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The grain boundary (GB) plays a critical role in a material’s properties and device performance. Therefore, the characterization of a GB’s atomic structure and electrostatic characteristics is a matter of great importance for materials science. Here, we report on the atomic structure and electrostatic analysis of a GB in a SrTiO3 bicrystal by four-dimensional scanning transmission electron microscopy (4D-STEM). We demonstrate that the Σ5 GB is Ti-rich and poor in Sr. We investigate possible effects on the variation in the atomic electrostatic field, including oxygen vacancies, Ti-valence change, and accumulation of cations. A negative charge resulting from a space-charge zone in SrTiO3 compensates a positive charge accumulated at the GB, which is in agreement with the double-Schottky-barrier model. It demonstrates the feasibility of characterizing the electrostatic properties at the nanometer scale by 4D-STEM, which provides comprehensive insights to understanding the GB structure and its concomitant effects on the electrostatic properties.

ACS applied materials & interfaces 11(28), 25378 - 25387 (2019). doi:10.1021/acsami.9b04449, Published by ACS, Washington, DC

Advanced electronic materials 0, 2001069 (2021). doi:10.1002/aelm.202001069, Published by Wiley-VCH Verlag GmbH & Co. KG, Weinheim

Significant structural evolution occurs during the deposition of ${\mathrm{CuInSe}}_{2}$ solar materials when the Cu content increases. We use in situ heating in a scanning transmission electron microscope to directly observe how grain boundaries migrate during heating, causing nondefected grains to consume highly defected grains. Cu substitutes for In in the near grain boundary regions, turning them into a Cu-Se phase topotactic with the ${\mathrm{CuInSe}}_{2}$ grain interiors. Together with density functional theory and molecular dynamics calculations, we reveal how this Cu-Se phase makes the grain boundaries highly mobile.

We report a software tool for post-correcting the linear and nonlinear image distortions of atomically resolved 3D spectrum imaging as well as 4D diffraction imaging. This tool improves the interpretability of distorted scanning transmission electron microscopy spectrum/diffraction imaging data., Specimen and stage drift as well as scan distortions can lead to a mismatch between true and desired electron probe positions in scanning transmission electron microscopy (STEM) which can result in both linear and nonlinear distortions in the subsequent experimental images. This problem is intensified in STEM spectrum and diffraction imaging techniques owing to the extended dwell times (pixel exposure time) as compared to conventional STEM imaging. As a consequence, these image distortions become more severe in STEM spectrum/diffraction imaging. This becomes visible as expansion, compression and/or shearing of the crystal lattice, and can even prohibit atomic resolution and thus limits the interpretability of the results. Here, we report a software tool for post-correcting the linear and nonlinear image distortions of atomically resolved 3D spectrum imaging as well as 4D diffraction imaging. This tool improves the interpretability of distorted STEM spectrum/diffraction imaging data.

The initial interfacial reactions of crystalline nickel and amorphous silicon carbide (Ni/a-SiC) thin films were investigated by means of X-ray diffraction (XRD) analysis, high-resolution transmission electron microscopy [(HR)TEM], Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Upon annealing at 500 °C, in the initial stage (

The utilization of interface effects in epitaxial systems at the nanoscale has emerged as a very powerful approach for engineering functional properties of oxides. Here we present a novel structure fabricated by a state-of-the-art oxide molecular beam epitaxy method and consisting of lanthanum cuprate and strontium (Sr)-doped lanthanum nickelate, in which interfacial high-temperature superconductivity (Tc up to 40 K) occurs at the contact between the two phases. In such a system, we are able to tune the superconducting properties simply by changing the structural parameters. By employing electron spectroscopy and microscopy combined with dedicated conductivity measurements, we show that decoupling occurs between the electronic charge carrier and the cation (Sr) concentration profiles at the interface and that a hole accumulation layer forms, which dictates the resulting superconducting properties. Such effects are rationalized in the light of a generalized space-charge theory for oxide systems that takes account of both ionic and electronic redistribution effects.

This work investigates the conductivity and structure of nanocrystalline CaF2 films grown at 200 °C by thermal evaporation. The in-plane conductivity is enhanced by several orders of magnitude compared to lightly doped bulk samples of CaF2, which independently confirms the finding of a previous work [Modine et al., J. Appl. Phys. 74, 2658 (1993)]. Upon heating above 200 °C, the enhancement is partially annealed out, and the activation energy increases continuously from 0.7 to 1.0 eV, which contradicts the annealing model proposed previously. The enhancement is seen only in an ∼20-nm thick region adjacent to the substrate, but this may be because the films show substantial porosity outside this region. A 5–10 nm grain size and a high density of grain boundaries are observed by high-resolution transmission electron microscopy. A 2–4 nm interfacial amorphous layer is seen in films grown on Al2O3, but such a layer is absent on MgO and evidently not responsible for the enhanced conduction. Overall, the evidence points to grain boundaries and/or dislocations as providing fast transport pathways. These results help to reconcile previous reports of enhanced ion transport in CaF2, and they are also relevant for understanding the enhancement mechanism in CaF2-based composites and antifluorite-structured materials such as Li2O.

Significant structural evolution occurs during the deposition of CuInSe2 solar materials when the Cu content increases. We use in situ heating in a scanning transmission electron microscope to directly observe how grain boundaries migrate during heating, causing nondefected grains to consume highly defected grains. Cu substitutes for In in the near grain boundary regions, turning them into a Cu-Se phase topotactic with the CuInSe2 grain interiors. Together with density functional theory and molecular dynamics calculations, we reveal how this Cu-Se phase makes the grain boundaries highly mobile.

The delafossite compound PdCoO${}_{2}$ is composed of highly conducting Pd and insulating CoO${}_{2}$ layers. As a consequence of this lattice architecture, the thermopower of PdCoO${}_{2}$ was predicted to be extremely anisotropic. Because of the limited size of available single crystals, however, these predictions had not been tested experimentally. The authors of this paper show that the electric and thermoelectric transport parameters of PdCoO${}_{2}$ along the main crystallographic directions can be determined from measurements on thin films grown on substrates with different offcut angles. The method is applicable to a wide range of thermoelectric materials. The experimental results confirm the predicted thermopower anisotropy of PdCoO${}_{2}$ and thus provide interesting perspectives for thermoelectric device applications.

Metal nanoparticles are the most frequently used nanostructures in plasmonics. However, besides nanoparticles, metal nanowires feature several advantages for applications. Their elongation offers a larger interaction volume, their resonances can reach higher quality factors, and their mode structure provides better coupling into integrated hybrid dielectric-plasmonic circuits. It is crucial though, to control the distance of the wire to a supporting substrate, to another metal layer or to active materials with sub-nanometer precision. A dielectric coating can be utilized for distance control, but it must not degrade the plasmonic properties. In this paper, we introduce a controlled synthesis and coating approach for silver nanowires to fulfill these demands. We synthesize and characterize silver nanowires of around 70 nm in diameter. These nanowires are coated with nm-sized silica shells using a modified Stöber method to achieve a homogeneous and smooth surface quality. We use transmission electron microscopy, dark-field microscopy and electron-energy loss spectroscopy to study morphology and plasmonic resonances of individual nanowires and quantify the influence of the silica coating. Thorough numerical simulations support the experimental findings showing that the coating does not deteriorate the plasmonic properties and thus introduce silver nanowires as usable building blocks for integrated hybrid plasmonic systems.

Aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) has enabled atomically resolved imaging of molecules adsorbed on low-dimensional materials like carbon nanotubes, graphene oxide and few-layer-graphene. However, conventional methods for depositing molecules onto such supports lack selectivity and specificity. Here, we describe the chemically selective preparation and deposition of molecules-like polyoxometalate (POM) anions [PW12O40]3− using electrospray ion-beam deposition (ES-IBD) along with high-resolution TEM imaging. This approach provides access to sub-monolayer coatings of intact molecules on freestanding graphene, which enables their atomically resolved ex situ characterization by low-voltage AC-HRTEM. The capability to tune the deposition parameters in either soft or reactive landing mode, combined with the well-defined high-vacuum deposition conditions, renders the ES-IBD based method advantageous over alternative methods such as drop-casting. Furthermore, it might be expanded towards depositing and imaging large and nonvolatile molecules with complex structures.

The determination of atom positions from atomically resolved transmission electron micrographs is fundamental for the analysis of crystal defects and strain. In recent years annular bright-field (ABF) imaging has become a popular imaging technique owing to its ability to map both light and heavy elements. Contrast formation in ABF is partially governed by the phase of the electron wave, which renders the technique more sensitive to the tilt of the electron beam with respect to the crystal zone axis than high-angle annular dark-field imaging. Here we show this sensitivity experimentally and use image simulations to quantify this effect. This is essential for error estimation in future quantitative ABF studies.

Nanomaterials 8(9), 693 - (2018). doi:10.3390/nano8090693, Published by MDPI, Basel

Cu(In,Ga)Se₂ (CIGS)-based solar cells reach high power-conversion efficiencies of above 22%. In this work, a three-stage co-evaporation method was used for their fabrication. During the growth stages, the stoichiometry of the absorbers changes from Cu-poor ([Cu]/([In] + [Ga]) 1) and finally becomes Cu-poor again when the growth process is completed. It is known that, according to the Cu-In-Ga-Se phase diagram, a Cu-rich growth leads to the presence of Cu₂–ₓSe (x = 0–0.25), which is assumed to assist in recrystallization, grain growth, and defect annihilation in the CIGS layer. So far, Cu₂–ₓSe precipitates with spatial extensions on the order of 10–100 nm have been detected only in Cu-rich CIGS layers. In the present work, we report Cu₂–ₓSe platelets with widths of only a few atomic planes at grain boundaries and as inclusions within grains in a polycrystalline, Cu-poor CIGS layer, as evidenced by high-resolution scanning transmission electron microscopy (STEM). The chemistry of the Cu–Se secondary phase was analyzed by electron energy-loss spectroscopy, and STEM image simulation confirmed the identification of the detected phase. These results represent additional experimental evidence for the proposed topotactical growth model for Cu–Se–assisted CIGS thin-film formation under Cu-rich conditions.

Electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy are two of the most common means for chemical analysis in the scanning transmission electron microscope. The marked progress of the instrumentation hardware has made chemical analysis at atomic resolution readily possible nowadays. However, the acquisition and interpretation of atomically resolved spectra can still be problematic due to image distortions and poor signal-to-noise ratio of the spectra, especially for investigation of energy-loss near-edge fine structures. By combining multi-frame spectrum imaging and automatic energy-offset correction, we developed a spectrum imaging technique implemented into customized DigitalMicrograph scripts for suppressing image distortions and improving the signal-to-noise ratio. With practical examples, i.e. SrTiO 3 bulk material and Sr-doped La 2 CuO 4 superlattices, we demonstrate the improvement of elemental mapping and the EELS spectrum quality, which opens up new possibilities for atomically resolved EELS fine structure mapping.

Among the range of complex interactions, especially at the interfaces of epitaxial oxide systems, contributing to the occurrence of intriguing effects, a predominant role is played by the local structural parameters. In this study, oxide molecular beam epitaxy grown lanthanum cuprate-based bilayers (consisting of a metallic (M) and an insulating phase (I)), in which high-temperature superconductivity arises as a consequence of interface effects, are considered. With the aim of assessing the role of the dopant size on local crystal structure and chemistry, and on the interface functionalities, different dopants (Ca2+, Sr2+ and, Ba2+) are employed in the M-phase, and the M–I bilayers are investigated by complementary techniques, including spherical-aberration-corrected scanning transmission electron microscopy. A series of exciting outcomes are found: (i) the average out-of-plane lattice parameter of the bilayers is linearly dependent on the dopant ion size, (ii) each dopant redistributes at the interface with a characteristic diffusion length, and (iii) the superconductivity properties are highly dependent on the dopant of choice. Hence, this study highlights the profound impact of the dopant size and related interface chemistry on the functionalities of superconducting oxide systems.

Variations in growth conditions associated with different deposition techniques can greatly affect the phase stability and defect structure of complex oxide heterostructures. We synthesized superlattices of the paramagnetic metal LaNiO3 and the large band gap insulator LaAlO3 by atomic layer-by-layer molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) and compared their crystallinity, microstructure as revealed by high-resolution transmission electron microscopy images and resistivity. The MBE samples show a higher density of stacking faults, but smoother interfaces and generally higher electrical conductivity. Our study identifies the opportunities and challenges of MBE and PLD growth and serves as a general guide for the choice of deposition technique for perovskite oxides., Comment: APL in press

Dependence of the electrical properties on grain-boundary plane orientation is examined by a combination of high-resolution transmission electron microscopy, impedance spectroscopy, and electron energy-loss spectrometry using two kinds of SrTiO3 Σ5 ([1 0 0]/36.8°) bicrystalline grain boundaries: symmetric (3 1 0) (18.4°/18.4°) and asymmetric (8.4°/28.4°). While the symmetric grain boundary is observed to be straight with the symmetric (3 1 0)//(3 1 0) plane orientation, the asymmetric grain boundary is faceted into symmetric (3 1 0)//(3 1 0) and (2 1 0)//(2 1 0), and asymmetric (1 0 0)//(4 3 0). Grain-boundary impedance is observed only in the asymmetric grain boundary, and the electron energy-loss spectrometry quantification indicates that the asymmetric (1 0 0)//(4 3 0) facets are more oxygen-deficient than the symmetric ones. The results suggest that the asymmetric (1 0 0)//(4 3 0) facets are the most resistive among the three different facets.

The fabrication of radial superlattices is demonstrated for three different hybrid material systems. Inherently strained pseudomorphic InGaAs/Fe3Si bilayers are rolled-up to produce radial semiconductor/magnetic heterostructures. Apart from this epitaxially based material system, radial InAlGaAs/GaAs/Cr superlattices are investigated as an example for periodic semiconductor/metallic multilayers. Finally, rolled-up InGaAs/GaAs/1-hexadecanethiol layers are studied as a new class of semiconductor/organic short-period superlattices. The radial superlattices are examined structurally, and particular attention is paid to the interfaces of the periodic hybrid heterostructures. These investigations reveal that, except for the semiconductor/organic hybrid material system, always a new interface layer forms, modifying the initial rolled-up layer system. The study demonstrates the potential to fabricate periodic layer systems from pure single-crystalline material, single-crystalline/poly-crystalline material as well as single-crystalline/non-crystalline material, which cannot be realized by any planar growth techniques. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The microstructural evolution of Cu In,Ga Se2 absorber layers during a three stage type coevaporation process was studied to elucidate the effect of a Cu rich stage on the formation of extended structural defects. Defect densities for two Cu poor samples, one interrupted before and one after this crucial Cu rich composition stage, were investigated by scanning transmission electron microscopy STEM imaging. The structure and chemical nature of individual defects were investigated by aberration corrected high resolution STEM in combination with electron energy loss spectroscopy on the atomic scale. In spite of the different defect densities between the two samples, most of the individual defects exhibited similar chemistry. In particular, the elemental distributions ofatomic columns at 112 twin planes, which are very frequent in Cu In,Ga Se2 thin films, were found to be the same as in the defect free grain interiors. In contrast, within grain boundaries, dislocation cores, and other structurally more complex defects, elemental redistributions of Cu and In were observed. VC 2016 Author s . All article content, except where otherwise noted, is licensed under aCreative Commons Attribution CC BY license http creativecommons.org licenses by 4.0

Single crystals of potassium niobate were compressed over a range of temperatures (21 °C to 900 °C) and examined using electron microscopy. The material did not behave in a brittle manner; samples sustained up to 3.7% strain. There was a trend of decreasing strength with increasing temperature, with a (superimposed) increase between 300 °C and 500 °C. Characterization revealed slip lines consistent with slip on {110} planes, domain activity and cracking. Dislocations consistent with the {110} slip system were observed in all specimens, while dislocations most likely on the {100} system were also observed in specimens compressed at 900 °C. Domain walls were observed in large numbers only in specimens tested between 300 °C and 500 °C. It is proposed that the shape of the strength-temperature curve results from the combination of contributions from dislocation slip systems and mobility and a strong effect of domain walls only acting in the intermediate temperature range., This work was supported in part by DFG Project MR 22/4-2. M. C.-R. would like to acknowledge funding from a JAE/DOC contract awarded by the Spanish Consejo Superior de Investigaciones Cientificas (CSIC), co-financed by the European Social Fund.

Several low-angle symmetrical [0 0 1]-tilt grain boundaries and an asymmetrical grain boundary with both tilt and twist components were examined by high-resolution transmission electron microscopy, conventional transmission electron microscopy, and impedance spectroscopy. The symmetrical tilt grain boundaries consist of isolated dislocation cores and the Burgers vectors are translation vectors of the crystal. Strain analysis shows that the strain fields around the dislocation cores overlap with increasing misorientation angle. The a.c. impedance response of the low-angle grain boundaries reveals a marked blocking effect for charge transport across the low-angle symmetrical grain boundaries, which increases with increasing misorientation angle. In the case of the mixed asymmetrical grain boundary, however, the blocking effect is low despite the large misorientation. The resistance and electrical potential of this grain boundary were calculated and compared with those obtained from the symmetrical grain boundaries. A relationship between microstructure and macroscopic electrical property can approximately be arrived by considering anion vacancies to be preferentially situated in highly distorted regions such as dislocation cores.

In situ high-resolution TEM imaging of an ion-milled SrTiO3 sample during annealing at 925 and 940 °C is reported. Regions that were amorphized during the ion-milling at room temperature are observed to crystallize, forming low-angle grain boundaries. At the grain boundaries, perfect a〈0 0 1〉 dislocations and two climb-dissociated a/2〈0 1 1〉 dislocations were observed. The experimental observations also include dynamic dislocation phenomena, such as glide, climb, and annihilation. Interestingly, the separation of the two a/2〈0 1 1〉 partial dislocations in the low-angle grain boundaries is not constant, but temporarily fluctuates around a mean value of 2 nm.

Donor-doped SrTiO3 ceramics have found application in sensors, varistors, grain boundary layer capacitors and catalysts. This wide range of applications is closely related to the defect chemistry of SrTiO3 and the fact that the properties can be strongly changed by varying the processing parameters. Oxidation of an initially reduced donor-doped SrTiO3 ceramics, for example, leads to a strongly enhanced resistivity, which is generally assumed to result from the formation of cation vacancies. This formation of cation vacancies, however, raises the question of the whereabout of the expelled Sr-ions. In this contribution, the structural and chemical phenomena observed after high temperature oxidation (at 1200°C for 30 hours) of 5 at.% Nb-doped polycrystalline SrTiO3 are reported. This reoxidation procedure leads to the formation of Sr-rich islands on the surface. These islands exhibit characteristic shapes, areal densities, and sizes, that depend on the surface orientation of the underlying grain. A correlation between grain orientation (determined by orientation imaging microscopy) and tendency towards island formation was found. The structure and the composition of the islands were investigated by transmission electron microscopy and significant differences were observed for different islands. The bulk interior was also investigated after reoxidation. Sr-rich secondary phases were found at the triple grain junctions and could be identified as a Ruddlesden-Popper phase. Moreover, surprising compositional gradients including Sr enrichment were observed in the grain interior beneath the surface. The results are discussed in terms of the defect chemistry of SrTiO3. Nb-dotiertes (5 At.%), polycrystallines SrTiO3, das in einer reduzierenden Atmosphare gesintert wurde, zeigt bei weiterer Temperaturbehandlung bei 1200°C unter Sauerstoffatmosphare (Reoxidation) erhebliche strukturelle und chemische Veranderungen. Diese erfolgen sowohl an der Oberflache, in den oberflachennahen Kornern und an den Korngrenzen. Auf der polierten Oberflache einer reduzierten, polykristallinen Probe bilden sich nach 30-stundiger Oxidation „Inseln“ mikrokristalliner Grose. Form, Haufungsdichte und laterale Anordnung der Inseln zeigen dabei eine charakteristische Abhangigkeit von der Orientierung der Oberflache. Mit Hilfe von OIM-Messungen konnten drei Klassen von Oberflachenorientierungen unterschieden werden, die sich hinsichtlich der Inselbildung signifikant unterscheiden: (111)-, (122)- und (112)-Oberflachen zeigen eine hohe Inseldichte. (001)-, (013)- und (114)-Oberflachen zeigen eine geringe Inseldichte. (011)-, (133)- und (012)-Oberflachen zeigen eine mittlere Inseldichte. Da die Haufungsdichte der Inseln als Mas fur die Oxidationsneigung der Oberflachen gelten kann, zeigt eine (111)-Oberflache die hochste, eine (001)-Oberflache die niedrigste und eine (011)-Oberflache eine mittlere Oxidationsneigung. Struktur und Zusammensetzung der Inseln unterscheiden sich in Abhangigkeit von der Oberflachenorientierung in signifikanter Weise. Dies wurde fur je eine Insel auf der (023)- bzw. (012)-Oberflache nachgewiesen. Die untersuchte Insel auf der (023)-Oberflache zeigte bei einer Hohe von 250 nm ein mit der Volumenphase identisches Elektronenbeugungsbild (mit einer hoheren Intensitat der 100 Super-Reflexe). Dies deutet darauf hin, dass die Insel eine Perowskit-Struktur besitzt. Die chemische Analyse mit Hilfe von XEDS-Messungen zeigen, dass die stochiometrische Zusammensetzung der Insel nahe der Grenzflache derjenigen des SrTiO3 Volumens entspricht. Die Zusammensetzung andert sich kontinuerlich in Wachstumsrichtung der Insel und wird dabei zunehmend Sr(2+)-reicher auf Kosten der Ti(4+)-Ionen. Die Perowskit-Struktur der Insel bleibt jedoch erhalten. Es ist anzunehmen, dass die Ti(4+)-Ionen in Wachstumsrichtung allmahlich durch Sr(2+)-Ionen in Form von Defekten ersetzt werden. Dies entspricht einer strukturellen und chemischen Veranderung der (023)-Insel in Wachstumsrichtung von SrTiO3 zu Sr2O2 durch Bildung von Sr(1)(Ti(1-x)Sr(x))O(3-x) (x wachst in Wachstumsrichtung). In diesem Modell wurden Sauerstoffleerstellen fur den Ladungsausgleich der -Defekte sorgen. Dagegen zeigt die untersuchte 900 nm hohe Insel auf der (012)-Oberflache ein vom SrTiO3-Volumen deutlich verschiedenes Elektronenbeugungsbild. Die gemessenen Gitterebenenabstande in der Insel stimmen gut mit den in der Literatur genannten Werten fur SrO uberein. Auch die XEDS-Analysen zeigen lediglich das Vorhandensein von Sr(2+)-Ionen in der Insel. Beides legt nahe, dass diese Insel aus SrO besteht mit der SrO-(260)-Ebene als Grenzflache zu SrTiO3. Das Wachstum der SrO-Inseln auf der SrTiO3-(012)-Oberflache resultiert in einer Gitterfehlpassung von 4% in [210]SrTiO3-Richtung beziehungsweise ~30% in [001]SrTiO3-Richtung der Grenzflache. Nach der Reoxidation bildet sich in der Nahe der Oberflache eine optisch transparente Schicht, deren Dicke etwa 50-70 mikrometer betragt. In dieser Schicht last sich eine ausgepragte Inhomogenitat der Kationen nachweisen. In der Nahe der Oberflache findet eine Anreicherung von Sr(2+)-Ionen statt. Anderseits liegt im tieferen Bereich der reoxidierten Schicht ein Ti(4+)-Uberschuss vor. Hinsichtlich Nb(5+) -Ionen lassen sich keine signifikante Konzentrationsunterschiede in der Oxidationsschicht nachweisen. Der starke Gradient des chemischen Potentials des Sauerstoffs zwischen Oberflache und Probeninneren wirkt jedoch als treibende Kraft fur eine kinetische Entmischung der Kationen. Voraussetzung fur die kinetische Entmischung sind unterschiedliche Beweglichkeiten der verschiedenen Kationen, wie dies in SrTiO3 der Fall ist. Die in dieser Arbeit beschriebenen Messungen stellen den ersten experimentellen Nachweis fur eine kinetische Entmischung in SrTiO3 dar. Es ist anzunehmen, dass in oberflachennahen Bereichen (hoherer p(O2)-Bereich) uberschussige Sr(2+)-Kationen die Ti(4+)-Gitterplatze besetzen und hierdurch -Defekte verursachen, die elektrische Ladung von kompensieren. An den Trippl punkten last sich nach der Reoxidation eine Sr(2+)-reiche zweite Phase (Sr2TiO4) nachweisen. Dies macht sich im TEM-Beugungsbild bei Projektion auf die [100] bzw. [210] Zonen-achse durch eine zusatzlichen Reflexion in [001]-Richtung bemerkbar. Sr2TiO4 gehort zur homologen Reihe Sr(n+1)Ti(n)O(3n+1), die als Ruddlesden-Popper Phasen bekannt sind. Auf Grund der bislang gewonnen Daten kann die Existenz der anderen Reihenmitglieder (n = 2, 3, ...) nicht ausgeschlossen werden. Damit konnte zum ersten Mal eine durch Reoxidation verursachte Korngrenzen-Phase in SrTiO3 nachgewiesen werden.