Octahedral Defects Research Articles

Defect cluster engineering in ZnGa2−x(Mg/Ge)xO4:Cr3+ nanoparticles for remarkably improved NIR persistent luminescence

AbstractRecently, study on Cr3+‐doped zinc gallate and zinc gallogermanate persistent phosphors has become a hot topic in persistent luminescence and bio imaging areas, because of their near infrared (NIR) emission and long afterglow. However, regulation of efficient traps and improvement of persistent luminescence through bottom‐up design are the key challenge. Here, we recommend a new paradigm of chemical unit co‐substitution with [Mg2+‐Ge4+] substituting for [Ga3+‐Ga3+] in ZnGa2O4, which contributes to the opposite charged and distorted octahedral defects of MgGa′ and GeGa· in pair around the CrN2 ions. The formed defect clusters of MgGa′‐CrN2‐GeGa·, which are closely related to the trap depth, can be accurately regulated through varying the doping content of Mg2+/Ge4+ in the resulting spinel solid solutions of ZnGa2−x(Mg/Ge)xO4:Cr3+ (x = 0–1.25). Moreover, the defect clusters cannot only store and recharge visible and UV radiations that contributes to the long lasting NIR persistent luminescence but also can enhance the NIR emission intensity at ~695 nm. The persistent luminescence induced by UV light excitation exhibits an improvement at a deeper trap depth, but it follows an opposite law through visible light excitation. The prepared nanoparticles have the advantages of intense NIR emission, long lasting afterglow, and excellent rechargeability for visible/UV radiations, so they are the potential nanoprobes for long‐term bio imaging in living animals.

Silver incorporated into cryptomelane-type Manganese oxide boosts the catalytic oxidation of benzene

Different amounts of silver were successfully incorporated into cryptomelane-type manganese oxide (K-OMS-2) via a one-step hydrothermal method for application in the catalytic combustion of benzene. Silver incorporation could promote the benzene oxidation performance of the catalysts. The silver doping effect was addressed in terms of the relationship between structure and activity. The prepared catalysts were characterized by ICP-OES, BET, XRD, Raman, FE-SEM, TEM, XPS, XAFS, H2-TPR and CO-TPD. The best precursor Mn/Ag mole ratio was 40. The resulting K/Ag-OMS-40 catalyst exhibited the highest activity in terms of benzene combustion and good tolerance to chlorine poisoning, all of which make it a promising candidate as an alternative to noble metal supported catalysts. All catalysts after silver incorporation maintained the structural integrity of the cryptomelane structure but with decreased crystalline size, which significantly increased the surface area and number of defects of the catalyst. The silver species, mostly in the form of Ag+, were well dispersed and partially replaced K+ in the tunnels of cryptomelane. K/Ag-OMS-40 had the largest surface area, the smallest nanorods and most abundant Mn octahedral defects. The large number of active oxygen species derived from the high Mn3+ content and Ag-O-Mn bridge bonds appeared to play critical roles in VOC decomposition.

Nitrogen nanoinclusions in milky diamonds from Juina area, Mato Grosso State, Brazil

A unique set of diamonds with a ‘milky’ optical appearance from the Rio Soriso placer deposit in the Juina area, Mato Grosso, Brazil was studied by combined transmission electron microscopy (TEM) and fourier transform infrared (FTIR) spectroscopy. The main characteristics of the studied samples are large numbers of randomly distributed {111}-faceted octahedral defect nanostructures. The dislocation densities of the focused ion beam (FIB) foils are generally low. Dislocation loops are observed only around larger inclusions. The inclusion size shows a bimodal distribution and spreads around values of 20 and 200nm. Electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray (EDX) spectroscopy mapping of both subsets yield high nitrogen contents for all sealed inclusions. In cases where the nanoinclusions touch the surface of the FIB section no nitrogen signal could be detected, indicating the loss of a fluid or gas phase as the carrier of nitrogen. FTIR mapping of the same regions showed a strong correlation between structurally bound nitrogen, hydrogen and the abundance of nanoinclusions. We propose that the most likely phase included in these nanoinclusions is NH3. These nanoinclusions could be the result of a high-temperature episode or of long residence times at shallower depths and lower temperatures. Thus they might represent the last stage of the nitrogen aggregation, or they may be syngenetic trapped NH-bearing source fluids.

Octahedral tilt transitions in the relaxor ferroelectric Na1/2Bi1/2TiO3

The kinetics of octahedral tilt transitions in the lead-free relaxor material sodium bismuth titanate Na1/2Bi1/2TiO3 (NBT) is investigated by electronic structure calculations within density functional theory. Energy barriers for transitions between tetragonal, rhombohedral and orthorhombic tilts in cation configurations with [001]- and [111]-order on the A-sites are determined by nudged elastic band calculations. By tilting entire layers of octahedra simultaneously we find that the activation energy is lower for structures with 001-order compared to such with 111-order. The energetic coupling between differently tilted layers is, however, negligibly small. By introducing a single octahedral defect we create local tilt disorder and find that the deformation energy of the neighboring octahedra is less in a rhombohedral than in a tetragonal structure. By successively increasing the size of clusters of orthorhombic defects in a rhombohedral matrix with 001-order, we determine a critical cluster size of about 40Å . Thus groups of about ten octahedra can be considered as nuclei for polar nanoregions, which are the cause of the experimentally observed relaxor behavior of NBT.

ChemInform Abstract: Solvothermal Synthesis of the Defect Pyrochlore KNbWO6·H2O and Its Application in Pb2+ Removal.

AbstractThe octahedral defect pyrochlore KNbWO6·H2O is prepared by a two‐step solvothermal process starting with a mixture of KOH and Nb2O5 (H2O, autoclave, 180 °C, 2 d) to form a solution of K8Nb6O19 which is then dissolved in octanol and mixed with H2WO4 (pH 7.2 adjusted with HCl, autoclave, 220 °C, 2 d).

Solvothermal synthesis of the defect pyrochlore KNbWO6·H2O and its application in Pb2+ removal

The octahedral defect pyrochlore KNbWO6·H2O is prepared by a two-step solvothermal process. It shows an excellent performance in the removal of toxic Pb2+ by ion exchange. The removal process fits well with the Langmuir isotherm, and the maximum removal capacity is 86.95 mg g−1 at pH 5.0. High selectivity to Pb2+ is observed in an aqueous solution also containing Mn2+, Cd2+ and Co2+. The kinetics of the ion exchange process can be expressed by the pseudo-second-order rate kinetic model.

OH in diopside and enstatite at 6 GPa in the system CaO–MgO–SiO2–H2O

Single crystals of pure diopside (CaMgSi 2 O 6 ) were synthesized at 6 GPa or 8 GPa and between 1300 °C and 1150 °C under water-saturated conditions coexisting with forsterite + enstatite, enstatite + coesite, wollastonite + coesite or forsterite + wollastonite, and the incorporation mechanisms of OH in the pyroxenes in the respective phase assemblage were studied by FTIR-spectroscopy. The IR spectra of diopside exhibit two different OH-absorption bands: one prominent band at 3357 cm −1 that appears in all spectra, whereas another band at 3598 cm −1 only appears in spectra of diopside synthesized under lower silica activity ( i.e ., coexisting with forsterite). The band at 3598 cm −1 indicates a low availability of Si and can be assigned to tetrahedral OH-defects (T-site vacancies), while the band at 3357 cm −1 can be assigned to octahedral defects (M-site vacancies). Enstatite crystals from the assemblages diopside + enstatite + coesite and diopside + enstatite + forsterite exhibit an additional absorption band at 3436 cm −1 when compared to enstatite synthesized in the system MgO–SiO 2 –H 2 O. This absorption band could be caused by generation of additional hydrous defects due to the incorporation of Ca that amounts up to 1.8 wt% CaO in enstatite coexisting with diopside. The water content of diopside coexisting with enstatite and coesite clusters around 145 ppm (wt), while the water content of diopside from all other phase assemblages clusters around 60 ppm (wt). The new results suggest that the water content in pyroxenes correlates with silica activity during formation.

The potential use of OH-defects in enstatite as geobarometer

In this study, single crystals of pure enstatite (Mg2Si2O6) were synthesised under water-saturated conditions at 4 and 8 GPa and 1,150°C with variable silica activity, leading to phase assemblages enstatite + forsterite, enstatite or enstatite + coesite. Run products were investigated using an FTIR spectrometer equipped with a focal plane array detector enabling IR imaging with a lateral pixel resolution of 2.7 μm. IR spectra within the OH-absorption region show two different groups of absorption bands: group 1 (wavenumbers at 3,592 and 3,687 cm−1) shows strongest absorptions for E||n β, whereas group 2 (wavenumbers at 3,067 and 3,362 cm−1) shows strongest absorptions for E||n γ. The groups are related to different defect types, group 1 to tetrahedral defects (T-site vacancies) and group 2 to octahedral defects (M-site vacancies). The intensity ratio of the bands within one group (i.e. A 3067/A 3362 and A 3592/A 3687) and the intensity ratio of E||n γ and E||n α in group 2 bands remain constant within error. In contrast, the intensity ratio of group 2 to group 1 absorption bands [e.g. (A 3362)/(A 3687)] is sensitive to the SiO2 activity and pressure. On the basis of the results of this and previous studies, a barometer for pure orthoenstatite coexisting with forsterite can be formulated: $$ P\,[{\text{GPa}}] = 1.056 + \sqrt {{\frac{{1.025 - A_{{\left( {3362} \right)/\left[ {(3362) + (3687)} \right]}} }}{0.009}}} , $$ where A (3362) and A (3687) are the integral absorbances of the component E||n γ of the absorption bands at 3,362 cm−1 and the component E||n β of the absorption band at 3,687 cm−1, respectively.

FTIR spectroscopy with a focal plane array detector: A novel tool to monitor the spatial OH-defect distribution in single crystals applied to synthetic enstatite

Single crystals of pure enstatite (Mg2Si2O6) were synthesized under water-saturated conditions at 6 GPa and 1250 °C and variable silica activity. Run products were investigated using a novel technology: a FTIR spectrometer equipped with a focal plane array detector enabling IR-imaging with a spatial pixel resolution of 2.7 μm. IR spectra within the OH-absorption region show strong pleochroic behavior: absorption bands at 3687 and 3592 cm−1 show strongest absorptions for E||nβ, whereas absorption bands at 3362 and 3067 cm−1 show strongest absorptions for E||nγ. Furthermore, absorption bands are sensitive to the silica activity—the ratio of the integral absorbance of the absorption bands at 3687 and 3592 cm−1 to the absorption bands at 3362 and 3067 cm−1 increases with increasing Mg/Si-ratio of the bulk charge. The most probable interpretation is an assignment of the high-energy absorption bands to tetrahedral (T-site) defects caused by a lower availability of Si and the low-energy absorption bands to octahedral (M-site) defects caused by a lower availability of Mg. All crystals show an internal zonation pattern with an increasing T-site to M-site defect ratio from core to rim, which is interpreted to be caused by changing silica-activity and T during the experiments. The defect ratio and the zonation pattern are applied as a monitor of crystal growth conditions.

The role of the coordination defect: A new structural description of four fluorite-related sesquioxide minerals, bixbyite (Mn 2O 3), braunite (Mn 7SiO 12), braunite II (CaMn 14SiO 24), parwelite (Mn 10Sb 2As 2Si 2O 24), and their structural relationships

The anion-deficient, fluorite-related structures of the manganese-based minerals bixbyite (Mn 2O 3), braunite (Mn 7SiO 12), braunite II (CaMn 14SiO 24) and parwelite (Mn 10Sb 2As 2Si 2O 24) are reinterpreted in terms of the coordination defect (CD) theory to gain new insights into their structural interrelationships. CDs are extended, octahedral defects centred by an anion vacancy and including its immediate atomic environment: it is represented as □ M 4O 6, where the symbol □ is the anion vacancy. The bixbyite motif is a CD dimer (two edge-sharing octahedra), and this motif repeats, by further edge-sharing, around the 2-fold screw axes of the cubic structure. These same dimers are present in each of the other structures, but the presence of Si 4+ in braunite and braunite II, together with that of other foreign cations such as As 5+ and Sb 5+ in parwelite, leads to different juxtapositions of these motifs. Moreover, the structure of braunite, Mn 2+(Mn 3+) 6SiO 12, reflects the clustering of 12 Mn 3+-centred octahedra (MnO 6) around a central SiO 4 tetrahedron to generate a structure for the [(Mn 3+) 6SiO 12] 2− anion which is almost identical to that of the well-known cuboctahedral structure of the PO 4-centred heteropolytungstate anion, [(W 6+) 12PO 40] 3−. The structure of braunite II, [Ca(Mn 3+) 14SiO 24], is simply an intergrowth of slabs of bixbyite- and braunite-type structures, linked by the CaO 8 cubes of the latter. Our various analyses of the reported structure of parwelite in terms of the only possible vacancy assignment have led to some apparent anomalies. We report briefly on these, and have decided to seek confirmation of the reported structure as a consequence. Despite the increasing complexity of these structures, there are clear and defining relationships in the distribution of CDs. The assumption of a close relationship to the fluorite parent in all these structures is based on the observation that the cation sub-lattices are essentially face-centred cubic, with the anions in the tetrahedral sites, so there is little variation from this between one structure and another. The cation contents, however, are very different in the four structures discussed here — a single cation species in bixbyite, two in the braunites and four in parwelite. This factor, and the topology of the CD arrangements, are structure-determining and confirm the close relationships between these four minerals.

Comparison of the Impurity Effects on Lattice Dynamics in K2SnCl6 between Isomorphic and Nonisomorphic Systems Near the Structural Phase Transition Temperature Revealed by Nuclear Resonance

Nuclear resonance studies of the two different types impurity doped potassium hexachloro-stannates, the isomorphic system such as (K-Rb)2SnCl6 and K2(Sn-Re)Cl6 and the nonisomorphic system K2SnCl6:Al3+ in the high temperature cubic phase revealed contrasting features with one the other characterized by static in the former and dynamic feature in the latter case respectively. The resonance spectra of the nonisomorphic system indicate additionally a sign of the local structural transition above the conventional structural phase transition temperature. This seems to be triggered by the ligand-deficient octahedral defects and can be explained in terms of the enhanced activity of the octahedral defects for the hindered rotation.

Hydrogen and minor element incorporation in synthetic rutile

AbstractThe solubility and incorporation mechanisms of H and various trivalent and divalent cations in synthetic rutile have been investigated. Experiments performed using different bulk Fe2O3 contents demonstrate that Fe3+ substitutes onto the main Ti site, charge-balanced by oxygen vacancies. Under more reducing conditions in Fe-poor systems, the concentration of Ti interstitials in rutile is increased, resulting in a decrease in H solubility. Variation in the solubility of different oxides in rutile as a function of ionic radius implies substitution onto the main Ti site, probably charge-balanced by oxygen vacancies. To a lesser degree, substitution of trivalent and divalent cations is locally charge-balanced by H incorporation. Variation in OH-stretching frequencies in infrared spectra as a function of composition implies that octahedral defects and structurally-incorporated H are coupled. However, in all samples, some of the H is also decoupled from substitutional impurities, as is evident from an OH-absorption band at 3279 cm–1. This band corresponds to the main OH band seen in spectra of many natural rutiles, implying that in most rutiles, H defects are decoupled from substitutional defects.

Quantum chemical study of the lanthanide bond length contraction on Ln3+-doped Cs2NaYCl6 crystals (Ln=Ce to Lu)

The lanthanide–chlorine bond length, Re, and the frequency of the symmetric stretching mode, ν̄a1g, of the (LnCl6)3− octahedral defect clusters embedded in Cs2NaYCl6 have been calculated for all 14 Ce3+ to Lu3+ impurities in their ground 4fn electronic state using wave-function-based ab initio methods of solid state quantum chemistry which include relativistic effects and electron correlation within the (LnCl6)3− defect clusters and quantum mechanical interactions between the (LnCl6)3− electronic group and the Cs2NaYCl6 embedding host ions. The bond distance values obtained provide useful data to improve the Judd–Morrison model of the 4f→5d energy separation by explicitly including the local distortions the Ln3+ ions produce in the Cs2NaYCl6 host. The values of the structural parameters Re and ν̄a1g, and their variation across the series have also been studied using simpler models of the embedding host (in vacuo and Madelung embeddings), which has revealed that host effects, particularly those associated with quantum mechanical interactions, strengthen the Ln–Cl bond (decreasing the bond distances and increasing the frequencies of the symmetric bond stretch) and are smaller towards the right end of the series. Electron correlation within the (LnCl6)3− clusters also reduces the bond distance values, but this reduction increases going right from Ce to Lu; its effects on the frequencies of the symmetric stretching mode are negligible. The comparison of the theoretical results with the few available experiments is very satisfactory.

The nitrogen aggregation sequence and the formation of voidites in diamond

High-temperature annealing of type IaB diamonds containing platelets caused the conversion of the platelets to dislocation loops and the formation of octahedral shaped defects [T. Evans, I. Kiflawi, W. Luyten, G. Van Tendeloo, G.S. Woods, Proc. R. Soc. Lond. A 449 (1995) 295]. The chemical composition of these octahedral defects was investigated, and they were found to contain molecular nitrogen, thus showing them to be the same as the voidite defects observed in natural diamonds. This demonstrates the last stage of the sequence of the aggregation of nitrogen in diamonds. The amount of nitrogen in the ‘man-made’ voidites was found to be similar to the amount of nitrogen in the platelets before their conversion to dislocation loops. Also, a possible mechanism for the formation of B centres from A centres is discussed.

Analysis of Side-Wall Structure of Grown-in Twin-Type Octahedral Defects in Czochralski Silicon

We analyzed the side-wall structure of grown-in octahedral defects in Czochralski silicon standard wafers for large-scale integrated circuits. There are two types of twin octahedral defects: an overlapping type and an adjacent type. In the twin octahedral defects of the overlapping type, a hole is formed in the connection part. The side-wall layer in the hole part is formed continually and is the same thickness as the side-wall layers of both octahedrons. In the twin octahedral defects of the adjacent type, a partition layer is formed in the connection part. Our electron energy-loss spectroscopy analyses identified that the side-wall layer includes SiO2.

Gate Oxide Defects in MOSLSIs and Octahedral Void Defects in Czochralski Silicon

The origin of insulator defects in gate oxides and poly-oxides was thoroughly investigated. We clarified that octahedral void defects originating in a Czochralski silicon substrate are responsible for gate-oxide defects and that polyhedral void defects produced during annealing or oxidation are responsible for defects in insulators on poly-silicon. These are expected to be the principal defects affecting the yield and reliability of next-generation metal-oxide-silicon large-scale integrated-circuits or flash memories. In addition, defects in the buried oxides of a silicon-on-insulator substrate were also examined. Octahedral defects or polyhedral defects were observed just under the buried-oxide defects. Octahedral defects and polyhedral defects may be common in standard metal-oxide-silicon large-scale integrated-circuits, flash memories, and silicon-on-insulator substrates.

Computer Modelling of Lithium and Proton Intercalation in Spinel Lithium Manganates: Effect of Octahedral Vacancies

The effect of octahedral Mn vacancies on lithium and proton intercalation in the spinel structure of lithium manganate is investigated by means of atomistic simulation techniques. Prefered insertion sites and migration pathways for Li ions in the interstitial space of the lattice are calculated. The computations indicate an energetic preference for both Li ions and protons to cluster around the octahedral defects to compensate the local charge.

Octahedral Void Defects Causing Gate-Oxide Defects In Moslsis

AbstractWe found oxide defects originating in standard Czochralski silicon and proposed the sacrificial oxidation method to eliminate these defects in about 1979. Later, N2 annealing and H2 annealing methods were proposed successively, and these three elimination methods have been successfully introduced into actual fabrication lines for highly reliable integrated circuits. However, the origin of the defect was not clarified until recently. We combined copper decoration and TEM in order to observe the origin of the oxide defects and for the first time, observed octahedral void defects systematically at the oxide defects with standard Czochralski silicon. The sizes of the defects are typically 0.1–0.2 microns. These Si-crystalline defects are the origin of oxide defects and, at the same time, may be the origin of crystal originated particles. Recently, we have observed octahedral void defects in the bulk of the standard Czochralski silicon too. Some experimental findings suggest that some impurities on the side wall of the octahedral void defect induce dielectric breakdown of the gate-oxides.

Growth of a nitrogen defect cluster in a BCC lattice examined by a lattice theory

The potential energy of an octahedral defect cluster in a bcc lattice has been examined by a lattice theory coupled with an eigenstrain method. By examining the energetics of the diffusional approach of an interstitial atom to an Fe 16N 2 precipitate, a high energy barrier was found before the nitrogen atom reached a stable site on the flat surface. On the other hand, the nitrogen atom which approaches from the edge side of the precipitate does not encounter such a barrier. This explains the experimental observation that Fe 16N 2 is formed as a thin plate without an increase in the thickness, even though a spherical cluster is calculated to be of lower energy.

Octahedral defects in a b.c.c. lattice examined by lattice theory

Displacements of atoms, induced by single or multiple interstitials located at octahedral sites in a b.c.c. lattice, were examined using an eigenstrain method in lattice theory with the harmonic approximation. It is shown that the assignment of proper eigenstrains yields the correct magnitude of the potential energy for hydrogen, carbon and nitrogen in α-iron. It is also shown that the precipitate structure of Fe 16N 2 proposed by Jack takes a minimum potential energy among various kinds of plausible interstitial agglomerates.