Grain Boundary Resistance Research Articles

Designing a new KBT-based binary solid solution as a candidate for dielectric energy storage materials

Dielectric energy storage capacitors offer great potential in pulsed power devices due to the high power density and fast charging-discharging rate. Designing a host material with high field-induced polarization is of importance for developing dielectric energy storage materials via further composition modulation. In this paper, we compare the microstructure, dielectric, and ferroelectric properties as well as the energy storage performance of samples K1/2Bi1/2TiO3(KBT), 75KBT-25BiFeO3 (KBTF25), and 88KBT-12Bi0.85Nd0.15FeO3 (KBNTF12) in detail. It is found that, among three samples, sample KBNTF12 possesses the most complex local structure coexisting of a four-distortions with different polarities; meanwhile, sample KBNTF12 behaves as a strong relaxor, thus giving a high field-induced polarization. Besides, sample KBNTF12 realizes the highest electric breakdown strength Eb among three samples, which is resorted to the highest resistivity of grain boundary. Highest ΔP and Eb of sample KBNTF12 among three samples render it achieve ultrahigh stored energy density Ws of 6.94 J/cm3, high recoverable energy density Wr of 5.23 J/cm3, and high efficiency η of 75.4%. Our work suggests that 88KBT-12BNF binary composition be an optimal candidate for dielectric energy storage ceramics.

Simultaneous enhancements of strength and toughness by multiscale lamellar structure in Ti2AlNb based intermetallic

Multi-scale lamellar structure significantly improves toughness of Ti2AlNb based alloys, which are inherently brittle intermetallics, without compromising their strength. This structure was achieved through-B2-transus-forging (TBTF) combined with O + B2 two-phase region heat treatments. Various types of multi-scale lamellar structures were obtained by controlling the cooling rate after TBTF. These variations were mainly attributed to differences in the distribution, content, and size of the thick lamellar O phase and the size and crystallographic orientation of B2 grain. By analyzing the microstructural characteristics and crystallographic orientation near the crack propagation path, it was found that the crack propagation resistance of thick lamellae, sub grain and grain boundaries (GBs) O phase increased sequentially, accompanied by more tortuous crack propagation path. Moreover, B2 grains with high misorientation significantly deflected the crack propagation by cleavage ridges between adjoining cleavage planes. Additionally, the development of numerous secondary cleavage ridges, resulting from the transition through varying secondary cleavage planes in distinct sub B2 grains, further hindered the quick propagation of cracks. It was clarified that the cleavage planes were dominantly belonging to {110}. These findings provided valuable guidance for the design of damage tolerance strategies for Ti2AlNb-based intermetallics.

First-principles study on the corrosion resistance of iron oxide surface and grain boundary in austenitic steel to lead–bismuth eutectic

In this paper, the corrosion properties of austenitic steel with and without protection of Fe3O4 scale was investigated based on first-principles calculations. The results show that lead–bismuth eutectic (LBE) is only adsorbed at some local positions on Fe3O4 scale, but is stably adsorbed at various sites on the Fe surface. The adsorption of LBE reduces the escape energy of Fe on Fe3O4 scale and pure Fe surface, and pure Fe surface is more susceptible to LBE corrosion. Moreover, the interaction between common alloying elements (Ni, Cu, Mo, Mn, Cr, Nb, V, Si, and Al) and oxygen atoms are investigated. Among them, Ni and Cu are weakly bound to O and most prone to escape from the Fe3O4 scale. Mo, Mn, and Cr have a significant escape tendency, while Nb, V, Si, and Al are not susceptible to escape. LBE will embrittle the grain boundary (GB) under failure of oxide layer. Ti, Cr and Ni all improve the strength of the GB structure, but the strengthening effect is limited, and GB embrittlement is dominated by Pb and Bi.

On the dielectric and magnetic properties of Al doped Pr:123 for advanced devices: A comparison with ZnO

For ZnO comparison, we report here the dielectric and magnetic properties of PrBa2Cu3-3xAl3xOy (Al:Pr123) samples with (0.00 ≤ x ≤ 1.00). The dielectric constant (ε′), ac electrical conductivity (σac) and F-factor were decreased as x increased to 1.00, but the q-factor was increased. As compared to ZnO, the x ≤ 0.05 samples show higher values of ε′, σac and F-factor, as well as q-factor, but at x ≥ 0.10. In addition, the binding energy was increased from 0.423 to 0.672 eV as x increased to 0.30, but above that it significantly enhanced until reach to 38.825 eV. The Cole-Cole plot shows a complete circle for the samples of x ≤ 0.05, and semicircular arcs for the x ≥ 0.10 and ZnO. Moreover, the impedance of grain and grain boundaries is significantly increased as x increases to 1.00, but they are lower than of ZnO. Although ZnO exhibits poor ferromagnetic behavior, the Al: Pr123 samples show strong ferromagnetic behavior with evaluated magnetization parameters. Moreover, these outcomes strongly recommend the Al: Pr123 samples, better than ZnO, for the devices of integrated circuits, solar cells, super-capacitors and spintronics.

Contribution of grain boundary to strength and electrical conductivity of annealed copper wires

The effect of grain boundaries on the strength and electrical conductivity of annealed copper wires was studied. After annealing at 100 °C for 30 min, the copper wires retained a fiber-like structure. The increase in electrical conductivity is believed to stem from the decrease of crystallographic defects introduced by drawing. Recrystallization occurred when the annealing temperature reached 150 °C. The formation of small recrystallized grains led to the introduction of additional grain boundaries perpendicular to the drawing direction, resulting in a slight decrease in electrical conductivity. When the annealing temperature rose up to 200 °C, complete recrystallization took place in the copper wires. The grain boundaries parallel to the drawing direction play an important role in boundary strengthening, while the grain boundaries perpendicular to the drawing direction play an important role in both boundary strengthening and electron scattering. The electrical resistivity of grain boundaries in fully recrystallized copper wires at room temperature was determined experimentally, and an empirical relation is proposed to quickly determine the electric conductivity of copper wires at room temperature based on the boundary spacing along the drawing direction.

Microscale Imaging of Thermal Conductivity Suppression at Grain Boundaries.

Grain-boundary engineering is an effective strategy to tune the thermal conductivity of materials, leading to improved performance in thermoelectric, thermal-barrier coatings and thermal management applications. Despite the central importance to thermal transport, a clear understanding of how grain boundaries modulate the microscale heat flow is missing, owing to the scarcity of local investigations. Here, thermal imaging of individual grain boundaries is demonstrated in thermoelectric SnTe via spatially resolved frequency-domain thermoreflectance. Measurements with microscale resolution reveal local suppressions in thermal conductivity at grain boundaries. Also, the grain-boundary thermal resistance - extracted employing a Gibbs excess approach - is found correlating with the grain-boundary misorientation angle. Extracting thermal properties, including thermal boundary resistances, from microscale imaging can provide comprehensive understanding of how microstructure affects heat transport, crucially impacting the materials design of high-performance thermal-management and energy-conversion devices. This article is protected by copyright. All rights reserved.

Atomic-scale Origin of the Low Grain-boundary Resistance in Perovskite Solid Electrolyte Li0.375Sr0.4375Ta0.75Zr0.25O3.

Atomic-scale Origin of the Low Grain-boundary Resistance in Perovskite Solid Electrolyte Li0.375Sr0.4375Ta0.75Zr0.25O3.

Inhibition effect of segregation and chemical order on grain boundary migration in NbMoTaW multi-principal element alloy

The impacts of solute segregation and chemical order on grain boundary (GB) migration are investigated by atomistic simulations in the NbMoTaW multi-principal element alloy (MPEA). Assisted by a contrived Nb-rich model, it is found that solute segregation and chemical order synergistically inhibit GB migration. Nb segregation increases the critical stress for GB migration, and the presence of chemical order further enhances the resistance of GB to plastic deformation. The destruction of local ordering structures is responsible for the difficult GB migration. Transition pathway analyses show that GB modified with both Nb segregation and chemical order requires high migration barrier, and the prior migration of GB sites tends to avoid regions with heavier chemical order. These results provide new insight into how chemical complexity affects elementary GB motion and contribute to manipulating the stability of MPEAs.

Giant permittivity in (Nb0.5La0.5)xTi1‐xO2 ceramics prepared by slip casting in a strong magnetic field

AbstractA series of textured (Nb0.5La0.5)xTi1‐xO2 (x = 0, 0.0025, 0.005, 0.01) ceramics were sintered in a nitrogen environment after magnetic slip casting (12 T). Component x ranges from 0.0025 to 0.01 while the degree of orientation increases from 0.49 to 0.88. (Nb0.5La0.5)0.01Ti0.99O2 ceramics in the parallel magnetic field's plane have a high permittivity ɛr ≈ 1.6 × 104 and the ultralow dielectric loss tanδ ≈ 0.0038 at 104 Hz. The temperature coefficient value of η ≤ ± 7.1% between 218–473 K, fulfilling the X9R requirements. The giant permittivity properties of textured ceramics are mainly derived from internal barrier layer capacitor impacts, electron hopping, and electron‐pinned defect‐dipoles polarization. The microstructure evolution of sintered ceramics was modified by texturing in a magnetic field, leading to higher activation energies of dielectric relaxations and resistance of grain boundaries and grains. This excellent performance is expected to show great potential in electronic devices' miniaturization and high‐density energy storage.

In Situ Tensile Observation of the Effect of Annealing on Fracture Behavior of Laser Additive Manufactured Titanium Alloy.

The use safety of laser additive manufactured (LAM) titanium alloys is closely related to each one's fracture failure mode. In this study, in situ tensile tests were carried out to study the deformation and fracture mechanisms of LAM Ti6Al4V titanium alloy before and after annealing treatment. The results showed that plastic deformation promoted slip bands to occur inside the α phase and shear bands to generate along the α/β interface. In the as-built sample, cracks initiated in the equiaxed grains and propagated along the columnar grain boundary, showing a mixed fracture mode. However, it transformed into a transgranular fracture after annealing treatment. The widmanstatten α phase acted as a barrier for slip movement and improved the crack resistance of grain boundaries.

Increase of the ionic conductivity of perovskite-type lithium-ion conductor by bacterial cellulose templating

Solid-state lithium-ion conductors suffer the disadvantages of high grain-boundary resistance. Perovskite-type LLTO was prepared via bacterial cellulose templating in this paper. BET analysis indicated that a broad range of pores formed in the LLTO templated onto bacterial cellulose. XRD examinations showed that the crystallinity of LLTO reduced upon being templated onto bacterial cellulose. SEM observations indicated that grains of LLTO pellets with bacterial cellulose became much larger and well-connected. The boundaries between grains of LLTO with bacterial cellulose became much less sharp, and the grains were almost inseparable. Under the influence of BC, the average grain-boundary thickness decreased. LLTO with 2% bacterial cellulose exhibited the highest total conductivity, 9.38 × 10−5 S/cm, which increased by 146% compared with pure LLTO. Both the reduced crystallinity and the decreased grain-boundary thickness contributed to the increase of the total conductivity by facilitating the migration of lithium ions across the grain boundaries. An electrochemical test cell of Li4Ti5O12//LLTO-2%BC//LiCoO2 was demonstrated.

Halide‐based solid electrolytes: The history, progress, and challenges

AbstractLithium metal solid‐state batteries (LMSBs) have attracted extensive attention over the past decades, due to their fascinating advantages of safety and potential for high energy density. Solid‐state electrolytes (SEs) with fast ionic transport and excellent stability are indispensable components in LMSBs. Heretofore, a series of inorganic SEs have been extensively explored, such as sulfide‐ and oxide‐based electrolytes. Unfortunately, they both have difficulty in achieving a satisfactory balance of conductivity and stability, and oxides suffer from a high impedance of grain boundaries, while sulfides encounter poor stability. Halide‐based solid electrolytes are gradually emerging as one of the most promising candidates for LMSBs due to their advantages of decent room temperature ionic conductivity (>10−3 S cm−1), good compatibility with oxide cathode materials, good chemical stability, and scalability. Herein, research and development of the widely studied metal halide SEs including fluorides, chlorides, bromides, and iodides are reviewed, mainly focusing on the structures and ionic conductivities as well as preparation methods and electrochemical/chemical stabilities. And then, based on typical metal halide solid electrolytes, we emphasize the interface issues (grain boundaries, cathode−electrolyte and electrolyte–anode interfaces) that exist in the corresponding LMSBs and summarize the related work on understanding and engineering these interfaces. Furthermore, the typical (or in situ) characterization tools widely used for solid‐state interfaces are reviewed. Finally, a perspective on the future direction for developing high‐performance LMSBs based on the halide electrolyte family is put out.

Enhanced grain connection and ionic conductivity of Na3.3La0.3Zr1.7Si2PO12 ceramic electrolyte by adding Na2B4O7

NASICON-type Na3Zr2Si2PO12 (NZSP) is supposed to be one of the greatest feasible solid electrolytes due to its high electrochemical performance and safety. Herein, Na2B4O7 (NBO) additive is proposed to enhance the grain connection and ionic conductivities, and reduce the sintering temperature. The grain boundary microstructure of Na3.3La0.3Zr1.7Si2PO12 (NLZSP) is adjusted via introducing NBO additive to facilitate the densification sintering at 950 °C. NLZSP with 3 wt% NBO (NZSP(NBO3)) demonstrates an optimized total ionic conductivity (σt) of 1.81 mS cm−1 at 25 °C and low activation energy (Ea) of 0.22 eV. EIS and SEM analysis reveals that NBO additive promotes more intimate contact between NLZSP grains and extensively reduces the grain-boundary resistance (Rgb) from 135 Ω cm2 for NLZSP to 8 Ω cm2 for NLZSP(NBO3). Besides, wide electrochemical stability window of 5 V vs Na+/Na and galvanostatic sodium stripping-plating up to 400 h reconfirms the super stability of NLZSP(NBO3)/Na interface, while small contact angle of 82° will bring better wettability and interface contact of NLZSP(NBO3)/Na. Solid-state sodium metal batteries (SMBs) based reduced graphene oxide wrapped NaTi2(PO4)3 (NTP@rGO) 3D conductive cathode and NLZSP(NBO3) ceramic electrolyte shown excellent rate performance and cycle stability (91.4% of capacity retention after 200 cycles at 1C). Hence, NLZSP(NBO) ceramic electrolyte exhibits a significant advantage in enhancing grain connection, regulating ionic conductivity and reducing sintering temperature, and is anticipated to be used in all solid-state sodium ions batteries (ASSSIBs).

Atomic-scale origin of the low grain-boundary resistance in perovskite solid electrolyte Li0.375Sr0.4375Ta0.75Zr0.25O3

Oxide solid electrolytes (OSEs) have the potential to achieve improved safety and energy density for lithium-ion batteries, but their high grain-boundary (GB) resistance generally is a bottleneck. In the well-studied perovskite oxide solid electrolyte, Li3xLa2/3-xTiO3 (LLTO), the ionic conductivity of grain boundaries is about three orders of magnitude lower than that of the bulk. In contrast, the related Li0.375Sr0.4375Ta0.75Zr0.25O3 (LSTZ0.75) perovskite exhibits low grain boundary resistance for reasons yet unknown. Here, we use aberration-corrected scanning transmission electron microscopy and spectroscopy, along with an active learning moment tensor potential, to reveal the atomic scale structure and composition of LSTZ0.75 grain boundaries. Vibrational electron energy loss spectroscopy is applied for the first time to reveal atomically resolved vibrations at grain boundaries of LSTZ0.75 and to characterize the otherwise unmeasurable Li distribution therein. We find that Li depletion, which is a major reason for the low grain boundary ionic conductivity of LLTO, is absent for the grain boundaries of LSTZ0.75. Instead, the low grain boundary resistivity of LSTZ0.75 is attributed to the formation of a nanoscale defective cubic perovskite interfacial structure that contained abundant vacancies. Our study provides new insights into the atomic scale mechanisms of low grain boundary resistivity.

Effect of annealing on the valence state of Ce ions and electrical properties in (ZrO2)0·88(CeO2)0.12 and (ZrO2)0.89(Sc2O3)0·1(CeO2)0.01

For (ZrO2)0·88(CeO2)0.12 (CEZ-12) and (ZrO2)0.89(Sc2O3)0·1(CeO2)0.01 (10Sc1CeSZ) sintered at 1450 °C, the effect of annealing at 600 °C in air for 500, 1000, and 2000 h on the valence state of Ce and the material electrical properties was investigated. For CEZ-12 and 10Sc1CeSZ, the XRD patterns showed no CeO2 peak before and after annealing. Further, the SEM images of the surfaces before and after annealing showed no change in the crystal grain size. No change in the apparent densities was observed either. On the other hand, XPS revealed that most of the Ce was trivalent before annealing, with some tetravalent Ce forming following annealing. The bulk resistivity, grain-boundary resistivity, and electrode interface resistivity were not significantly affected by annealing and the difference in annealing time.

Atomic-scale study clarifying the role of space-charge layers in a Li-ion-conducting solid electrolyte

Space-charge layers are frequently believed responsible for the large resistance of different interfaces in all-solid-state Li batteries. However, such propositions are based on the presumed existence of a Li-deficient space-charge layer with insufficient charge carriers, instead of a comprehensive investigation on the atomic configuration and its ion transport behavior. Consequently, the real influence of space-charge layers remains elusive. Here, we clarify the role of space-charge layers in Li0.33La0.56TiO3, a prototype solid electrolyte with large grain-boundary resistance, through a combined experimental and computational study at the atomic scale. In contrast to previous speculations, we do not observe the Li-deficient space-charge layers commonly believed to result in large resistance. Instead, the actual space-charge layers are Li-excess; accommodating the additional Li+ at the 3c interstitials, such space-charge layers allow for rather efficient ion transport. With the space-charge layers excluded from the potential bottlenecks, we identify the Li-depleted grain-boundary cores as the major cause for the large grain-boundary resistance in Li0.33La0.56TiO3.

Decoupling the electrical resistivity contribution of grain boundaries in dilute Fe-alloyed Cu thin films

To study the role of chemical composition on the resistivities of grains and grain boundaries (GB) for dilute Fe-alloyed Cu thin films, Cu films with grain sizes varying over three orders of magnitude and compositions of 0.025 and 0.25 at.% Fe were prepared by magnetron co-sputtering. Character, morphology and compositions of bulk and GBs were studied using electron backscatter diffraction, transmission electron microscopy and atom probe tomography, respectively. The specific resistivities of both individual GBs and within grains were obtained through local electrical measurements assisted by micromanipulation in situ within a scanning electron microscope. In addition, global resistivity characterisation of the thin films allowed for calculation of the GB reflection coefficient. A decoupling of GB and grain interior resistivities is found with alloying, where the GB resistivity increases by an order of magnitude while the grain interior is affected only to a minor extent in comparison.

A Co-rich chemically complex intermetallic alloy with extraordinary strength-ductility synergy

High-strength ordered intermetallic alloys are always sought-after in sophisticated structural applications. However, their practical applications have long been hindered by the severe grain-boundary embrittlement. Here, we designed a Co-rich chemically complex intermetallic alloy (CCIMA) with the L12-type ordered structure, which exhibits an ultrahigh tensile strength of ∼1,611 MPa and a substantial ductility of ∼37%. These exceptional strength-ductility combination outperforms the majority of common Co-rich intermetallic alloys. The multi-addition of Ta, Ti, and V elements is largely responsible for the significantly increased antiphase boundary energy of the L12 superlattice, which accounts for the high strength. This high degree of ductility is attributed to both the increased fracture resistance of grain boundaries brought about by co-segregation-induced order-to-disorder phase transformation, as well as the high work-hardening capability.

Grain boundary complexions formed by chemical plating of Cu enhance the thermoelectric properties of Sn0.94Mn0.09Te

Grain boundaries (GBs) often lead to increased electrical resistivity due to the extra GB resistance. This restricts the improvement of thermoelectric performance by nanostructuring. We demonstrate that the electrical conductivity can be improved without sacrificing the Seebeck coefficient by chemically decorating GBs with Cu in SnTe-based compounds. Cu-rich GB complexions are formed by sintering Cu-decorated Sn0.94Mn0.09Te powders via electroless plating. We find that the electrical conductivity increases while remaining the Seebeck coefficient upon increasing the Cu content. This indicates that the effect of chemical plating Cu is to modify the GB properties rather than playing as dopants to tune the carrier concentration of the matrix. Moreover, these Cu-rich GB complexions significantly enhance the scattering of phonons at high temperatures. As a consequence, the ZT value is improved from 0.65 for the pristine Sn0.94Mn0.09Te to 1.05 at 876 K for the Cu-incorporated Sn0.94Mn0.09Te.

Effects of defects on electrical transport properties of anatase TiO<sub>2</sub> polycrystalline under high pressure: AC impedance measurement

The electrical transport properties of anatase TiO<sub>2</sub> polycrystalline have been systematically investigated by using high pressure <i>in-situ</i> impedance spectroscopy measurements. The anomalous behaviors of resistance, parameter factor and relaxation frequency of grain and grain boundary can be found at 6.4, 11.5 and 24.6 GPa. The results indicate that the first two discontinuous points (6.4 and 11.5 GPa) correspond to the phase transitions of TiO<sub>2</sub> from anatase to α-PbO<sub>2</sub> and then to baddeleyite, respectively. Above 24.6 GPa, TiO<sub>2</sub> completely transforms into the baddeleyite phase. Based on the change of grain resistance and grain boundary resistance under pressure, intrinsic defects play a crucial effect in the electrical transport properties of TiO<sub>2</sub> at high pressures. At 6.4 GPa, the occurrence of phase transition gives rise to the variation of defects’ role, from a deep energy level defect (as a recombination centre) changes into a shallow energy level defect (providing carriers for the conduction and valence bands). In addition, the position of defect in energy band changes with pressure increasing. The phase transition of TiO<sub>2</sub> at 6.4 GPa is the rearrangement of TiO<sub>6</sub> octahedron, while the other one at 11.5 GPa can be attributed to the migration of oxygen Schottky defects from inner to surface. Combining the packing factor and relaxation frequency, the electrical transport properties of TiO<sub>2</sub> under pressure are revealed, the packing factor and the relaxation frequency are closely related to the mobility and the carrier concentration, respectively. The activation energy of grain and grain boundary decrease with the pressure elevating, indicating that the transport of carriers in grain and grain boundary become easier under pressure, and the former is smoother than the latter owing to the activation energy of grain being smaller than that of grain boundary in the same pressure range. Moreover, the relaxation frequency ratio of TiO<sub>2</sub> grain and TiO<sub>2</sub> grain boundary decreases with pressure increasing, and the grain boundary effect under high pressure is not obvious.