| 1. |
- Han, Yilin, et al.
(författare)
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171 Scandium-based full Heusler compounds : A comprehensive study of competition between XA and L21 atomic ordering
- 2019
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Ingår i: Results in Physics. - : Elsevier. - 2211-3797. ; 12, s. 435-446
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Tidskriftsartikel (refereegranskat)abstract
- The site-preference rule (SPR), which is widely used to design and study the properties of full-Heusler alloys X2YZ, is applied to determine the positions of different transition-metal elements with various numbers of valence electrons in Heusler alloys. The scandium-based full Heusler alloys should form an XA structure according to the SPR, because the transition-metal element Sc with fewer valence electrons tends to occupy the Wyckoff sites A(0, 0, 0) and B(0.25, 0.25, 0.25). As opposed to previous investigations, L21-type scandium-based full Heusler alloys, which do not follow the SPR, are also considered in this work. Theoretical computations are used to study the atomic-site preferences of 171 scandium-based full Heusler alloys, and the results indicate that most of these alloys form L21-type structures rather than XA-type structures. Two possible orderings are also studied in terms of their difference in charge density. Furthermore, the ground state, electronic structure, and magnetic characteristics of these alloys are also investigated in detail in both XA and L21 structures. The results reveal dramatic differences between XA- and L21-type alloys. This study thus presents a counterexample of the SPR rule and should provide significant guidance for the future design of full-Heusler alloys.
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| 2. |
- Wang, Xiangjian, et al.
(författare)
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Large electrical strain in lead-free K0.5Na0.5NbO3-based ceramics by heterovalent doping
- 2023
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Ingår i: Journal of Materiomics. - : Elsevier. - 2352-8478 .- 2352-8486. ; 9:5, s. 959-970
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Tidskriftsartikel (refereegranskat)abstract
- Heterovalent doped (K0.48-0.07xNa0.52-0.43xBi0.5x)(Nb0.95-0.95xSb0.05-0.05xZrx)O3 ceramics were fabricated using conventional solid-state reaction. Then, the phase structures, dielectric, ferroelectric, and electric-strain properties were investigated. The compositions were tuned to be located at polymorphic phase boundary with increasing heterovalent Bi3+ and Zr4+ doping levels. A large strain of 0.19% was obtained at relatively low electric fields of 30 kV/cm in the composition of x = 0.04. The normalized large-signal d33* values were approximately 633 pm/V under a low driving electric field of 30 kV/cm, which were comparable or larger than the values reported for other lead-free families. The large strains obtained can be attributed to the formation of nanodomains and high-density domain walls, which were confirmed by the observations of domain morphology using transmission electron microscopy (TEM) technique. Excellent temperature stability of the strain properties of the x = 0.04 sample could be ascribed to the sluggish behaviour for the local structural heterogeneity in heterovalent-ion doped KNN ceramic. Theoretical simulations revealed that the Zr4+ produce the local stress at the BO6 octahedra and Bi3+ could yield off-centering of AO12 ployhedron due to the nature of Bi 6s lone pair electrons, which induced lattice expansion and local distortions in the sample. The local displacements are strongly anisotropic in heterovalent-ion doped system. It is believed that random local fields exist in these compositions owing to the eixstence of charge distribution. Such heterovalent doping of Bi3+ and Zr4+ could destory simutiously the orthorhombic symmetry and the short-range ferroelecctric order, leading to the formation of complex nanodomains and local structral hetergenenity. Heterovalent doping may, therefore, offer a new avenve to design novel K0.5Na0.5NbO3 (KNN) -based materials for their mutifunctional applications.
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| 3. |
- Wu, Mengxin, et al.
(författare)
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Site preference and tetragonal distortion inpalladium-rich Heusler alloys
- 2019
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Ingår i: IUCrJ. - Chester : International Union of Crystallography (IUCr). - 2052-2525. ; 6, s. 218-225
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Tidskriftsartikel (refereegranskat)abstract
- In this work, two kinds of competition between different Heusler structure types are considered, one is the competition between XA and L2(1) structures based on the cubic system of full-Heusler alloys, Pd(2)YZ (Y = Co, Fe, Mn; Z = B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb). Most alloys prefer the L2(1) structure; that is, Pd atoms tend to occupy the a (0, 0, 0) and c (0.5, 0.5, 0.5) Wyckoff sites, the Y atom is generally located at site b (0.25, 0.25, 0.25), and the main group element Z has a preference for site d (0.75, 0.75, 0.75), meeting the well known site-preference rule. The difference between these two cubic structures in terms of their magnetic and electronic properties is illustrated further by their phonon dispersion and density-of-states curves. The second type of competition that was subjected to systematic study was the competitive mechanism between the L2(1 )cubic system and its L1(0) tetragonal system. A series of potential tetragonal distortions in cubic full-Heusler alloys (Pd(2)YZ) have been predicted in this work. The valley-and-peak structure at, or in the vicinity of, the Fermi level in both spin channels is mainly attributed to the tetragonal ground states according to the density-of-states analysis. Delta E-M is defined as the difference between the most stable energy values of the cubic and tetragonal states; the larger the value, the easier the occurrence of tetragonal distortion, and the corresponding tetragonal structure is stable. Compared with the Delta E-M values of classic Mn-2 based tetragonal Heusler alloys, the Delta E(M )values of most Pd(2)CoZ alloys in this study indicate that they can overcome the energy barriers between cubic and tetragonal states, and possess possible tetragonal transformations. The uniform strain has also been taken into consideration to further investigate the tetragonal distortion of these alloys in detail. This work aims to provide guidance for researchers to further explore and study new magnetic functional tetragonal materials among the full-Heusler alloys.
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| 4. |
- Geng, Wenping, et al.
(författare)
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Conductive Domain-Wall Temperature Sensors of LiNbO3 Ferroelectric Single-Crystal Thin Films
- 2021
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Ingår i: IEEE Electron Device Letters. - : IEEE. - 0741-3106 .- 1558-0563. ; 42:12, s. 1841-1844
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Tidskriftsartikel (refereegranskat)abstract
- Domain wall current (DWC) plays a key role in storage devices, logic devices and sensors due to its high on-off ratio and nano structure size in the era of nanoelectronics technology. In this work, the DWC of single crystal LiNbO3 thin film was studied by piezoresponse force microscope (PFM) and conducting atomic force microscope (c-AFM). We mainly focus on voltage and temperature dependence of DWC which increases with the voltage and temperatures. Based on this research, the packaged DWC temperature sensor is fabricated and applied in wide temperature range. The existence of domain walls makes the current on-off ratio as high as 103 at the voltage of 15 V. Our study shows that DWC has a negative temperature coefficient (NTC) from 140 K to 500 K. The current increases from 3 pA to 57 μA, which is attributed to the conductivity of switched domain. This work proposes a new type temperature sensor with wide temperature range and high compatibility and sensitivity. In addition, it provides support for harsh environment applications of ferroelectric domain engineering devices.
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| 5. |
- Geng, Wenping, et al.
(författare)
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Giant negative electrocaloric effect in antiferroelectric La-modified PbZrO3 thin films within wide temperature range
- 2021
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 886
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Tidskriftsartikel (refereegranskat)abstract
- Antiferroelectric thin films have exhibited outstanding negative electrocaloric effect (ECE), which are potential candidate regarding to the solid-state refrigeration technology. In this work, Pb0.97La0.02ZrO3 (PLZ) antiferroelectric thin films were prepared on LaNiO3(LNO)/Pt electrode and LNO electrode by sol-gel method. Giant negative electrocaloric effect (ΔT ~ −13.2 K) can observed in wide temperature range (213–493 K) that deposited on composite electrode, which can be attributed to better electric conductivity of LNO/Pt composite electrode than LNO electrode. In addition to outstanding negative ECE, positive ECE also can be obtained near curie temperature, which is caused by phase transition from ferroelectric (FE) to paraelectric (PE) state. The optimized ECE property contributed to the phase transition and introduction of composite electrode, which pave the giant prospect considering high-efficiency solid-state refrigeration devices through combination of positive and negative ECE.
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| 6. |
- Geng, Wenping, et al.
(författare)
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Permanent charged domain walls under tip-poling engineering
- 2021
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 9:44, s. 15797-15803
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Tidskriftsartikel (refereegranskat)abstract
- Charged domain walls (CDWs) have attracted considerable attention owing to their tunable properties related to high-density information storage and nanoelectronics devices. The excellent time endurance of conductivity is a pressing need, which is directly related to the domain stability and boundary conditions. In this study, we propose an effective method to promote the permanent formation of charged domain walls aimed with tip-induced electric fields. The permanent domain structures and CDWs are attributed to the robust stimulus with tip dimensions combined with effective screening conditions. This interesting conductivity near the domain walls is three orders of magnitude higher than the domain inner, and exhibits attractive anti-fatigue properties with the value of ∼60 pA for the duration of more than one month. In addition, the tunable mechanism of CDWs in LiNbO3 thin films is related to carrier gathering near the domain walls for the inclined boundary. These inclined head-to-head domain walls exhibit conductive features only along the negative direction, which can be modulated by the application of a sub-coercive voltage. The results demonstrate the stable manipulation of domain reversal and charged domain walls in LiNbO3 thin films, highlighting them as a critical component, especially for multiple-state logic circuits and potential ferroelectric diode applications in non-volatile memories and nanoelectronics devices.
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| 7. |
- Shi, P., et al.
(författare)
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Large energy storage properties of lead-free (1-x)(0.72Bi0.5Na0.5TiO3-0.28SrTiO3)-xBiAlO3 ceramics at broad temperature range
- 2019
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 784, s. 788-793
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Tidskriftsartikel (refereegranskat)abstract
- (1-x)(0.72Bi0.5Na0.5TiO3-0.28SrTiO3)-xBiAlO3 (BNT-ST-xBA) lead-free ceramics were prepared through solid-state sintering methods. The structural, dielectric and energy storage properties of the ceramics were studied in this work. A large energy storage density of BNT-ST-0.01BA ceramics exceeding 1.746 J/cm3 has been obtained. The ceramics exhibit a good thermal stability at the temperature ranging from 20 °C to 120 °C. In addition, energy storage properties are relatively stable after completing 10000 electrical cycles, which shows promising potential for energy storage devices at a high temperature region.
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| 8. |
- Sun, Haonan, et al.
(författare)
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Large energy storage density in BiFeO3-BaTiO3-AgNbO3 lead-free relaxor ceramics
- 2020
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 40:8, s. 2929-2935
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Tidskriftsartikel (refereegranskat)abstract
- Lead-free (0.70-x)BiFeO3-0.30BaTiO3-xAgNbO3+5‰mol CuO (abbreviated as BF-BT-xAN) ceramics were fabricated using a modified thermal quenching technique. BF-BT-xAN ceramics are of a perovskite structure with morphotropic phase boundary (MPB) and show strong relaxor properties. Remarkably, the high recoverable energy storage density of 2.11 J/cm3 is obtained for BF-BT-xAN with x = 0.14. For the x = 0.14 ceramics, its energy storage efficiency is as high as 84 % at relative low field of 195 kV/cm, together with an outstanding thermal stability in a broad temperature range from 25 °C to 150 °C. In addition, this ceramic maintains superior energy storage performance even after 8 × 104 electrical cycles due to its high densification after doping Ag2O and Nb2O5. The result suggests that lead-free BF-BT-xAN ceramics may be promising candidate for dielectric energy storage application.
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| 9. |
- Wang, Xiangjian, et al.
(författare)
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Enhanced piezoelectric, electrocaloric and energy storage properties at high temperature in lead-free Bi0.5(Na1-xKx)0.5TiO3ceramics
- 2019
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Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 45:4, s. 4274-4282
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Tidskriftsartikel (refereegranskat)abstract
- The piezoelectric, electrocaloric and energy storage properties were systemically investigated in lead-free Bi0.5(Na1-xKx)0.5TiO3 ceramics from room temperature to high temperature region. These ceramics can be poled completely to obtain large piezoelectric coefficient (104–153 pC/N) at low electric field of ~30 kV/cm. The piezoelectric propertyshows good thermal stability due to high depolarization temperature (Td). For BNKT20, a large low electric field-induced strain of 0.36% is obtained at 120 °C under 50 kV/cm, the corresponding normalized strain coefficient is up to 720 pm/V, which is larger than other BNT-based ceramics at high temperature region. The electrocaloric properties of these ceramics are studied via indirect and direct methods. Large EC value (~1.08 K) in BNKT20ceramic is obtained at 50 kV/cm using indirect calculation. Above 100 °C, the dielectricenergy storage density and efficiency of BNKT20 is still up to ~0.85 J/cm3 and 0.75, respectively. The BNKTx ceramics may become promising candidates in the fields of actuators, electrocaloric cooling and energy storage at high temperature region.
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| 10. |
- Wang, Xiangjian, et al.
(författare)
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Ferroelectric and antiferroelectric distortions coupling of nitride perovskite LaWN3 under epitaxial strain using first-principles calculations
- 2022
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Ingår i: Europhysics letters. - : Institute of Physics (IOP). - 0295-5075 .- 1286-4854. ; 140:5
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Tidskriftsartikel (refereegranskat)abstract
- LaWN3, a novel nitride perovskite, have been synthesized and its piezoelectric properties have been investigated (TALLEY K. R. et at., Science, 374 (2021) 1488). However, the understanding of its ferroelectric properties under the external strain is still lacking. Here, the misfit-strain-dependent coupling between anti-ferrodistortions (AFD) and ferroelectric (FE) distortions has been studied by using a first-principle approach. It can be observed that AFD and FE distortions can work cooperatively with each other as the compressive strain increases, and the coupling energy between them is found to work in different ways under various strains. Our results show that the coupling tends to stabilize the ground structure when the compressive strain is smaller than -1.9%, it works oppositely when the compressive strain becomes larger than 1.9%. Our results can provide us with more hints about the influence of the epitaxial strains on the intrinsic coupling behavior in the perovskite ferroelectric compounds, which is very important for us to design and fabricate new kinds of functional materials.
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