Helen Lai Wa Chan

Dynamic magnetomechanical properties of Terfenol-D/epoxy pseudo 1-3 composites

Terfenol-D/epoxy pseudo 1-3 composites were fabricated by embedding and aligning Terfenol-D particles with a size distribution of 10–300μm in a passive epoxy matrix using six Terfenol-D volume fractions (υf) ranging from 0.22 to 0.72. The dependence of the dynamic relative permeability (μr33T), elastic modulus (E3H), and dynamic strain coefficient (d33) on υf was investigated as a function of magnetic bias field (HBias). The HBias response data showed that the built-in non-180° domain states related to residual compressive stresses in the composites result in a significant decrease in μr33T for HBias 0.5. The present study provides a useful guide to optimize the composite properties for transducer design.

Water dispersible ultra-small multifunctional KGdF4:Tm3+, Yb3+ nanoparticles with near-infrared to near-infrared upconversion

Ultra-small multifunctional KGdF4:Tm3+,Yb3+ nanoparticles with near-infrared to near-infrared upconversion are synthesized. The average sizes of KGdF4:Tm3+ 2%, Yb3+ 20% core-only and KGdF4:Tm3+ 2%, Yb3+ 20%/KGdF4 core–shell nanoparticles are ∼3.7 nm and ∼7.4 nm, respectively, which fall within the reported optimal sizes (<10 nm) for bioimaging probes. The excitation and emission at 980 and 803 nm are favorable to deeper tissue penetration and reduced autofluorescence. The weak upconversion luminescence of the ultra-small core-only nanoparticles is overcome by the use of the core–shell approach. The magnetic mass susceptibility and magnetization of the ultra-small core-only and core–shell nanoparticles were determined, and are close to those of large nanoparticles (26 and 50 nm) used for magnetic resonance imaging and bio-separation. There is no variation in the magnetic properties with the nanoparticles’ sizes between the core-only (∼3.7 nm) and core–shell (∼7.4 nm) nanoparticles, which differs from the size-dependent luminescence. The oleate-capped core–shell nanoparticles were further encapsulated with a PEG-phospholipid shell to endow them with dispersibility in water, which is indispensable for future biological applications.

Converse magnetoelectric effect in three-phase composites of piezoceramic, metal cap, and magnet

We report experimentally and theoretically the converse magnetoelectric (CME) effect in a three-phase piezoceramic-metal-cap-magnet composite made by sandwiching a thickness-polarized Pb(ZrxTi1−x)O3 (PZT) disk between two truncated conical brass caps and two thickness-magnetized SmCo disks. The reported CME effect originates from the product of the converse piezoelectric effect in the PZT disk, the mechanical transformation/amplification effect in the brass caps, and the magnetic induction effect in the SmCo disks. The composite exhibits a large CME coefficient (αB) in excess of 2mG∕V with a flat response in the broad frequency range of 0.1–100kHz. The measured magnetic flux density shows an extremely linear relationship to the applied voltage with amplitude varying from 10to100V over a wide range of detection distance of 0.7–6.5mm. This electromechanomagnetically coupled effect enables applications of the composite in coil-free magnetic flux control devices, featuring smaller Joule heating loss, wider operational bandwidth, and greater property-tailorable flexibility compared to conventional electromagnet-based devices.We report experimentally and theoretically the converse magnetoelectric (CME) effect in a three-phase piezoceramic-metal-cap-magnet composite made by sandwiching a thickness-polarized Pb(ZrxTi1−x)O3 (PZT) disk between two truncated conical brass caps and two thickness-magnetized SmCo disks. The reported CME effect originates from the product of the converse piezoelectric effect in the PZT disk, the mechanical transformation/amplification effect in the brass caps, and the magnetic induction effect in the SmCo disks. The composite exhibits a large CME coefficient (αB) in excess of 2mG∕V with a flat response in the broad frequency range of 0.1–100kHz. The measured magnetic flux density shows an extremely linear relationship to the applied voltage with amplitude varying from 10to100V over a wide range of detection distance of 0.7–6.5mm. This electromechanomagnetically coupled effect enables applications of the composite in coil-free magnetic flux control devices, featuring smaller Joule heating loss, wider op...

Raman scattering spectra and ferroelectric properties of Bi1−xNdxFeO3(x=0–0.2) multiferroic ceramics

Single-phase Bi1−xNdxFeO3 (BNFOx) (x=0–0.2) multiferroic ceramics were prepared to study the effects of Nd substitution on their crystal structures, Raman scattering spectra, and ferroelectric properties. Rietveld refinement of x-ray diffraction data showed a gradual change in crystal structure from rhombohedral to pseudotetragonal via triclinic with increasing x. The evolvement of Raman normal modes with increasing x suggested that such structural change is accompanied by the weakening of long-range ferroelectric order. The simultaneous occurrence of abrupt mode evolvement and ferroelectric-paraelectric transition in BNFOx=0.175 and BNFOx=0.2 was explained according to the change of Bi–O covalent bonds as a result of the decline in the stereochemical activity of the Bi lone electron pair at 0.175⩽x⩽0.2.

Structural transformation and ferroelectric?paraelectric phase transition in Bi1?x Lax FeO3 (x = 0?0.25) multiferroic ceramics

Bi1−xLaxFeO3 (x = 0–0.25) multiferroic ceramics were prepared to study the compositional driven structural transformation and ferroelectric– paraelectric phase transition. Rietveld-refined crystal structure parameters revealed the existence of a rhombohedral R3c symmetry in BiFeO3, a triclinic P1 symmetry in Bi0.95La0.05FeO3, Bi0.9La0.1FeO3 and Bi0.85La0.15FeO3, a pseudotetragonal P4mm symmetry in Bi0.8La0.2FeO3 and a pseudotetragonal P4/mmm symmetry in Bi0.75La0.25FeO3. La substitution led to the ferroelectric–paraelectric phase transition accompanying abrupt changes of Raman scattering spectra in Bi0.8La0.2FeO3 and Bi0.75La0.25FeO3, besides the release of weak ferromagnetism in Bi0.85La0.15FeO3, Bi0.8La0.2FeO3 and Bi0.75La0.25FeO3. Ferroelectricity with remnant polarization of >9.8 µC cm−2 and piezoelectricity with d33 coefficient of >25 pC/N were confirmed in all compositions except for Bi0.75La0.25FeO3.

Converse magnetoelectric effect in laminated composites of PMN-PT single crystal and Terfenol-D alloy

We have found experimentally and theoretically that laminated composites comprising one layer of length-magnetized Tb0.3Dy0.7Fe1.92 (Terfenol-D) magnetostrictive alloy sandwiched between two layers of thickness-polarized, electro-parallel-connected 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (PMN–PT) piezoelectric single crystal have a large converse magnetoelectric effect characterized by a large magnetic induction in response to an applied ac voltage. The reported converse magnetoelectric effect originates from the product of the converse piezoelectric effect in the PMN–PT layers and the converse magnetostrictive effect in the Terfenol-D layer. Large converse magnetoelectric coefficient in excess of 105mG∕V is obtained in the composites at a low magnetic bias field of 170Oe. The measured magnetic induction has an excellent linear relationship to the applied ac voltage with amplitude varying from 50to160V. These made the composites to be a promising material for direct realization of core-free magnetic flux control de...

Reduced ferroelectric coercivity in multiferroic Bi0.825Nd0.175FeO3 thin film

Bi0.825Nd0.175FeO3 (BNFO) thin film is grown on Pt∕TiO2∕SiO2∕Si substrate by pulsed laser deposition, and its multiferroic properties are compared with those of BiFeO3 (BFO) thin film. With limited Fe2+ ions and its twinborn oxygen vacancies, both samples show low dielectric losses of <0.026 at 100Hz and high maximum ferroelectric polarizations of ∼34μC∕cm2. The ferroelectric coercive field of BNFO is reduced by ∼40%, reaching a low value of 235kV∕cm, compared to that of BFO due to the increased ratio of 180° and curved ferroelectric domains to total ferroelectric domains and better nucleation of the ferroelectric domains at the BNFO∕Pt interface. The Raman scattering spectra confirm that the ferroelectric polarizations of both samples originate in the stereochemical activity of the Bi lone electron pair. Weak ferromagnetism is observed in both samples as a result of the limited amount of Fe2+ ions and γ‐Fe2O3 impurity.

Towards pure near-infrared to near-infrared upconversion of multifunctional GdF 3 :Yb 3+ ,Tm 3+ nanoparticles

Nearly pure near-infrared to near-infrared (NIR-to-NIR) upconversion in GdF(3) host with 23% Yb(3+) and 1% Tm(3+) under 980 nm excitation is firstly reported. The ratio of the intensity of the emission at 807 nm to that at 478 nm can reach to 105, and the intensity of the emission at 807 nm is preserved. Moreover, the excitation and the emission at 980 and 807 nm are away from the visible region. These are beneficial to deeper tissue penetration and reduced autofluorescence. Raman spectroscopy measurements suggest the high probability of NIR emission in GdF(3) host. Our results indicate that the reported multifunctional nanoparticles are promising in bio-imaging and bio-separation.

Enhanced magnetoelectric effect in longitudinal-transverse mode Terfenol-D/Pb(Mg1/3Nb2/3)O3-PbTiO3 laminate composites with optimal crystal cut

Magnetoelectric (ME) laminate composite consisting of optimal crystal cut thickness-polarized piezoelectric 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (PMN-PT) single crystal and the length-magnetized magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy has been fabricated. The cut optimization of PMN-PT crystal greatly enhances the longitudinally magnetized-transversely polarized (L‐T) mode ME effect, which has a superior ME voltage coefficient αE of ∼3.02V∕cmOe in low frequency band. Near the resonance frequency of 95kHz, the coefficient dramatically increases and reaches the maximized value of 33.2V∕cmOe, which is almost two times larger than the previously reported ⟨001⟩-oriented PMN-PT crystal based L‐T mode laminate composite.

Energy harvesting with piezoelectric drum transducer

Piezoelectric materials can convert ambient vibrations into electrical energy. In this letter, the capability of harvesting the electrical energy from mechanical vibrations in a dynamic environment through a piezoelectric drum transducer has been investigated. Under a prestress of 0.15N and a cyclic stress of 0.7N, a power of 11mW was generated at the resonance frequency of the transducer (590Hz) across an 18kΩ resistor. It is found that the energy from the transducer increases while the resonance frequency of the transducer decreases when the prestress increases. The results demonstrate the potential of the drum transducer in energy harvesting.