<scp>DC</scp> Electric Field‐Enhanced Grain‐Boundary Mobility in Magnesium Aluminate During Annealing

Rufner, Jorgen F.; Kaseman, Derrick C.; Castro, Ricardo H. R.; Benthem, Klaus van

doi:10.1111/jace.14157

Cited by 17 publications

(10 citation statements)

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“…47,48 Plotting cation distribution profiles as a function of normalized space coordination [ie, CS divided by the Debye length (L D )] ( Figure 4B) indicated the effect of grain size on charge distribution in nano-scale MAS. Maier 29,38 proposed that for ionic materials with grains smaller than four times the L D , the GC is no longer electrically neutral and the sample is considerably influenced by accumulation or depletion of charge at the boundaries. For the nonstoichiometric MAS studied in this work, the L D was estimated to range between 3.5 and 9.0 nm (Supplemental Material A.3 in Data S1).…”

Section: Cation Distribution and Lattice Orderingmentioning

confidence: 99%

“…Moreover, the use of EFs is associated with reductions in grain growth and flow stress in ionic materials . Rufner et al . reported that applying a DC electric field of 1000 V/cm at 1300°C enhanced grain‐boundary (GB) mobility in MAS.…”

Section: Introductionmentioning

confidence: 99%

“…35,36 Moreover, the use of EFs is associated with reductions in grain growth and flow stress in ionic materials. 34,35,37 Rufner et al 38 reported that applying a DC electric field of 1000 V/cm at 1300°C enhanced grainboundary (GB) mobility in MAS. The authors argued that the application of an EF on the accumulated charge in the vicinity of the grain boundaries reduced the activation energy for cation mobility across boundaries due to the space-charge layer, as previously reported by Jeon et al for alumina ceramics.…”

Section: Introductionmentioning

confidence: 99%

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Charge distribution in nano‐scale grains of magnesium aluminate spinel

et al. 2016

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Charge distribution in magnesium aluminate spinel (MAS) results in the formation of a space‐charge region that plays a critical role in assigning functional properties. Significant theoretical advances explaining this phenomenon have been accomplished, even though quantitative experimental support from nano‐scale granular MAS is only indirect. In this work, the electrostatic potential distribution in nano‐scale grains of nonstoichiometric MAS (MgO·0.95Al2O3 and MgO·1.07Al2O3) was measured by off‐axis electron holography (OAEH) and compared to the distribution of cations and defects in this material as measured by electron energy‐loss spectroscopy (EELS). In this manner, we studied the roles of composition, grain size, and applied electric field (EF) on the formation of a space‐charge region. We quantitatively demonstrated that regardless of grain size, the vicinity of MgO·0.95Al2O3 grain boundaries presented an excess of Mg+2 cations, whereas the vicinity of MgO·1.07Al2O3 grain boundaries included an excess of Al+3 cations. The degree of structural disorder (ie, the inversion parameter, i) indicated that as‐synthesized MAS were significantly disordered (i between 0.37 and 0.41), with values decreasing toward equilibrium ordering values following annealing (i between 0.27 and 0.31). The application of an external ~150 V/cm EF during annealing further enhanced lattice ordering (i between 0.16 and 0.19). Such variations in the distribution of cations and defects should determine the space‐charged potential (SCP). However, using these measurements to calculate the SCP was not possible due to the wide range of values reported for formation energies of defects (0.82‐8.78 eV). Consequently, we correlated local ionic ordering with electrostatic potential in nonstoichiometric MAS. The magnitudes of the SCP in both MgO·0.95Al2O3 and MgO·1.07Al2O3 decreased following annealing from −3.4 ± 0.3 V and 2.0 ± 0.2 V to −2.0 ± 0.2 V and 1.6 ± 0.1 V, respectively.

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Section: Cation Distribution and Lattice Orderingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Charge distribution in nano‐scale grains of magnesium aluminate spinel

et al. 2016

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“…Mohan et al [51] also discussed Zr segregation at spinel grain boundaries (with addition of zirconia) limiting grain growth and grain boundary migration. On the other hand, Rufner et al [58] observed enrichment of Al at spinel-spinel grain boundaries (undoped spinel) resulting in reduced Mg/Al ratio at the interface. Nuns et al [59] also reported previously the enrichment of Al and O at spinel-spinel boundaries (in undoped sample) while Mg was found to be depleted.…”

Section: Qualitative Observations Of Elemental Segregation At Grain Boundariesmentioning

confidence: 99%

Correlations of grain boundary segregation to sintering techniques in a three-phase ceramic

Syed

Ohtaki

et al. 2020

Materialia

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The effects of using different sintering techniques (conventional, flash and spark plasma sintering) on grain boundary segregation were investigated in a 3-phase polycrystalline ceramic containing cubic 8 mol% Y 2 O 3 stabilized ZrO 2 (YSZ), -Al 2 O 3 and MgAl 2 O 4 . Six types of interfaces for each sintered sample were analyzed for grain boundary chemistry. Using aberration-corrected STEM and EDS, we show Al segregation at YSZ-YSZ boundaries, and Y/Zr segregation at Al 2 O 3 -Al 2 O 3 , MgAl 2 O 4 -MgAl 2 O 4 and MgAl 2 O 4 -Al 2 O 3 boundaries. YSZ-MgAl 2 O 4 and YSZ-Al 2 O 3 heterointerfaces, in contrast, do not show elemental segregation. Our results show that the type of segregation at different boundaries does not change with different sintering processes, indicating that elemental segregation mainly depends on initial sample composition, although the amount of segregation can vary. Quantitative analyses reveal that spark plasma sintering (950°C for 5 min, 100 MPa) results in relatively higher average segregation at grain boundaries and heterointerfaces compared to conventional sintering (1550°C for 10 h), suggesting that low temperatures result in higher grain boundary segregation. The average segregation concentrations at the grain boundaries of our flash sintered sample (estimated to reach 1700°C for 6 s) were found to be consistently similar to long-annealed spark-plasma sintered sample (1350°C for 20 h), suggesting that very high temperatures reached during flash process can achieve similar segregation concentrations compared to a SPS sample annealed for several hours at lower temperature. The presence of other phases in multi-phase systems can modify the grain boundary chemistry and segregation compared to segregation in single-phase ceramics.

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“…Majidi and co‐workers have employed in situ transmission electron microscopy (TEM) to demonstrate that non‐contacting electrostatic fields applied to partially stabilized ZrO 2 trigger modest densification at temperatures that do not lead to appreciable densification in the absence of any electric field . More recently, Rufner et al have reported field‐induced grain growth in MgAl 2 O 4 , while Rheinheimer et al confirmed similar findings for SrTiO 3 . Hughes and co‐workers have recently used bicrystals of (100) twist grain boundaries in SrTiO 3 to demonstrate that an applied electric field changes the atomic and electronic grain‐boundary core structures .…”

Section: Introductionmentioning

confidence: 99%

Effects of electrostatic field strength on grain‐boundary core structures in SrTiO₃

Hughes

Benthem

2019

J Am Ceram Soc

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Understanding interactions between externally applied electric fields and the interfacial structures of nanoscale ceramics is important for controlling their functional properties. In ceramic oxides, functional properties are determined by oxygen vacancy concentrations near and within grain-boundary core structures. In this study it is shown that the application of electrostatic fields ranging from 0 to nominally 170 V/cm during diffusion bonding of bicrystals alters the atomic and electronic core structures of (100) twist grain boundaries in SrTiO 3 . The applied electric field strength affects local oxygen vacancy concentrations and ordering of the oxygen sublattice. Results for this model system indicate that electrostatic fields applied during ceramic manufacturing can be employed as a new processing parameter to tailor defect structure configurations and obtain unprecedented ceramic microstructures. The ability to manipulate interface configurations with electric fields in the absence of any sintering additives may have far reaching implications for tuning polarization and band structures in electroceramics while avoiding effects of often unwanted dopants.

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DC Electric Field‐Enhanced Grain‐Boundary Mobility in Magnesium Aluminate During Annealing

Cited by 17 publications

References 48 publications

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Correlations of grain boundary segregation to sintering techniques in a three-phase ceramic

Effects of electrostatic field strength on grain‐boundary core structures in SrTiO₃

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DC Electric Field‐Enhanced Grain‐Boundary Mobility in Magnesium Aluminate During Annealing

Cited by 17 publications

References 48 publications

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Correlations of grain boundary segregation to sintering techniques in a three-phase ceramic

Effects of electrostatic field strength on grain‐boundary core structures in SrTiO3

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Effects of electrostatic field strength on grain‐boundary core structures in SrTiO₃