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"Jing, Feng"
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Lead-free piezoceramics: Status and perspectives
The field of lead-free piezoceramics, which aims to replace lead zirconate titanate (PZT) and related perovskite materials, has been vibrant for almost 15 years. Once the science in this field attained a certain stage of maturity, materials with properties better than PZT have appeared, and the first products are about to reach the marketplace. This article describes the three most promising lead-free piezoceramics currently under discussion to replace PZT. Each has a pronounced property profile geared for specific applications. Guidelines for directions for fundamental future research on as well as technology transfer to industry of lead-free piezoceramics are provided.
Journal Article
Exceptional figure of merit achieved in boron-dispersed GeTe-based thermoelectric composites
GeTe is a promising p-type material with increasingly enhanced thermoelectric properties reported in recent years, demonstrating its superiority for mid-temperature applications. In this work, the thermoelectric performance of GeTe is improved by a facile composite approach. We find that incorporating a small amount of boron particles into the Bi-doped GeTe leads to significant enhancement in power factor and simultaneous reduction in thermal conductivity, through which the synergistic modulation of electrical and thermal transport properties is realized. The thermal mismatch between the boron particles and the matrix induces high-density dislocations that effectively scatter the mid-frequency phonons, accounting for a minimum lattice thermal conductivity of 0.43 Wm
−1
K
−1
at 613 K. Furthermore, the presence of boron/GeTe interfaces modifies the interfacial potential barriers, resulting in increased Seebeck coefficient and hence enhanced power factor (25.4 μWcm
−1
K
−2
at 300 K). Consequently, we obtain a maximum figure of merit
Z
max
of 4.0 × 10
−3
K
−1
at 613 K in the GeTe-based composites, which is the record-high value in GeTe-based thermoelectric materials and also superior to most of thermoelectric systems for mid-temperature applications. This work provides an effective way to further enhance the performance of GeTe-based thermoelectrics.
Doping approach is a conventional method to increase ZT values of thermoelectric materials. Here, authors propose a facile strategy to enhance thermoelectric performance by mixing boron particles into GeTe-based thermoelectric materials, leading to a ZT value of 2.45 at 613 K.
Journal Article
3D charge and 2D phonon transports leading to high out-of-plane ZT in n-type SnSe crystals
Heat can be converted into electricity by thermoelectric materials. Such materials are promising for use in solid-state cooling devices. A challenge for developing efficient thermoelectric materials is to ensure high electrical but low thermal conductivity. Chang et al. found that bromine doping of tin selenide (SnSe) does just this by maintaining low thermal conductivity in the out-of-plane direction of this layered material. The result is a promising n-type thermoelectric material with electrons as the charge carriers—an important step for developing thermoelectric devices from SnSe. Science , this issue p. 778 In the out-of-plane direction, n-type SnSe shows intriguing thermoelectric properties. Thermoelectric technology enables the harvest of waste heat and its direct conversion into electricity. The conversion efficiency is determined by the materials figure of merit ZT . Here we show a maximum ZT of ~2.8 ± 0.5 at 773 kelvin in n-type tin selenide (SnSe) crystals out of plane. The thermal conductivity in layered SnSe crystals is the lowest in the out-of-plane direction [two-dimensional (2D) phonon transport]. We doped SnSe with bromine to make n-type SnSe crystals with the overlapping interlayer charge density (3D charge transport). A continuous phase transition increases the symmetry and diverges two converged conduction bands. These two factors improve carrier mobility, while preserving a large Seebeck coefficient. Our findings can be applied in 2D layered materials and provide a new strategy to enhance out-of-plane electrical transport properties without degrading thermal properties.
Journal Article
Constructing phase boundary in AgNbO3 antiferroelectrics: pathway simultaneously achieving high energy density and efficiency
Dielectric capacitors with high energy storage density (
W
rec
) and efficiency (
η
) are in great demand for high/pulsed power electronic systems, but the state-of-the-art lead-free dielectric materials are facing the challenge of increasing one parameter at the cost of the other. Herein, we report that high
W
rec
of 6.3 J cm
-3
with
η
of 90% can be simultaneously achieved by constructing a room temperature M2–M3 phase boundary in (1-
x
)AgNbO
3
-
x
AgTaO
3
solid solution system. The designed material exhibits high energy storage stability over a wide temperature range of 20–150 °C and excellent cycling reliability up to 10
6
cycles. All these merits achieved in the studied solid solution are attributed to the unique relaxor antiferroelectric features relevant to the local structure heterogeneity and antiferroelectric ordering, being confirmed by scanning transmission electron microscopy and synchrotron X-ray diffraction. This work provides a good paradigm for developing new lead-free dielectrics for high-power energy storage applications.
Dielectric capacitors are widely used in electronic systems but they possess inferior energy density in comparison with other electrochemical energy storage. Here, the authors construct a diffused phase boundary to simultaneously achieve high energy storage density and efficiency in AgNbO
3
antiferroelectrics.
Journal Article
Wide-temperature-range thermoelectric n-type Mg3(Sb,Bi)2 with high average and peak zT values
Mg
3
(Sb,Bi)
2
is a promising thermoelectric material suited for electronic cooling, but there is still room to optimize its low-temperature performance. This work realizes >200% enhancement in room-temperature
zT
by incorporating metallic inclusions (Nb or Ta) into the Mg
3
(Sb,Bi)
2
-based matrix. The electrical conductivity is boosted in the range of 300–450 K, whereas the corresponding Seebeck coefficients remain unchanged, leading to an exceptionally high room-temperature power factor >30 μW cm
−1
K
−2
; such an unusual effect originates mainly from the modified interfacial barriers. The reduced interfacial barriers are conducive to carrier transport at low and high temperatures. Furthermore, benefiting from the reduced lattice thermal conductivity, a record-high average
zT
> 1.5 and a maximum
zT
of 2.04 at 798 K are achieved, resulting in a high thermoelectric conversion efficiency of 15%. This work demonstrates an efficient nanocomposite strategy to enhance the wide-temperature-range thermoelectric performance of n-type Mg
3
(Sb,Bi)
2
, broadening their potential for practical applications.
The utilization of Mg
3
(Sb,Bi)
2
in thermoelectric devices is hindered by its low performance near room temperature. Here, authors report thermoelectric performance enhancement of Mg
3
(Sb,Bi)
2
within a wide temperature range by incorporating metallic inclusions at grain boundaries. (279 in total)
Journal Article
Highly stabilized and efficient thermoelectric copper selenide
The liquid-like feature of thermoelectric superionic conductors is a double-edged sword: the long-range migration of ions hinders the phonon transport, but their directional segregation greatly impairs the service stability. We report the synergetic enhancement in figure of merit (ZT) and stability in Cu
1.99
Se-based superionic conductors enabled by ion confinement effects. Guided by density functional theory and nudged elastic band simulations, we elevated the activation energy to restrict ion migrations through a cation–anion co-doping strategy. We reduced the carrier concentration without sacrificing the low thermal conductivity, obtaining a ZT of ∼3.0 at 1,050 K. Notably, the fabricated device module maintained a high conversion efficiency of up to ∼13.4% for a temperature difference of 518 K without obvious degradation after 120 cycles. Our work could be generalized to develop electrically and thermally robust functional materials with ionic migration characteristics.
Cu
2
Se is of interest for thermoelectrics as it is environmentally sustainable and has a high figure of merit ZT; however, copper ion migration impacts device stability. Here a co-doping strategy that combines steric and electrostatic effects is shown to improve device stability as well as improving
ZT
to 3.
Journal Article
Lead-free ferroelectric materials: Prospective applications
The year of 2021 is the 100th anniversary of the first publication of ferroelectric behaviour in Rochelle salt, focussing on its piezoelectric properties. Over the past many decades, people witnessed a great impact of ferroelectricity on our everyday life, where numerous ferroelectric materials have been designed and developed to enable the advancement of diverse applications. Now the driving forces for ferroelectric studies stem from regulations on environment, human health and sustainable society development. This leads to the resurgence of lead-free ferroelectric materials for the expectation of replacing the state-of-the-art lead-based counterparts. The next wave of explorations into ferroelectric materials maybe related to the Internet-of-Things, which requires millions of self-powered sensors and memories. This will promote research on ferroelectrics for sensing, energy harvesting and storage, communication and non-volatile memories, from centimetre scale to micro and nanoscale. This review gives a brief discussion from the materials viewpoint, on the challenges and current status of lead-free ferroelectrics based on prospective applications.
Graphic Abstract
Journal Article
Heterovalent-doping-enabled atom-displacement fluctuation leads to ultrahigh energy-storage density in AgNbO3-based multilayer capacitors
Dielectric capacitors with high energy storage performance are highly desired for next-generation advanced high/pulsed power capacitors that demand miniaturization and integration. However, the poor energy-storage density that results from the low breakdown strength, has been the major challenge for practical applications of dielectric capacitors. Herein, we propose a heterovalent-doping-enabled atom-displacement fluctuation strategy for the design of low-atom-displacements regions in the antiferroelectric matrix to achieve the increase in breakdown strength and enhancement of the energy-storage density for AgNbO
3
-based multilayer capacitors. An ultrahigh breakdown strength ~1450 kV·cm
−1
is realized in the Sm
0.05
Ag
0.85
Nb
0.7
Ta
0.3
O
3
multilayer capacitors, especially with an ultrahigh U
rec
~14 J·cm
−3
, excellent η ~ 85% and P
D,max
~ 102.84 MW·cm
−3
, manifesting a breakthrough in the comprehensive energy storage performance for lead-free antiferroelectric capacitors. This work offers a good paradigm for improving the energy storage properties of antiferroelectric multilayer capacitors to meet the demanding requirements of advanced energy storage applications.
AgNbO
3
has a potential for high power capacitors due to its antiferroelectric characteristics. Here, the authors achieve multilayer capacitors with energy-storage density of 14 J·cm
−3
by heterovalent-doping-enabled atom-displacement fluctuation.
Journal Article
Global burden of hip fracture: The Global Burden of Disease Study
Summary
This study is the first to measure global burden of hip fracture in patients aged 55 years and older across 204 countries and territories from 1990 to 2019. Our study further proved that the global burden of hip fracture is still large. Hip fractures among males are perhaps underestimated, and older adults should be given more attention.
Purpose
Hip fracture is a tremendous universal public health challenge, but no updated comprehensive and comparable assessment of hip fracture incidence and burden exists for most of the world in older adults.
Methods
Using data from the Global Burden of Diseases (GBD) 2019, we estimated the number and rates of the incidence, prevalence, and years lived with disability (YLD) of hip fracture across 204 countries and territories in patients aged 55 years and older from 1990 to 2019.
Results
In 2019, the incidence, prevalence, and YLDs rates of hip fracture in patients aged 55 years and older were 681.35 (95% UI 508.36–892.27) per 100000 population, 1191.39 (95% UI 1083.80–1301.52) per 100000 population, and 130.78 (95% UI 92.26–175.30) per 100000 population. During the three decades, the incidence among people aged below 60 years showed a downward trend, whereas it showed a rapid upward trend among older adults. All the numbers and rates of hip fractures among females were higher than those among males and increased with age, with the highest number and rate in the highest age group. Notably, the male to female ratio of the incidence for people aged over 55 years increased from 0.577 in 1990 to 0.612 in 2019. Falls were the leading cause among both sexes and in all age groups.
Conclusions
The incidence and the number of hip fractures among patients aged 55 years and older increased over the past three decades, indicating that the global burden of hip fracture is still large. Hip fractures among males are perhaps underestimated, and older adults should be given more attention.
Journal Article