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The UnitCell Tools package was developed to determine unit-cell parameters of a crystal from a single electron diffraction pattern with high-order Laue zone reflections acquired in the conventional transmission electron microscope., Electron diffraction techniques in transmission electron microscopy (TEM) have been successfully employed for determining the unit-cell parameters of crystal phases, albeit they exhibit a limited accuracy compared with X-ray or neutron diffraction, and they often involve a tedious measurement procedure. Here, a new package for determining unit-cell parameters from a single electron diffraction pattern has been developed. The essence of the package is to reconstruct a 3D reciprocal primitive cell from a single electron diffraction pattern containing both zero-order Laue zone and high-order Laue zone reflections. Subsequently, the primitive cell can be reduced to the Niggli cell which, in turn, can be converted into the unit cell. Using both simulated and experimental patterns, we detail the working procedure and address some effects of experimental conditions (diffraction distortions, misorientation of the zone axis and the use of high-index zone axis) on the robustness and accuracy of the software developed. The feasibility of unit-cell determination of the TiO2 nanorod using this package is also demonstrated. Should the parallel-beam, nano-beam and convergent-beam modes of the TEM be used flexibly, the software can determine unit-cell parameters of unknown-structure crystallites (typically >50 nm).

In response to Wierzchos et al. (1) regarding the mechanism of water extraction from gypsum rock by desert colonizing microorganisms (2), we provide details that refute their incorrect assessments. We carefully selected areas without microorganism colonies that only contained gypsum, as confirmed by X-ray diffraction (XRD), for our culture experiments. Raman is useful for localized analysis of phase on surfaces, but here, it is complementary to XRD, which provides sample-wide detection (3, 4). Furthermore, selected area electron diffraction (SAED) confirms anhydrite, exhibiting arcs at 0.347 ± 0.003 nm and 0.278 ± 0.002 nm [(200) and (211) planes, respectively] with a [01−1] zone axis (Fig. 1 A and B ). The closest reflection for gypsum, the (130) plane, was not observed. SAED and fast Fourier transform (FFT) show twofold symmetry of the arcs, while the gypsum (130) plane exhibits fourfold symmetry, which was not observed. Finally, the crystal morphology of gypsum (monoclinic) was observably different from anhydrite (orthorhombic) (Fig. 1 C − F ). Thus, XRD, high-resolution … [↵][1]1To whom correspondence may be addressed. Email: david.k{at}uci.edu. [1]: #xref-corresp-1-1

Nd2Fe14B and Nd2 − xDyxFe14B (x = 0.25,0.50) particles were prepared by the modified co-precipitation followed by reduction-diffusion process. Bright field scanning transmission electron microscope (BF-STEM) image revealed the formation of Nd-Fe-B trigonal prisms in [-101] viewing zone axis, confirming the formation of Nd2Fe14B/Nd2 − xDyxFe14B. Accurate site for the Dy substitution in Nd2Fe14B crystal structure was determined as “f” site by using high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It was found that all the “g” sites are occupied by the Nd, where’s and Dy occupied only the “f” site. Anti-ferromagnetic coupling at “f” site decreased the magnetic moment values for Nd1.75Dy0.25Fe14B (23.48 µB) and Nd1.5Dy0.5Fe14B (21.03 µB) as compared to Nd2Fe14B (25.50 µB). Reduction of magnetic moment increased the squareness ratio, coercivity and energy product. Analysis of magnetic anisotropy at constant magnetic field confirmed that “f” site substitution did not change the patterns of the anisotropy. Furthermore, magnetic moment of Nd2Fe14B, Nd2 − xDyxFe14B, Nd (“f” site), Nd (“g” site) and Dy (“f” site) was recorded for all angles between 0-180o.

International audience; Dioctahedral micas are composed of two tetrahedral sheets and one octahedral sheet to form TOT or 2:1 layers. These minerals are widespread and occur with structures differing by (i) the layer stacking mode (polytypes), (ii) the location of vacancies among non-equivalent octahedral sites (polymorphs), and (iii) the charge-compensating interlayer cation and isomorphic substitutions. The potential of parallel-illumination electron diffraction (ED) is assessed here to determine the polytype/polymorph of individual crystals of finely divided dioctahedral micas and to image their morphology. ED patterns are calculated along several zone axes close to the c *-and c-axes using the kinematical approximation for trans-and cis-vacant varieties of the four common mica polytypes (1 M , 2 M 1 , 2 M 2 , and 3 T). When properly oriented, all ED patterns have similar geometry, but differ by their intensity distribution over hk reflections of the zero-order Laue zone. Differences are enhanced for ED patterns calculated along the [001] zone-axis. Identification criteria are proposed for polytype/polymorph identification, based on the qualitative distribution of bright and weak reflections. A database of ED patterns calculated along other zone-axes is provided in case the optimum [001] orientation cannot be found. Different polytype/polymorphs may exhibit similar ED patterns depending on the zone axis considered.

CaBi8−xEu x Ti7O27 (CBT-BIT-xEu3+, x = 0.00, 0.05, 0.10, 0.15, and 0.20) intergrowth-structured ceramics were synthesized using a solid-state reaction method. The intergrowth structures were successfully obtained and clearly observed by HR-TEM along the [ $$\bar {1}10$$ ] zone axis. Raman patterns indicated that Eu3+ preferred to occupy the A sites in pseudo-perovskite layers and increased the orthorhombicity and structural distortion degree of TiO6 octahedra, which was further supported by refined structural parameters produced by GSAS software. As a consequence of increased orthorhombicity, the Curie temperature was increased from 736 °C for pure CBT-BIT to 758 °C for CBT-BIT-0.1Eu3+ ceramic. Simultaneously, CBT-BIT-0.1Eu3+ achieved the strongest red–orange emission and the CIE chromaticity coordinates calculated to be (0.627, 0.372), which suggested the potential applications of this material in high-temperature electrooptic applications.

The crystal structure of martensite in Cu-27at.%Zn-9.0 at.%Al alloy has been studied by using spherical-aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and geometrical phase analysis (GPA) to examine possible changes in atomic rearrangements during martensitic transformation of this ternary system. Observation along [ 100 ] M zone axis is suitable for examining a chemical order of the martensite, and showed that, despite the non-stoichiometry of the alloy, atomic columns containing Al atoms are imaged and distinguished from the others. On the other hand, observation along [ 010 ] M zone axis directly revealed that the parent and martensitic phases possess L21 and 18R ( 2 1 ‾ ) structures, respectively. These observations suggested that the martensite retained the local chemical order of the parent phase without shuffling before and after the transformation. GPA revealed that the interface between the two phases was coherent with tilting of the basal plane approximately 6° across the boundary, which makes otherwise large inclination small during the martensitic transformation.

This work aimed to study the crystalline structure of TT-,T-phases of Nb2O5 nanoparticles through XRD, Rietveld refinement, and HRTEM, using geometric phase analysis (GPA). The results show the presence of distorted NbO6 and NbO7 polyhedral, producing strain effects, mainly in the plane boundaries and along the b-c plane. XRD and HRTEM analyses show the TT→T transition at 700 °C, with increased particle size and increased strain in the boundaries between nanoparticles. The sample calcinated at 700 °C presents segregation of the TT-(001), (100), and T-(130) planes, where the strain effect is more relevant along the [100] zone axis and between phases.

The effect of morphology of the long-period stacking ordered (LPSO) phase on mechanical properties of the Mg-7Gd-3Y-1Nd-1Zn-0.5Zr (wt.%) alloy have been studied. The results reveal that the block-like 14H-LPSO phases in and near grain boundaries can be formed during heat treatment at high temperature, but low temperatures is conducive to form the needle-like 14H-LPSO phases within α-Mg grains. During heat treatment at fixed temperature for different time, the preferential nucleation sites of the 14H-LPSO phases are located in grain boundaries, then the14H-LPSO phases grow into the α-Mg matrix in the form of needle-like, the needle-like 14H-LPSO phases gradually decrease its length after growing a certain stage, at last the needle-like 14H-LPSO phases disappear completely. The decomposition of the block-like 14H-LPSO phases is found during furnace cooling after homogenization. After decomposition of the block-like 14H-LPSO phases, the rapid diffusion of Zn atoms into α-Mg matrix leads to form the needle-like 14H-LPSO phases within α-Mg matrix, but the retention of RE atoms in grain boundaries results in forming the Mg-RE particles. After extrusion and subsequent ageing, it is found that the alloy with the needle-like 14H-LPSO phases exhibit superior elongation than the alloy without the needle-like 14H-LPSO phase. The precipitates of peak-aged alloys are studied by TEM. The 11 2 − 0 > α demonstrates that the stacking faults can be observed, the serious lattice distortion appears near the stacking fault. The [0001] zone axis shows that the β′ and a new rod phase are found, and the enrichment of RE atoms are detected in the two phase by HADDF-STEM. It seems to be that the rod phase can be subdivided into a plurality of mutually parallel structure unit.

4H- and 6H-SiC grown by physical vapor transport method were investigated by transmission electron microscopy (TEM). From the TEM diffraction patterns observed along the [11-20] zone axis, 4H- and 6H-SiC were identified due to their additional diffraction spots, indicating atomic stacking sequences. However, identification was not possible in the [10-10] zone axis due to the absence of additional diffraction spots. Basal plane dislocations (BPDs) were investigated in the TEM specimen prepared along the [10-10] zone axis using the two-beam technique. BPDs were two Shockley partial dislocations with a stacking fault (SF) between them. Shockley partial BPDs arrayed along the [0001] growth direction were observed in the investigated 4H-SiC. This arrayed configuration of Shockley partial BPDs cannot be recognized from the plan view TEM with the [0001] zone axis. The evaluated distances between the two Shockley partial dislocations for the investigated samples were similar to the equilibrium distance, with values of several hundreds of nanometers or even values as large as over a few micrometers.

Precipitate structures in Al-3Cu (wt%) and Al-3Cu-1.78Mg (wt%) alloys aged at 190 °C for 2 minutes were studied by transmission electron microscopy and high resolution transmission electron microscopy. New models named ordered structures were proposed for the fine precipitates formed in the two aged alloys. Ordered structures in Al-Cu alloys were composed by Al and Cu atoms, and by Al, Cu and Mg atoms together in Al-Cu-Mg alloys. By simulating selected area electron diffraction (SAED) patterns of Al-Cu-(Mg) alloys containing plate-shaped ordered structures and taking into account the influence of the plate shape of ordered structures on their electron diffraction characteristics, [001] zone axis SAED patterns of the two alloys were interpreted. It was concluded that volume expansions of the two aged alloys occurring at the early aging stage are caused by the lattice expansions as ordered structures are formed, and ordered structures are the nuclei for the GP zones in Al-Cu alloys.

The orientation relationships and interfacial planes of the theta (θ)-Al2Cu/Cu and gamma2 (γ2)-Al4Cu9/Cu interfaces formed on the Cu (001) and (111) surfaces have been studied by transmission electron microscopy (TEM). Epitaxial thin Cu films are grown on the single-crystal NaCl surfaces and then Al is evaporated to form θ-Al2Cu and γ2-Al4Cu9. Results showed that the θ-Al2Cu first formed and then the γ2-Al4Cu9 formed. The orientation relationships at the Al/Cu interface were found: (1) [110]θ//[111]Cu (zone axis) and ( 1 ¯ 10 ) θ // ( 1 ¯ 1 ¯ 2 ) Cu on the (111)Cu surface, (2) the (110)γ2 surface is the interface with both the Cu (001) and (111) surfaces with a common orientation relationship of ( 1 ¯ 11 ) γ2// ( 1 1 ¯ 0 ) Cu, and (3) [110]θ//[110]γ2 (zone axis) and ( 1 ¯ 10 ) θ// ( 1 ¯ 1 2 ¯ ) γ2 on the (111)Cu surface. The θ/Cu, γ2/Cu, and γ2/θ interfaces were further analyzed. The γ2-Al4Cu9 phase has good orientation relationships to Cu and therefore low interfacial energies. In addition, the energy of formation of γ2-Al4Cu9 is about 1.2 times than that of eta (η)-AlCu. Therefore γ2-Al4Cu9 nucleates first after θ-Al2Cu.

Novel triangularly arranged needle-shaped precipitates in zirconium based alloys were firstly observed and systematically investigated, which were indexed as single hexagonal structured ω phase while obeying the orientation relationship with the α phase matrix: {0001}α∥{11 2 ‾ 0}ω and 2 ‾ 0>α∥ ω. In particular, viewed along [0001]ω zone axis, the ω phase needles were 60° triangularly arranged and paralleled to (2 1 ‾ 1 ‾ 0)ω, (11 2 ‾ 0)ω and ( 1 ‾ 2 1 ‾ 0)ω planes, respectively. Based on electron microscopy analysis, a model for understanding the formation of these precipitates was proposed: planar periodicity distribution of dissimilar atoms in these ω phase needles resulted in the needle-shaped morphology as well as the triangular arrangement.

Summary Honeycomb-layered phases Na3M2XO6 (M = Ni, Cu, Co; X = Sb, Bietc.) have been intensively pursued as high-voltage and high-rate capability cathode materials for Na-ion batteries (NIBs), but the crystal structure is not well elucidated. Herein, structural analysis was conducted on pristine Na3Ni2SbO6 material using electron microscopy and associated spectroscopies to reveal its crystallographic features. Experimental observations along multiple zone axes indicate that structural disorder is intrinsic in the pristine Na3Ni2SbO6, characteristic of randomly stacked layers with three variants of monoclinic structure. Stacking disorder is demonstrated by the non-vertical relationship of adjacent Ni2SbO6 layers in [100] zone axis, the different Ni/Sb atomic arrangements in [010] zone axis, and the Ni/Sb random overlap in [001] zone axis. The insight on the structural disorder may inspire studies on their phase transformations upon cycling and provide some clues to potentially solve the voltage/capacity decay problems of these honeycomb-layered materials., Graphical Abstract, Highlights • The intrinsic structural disorder in Na3Ni2SbO6 is unambiguously revealed • Detailed atomic-resolution STEM imaging and crystallography analysis are conducted • The structural disorder is associated with three variants of a monoclinic phase, Imaging Methods in Chemistry; Materials Science; Energy Materials

The precipitation sequence of a Cu-Ni-Be alloy is: α-Cu supersaturated solid solution → Guinier-Preston (G.P.) zones → metastable γ″ → γ′ → stable γ (NiBe) phase. The micro-hardness and electrical conductivity during the aging process were measured. The precipitation characteristics and the distribution of the γ″ phase, under peak aging conditions, were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area diffraction pattern (SADP), and high-resolution transmission electron microscopy (HRTEM). The results show that the orientation relationship of the γ′′ phase/α-Cu matrix is: (001)p//(001)α, [100]p//[110]α (p: Precipitates, α: α-Cu supersaturated solid solution), which is in accordance with the Bain relationship in a FCC/BCC (face centered cubic/body centered cubic) structure, with the unique habit plane being {001}α. While the zone axis is parallel to [001]α, three forms of γ″ phases are distributed on the projection surface at the same time. The (001) reciprocal-lattice positions of γ′′ phase in SADP are diffusely scattered, which is consistent with the variation of the d(001) value of the γ′′ phase. The intra-range variation is related to the distortion of the (001) plane of the γ″ phase, due to interfacial dislocations and distortion strain fields. The lattice of the γ″ phase in the HRTEM images was measured as a = b = 0.259 ± 0.002 nm and c = 0.27–0.32 nm. With the increase of thermal exposure time, the stable γ phase has a NiBe phase structure (Standard Card Number: PDF#03-1098, a = b = c = 0.261 nm), and the long diffuse scattering spots will transform into single bright spots. The edge dislocation, generated by interfacial mismatch, promotes the formation of an optimal structure of the precipitated phase, which is the priority of growth in the direction of [110]p.

Variations in deformation kink band formation behavior with loading orientation were examined by the combination of experiment and computer simulation, using the Zn single crystal as a model material. Based on the results, the controlling factors for the formation behavior of deformation kink bands and its general features were discussed. Due to compression parallel to the basal plane, several deformation bands formed in the Zn single crystal. By the examination of the crystallographic nature of the deformation bands, they were found to exhibit three characteristic features: an ambiguous crystal rotation axis on the [0001] zone axis, an arbitrary rotation angle with a wide variation, and a variation in the crystal rotation angle within the deformation band boundary itself. In addition, an analysis protocol to classify the nature of the deformation bands via the observation on (0001) was newly proposed. As a result, the deformation bands formed in the Zn single crystal were confirmed to be predominantly deformation kink bands rather than deformation twining. Among the abovementioned three crystallographic features, we first experimentally confirmed by using the single crystal that the variations in the rotation axis in deformation kink bands exhibit a strong dependence on loading orientation. Using computer simulation based on the crystal plasticity finite element analysis, the origin of the variation in rotation axis in deformation kink bands was clarified to be due to the initiation of different types of basal dislocations that construct the deformation kink band boundaries, which depends on the loading orientation. In addition, the variations in types of the dislocations owing to the internal stress were found to cause the significant waviness of the deformation band boundaries on (0001) specimen surface.

This study aims to investigate the tension and compression properties and precipitation behavior of pre-twinned ZK60 alloys. It was found that aging treatment can effectively reduce the tension–compression yield asymmetry of pre-twinned ZK60 alloy. For the pre-twinned sample with 10 h aging treatment, the yield asymmetry ratio is nearly equal to 1. Precipitate behavior in {10–12} extension twins of ZK60 Mg alloy were characterized by TEM. Three different morphologies of precipitates, [0001] twin rods, (0001) twin plates and [11–20] twin laths were observed in {10–12} extension twins. The precipitates constituted Mg 4 Zn 7 or MgZn 2 phases. The Mg 4 Zn 7 phases have two variant orientations of the [010] zone axis, [010] Mg4Zn7 ‖ [0001] twin and (−201) Mg4Zn7 ‖ (‐12‐10) twin or (−201) Mg4Zn7 ‖ (10–10) twin , while the MgZn 2 phases have an orientation of [‐12‐10] MgZn2 ‖ [0001] twin and (10–12) MgZn2 ‖ (10–10) twin . [11–20] twin laths as a new morphology of the precipitates have been found in ZK60 alloy, which have an orientation relationship of [010] Mg4Zn7 ‖ [0001] twin and (−201) Mg4Zn7 ‖ (‐12‐10) twin . Finally, the influences of aging treatment on yield asymmetry of pre-twinned ZK60 alloy are addressed and discussed.

The CrysTBox software for electron diffraction analysis and visualization is presented. Among others, the software offers an automated zone axis determination using selected area diffraction, convergent beam diffraction and nanodiffraction patterns, ring diffraction evaluation, and interactive crystal visualization in both direct and reciprocal space., Three tools for an automated analysis of electron diffraction pattern and crystallographic visualization are presented. Firstly, diffractGUI determines the zone axis from selected area diffraction, convergent beam diffraction or nanodiffraction patterns and allows for indexing of individual reflections. Secondly, ringGUI identifies crystallographic planes corresponding to the depicted rings in the ring diffraction pattern and can select the sample material from a list of candidates. Both diffractGUI and ringGUI employ methods of computer vision for a fast, robust and accurate analysis. Thirdly, cellViewer is an intuitive visualization tool which is also helpful for crystallographic calculations or educational purposes. diffractGUI and cellViewer can be used together during a transmission electron microscopy session to determine the sample holder tilts required to reach a desired zone axis. All the tools offer a graphical user interface. The toolbox is distributed as a standalone application, so it can be installed on the microscope computer and launched directly from DigitalMicrograph (Gatan Inc.).

A convergent-beam electron diffraction (CBED) method is proposed for polarity determination, in which polarity is determined from the intensity asymmetry of any of the hkl–\overline h\overline k\overline l Friedel pairs appearing in a zone-axis CBED pattern with a symmetric arrangement of Bijvoet pairs of reflections. The intensity asymmetry occurs as a result of multiple scattering among Bijvoet pairs of reflections in the CBED pattern. The appropriate zone-axis orientations for polarity determination are deduced for 19 of the 25 polar point groups from symmetry considerations so as to observe Bijvoet pairs of reflections symmetrically in a single CBED pattern. These appropriate zone-axis orientations deduced for the 19 polar point groups coincide with nonpolar directions. This is because the nonpolar directions for these point groups are perpendicular to an even-fold rotation axis, which guarantees the symmetric arrangement of Bijvoet pairs of reflections with respect to the symmetry (m–m′) line in a CBED pattern taken along any of the appropriate zone-axis orientations. The m–m′ line in the CBED pattern is proved to be perpendicular to the trace of the even-fold rotation axis. On the other hand, if the nonpolar direction is either perpendicular to a mirror plane or parallel to a roto-inversion axis as in the four point groups m, 3m1, 31m, \overline 6, the nonpolar direction cannot be used as the appropriate zone-axis orientation for polarity determination because the Bijvoet pairs of reflections are not arranged symmetrically in the CBED pattern. The validity of the CBED method is confirmed both by experiment and by calculation of CBED patterns.

The twin boundary (TB), a typical planar defect, occurs naturally in molecular explosives and manipulates their sensitivities to external stimuli. We systemically studied the formation and growth mechanisms of the TBs in the β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) crystal by using self-consistent charge density functional tight binding with dispersion corrections. The three TB species along the [010] zone axis based upon the experiments were considered. The (001)/[010] TB species are more favorable energetically than other TB species. The twinning in β-HMX most probably occurs on the (001) plane rather than on the (101) plane, which reproduces the naturally occurred twinned crystals in the experiments well. The TB-induced symmetry breaking alters not only the geometries but also on the electronic structures of the HMX molecules located at TB. The inner surface, outer surface, and intersection of the two surfaces are suggested to play vital roles in sensitizing the condensed phase β-HMX and to act as a trigger in initiating the chemical decomposition. The HMX molecule is most likely to be adsorbed in the concave site on (001) plane through either normal or twinning pathway in a competitive manner. After the grooves on (001) surface being filled, new grooves merge naturally for further adsorption.

Single crystal Fe2O3 icositetrahedra have been synthesized by a facile hydrothermal synthesis method in the presence of dihydrogen phosphate ions. The icositetrahedron particles are of hexagonal shape and enclosed by 24 quadrilaterals. It could be seen as a particle with six equivalent {110} facets added to the truncated hexagonal bipyramidal structure, that is, it is enclosed by six {110} planes, six {104} planes and twelve {113} planes. Dihydrogen phosphate ions play an important role in the formation of α-Fe2O3 icositetrahedron particles, because high concentration of [H2PO4]− drives the ferric oxide nanocrystals growth along the [006] zone axis. Furthermore, the as-synthesized Fe2O3 icositetrahedron single crystals show comparative photocatalytic activities on the degradation of cationic dye Rhodamine B, which make them promising candidates for catalysts and sensing materials.

The 1:2 ordered structure of Ba(B′1/3B′′2/3)O3 perovskites was studied in detail by transmission electron microscopy from different projections (〈110〉c, 〈111〉c and 〈112〉c) in Ba((Co, Zn, Mg)1/3Nb2/3)O3 ceramics. For the 〈110〉c and 〈112〉c zone axes, the occurrence of 1/3{111}-type superlattice reflections in their corresponding selected area electron diffraction images directly revealed the 1:2 ordered structure. The most informative 〈110〉c zone gave two sets of 〈111〉c ordering variants, providing a convenient way to detect the twin boundaries. The 〈112〉c zone axis variant with only one set of 〈111〉c axes could be used to detect single anti-phase boundaries. In addition, the 〈111〉c zone axis, which is parallel to the ordering direction, clearly showed the hexagonal symmetry of a 1:2 ordered structure in the corresponding high-resolution transmission electron microscopy image. For a completely ordered sample, there are always a certain proportion of areas without a superperiod lattice. These areas should also be the ordered domains, the variants of which are not perpendicular to the given zone axis.

All of the $A{B}_{2}$ Laves phases discovered so far satisfy the general crystalline structure characteristic of translational symmetry; however, we report here a new structured Laves phase directly precipitated in an aged Mg-In-Ca alloy by using aberration-corrected scanning transmission electron microscopy. The nanoprecipitate is determined to be a ${(\mathrm{Mg},\mathrm{In})}_{2}\mathrm{Ca}$ phase, which has a $C14$ Laves structure (hcp, space group: $P{6}_{3}/mmc$, $a=6.25\text{ }\text{ }\AA{}$, $c=10.31\text{ }\text{ }\AA{}$) but without any translational symmetry on the ${(0001)}_{p}$ basal plane. The ${(\mathrm{Mg},\mathrm{In})}_{2}\mathrm{Ca}$ Laves phase contains two separate unit cells promoting the formation of five tiling patterns. The bonding of these patterns leads to the generation of the present Laves phase, followed by the Penrose geometrical rule. The orientation relationship between the Laves precipitate and Mg matrix is ${(0001)}_{p}//{(0001)}_{\ensuremath{\alpha}}$ and ${[1\overline{1}00]}_{p}//{[11\overline{2}0]}_{\ensuremath{\alpha}}$. More specifically, in contrast to the traditional view that the third element would orderly replace other atoms in a manner of layer by layer on the close-packed ${(0001)}_{L}$ plane, the In atoms here have orderly occupied certain position of Mg atomic columns along the ${[0001]}_{L}$ zone axis. The finding would be interesting and important for understanding the formation mechanism of Laves phases, and even atom stacking behavior in condensed matter.

International audience; Silicon nanowires have been grown by a plasma-assisted vapour–liquid–solid method using tin as the catalyst. Transmission electron microscopy in the [1-210] zone axis shows that the diamond hexagonal (P63/mmc) crystal structure is present in several nanowires. This is the first unambiguous proof of the natural occurrence of this metastable phase to our knowledge.

Formation of curious deformation bands has been reported as one of the deformation mechanisms occurring in an Mg-based long-period stacking ordered (LPSO) phase. The origin of the deformation band is still unknown, and the possibility of the deformation kink band and/or the deformation twin has been discussed. To clarify this, the crystallographic nature of deformation bands formed in the LPSO phase was examined by scanning electron microscope–electron backscatter diffraction (SEM-EBSD) pattern analysis. The results were compared to those of the deformation kink bands formed in hcp-Zn and deformation twins formed in hcp-Mg polycrystals. The deformation bands in the LPSO phase was confirmed not to exhibit a fixed crystal orientation relationship with respect to the matrix, different from the case shown in the deformation twin. Instead, the deformation band in the LPSO phase showed three arbitrariness on its crystallographic nature: an ambiguous crystal rotation axis that varied on the [0 0 0 1] zone axis f...

In the field of electron microscopy the replica technique is known as an indirect method and also as an extraction method that is usually applied on metallurgical samples. This contribution describes a fast and simple transmission electron microscopic (TEM) sample preparation by complete removal of nanoparticles from a substrate surface that allows the study of growth mechanisms of nanostructured coatings. The comparison and combination of advanced diffraction techniques in the TEM and scanning electron microscopy (SEM) provide possibilities for operators with access to both facilities. The analysis of TEM-derived diffraction patterns (convergent beam electron diffraction) in the SEM/electron backscatter diffraction software simplifies the application, especially when the patterns are not aligned along a distinct zone axis. The study of the TEM sample directly by SEM and transmission Kikuchi diffraction allows cross-correlation with the TEM results.

The early precipitation behavior of long-range-ordered (LRO) Ni 2 (Cr,Mo) strengthening phase in a Ni–21Cr–17Mo (wt%) superalloy that was subjected to a patent two-step heat treatment (705 °C/16 h/furnace cooling – 605 °C/32 h/air cooling) was revealed by means of transmission electron microscopy (TEM) and electron diffraction pattern (EDP) analysis. The coherent interfacial structure between the long-range-ordered Ni 2 (Cr,Mo) precipitate and the Ni-based matrix leads to the excellent strengthening effect of the alloy. High-spatial-resolution energy-disperse X-ray spectrum (EDX) analysis reveals that the Ni 2 (Cr,Mo) precipitates were slightly rich in Mo. The minor microstructure change after the key first-step heat treatment was especially focused on. It was found that weak streak fringes were present along 〈 311 〉 Ni - base ⁎ directions in the EDP along the [112] zone axis and the ordered nano-regions parallel to {311} Ni-base planes were distributed homogeneously in the matrix. Combined with the detailed microstructural characteristic, it is concluded that Mo atoms might enrich at every two {311} Ni-base planes during the first step of aging at high temperature (705 °C), which could increase the transition temperature of Ni 2 Cr resulting in its formation when aging at the second aging step of 605 °C. Meanwhile, Ni 2 (Cr,Mo) phase precipitates by the substitution of Mo atoms for Cr atoms every three {311} Ni-base planes in Ni 2 Cr phase with the continuous long-range diffusion of Mo atoms.

We investigated the ultrastructure and crystallographic orientation of spicules from the calcareous sponge Paraleucilla magna (subclass Calcaronea) by transmission and scanning electron microscopy using two different methods of sample preparation: ultramicrotomy and focused ion beam (FIB). It was found that the unpaired actine from the spicules was oriented in the [2 1 1] zone axis. The plane that contains the unpaired actine and divides symmetrically the paired actines is the (� 1 2 0). This plane is a mirror plane of the hexagonal lattice system. All the spicule types analyzed presented the same crystallographic orientation. Electron nanodiffraction maps from 4 lm � 4 lm regions prepared by FIB showed disorientation of

When twin variants interact, TTBs form and consequently affect twinning and detwinning processes. In this paper, we study twin–twin interactions by combining experimental observations and theoretical analysis. Mg single crystals are cyclically loaded in [0 0 0 1] and [ 1 0 1 ¯ 0 ] directions, respectively. Experimental characterization reveals the character of the twin–twin boundary and three kinds of twin–twin structures: a quilted-looking twin structure consisting of twins arrested at other twin boundaries, an “apparent crossing” twin structure which links twins impinging independently on each side of twin lamella and a double twin structure that results from secondary twins being nucleated at twin–twin interfaces. According to their crystallography, twin–twin interactions are classified into Type I for two twin variants sharing the same 〈 1 1 2 ¯ 0 〉 zone axis and Type II for two twins with different zone axes. For Type I twin–twin interactions, one twin does not transmit across the twin boundary and into the other twin. For Type II twin–twin interactions, one twin can transmit into the other only under some special loading conditions. In most cases twin transmission does not occur but, instead, twin–twin boundaries form that contain boundary dislocations. For Type I twin–twin interactions, the twin–twin boundary is a low angle tilt boundary with the habit plane being either the basal or the prismatic plane. For Type II twin–twin interactions, the twin–twin boundary is a high index crystallographic plane according to geometry analysis. Twin–twin boundary dislocations can be inferred by reactions of twinning dislocations associated with the two twin variants. An “apparent crossing” twin structure is thus a consequence of twin–twin boundary formation. Under reversed loading, detwinning is hindered because of the energetically unfavorable dissociation of boundary dislocations. Most interestingly, secondary twinning is activated at Type II twin–twin boundaries under reversed loading.

The Hartman–Perdok analysis has been carried out on the monoclinic P21/c polymorph of Hydroxyapatite (HAp) in order to find the character of the main {hkl} forms and foresee the possible profiles of the related surfaces. Then, the corresponding specific surface energies have been calculated, at 0 K, by ab initio quantum-mechanical calculations, and the HAp equilibrium shape has been obtained: a striking pseudohexagonal prism comes out from the close similarity of the surface energy of the three pinacoids {001}, {100}, and {102}, all developing around the [010] zone axis which runs parallel to the OH channels of the structure bulk. The most stable form, the pinacoid {010}, truncates the pseudohexagonal prism perpendicularly to the OH channels, while the less morphologically important monoclinic prisms {012}, {110}, and {112} complete the HAp equilibrium shape. Preliminary considerations are exposed about the morphological path: monoclinic polymorph → twinning → hexagonal polymorph. Finally, a simple kine...

The habit planes observed in numerous alloys during phase transformation can often be explained with the condition that the interface contains a single set of dislocations. Based on the unique matching condition in the habit plane, an analytical expression of the interface orientation in a general system has been derived. The orientations of habit planes are found to be confined on an elliptic cone corresponding to a particular Burgers vector. A simple method based on a superimposed diffraction pattern in the zone axis of the Burgers vector is proposed to specify the axes and parameters of the cones. The present analytical method provides a convenient mathematical tool for a systematic investigation of possible habit planes generated from either martensitic or precipitation transformation. The applications of the method to fcc/bct and hcp/bcc systems are presented. The calculated results have been tested against data in the literature, showing full agreement.

We report a new kind of artifact observed in the preparation of a TEM sample of zirconia by FIB, which consists in the deposition of metallic gallium nano-dots on the TEM sample surface. High resolution TEM images showed a microstructure of fine equiaxed grains of ~ 5 nm, with some of them possessing two particular characteristics: high contrast and well-defined fast Fourier transform. These grains could not be identified as any phase of zirconia but it was possible to identify them as gallium crystals in the zone axis [110]. Based on HRTEM simulations, the possible orientations between zirconia substrate and deposited gallium are discussed in terms of lattice mismatch and oxygen affinity.

The planar defect structure of coalesced GaN layers fabricated on ordered arrays of nanorods and grown by metal–organic vapour phase epitaxy has been studied using conventional and high-resolution transmission electron microscopy. During the process of coalescence, a boundary was created between two pyramids, where I1-type basal plane stacking faults propagating through the overgrown layers are terminated by Frank-Shockley partial dislocations. According to multislice HRTEM simulations of experimental observed images in the [ ] zone axis, the step-and hairpin-shaped basal prismatic stacking faults with inclined { } plane are consistent with Drum’s structural model, which has a lower formation energy compared with the model proposed by Amelinckx. Based on the observation that there are no stacking faults in the overgrown layers prior to the nanopyramid merging, the mechanism of coalescence induced stacking faults is proposed. This research contributes to the understanding of planar defect formation in III-...

Morphology, orientation and diffraction patterns of δ-Ni2Si precipitates in a Cu–Ni–Si alloy are investigated by TEM and HREM. Many disk-shaped nanosized δ-Ni2Si precipitates are uniformly distributed in Cu–1.5 wt%Ni–0.34 wt%Si alloy in an over-aging condition. The δ-Ni2Si precipitates preserve an orthogonal structure with a = 0.708 ± 0.005 nm, b = 0.504 ± 0.005 nm, and c = 0.364 ± 0.005 nm. The orientation relationships of six variants of δ-Ni2Si precipitates with Cu-matrix can be determined as (1 0 0)p||{0 0 1}Cu, [1 0 0]p||〈1 1 0〉Cu and [0 1 0]p||〈1 1 0〉Cu. Two typical diffraction pattern models under [0 0 1]Cu and [1 1 1]Cu zone axis are simulated according to diffraction effects of multiple variants, secondary diffraction and the size of particles, which coincide with the experimental results perfectly.

We report high-resolution transmission electron microscopy (HRTEM) observation of a high density of dislocations with edge components (~1016 m-2) in nanocrystalline (NC) body-centered cubic (bcc) Mo prepared by high-pressure torsion. We also observed for the first time of the ½ and pure edge dislocations in NC Mo. Crystallographic analysis and image simulations reveal that the best way using HRTEM to study dislocations with edge components in bcc systems is to take images along zone axis, from which it is possible to identify ½ pure edge dislocations, and edge components of ½ and mixed dislocations. The pure edge dislocations can only be identified from zone axis. The high density of dislocations with edge components is believed to play a major role in the reduction of strain rate sensitivity in NC bcc metals and alloys.

W-type strontium hexagonal ferrite, SrMe2+2Fe3+16O27 (Me2+: divalent cation), is a hard magnetic material that exhibits strong magneto-crystalline anisotropy (MCA), showing saturation magnetization, Ms, approximately 10% higher than that of M-type ferrite, one of the current mainstream materials. It is known that partial substitution of a divalent magnetic, nonmagnetic cations or a combination of both for Me2+ occupying appropriate Fe sites improves MCA and Ms, and it is thus important to investigate which Fe site and how much fraction in each site the dopant atoms are actually substituted for in order to find a guiding principle for further improvements of MCA and Ms. In this study, we have quantitatively determined the occupation sites of Zn2+ in Zn-doped W-type ferrite, SrZn2Fe16O27, using a suite of beam-rocking transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), theoretical dynamical elastic/inelastic electron scattering simulation and statistical analysis, an extended version of high-angular resolution electron channeling X-ray spectroscopy (HARECXS) [1]. The sintered specimen includes small amounts of hetero-phases which hamper the application of more macroscopic methods, such as neutron diffraction and synchrotron radiation. In this statistical beam-rocking TEM-EDX analysis, the intensity variations of characteristic X-ray peaks (incoherent channeling patterns (ICPs)) as functions of the incident beam direction with respect to a crystalline specimen reflect the occupation sites of the elements of interest, applicable to a small crystal grain, and the multivariate linear regression between the ICPs from the trace dopants and host elements allows us to quantitatively evaluate the dopant concentrations and their occupancies on different crystallographic sites [2]. The present material, however, has seven crystallographically inequivalent sites (the 2c as the hexagonal site, the 4e and 4fIV as the tetrahedral sites, and the 4f, 4fVI, 6g and 12k as the octahedral sites in the Wyckoff notation) for Fe, and accordingly the site-specific ICPs of the seven sites cannot be obtained separately. We have developed a scheme combining theoretical prediction of the site-specific ICPs, based on dynamical electron diffraction theory and the statistical atom-location by channeling-enhanced microanalysis (ALCHEMI) method [2] to overcome this difficulty, which was successfully applied to Co-doped M-type ferrite [3]. We have thus applied the scheme to present analysis. Figure 1 shows X-ray ICPs of the Sr-L, Fe-K, O-K and Zn-K lines obtained around the [1-20] zone axis, in which seven Fe sites are definitely separated in the projected atomic structure. The Zn-K ICP looks apparently different from some of the Fe-K ICPs, which qualitatively implies that Zn preferentially occupies some of the specific Fe sites, rather than all of them uniformly. Figure 2(a) shows the theoretical Fe-K ICP of the non-doped SrFe18O27, corresponding to Fig. 1(b), showing sufficiently good agreement with each other. The experimental site-specific Fe-K ICPs for the 12k, 6g, 4fVI, 4fIV, 4f, 4e and 2c sites can be thus obtained by the proportional distribution scheme of the experimental Fe-K ICP, as shown in Figs. 2(b-h), then followed by applying the statistical ALCHEMI method to Zn-K ICP (Fig. 1(d)) and site-specific Fe-K ICPs. Table 1 shows the derived parameters. This quantified result suggests that Zn mainly occupies 4e and 4fIV sites. The estimated Zn concentration of 3.1 atom% is slightly lower than the stoichiometric concentration, which is attributable to a grain-to-grain variation of impurity concentration. Ms arises due to a spontaneous molecular magnetic moment M0, the vector sum of the magnetic moments of Fe3+, Fe2+ and Zn2+ cations of 5μB, 4μB and 0μB, respectively, with the spin orientation considered. M0 was estimated to be 36.0μB and 37.6μB for the cases assuming the estimated Zn concentration and the stoichiometric Zn concentration, respectively. These values are close to the magnetization saturations of 35.0μB [4] and 38.2μB [5] previously reported for a similar W-type ferrite BaZn2Fe16O27. Keywords: EDX; electron channeling; ALCHEMI; HARECXS; W-type ferrite

Supported cobalt Fischer–Tropsch catalysts are characteristically nanoparticulate and the reduced SiC supported catalyst was found to contain both HCP and FCC polymorphs. This is reflected in the powder XRD patterns and generally there is a poor fit between the experimental and calculated diffractograms. This was ascribed to small crystallite sizes and the occurrence of disorder, manifested as peak broadening and peak shifts. Selected area electron diffraction data of suitably oriented cobalt catalyst grains on silicon carbide supports show non-periodic disorder in the zone axis orientations that contain the common (001) (HCP) and (111) (FCC) reciprocal lattice planes. Both FCC and HCP polymorphs are present in the same grains and these show disorder mainly in the HCP component. The disorder is further examined using high angle annular dark field (HAADF) scanning transmission electron microscopy at atomic resolution and the stacking sequences elucidated. Random sequences of mainly FCC are interrupted by HCP sequences and twin surfaces with reverse stacking sequences are also present. This study highlights the presence of significant disorder in cobalt catalyst grains confirmed by HAADF microscopy.

Guinier-Preston (GP) zones formed as nanometer-sized Cu-rich monolayers in α-Al matrix phase during aging process have been investigated using depth-sectioning technique, where through-focal high-angle annular dark-field (HAADF) images were recorded along a zone axis of the α-Al phase using aberration-corrected scanning transmission electron microscopy (STEM). HAADF intensities of the GP zones in the through-focal series vary with defocus settings, depending on the depths of the GP zones in the sample. Determination of the depth of a GP zone is not straightforward because the electron wave function of the STEM probe in the aligned crystalline material is affected by electron channeling. The depths of GP zones were then estimated via comparison with multislice simulations where GP zones were arranged at various depths in a supercell, and HAADF intensities were simulated with various defocus values. We show that the depth-sectioning technique can be used to investigate three-dimensional configurations of GP zones in the sample.

We present an overview of the Gd2(Zr2−xCex)O7 phase diagram, of interest as a model system for ceramic disposition of Pu (with Ce as a Pu surrogate). The fluorite related structures of this solid solution were determined using a modulated structure approach, to identify the underlying cation and vacancy ordering mechanisms from analysis of key satellite reflections in selected zone axis electron diffraction patterns. This revealed the formation of four structure types: pyrochlore for x 1.50. X-ray absorption (XAS) and electron energy loss (EELS) spectra confirmed the presence of Ce4+ as the dominant species in compositions across this system, remaining analogous to Pu4+.

Phase transition-induced lamellar domain structures together with the phase transition process in Ca [( Mg 1/3 Ta 2/3)0.9 Ti 0.1] O 3 complex perovskite ceramics have been investigated by high-resolution transmission electron microscopy. As the orthorhombic and monoclinic structures coexist in the present ceramics and even in a single grain, groups of lamellar domains have been observed and analyzed in the three characteristic zone axes of the parent cubic perovskite structure: 〈100〉, 〈110〉, and 〈111〉. zone axes. The antiparallel displacement of A-site cations, in-phase, and antiphase oxygen octahedra tilting and B-site 1:2 cation ordering cause superstructure reflections to destroy the symmetry of the parent cubic structure and subsequently induce domain structures. Groups of (010), (100) reflection twin domains and 90° rotation domains along the [100], [010], and [001] directions in the 〈100〉 and 〈110〉 zone axes are refined to be caused by the loss of reflection planes and fourfold rotation symmetry, whereas the loss of threefold rotoinversion and gain of twofold rotation symmetry lead to 120° and 180° rotation domains in the [111] zone axis. Rhombohedral 3 ¯ m and tetragonal 4/mmm structures are revealed to act as the bridging intermediate phase to make the first-order phase transitions from the parent cubic m 3 ¯ m structure to the orthorhombic mmm structure and monoclinic 2/m structure without group-subgroup relations continuous and diffusionless, and thus could occur via second order to form domain structures.

An unusual designated-tailoring on zone-axis preferential growth of surfactant-free ZnO mesocrystals with different features (shapes and sizes) was successfully achieved via an additive-free complex-precursor solution method. The formation of ZnO mesocrystals here is essentially determined by the characteristic of [Zn(OH)4]2– precursors, and an oriented nanoparicle aggregation with tailoring sizes and shapes can occur in different concentration of reactants at higher reaction temperature. Spindle-like ZnO mesocrystals with tunable sizes (along the c-axis direction) were synthesized by adjusting the concentration of hydroxyl ions, and peanut-like ZnO mesocrystals with controllable sizes (along the c-axis direction) and shapes (perpendicular c-axis direction) were prepared by tailoring the concentration of zinc ions. Structural and morphological evolutions were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and field...

Titanium carbonitride coating layers with star-shaped crystallite morphology were produced by chemical vapor deposition. Crystallites presenting a pentagonal symmetry nucleate at 880 °C and grow perpendicular to the surface by controlling the heating rate of the deposition process. Detailed transmission electron microscopy analyses of star-shaped crystallites along the [110] zone axis showed that each crystallite consists of five tetrahedra separated by (111) twins. A small-angle boundary consisting of edge dislocations forms as a result of elastic stress relaxation in the crystallites. The coatings presented a preferential texture in the direction (110) and an overall composition of Ti(C 0.15 N 0.85 ).

In this study, we presented comparative discrimination methods to identify various line and planar defects observed in nonpolar a-GaN epilayers on r-sapphire substrates. Unlike the case of conventional c-GaN, which is dominated by perfect threading dislocations, systematic identification of undistinguishable defects using transmission electron microscopy (TEM) is necessary to suppress the propagation of defects in nonpolar GaN epilayers. Cross-sectional TEM images near the [0 0 0 1] zone axis revealed that perfect mixed and pure screw type dislocations are visible, while pure edgeand basal stacking faults (BSFs) are not discernible. In tilted cross-sectional TEM images along the [ 1 2 ¯ 1 0 ] zone axis, the dominant defects were BSFs and partial dislocations for the g → = 1 ¯ 0 1 0 and 0 0 0 2 two-beam images, respectively. From plan-view TEM images taken along the [ 1 1 2 ¯ 0 ] axis, it was found that the dominant partial and perfect dislocations were Frank–Shockley and mixed dislocations, respectively. Prismatic stacking faults were observed as inclined line contrast near the [0 0 0 1] zone axis and were visible as band contrast in the two-beam images along the [ 1 2 ¯ 1 0 ] and [ 1 1 2 ¯ 0 ] zone axes.

Aluminum of commercial purity was processed by equal-channel angular pressing (ECAP) through two, four and eight passes at room temperature. A series of [1 1 4] convergent-beam electron diffraction (CBED) zone axis patterns were obtained using an electron probe with a diameter of 20 nm. Observations were recorded both immediately adjacent to the grain boundaries and in the grain interiors. Symmetry breaking of the higher-order Laue zone (HOLZ) lines was observed adjacent to the boundaries after two and four passes but not in the grain interiors. Pattern simulation of the CBED patterns taken from the two- and four-pass samples adjacent to the boundaries revealed a homogeneous strain with compressive and shear components. The presence of these homogeneous strains demonstrates that the internal stresses associated with the deformation of aluminum at room temperature are localized in the close vicinity, to within ∼20 nm, of the grain boundaries.

The orientation dependence of ϵ martensite during loading of a polycrystalline austenitic Fe-30Mn-4Si-2Al steel has been investigated by electron backscatter diffraction, emphasising the variant selection rule and plate–plate intersection reactions. Two types of plate–plate intersection reactions, which are characterised by incident shear direction of either 30° or 90° with respect to the intersection axis, were found in the grains along the [001]–[111] directions and [001]–[101] directions, respectively. In the intersecting volume of the latter type reaction, a γ phase rotated 90° from the austenite matrix along the ⟨011⟩ zone axis of the intersecting ϵ plates, which was theoretically predicted by Sleeswyk [A.W. Sleeswyk, Philos. Mag. 7 (1962) p.1597], has been experimentally observed for the first time.

The effect of high relative humidity (90% and 75% RH) on phase transformation and stability of CaCO3 polymorphs has been studied based on the structural and morphological changes from a colloidal solution based on Ca(OH)2 nanocrystals. Carbonation process has been confirmed indicating differences in nucleation and stability of CaCO3 polymorphs as a function of RH. Local fluctuations in the water/alcohol ratio significantly affect the precipitation/dissolution of anhydrous and hydrated polymorphs that are reflected in the particle size. Changes in lattice parameters and particle size are related to surface tension fluctuations, release of residual water and time of exposure. These results highly contribute to evaluate the stability of the Ca(OH)2 nanoparticles in high humidity conditions., This work was supported by the Government of the Community of Madrid (Spain), the GEOMATERIALES (S2009/MAT-1629/GEOMATERIALES) and CONSOLIDER-TCP (CSD2007-0058) programmes and by the JAE-Doc CSIC contracts.

Transition matrix, combine with high-resolution transmission electron microscopy (HRTEM) and stereographic projection, was used in this article to predict and characterize the orientations and electron diffraction patterns of β″ precipitates in Al-Mg-Si-(Cu) alloys. It was found that the β″ phases as the main strengthening precipitates had 12 variants with Al matrix, and the orientation relationships could be expressed as (010) β″//{100}Al, [001] β″//〈310〉Al, and [100] β″//〈230〉Al. Further, based on the C-centered monoclinic structure of β″ precipitate, a new diffraction patterns model under the [001]Al zone axis could be established, which was in good agreement with the experiment date. Further, it could be used to explain reasonably some issues (for example, the “cross-shaped” diffraction streaks phenomenon). Simultaneously, we also found that the β″ precipitates had only three different zone axes, [010] β″, [304] β″, and $$ \left[ {\bar{1}06} \right]_{{\beta^{\prime \prime } }} , $$ parallel to the [001]Al direction when they were precipitated from the Al matrix, and the β″ precipitate might deviate 1.6 deg from its original orientation because of the lattice relaxation.

TiO2 nanoparticles with enhanced solid solution of Cr up to 16 wt% in polymorphs of rutile, anatase, brookite, α-PbO2-type, and occasionally baddeleyite-type were synthesized via pulse laser ablation on ceramic TiO2 target dissolved with Cr2O3 or clamped Cr/Ti plates in air. Analytical electron microscopic observations indicated these nanocondensates have prevalent crystallographic shear (CS) along specific planes to form superstructures. The rutile type typically shows (100) and (010) CS besides the conventional ones rotating about the [111] zone axis as reported for ambient samples. The CS planes are parallel to (001) for anatase, (001) and ( $$ \overline{1} $$ 10) for brookite, whereas (001) and {1 $$ \overline{3} $$ 1} for the α-PbO2-type TiO2 with varied extent of Cr dissolution. Surface modification, as a result of Cr dissolution and/or internal stress, was observed for all the polymorphs.

The applicability of various convergent beam electron diffraction (CBED) methods to the polarity determination of LiNbO3 crystals in the space group R3c was examined. We show that the method of zone-axis CBED combined with dynamical simulation is applicable to the polarity determination of LiNbO3. The effects of the zone axis, the specimen thickness and the displacement of the homopolar atom on the polarity determination were studied. This method was also successfully applied to the polarity determination of a multiferroic BiFeO3 film deposited on a (111)Pt/TiO2/SiO2/Si substrate by pulsed laser deposition. It shows that about 30% of the grains in the BiFeO3 film are grown along the positive polar direction.