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Room-temperature creep tests of ZnS single crystals were conducted along the [001] direction under controlled light conditions in order to investigate the effect of light irradiation on the dislocation motion in ZnS. ZnS crystals stably deform by creep even at room temperature if the tests are conducted in complete darkness. It was found that the strain rate during a creep test can be immediately reduced by irradiating the sample with light having wavelengths of 365 nm or 436 nm even for the case when a sufficient density of mobile dislocations has been introduced due to preceding creep deformation. Surprisingly, the drop in strain rate by the light irradiation was several orders of magnitude. This drop in strain rate is believed to be due to a drastic decrease in the density of mobile dislocations, as well as the mobility of such dislocations, which are derived from the interaction with light-induced electrons and holes. It's also important to note that a significant incubation time appears when creep deformation resumes in the dark (light off) followed by loading under light irradiation during which the creep deformation is very small. This indicates that the light-induced free electrons and holes have long lifetimes in ZnS and, therefore, the existing dislocations continue interacting with electronic defects for several minutes after the light has been turned off. Image, graphical abstract [ABSTRACT FROM AUTHOR]

First-principles calculations were performed to investigate electronic and atomic structures of edge and screw dislocations in NaCl and AgCl. 1/2<110> edge and 1/2<110> screw dislocations, which are the ones due to the easiest slip system of these crystals, were treated in a first-principles manner. It was found that the edge dislocation has extended core structures over several atomic planes in both NaCl and AgCl. In contrast, the screw dislocation in AgCl showed the different shear strain around the dislocation core from that in NaCl although the one has a similar atomic structure in the two crystals. Local electronic structures around the dislocation cores in AgCl exhibit larger bonding interactions between atomic orbitals than those in NaCl, indicating that covalent interactions are more significant at the dislocation cores of AgCl. From excess dislocation energies, it was found that the dislocations in AgCl are much more stable than those in NaCl. Especially, the screw dislocation of AgCl has much smaller core energy than that of the edge dislocations. This suggests that the screw dislocations can be easily formed and multiplied in AgCl, which may be closely related to the observed ductility of AgCl. [ABSTRACT FROM AUTHOR]

A LiNbO bicrystal that contains a {2 $$ \bar{1} $$ $$ \bar{1} $$ 0} low-angle grain boundary with both of 2° tilt misorientation and a slight twist misorientation was fabricated, and resulting dislocation structure at the boundary was analyzed by using transmission electron microscopy (TEM) and scanning TEM. The observations revealed that two types of dislocations of b = 1/3 <2 $$ \bar{1} $$ $$ \bar{1} $$ 0> and b = <10 $$ \bar{1} $$ 0> are formed at the boundary. A 1/3 <2 $$ \bar{1} $$ $$ \bar{1} $$ 0> dislocation, which dissociates into two partial dislocations with a {2 $$ \bar{1} $$ $$ \bar{1} $$ 0} stacking fault in between, compensates only tilt misorientation of the boundary. On the other hand, it was found that a <10 $$ \bar{1} $$ 0> dislocation, which dissociates into three equivalent partial dislocations with b = 1/3 <10 $$ \bar{1} $$ 0>, has both edge and screw components in total. That is, the <10 $$ \bar{1} $$ 0> dislocations are formed to compensate the twist misorientation of the boundary, in addition to the tilt misorientation. It is interesting that the three partial dislocations from a <10 $$ \bar{1} $$ 0> dislocation are arranged in a zigzag pattern with left-right asymmetry. This special configuration is suggested to originate from the presence of stable stacking fault structure on the {2 $$ \bar{1} $$ $$ \bar{1} $$ 3} plane in LiNbO. [ABSTRACT FROM AUTHOR]

It is demonstrated from repeated loading-unloading high-temperature deformation tests of sapphire crystals deformed via basal slip that the deformation stresses go back to the same level as just before unloading after a small yield drop is observed during the re-loading process. This phenomenon suggests that basal dislocations that work as primary slip system regain the ability of glide motion even after they are dissociated into two partial dislocations via self-climb. That is, the climb-dissociated partials in basal dislocations introduced by previous deformation recombine onto the same basal plane so that they can glide again, resulting in the yield drop. [ABSTRACT FROM AUTHOR]

First principles calculations were performed to understand an electronic origin of high ductility in silver chloride (AgCl) with the rock salt structure. From calculations of generalised stacking fault energies for different slip systems, it was found that only the {1 1 0}slip system is favourably activated in sodium chloride (NaCl) with the same rock salt structure, whereas AgCl shows three kinds of possible slip systems along thedirection on the {0 0 1}, {1 1 0}, and {1 1 1} planes, which is in excellent agreement with experiment. Detailed analyses of the electronic structures across slip planes showed that the more covalent character of bonding of Ag–Cl than Na–Cl tends to make the slip motion energetically favourable. It was also surprising to find out that strong Ag–Ag covalent bonds across the slip plane are formed in the {0 0 1}〈1 1 0〉 slip system in AgCl, which makes it possible to activate the multiple slip systems in AgCl. [ABSTRACT FROM AUTHOR]

Inorganic semiconductors generally tend to fail in a brittle manner. Here, we report that extraordinary “ plasticity ” can take place in an inorganic semiconductor if the deformation is carried out “ in complete darkness. ” Room-temperature deformation tests of zinc sulfide (ZnS) were performed under varying light conditions. ZnS crystals immediately fractured when they deformed under light irradiation. In contrast, it was found that ZnS crystals can be plastically deformed up to a deformation strain of e t = 45% in complete darkness. In addition, the optical bandgap of the deformed ZnS crystals was distinctly decreased after deformation. These results suggest that dislocations in ZnS become mobile in complete darkness and that multiplied dislocations can affect the optical bandgap over the whole crystal. Inorganic semiconductors are not necessarily intrinsically brittle. [ABSTRACT FROM AUTHOR]

Dislocation structures in the (0 0 0 1)/〈 1 1 ¯ 0 0 〉 2° tilt grain boundary of alumina (α-Al 2 O 3 ) were investigated by atomic-resolution transmission electron microscopy (TEM). We found that the grain boundary basically consists of a periodic array of 1/3[ 1 ¯ 1 0 1 ], 1/3[ 0 1 ¯ 1 1 ], and 1/3[10 1 ¯ 1] dislocations, and these dislocations were dissociated into two partial dislocations with a stacking fault in between on the (0 0 0 1) plane. Atomic-resolution scanning TEM analysis revealed that the stacking fault is present on the anion sublattice, which has not been observed in alumina so far. The presence of the stable (0 0 0 1) anion stacking faults was theoretically supported using a first-principles calculation. Combining experimental and theoretical results, we demonstrate the dissociation reactions of the 1/3〈 1 ¯ 1 0 1 〉 dislocation and the associated stacking fault. [ABSTRACT FROM AUTHOR]

LiNbO is a ferroelectric material with a rhombohedral R3 c structure at room temperature. A LiNbO bicrystal with a $$ \{ {\overline{1} 2\overline{1} 0} \}/ {\langle}10\overline{1} 0{\rangle}$$ 1° low-angle tilt grain boundary was successfully fabricated by diffusion bonding. The resultant boundary was then investigated using high-resolution TEM. The boundary composed a periodic array of dislocations with $$ b = { 1}/ 3{\langle} \overline{1} 2\overline{1} 0{\rangle} $$. They dissociated into two partial dislocations by climb. A crystallographic consideration suggests that the Burgers vectors of the partial dislocations should be $$ 1/ 3{\langle}01\overline{1} 0{\rangle} $$ and $$ 1/ 3{\langle}\overline{1} 100{\rangle} $$, and a stacking fault on $$ \{ {\overline{1} 2\overline{1} 0} \} $$ is formed between the two partial dislocations. From the separation distance of a partial dislocation pair, a stacking fault energy on $$ \{ {\overline{1} 2\overline{1} 0} \} $$ was estimated to be 0.25 J/m on the basis of isotropic elasticity theory. [ABSTRACT FROM AUTHOR]

Abstract: The diffusion behavior of impurity cations was examined in deformed α-Al2O3 single crystals (sapphire) that had a high density of unidirectional basal dislocations. This behavior was examined in the temperature range of 1150–1400°C by secondary ion mass spectrometry depth profiling techniques. In order to investigate different pipe diffusion behaviors with different diffusing elements, diffusion behaviors of Cr and Ti were studied. Cr was expected to exhibit behavior similar to that of Al because both are isovalent and because of the complete mutual solubility of Cr2O3 and Al2O3 at high temperatures. Ti was selected because it is representative of an element that is hardly soluble and thus is expected to segregate at dislocations. The lattice and pipe diffusion kinetics were best described by the equations (m2 s–1) and (m4 s–1) for Ti, respectively and by equations (m2 s–1) and (m4 s–1) for Cr, respectively. A drastic decrease in the activation energy for Ti penetration was observed; however, such behavior was not observed for Cr penetration. This fact well explains that the electrical conductivity of deformed sapphire, which results from diffused Ti nanowires along the dislocations of the crystal. The behavior of Cr was similar to that of 18O, examined previously, in that their activation energies for lattice and pipe diffusion were similar. Because Cr diffusion was expected to mimic cation self-diffusion, it was assumed that the activation energy for pipe diffusion was not very low compared to that for bulk diffusion. This assumption is consistent with the fact that the activation energy for grain boundary diffusion in alumina and other ceramics is equal to or higher than that of bulk diffusion. Thus, the absolutely low temperature dependence of Ti pipe diffusion in sapphire may not be because of the enhanced migration of Ti along dislocations but because of other effects, such as the segregation of Ti or Ti clustering at dislocations. [Copyright &y& Elsevier]

Compression tests were conducted at 1400°C in air for undoped and Si-doped yttria-stabilized zirconia (YSZ) bicrystals with the same orientation relationship (Σ = 5, [001]/‘210’ grain boundary). It was found that the macroscopic grain-boundary slidings are observed during the deformation in both undoped and doped bicrystals, and the sliding displacements increase almost linearly with increasing total displacements. It is distinctly demonstrated that the Si-doped bicrystal exhibits a sliding displacement that is a few times larger than the undoped bicrystal. In addition, the total strain of the Si-doped bicrystal at a failure is much larger than that of the undoped bicrystal. It can be stated that Si doping in YSZ not only enhances the grain-boundary sliding but also suppresses its failure. [ABSTRACT FROM AUTHOR]

Abstract: We report electrical conductivity of Ti-nanowires in sapphire fabricated by utilizing lattice dislocations. We evaporated metallic Ti on a sapphire plate containing high density of uniaxial dislocations, and annealed the plate at high temperatures. As a result, it was found that Ti atoms intensely segregated along the dislocations within about 5nm in diameter, indicating the formation of Ti-nanowires inside sapphire. Furthermore, the nanowires were confirmed to have significant electrical conductivity even in sapphire insulator. [Copyright &y& Elsevier]

Abstract: A method to introduce high density of unidirectional dislocations in sapphire by a “two-stage deformation” technique and a heat-treatment of thin plate is proposed. After deformation of sapphire crystals by basal slip at 1400 °C, the samples were further deformed at 1200 °C as a second stage. It was found that twinning and cracking normally observed during deformation tests at 1200 °C were not observed in the crystals deformed using the two-stage deformation technique, and dislocation densities as high as 1.1×109/cm2 were obtained. This is because the glide dislocations generated at 1400 °C promoted slip over twinning in the additional deformation at 1200 °C. Subsequently, thin plates containing the high density of dislocations were annealed at 1400 °C for 30 min. As a result, it was found that dislocations in the thin plate were able to be straightened across its two opposite surfaces. This is believed to be due to the large image forces acting on the dislocations due to the free surface. [Copyright &y& Elsevier]

Flash events, which are electric power spikes occurring under an electric field and temperature above the threshold, can significantly accelerate mass diffusion over short periods of time. This study investigated the surface structure of the (001) surface of strontium titanate single-crystal treated by flash events caused by direct current (DC) and alternating current (AC) electric fields from a viewpoint of surface-related mass diffusion. The surface structuring caused by flash events was significantly different among DC and AC electric fields. The DC-flash event destabilized surface steps, causing them to wander and form surface mounds with a height of several tens of nanometers. In addition, numerous two-dimensional (2D) nuclei with a size of several nanometers are formed on the terraces. In contrast, the AC-flash event stabilized surface steps without the formation of surface mounds, causing them nearly straight with uniform terrace width at approximately 500 nm. 2D nuclei with a size of a few 10 nm were formed at the step edges with round shapes. Both methods were confirmed as evidenced by the formation of two-dimensional nuclei on the surface after the flash events, to enhance surface-related mass diffusion. [ABSTRACT FROM AUTHOR]

This study estimated the amount of oxygen deficiency in SrTiO 3 polycrystals that were flash sintered under direct current (DC) and alternating current (AC) electric fields, mainly by using the fine structural change of the Ti L 23 -edges collected by electron energy-loss spectroscopy. The DC electric field corresponded to formation of the maximum amount of oxygen deficiency at approximately δ = 0.07 as SrTiO 3−δ , which corresponds to a lattice expansion of roughly 0.1% as a lattice constant of SrTiO 3. Furthermore, the oxygen deficiency was distributed unevenly. The formation of dislocation networks in DC-flash-sintered SrTiO 3 polycrystals might be related to the lattice strain field caused by this nonuniform oxygen deficiency. In contrast, an AC electric field did not correspond to the oxygen deficiency of SrTiO 3 , which is similar to the results in thermally sintered SrTiO 3 polycrystals. [ABSTRACT FROM AUTHOR]

First‐principles calculations were performed to examine defect formation energies and site preference of substitutional divalent cations M2+ (M = Mg, Cu, Zn, Cd, Sr, Pb, and Ba) in hydroxyapatite (HAp, Ca10(PO4)6(OH)2) and carbonated apatite (CAp). All inequivalent substitutional sites of CO32- and M2+ were investigated to determine their most preferential sites. For all M2+ studied, their defect formation energies for the most stable substitutional sites were lower in CAp than in hydroxyapatite (HAp), demonstrating that M2+ are preferentially substituted into CAp over HAp. For Ca sites in CAp, correlations between the defect formation energies and Ca‐O bond lengths showed that bigger and smaller M2+ than Ca2+ are preferentially substituted for Ca sites with longer and shorter bond lengths than those in HAp, respectively. In addition, Ca sites with lower coordination numbers than 6 are preferentially substituted by Zn2+ and Cu2+ that originally tend to form 4‐ or 5‐fold coordination in their phosphate crystals. CO32- substitution is therefore likely to effectively stabilize substitutional foreign ions by modifying bond lengths and coordination numbers of Ca sites from those in pure HAp. These effects may play an important role in enhancing the M2+ solubility into CAp. [ABSTRACT FROM AUTHOR]

The external light environment has been reported to have a pronounced influence on the dislocation-based plasticity in various inorganic semiconductors. Herein, with a specific focus on the pyramidal slip in wurtzite structures, photoindentation tests were performed on the (0001) plane of ZnO crystal to activate the pyramidal slip and evaluate the effects of light on dislocation behaviors. Statistical analyses of the first pop-in events suggested that the corresponding maximum shear stresses in darkness were slightly smaller than those in 405 nm light, indicating a minor effect of light on dislocation nucleation event. Regarding nanoindentation creep tests, light illumination was found to suppress the indentation depth. Further transmission electron microscopy observations demonstrated that indentation-induced pyramidal dislocations were present deeper in darkness than in 405 nm light, revealing a suppressive effect of light illumination on the pyramidal slip in ZnO for the first time. [ABSTRACT FROM AUTHOR]

Flash healing, a technique for microcrack healing using a flash event, has recently attracted attention for effective microcrack healing of ceramics. To investigate the diffusion-accelerated phenomena that occur during flash healing, the flash-healing behavior of Vickers indentation microcracks on (001) zirconia single crystals was investigated, mainly from the viewpoint of microstructure analysis of the healed microcracks. Scanning electron microscopy and atomic force microscopy showed that the surface microcracks were rapidly healed. However, scanning transmission electron microscopy showed that a row of pores remained along the original microcrack inside the crystal, and the crystallographic orientation relationship on both sides of the microcrack was restored to that of the original single crystal. Compared with the findings for healing without an electric field, the distance from the pore closest to the surface was larger and the total pore volume was smaller for flash healing. These results suggest that flash treatment increases lattice diffusion. [ABSTRACT FROM AUTHOR]

Dislocations are one-dimensional lattice defects in crystalline materials, and unique atomic configurations at their core can affect functional properties of materials. Here we report on a [012] dislocation having a nonstoichiometric core structure in strontium titanate (SrTiO 3 ). TEM and STEM observations showed that a (001) low-angle tilt grain boundary consists of two types of dislocations. One is a [001] edge dislocation that compensates a tilt angle of the boundary as found in previous studies. The other is a [012] dislocation with both edge and screw component. This dislocation is considered to be formed to compensate a slight twist angle of the boundary. It is interesting that the [012] dislocations have a specific core structure with the dissociation into three partial dislocations of b = 1/2 [011], [001] and 1/2 [011]. At stacking faults formed with the dissociation, two (001) Ti-O layers were located to be neighbors across the stacking fault plane due to missing of a (001) Sr-O layer. In addition, the energy of the stacking fault was estimated to be 0.4 J/m 2 from the separation distances between partial dislocations. It is suggested that the [012] dislocation is formed due to presence of the nonstoichiometric stacking fault structure with low energy. [ABSTRACT FROM AUTHOR]

Light environment drastically alters the plasticity of zinc sulfide (ZnS) single crystals: they exhibit ductility in darkness while brittleness in lights. This study investigated their microscopic deformation modes of the light-environment-dependent plasticity, by using synchrotron X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning TEM (STEM) measurements. The XRD analyses disclosed that the ZnS crystals originally have two domains with almost the same volume fraction with a twin relationship and plastically deform in darkness, accompanying changes in the domain volume ratio (namely extinction of twins). It was also observed that the domain volume ratios become constant to be 0.2 at more than 10% plastic strains. The STEM analyses indicated that the deformation mode in darkness switches at around 10% plastic strain from slip deformation by glide of isolated partial dislocations to by simultaneous glide of paired partials inside the major domains. Although ZnS single crystals exhibited only a few percent of plastic strains in lights, localized glide of isolated partials and the resultant changes in domain volume ratios similar to in darkness were confirmed. That is, the deformation modes of ZnS at the initial stage were similar regardless of light environments although the macroscopic deformation behaviors were quite different. [Display omitted] [ABSTRACT FROM AUTHOR]

Thermally healed Vickers microcracks perpendicular to (001) surface of cubic zirconia single crystals were investigated mainly with scanning transmission electron microscopy. The orientational relationship of areas containing healed microcracks was completely restored to that of the original single crystal, but a row of pores corresponding to the unhealed state remained where the original microcrack was located. Isolated pore formation proceeded from dislocation recovery via heat treatment, which brought the inner surfaces of the microcrack into contact, followed by diffusion bonding via surface diffusion. Once isolated pores were formed, the total pore volume did not significantly change by increasing the healing temperature, although pore sizes increased and the number of pores decreased. Ostwald ripening became pronounced in pore microstructure evolution when pore elimination was dominated by lattice diffusion after complete crystallographic restoration to a single crystal. • Healing of microcracking in single crystal cubic zirconia investigated. • Microcrack partially healed by annealing at 1250–1400 °C for 10 min. • Crystallographic orientation was completely restored to original one after healing. • A row of pores with plate-like hexagonal and rhombic shapes remained. • Dislocation recovery closes crack, followed by diffusion bonding by surface diffusion. [ABSTRACT FROM AUTHOR]

Dislocation networks have been demonstrated to substantially enhance functional properties. As-sintered samples are virtually devoid of dislocations, new innovative techniques for introducing sufficiently high dislocation densities into polycrystalline ceramics are needed. While dislocation-based plasticity at high temperatures has been demonstrated for a large range of ceramic single crystals, plasticity in polycrystals is much less understood. Here, we demonstrate plastic strains in excess of several % based on dislocation motion in polycrystalline SrTiO3 at ≈ 1100 °C with 3.9 µm grain size. Ultra-high voltage electron microscopy reveals an associated increase in dislocation density by three orders of magnitude. Achievable strain rates are comparable to creep-based mechanisms and much less sensitive to applied stress than observed for metals. A specialized testing protocol allows quantification of the deformability via stress exponent, activation volume and activation enthalpy giving additional quantification. In conjunction with TEM images, the mechanical data gives insight into the underlying mechanisms. [ABSTRACT FROM AUTHOR]

First‐principles calculations were performed to reveal an effect of Ca vacancies on the stability of substitutional divalent cations M2+ (M = Mg, Zn, Sr) in Ca‐deficient hydroxyapatite (dHAp). M2+ concentrations up to 20 mol% in dHAp were considered, and the most stable substitutional sites and their lowest energy configurations in the dHAp lattice were examined with the aid of a generic algorithm method. It was found that defect formation energies of substitutional M2+ are lower in dHAp than in stoichiometric HAp (sHAp) at all M2+ concentrations. This indicates that these M2+ ions are more favorably involved in dHAp than in sHAp, which is in reasonable agreement with experiment. Detailed analyses on atomic structures in dHAp show that the presence of a Ca vacancy varies its surrounding Ca–O bond lengths over a wide area so that Ca–O polyhedrons with various sizes are produced. As a result, M2+ ions can predominantly occupy Ca sites at which M2+ fits better, depending on the ionic radii of M2+. For Zn2+ substitution in dHAp, its defect formation energy decreases more with the increasing concentrations and has the minimum value at 15 mol%. Such a trend can be understood from changes in effective coordination numbers of Zn in dHAp. [ABSTRACT FROM AUTHOR]

Rapid densification of ceramics has been realized and its merits were demonstrated through multiple approaches out of which UHS and flash sintering attract recent attention. So far, however, scalability remains difficult. A rise in throughput and scalability is enabled by the introduction of blacklight sintering powered by novel light source technology. Intense illumination with photon energy above the bandgap (blacklight) allows high absorption efficiency and, hence, very rapid, contactless heating for all ceramics. While heating the ceramic directly with light without any furnace promises scalability, it simultaneously offers highly accurate process control. For the technology transfer to industry, attainable material quality needs to be assured. Here, we demonstrate the excellent microstructure quality of blacklight‐sintered ceramics observed with ultrahigh voltage electron microscopy revealing an option to tune nanoporosity. Moreover, we confirm that electronic, electron, oxygen, and lithium‐ion conductivities are equal to conventionally sintered ceramics. This gives the prospect of transmitting the merits of rapid densification to the scale of industrial kilns. [ABSTRACT FROM AUTHOR]

Abstract: We have theoretically investigated proton sites and migration paths in La3NbO7 from first principles. Protons prefer the non-shared oxide ions to the isolated and the corner-shared oxide ions, which mainly results from repulsive electrostatic interactions with La3+ and Nb5+ cations. The calculated potential barriers for long-range proton migration pathways along the a axis and in the bc plane are 0.47eV and 0.61eV, respectively. This means the anisotropic proton conductivity of La3NbO7 reflects the selective preference of protons to non-shared oxide ions in the crystal. [Copyright &y& Elsevier]

Abstract: We have investigated the stable sites of interstitial oxide ions and the oxide-ion conduction mechanism in lanthanum germanate, La10(GeO4)6O3, by using first-principles calculations. Most stable positions of interstitial oxide ions are located at the center of two neighboring GeO4 tetrahedra. From first-principles molecular dynamics (FPMD) calculations, cooperative migration processes involving two or more oxide ions at interstitial and neighboring regular sites were observed, the so-called interstitialcy mechanism. This mechanism along the c axis was more frequent than that in the ab plane, which indicates the anisotropic oxide-ion conductivity in lanthanum germanate. [Copyright &y& Elsevier]

Abstract: LiNi0.5Mn1.5O4, which has a spinel framework structure, is a promising candidate for the cathode material of next-generation lithium-ion batteries with high energy density. We investigate the structural transition in Li x Ni0.5Mn1.5O4 (0 ≤ x ≤ 1) through first-principles calculations using the projector augmented wave method with the generalized gradient approximation. We calculate all the unique Li-site occupation configurations in a unit cell to obtain the total energies and the most stable structures for various compositions. Thermodynamic analysis shows that Li0.5Ni0.5Mn1.5O4 with x = 0.5 is the only stable phase for 0 < x < 1. The decomposition energy is lower than 0.1 eV for 0 < x < 0.5, but is distinctly higher for 0.5 < x < 1. The decomposition energy reaches 0.39 eV at x = 0.75. The ratios of the structures at room temperature are calculated from Boltzmann factors by using the energy differences between structures. The crystal structure of the unit cell changes gradually from x = 0 to 0.5, but changes markedly from x = 0.5 to 1. This first-principles study provides a general evaluation of the variation in the crystal structure with the composition of the bulk material, which affects the cyclability of the electrode. [Copyright &y& Elsevier]

Three-dimensional distribution of arsenic (As) dopants at Σ3{111}, Σ9{221}, Σ9{114}, and Σ9{111}/{115} grain boundaries (GBs) in silicon (Si) is examined by correlative analytical methods using atom probe tomography (APT) combined with low-temperature focused ion beam (LT-FIB), scanning transmission electron microscopy, and ab initio calculations. Σ3{111} GBs, consisting of only 6-membered rings with small bond distortions, do not exhibit an apparent As segregation. Meanwhile, it is hypothesized that As atoms would segregate at 5-membered rings in the other GBs via anisotropic bond distortions spontaneously introduced so as to lower the donor level, as Jahn-Teller distortions. In addition, APT combined with LT-FIB suggests preferential As segregation around stretched 1 1 ‾ 0 bonds reconstructed in Σ9{114} and Σ9{111}/{115} GBs, that are inevitably introduced in the 1 1 ‾ 0 tilt GBs with the tilt angle larger than 70.5°. It is hypothesized that As atoms would form As dimers at stretched 1 1 ‾ 0 bonds and the adjacent ⟨ 111 ⟩ bonds, due to the tendency of As with five valence electrons to form a three-coordinated configuration, which is efficiently attained by an As dimer of a long length. This work provides important insights into As segregation at GBs; it is mainly determined by electronic interactions depending on the characteristics of valence electrons of As atoms, as well as on local bond distortions at GBs, via anisotropic bond distortions and dimerization. [ABSTRACT FROM AUTHOR]

Alumina bicrystals with low-angle and near-Σ3 <0001> tilt grain boundaries were fabricated using diffusion bonding to study the dislocation structures in alumina grain boundaries. The resulting grain-boundary structures were investigated using high-resolution transmission electron microscopy, and the grain-boundary energies were analyzed using theoretical calculations. It was found that partial dislocations with Burg-vectors of the type 1/3<10&1macr;0> were periodically located in ers the boundaries and that a stacking fault between pairs of partials was formed in such boundaries. The length of the stacking fault decreased with increased misorientation angles, which was reasonably predicted by the theoretical calculation. In the case of a near-Σ3 grain boundary, an array of displacement shift complete dislocations with the Burgers vector of 1/3 was periodically formed along the boundaries. These boundaries did not have stacking faults. The spacing between the dislocations decreased with increased deviation angle from the exact-Σ3 boundary with the tilt angle of 60°. [ABSTRACT FROM AUTHOR]

Deformation twinning is a fundamental plastic deformation mode in crystals. Upon twinning, individual atoms must move in different directions to satisfy the twin symmetry, which is called atomic shuffling. However, actual atomic motions during shuffling are still unknown, especially for ionic compounds. Here, we report the dynamic twinning behavior dominated by the atomic shuffling in sapphire (α -Al 2 O 3). The propagation and annihilation of twins are revealed to be mediated by migration of step structures on the matrix/twin interfaces. The step migration is driven by cooperative motions of a group of five atoms with relatively few recombination of Al–O bonds. Our findings imply that the atomic shuffling associated with twinning is determined by a collective property of a group of several atoms. [Display omitted] [ABSTRACT FROM AUTHOR]

An enormous change in the dislocation-mediated plasticity has been found in a bulk semiconductor that exhibits the photoplastic effect. Herein, we report that UV (365 nm) light irradiation during mechanical testing dramatically decreases the fracture toughness of ZnS. The crack tip toughness on a (001) single-crystal ZnS, as measured by the near-tip crack opening displacement method, is increased by ∼45% in complete darkness compared to that in UV light. The increase in fracture toughness is attributed to a significant increase in the dislocation mobility in darkness, as explained by the crack tip dislocation shielding model. Our finding suggests a route toward controlling the fracture toughness of photoplastic semiconductors by tuning the light irradiation. [ABSTRACT FROM AUTHOR]

Understanding the irreversible deformation (dislocation activation and crack formation) of functional oxides, based on which various advanced electronic devices are fabricated, is critical for the optimal structural design and mechanical reliability. Here, we demonstrate the dislocation-based crack initiation and propagation in a model perovskite, single-crystal SrTiO3, at small scale. Using nanoindentation tests with spherical tips and etch pit study, we identify the sequence of the irreversible deformation events occurred in single-crystal (001) SrTiO3. For a locally stressed volume that is free of pre-existing cracks, the material undergoes the following processes: (1) purely elastic deformation; (2) dislocation activation on primary slip planes that are 45° inclined to the surface; (3) dislocation activation on secondary slip planes perpendicular to the surface; (4) crack initiation by dislocation pile-up; followed by (5) concurrent crack propagation and dislocation multiplication and motion at higher loads. Specifically, we focus on the crack formation caused by the dislocation pile-up beneath the spherical indenter. We also identify the favorable crack propagation planes to be {110} when the (001) surface is indented. These findings in cubic SrTiO3 are believed to be applicable for other ceramic materials with cubic structure. [ABSTRACT FROM AUTHOR]

The ionic conductivity of yttria-stabilized zirconia (YSZ) single crystals (10 mol %Y[sub 2]O[sub 3]-ZrO[sub 2]) was enhanced by introducing high density of dislocations. YSZ single crystals were systematically deformed by compression tests at 1300 °C, and their electrical conductivity was measured by an AC impedance method. It was confirmed that a great number of dislocations were introduced in YSZ by the high-temperature deformation, and the density reached up to more than 8 × 10[sup 12] m[sup -2], depending on the compression strains imposed on the samples. The electrical conductivity of the deformed samples was found to be larger than that of undeformed samples. Furthermore, samples with larger strains exhibited higher electrical conductivity, which indicates that dislocations generated by the plastic deformation play an important role to enhance the ionic conductivity of YSZ. [ABSTRACT FROM AUTHOR]

Incipient room-temperature plastic deformation in single-crystal SrTiO 3 at the nanoscale and the microscale is contrasted by applying a scale-dependent indentation technique. Using nanoindentation pop-in, nanoindentation creep, and an evaluation of dislocation spacing via etch pit study, we demonstrate a reversal of yield stress for crystals with different vacancy concentrations and pre-existing dislocation densities. A competing mechanism between dislocation nucleation and dislocation motion on crystal plasticity at different length scales is highlighted. This finding enables us to complete the understanding of dislocation-mediated plasticity for ceramic oxides at the nanoscale as compared to the microscale and macroscale. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Inorganic semiconductors show interesting mechanical behavior in response to their surrounding lighting environments. In fact, we recently found out that zinc sulfide (ZnS) shows the light-illumination controlled plasticity at room temperature. However, its mechanism is poorly understood. Here we report systematic density functional theory results of electronic and atomic structures of glide partial dislocations in ZnS. We have revealed that partial dislocations in ZnS have excess electrostatic fields localized around their cores and can trap electrons or holes, depending on excess ionic species at the cores. Such carrier-dislocation interactions can induce energetically more stable bond reconstruction at their cores, as compared with the case before carrier trapping. Reconstructed bonds at the dislocation cores should be broken upon dislocation glide, and thus can restrict the dislocation motion significantly. Such reduced dislocation motion due to core reconstruction should give rise to increased plastic deformation stresses, namely, hardening of the materials under light illumination. The present results provide a critical understanding of the experimentally observed light-illumination controlled plasticity in ZnS at the electronic level, which is opposed to previously reported plasticity and dislocation motion in other elemental and III-V semiconductors. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Recently, several creative processing techniques yielded thermoelectrics with reduced thermal conductivity and, thereby, an enhanced figure or merit. These were based on engineered complex microstructures with attendant dislocation structures. In this study, we implement highly controlled mesoscopic dislocation structures into the model thermoelectric SrTiO3 in order to quantify phonon scattering at dislocations. Both single crystals and polycrystalline material have been furnished with enhanced dislocation densities increased by a factor of 150–300 by plastic deformation. Thermal conductivity was measured using laser flash analysis between room temperature and 325 °C. Etch pit techniques and ultra-high voltage electron microscopy afford quantification of dislocation density. Experimental results were compared to predictions by the Debye-Callaway model. The latter revealed that dislocation densities of 1015 m−2 would be necessary for the reduction of thermal conductivity of SrTiO3 in the investigated temperature range, which could not be realized using the plastic deformation mechanism applied. [ABSTRACT FROM AUTHOR]

It has been reported that dislocations with 1/31¯101 edge component of the Burgers vector are formed in {11¯04}/112¯0 low-angle grain boundaries of alumina (α-Al2O3). These dislocations dissociate into two partial dislocations with a stacking fault on the (0001) plane (Tochigi et al. in J Mater Sci 46:4428-4433, 2011). However, the dissociation reaction of these dislocations has not been determined so far. In this study, the structures of the dissociated dislocations and the (0001) stacking fault were investigated by transmission electron microscopy and theoretical calculations. It was revealed that the dissociated dislocations were generated from the 1/31¯101 perfect edge dislocation by the reaction of 1/31¯101 → 1/184¯223 + 1/182¯42¯3. Furthermore, electron energy loss spectroscopy analysis was performed to examine the atomic/electronic structure of the (0001) stacking fault. In the observed spectra, a chemical shift and intensity decrease were found at the oxygen K-edge. Theoretical spectrum analysis using first-principles calculations revealed that the characteristic features of the spectra are originated from the local atomic configurations of the (0001) stacking fault. [ABSTRACT FROM AUTHOR]

Dislocations, one-dimensional lattice defects, are known to strongly interact with impurity atoms in a crystal. This interaction is generally explained on the basis of the long-range strain field of the dislocation. In ionic crystals, the impurity-dislocation interactions must be influenced by the electrostatic effect in addition to the strain effect. However, such interactions have not been verified yet. Here, we show a direct evidence of the electrostatic impurity-dislocation interaction in α-Al2O3 by visualizing the dopant atom distributions at dislocation cores using atomic-resolution scanning transmission electron microscopy (STEM). It was found that the dopant segregation behaviors strongly depend on the kind of elements, and their valence states are considered to be a critical factor. The observed segregation behaviors cannot be explained by the elastic interactions only, but can be successfully understood if the electrostatic interactions are taken into account. The present findings will lead to the precise and quantitative understanding of impurity induced dislocation properties in many materials and devices. [ABSTRACT FROM AUTHOR]

Abstract: Using large-scale molecular dynamics (MD) simulations, we investigate the energetics and local structures/stresses of partial dislocations, and , dissociated from the perfect basal edge dislocation in α-Al2O3. The validity of the model adopted in the simulation is confirmed by comparing with theoretical stress/strain distributions and with those experimentally obtained from a high-resolution transmission electron microscopy (HRTEM) observation. Partial dislocation pairs have a stable inter-core distance (∼2nm), which is also a phenomenon that is observed in the HRTEM experiments. The distance between the partials can be explained quantitatively by the balance between an elastic core–core repulsion and an effective attractive force against the extension of stacking faults (SFs). A comparison is made for two types of core structures of partial dislocations: a pair of partials with Al-terminated/O-terminated extra-half planes and that with Al-/Al-terminated ones. The overall tendency of the inter-core interaction and the equilibrium distances are the same in both cases, whereas the Al–O-terminated pair is slightly favourable in energy at the equilibrium distance. A residual shear stress on the SF plane is observed in the MD results, which can be attributed to local atomic structure in the SF. [Copyright &y& Elsevier]