussed.

“…A hydrophobic porous membrane (HPM) is set on liquid surface A. The membrane is hydrophobic so the liquid cannot wet it; and it is also made of electret material so that it can store a few quasi-permanent net charges 24 . There is a pore in the middle of the membrane and there are 4 fixed charges (FC) around the pore.…”

Section: Model Setup and Methodsmentioning

confidence: 99%

A Molecular Ratchet Model without Feedback Control

Jiang¹

2022

Preprint

Feedback controllers (which act like Maxwell's demon) can extract useful work by rectifying thermal fluctuations. However, feedback controllers consume energy, and the work extracted cannot compensate the energy consumed. In this paper, we propose a molecular ratchet model without any feedback controllers and report the simulation results to support its feasibility. In our model, we break the dynamic symmetry by using an electric field to create a concentration difference of solute ions between the two liquid surfaces of a solution. The simulation results show that our ratchet model can induce a continuous net solvent flux. In that sense, all the positive work extracted from the heat bath can be available energy because it doesn't need to compensate the energy cost of the feedback controller. Our work makes it possible to construct an entirely mechanical molecule-rectifying system as Szilárd expected.