Effects of frequency and temperature evolution of polar nanoregions on susceptibility dispersion and polarization mechanism in relaxors

A generic theory for the frequency and temperature effects on the characteristic evolution of polar nanoregions (PNRs) is essential for improving and optimizing the design of relaxor-based piezoelectric and electrocaloric cooling devices. Pauli's master equation was used to deduce analytical expressions for both the polarization dynamics and frequency-tunable susceptibility dispersions of relaxors. This was done by coupling the intrinsic equilibrium and dynamic factors of bulk relaxors and thin-films. It has been found that for relaxors to comply with Vogel-Fulcher relation, the evolution of PNR mean volume and coercive field of localized electric hysteresis for PNRs has to obey the classic Merz's switching law. The evolution of PNR mean volume in Pb(Mg 1/3Nb 2/3)O 3 crystal was calculated in the temperature range of 200-300 K and at different frequencies up to 10 12 Hz. Our results were in good agreement with the mean-field percolation theory and experimental correlation lengths. Hence, the proposed theory may serve as a new basis for studying the relationship between macroscopic dielectric, electrocaloric as well as other important properties of relaxors and evolutions of their typical microstructures. © 2011 American Institute of Physics.published_or_final_versio

Effects of volume evolution of static and dynamic polar nanoregions on the dielectric behavior of relaxors

Recent experiments revealed unusual dielectric behaviors of Pb(Mg 1/3Nb 2/3)O 3 originated from polar nanoregions (PNRs). Thus, Pauli's master equation is adopted to investigate the distinct dielectric responses, correlation strength, and volume evolutions of static and dynamic PNRs. Our findings have not only validated the percolation theory but also ascertained Lorentzian distribution of the rate of thermal change of PNR volume. Finally, based on Maxwell's equation the observed dielectric deviations of bulk permittivity from Curie-Weiss law are attributed to the thermal effects on static volume fraction and polarization rotation. © 2011 American Institute of Physics.published_or_final_versio

Modeling of enhanced electrocaloric effect above the Curie temperature in relaxor ferroelectrics

The electrocaloric (EC) effect offers promise as a means to realize solid-state refrigeration, which requires EC materials possessing a pronounced pyroelectric effect over a broad temperature range. Pauli's master equation is adopted to investigate the recently observed phenomenon of enhanced EC effect above the Curie temperature in relaxor ferroelectrics. The proposed approach allows the EC coefficient to be determined within the framework of classic Landau-Ginzburg-Devonshire thermodynamics and the Maxwell relation, taking into account both the depolarization effect and dielectric permittivity dispersion based on the concept of superparaelectricity and the nanopolar region. We analyze three contributions of the EC effect: temperature-dependent dielectric dispersion, intrinsic pyroelectric effect and enhanced dielectric stiffness. The maximum EC coefficient is determined through the derivatives of the three components with respect to temperature. The proposed approach, in which the evolution of polarization correlation length is accounted for, cannot only provide a microscopic explanation for the thermally driven enhancement of EC responses, but also improves upon the existing models for estimating the EC effect in paraelectric phase of relaxors. Finally, some potential approaches for engineering the enhancement of EC coefficient are also suggested. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.postprin

Anisotropic mechanism on distinct transition modes of tip-activated multipolorizaion switching in epitaxial BiFeO 3 films

Based on the extended Kittel's law, an anisotropic mechanism has been developed to investigate the complex multipolarization switching in (001) and (110) epitaxial BiFeO 3 films, under a biased-tip field. Switching inhomogeneity and domain wall width evolution have been specifically accounted for. It has been found that distinct switching modes, i.e., the breakdown mode of 71°-switched domain and the activation mode of 180°/ 109°switching, exist and dominate the switching orders within switching process. Our predicted switching orders show excellent agreements with the existing experimental data and phase-field results. A two-step procedure is also proposed to fabricate single-phase 71°ferroelastic domain array of controllable density using (001) BiFeO 3 films, which is favored in practice to significantly enhance the magnetoelectric coupling and photovoltage. © 2011 American Institute of Physics.published_or_final_versio

Continuous monitoring of sonomyography, electromyography and torque generated by normal upper arm muscles during isometric contraction : sonomyography assessment for arm muscles

2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Measurement of depth-dependence and anisotropy of ultrasound speed of bovine articular cartilage in vitro

Author name used in this publication: S. G. PatilAuthor name used in this publication: Y. P. ZhengAuthor name used in this publication: J. Y. WuAuthor name used in this publication: J. Shi2004-2005 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

Assessment of muscle fatigue using sonomyography : muscle thickness change detected from ultrasound images

Author name used in this publication: J. ShiAuthor name used in this publication: Y. P. ZhengAuthor name used in this publication: X. ChenAuthor name used in this publication: Q. H. HuangAccepted ManuscriptPublishe

Promoting green residential buildings in China: Bridging the gap between design and operation to improve occupants' residential satisfaction

© 2019 by the authors. While many studies have examined the supply of green residential buildings (GRBs), few have focused on the demand and living experience of them. This paper explores the antecedents of existing residents' repurchase intention and the effect of their residential satisfaction through a questionnaire survey in Sino-Singapore Tianjin Eco-city, China. Structural equation modeling was used to examine the role of proposed determinants. Multi-group analysis tested the moderating role of residential satisfaction. Results show that residents' satisfaction with respect to their homes in GRBs was heterogeneous with dissatisfied residents account for 55%. Residents' knowledge about GRBs, their environmental attitudes and perceived usefulness of GRB were key determinants of repurchase intentions but trust in relevant institutions was not. Residential satisfaction played a moderating role in predicting repurchase intentions. This study enlightens practitioners in both private and public sectors to improve occupancy experiences of existing residents and to understand the repurchase behaviors of existing customers, by bridging the gap between strong green design and construction and weak operation and maintenance of GRBs

Estimation of wrist angle from sonomyography using support vector machine and artificial neural network models

2008-2009 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

Sonomyography : monitoring morphological changes of forearm muscles in actions with the feasibility for the control of powered prosthesis

Author name used in this publication: Y. P. ZhengAuthor name used in this publication: M. M. Fa. ChanAuthor name used in this publication: J. ShiAuthor name used in this publication: X. ChenAuthor name used in this publication: Q. H. Huang2006-2007 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe